Global estimates on the number of people blind or visually impaired by glaucoma: A meta-analysis from 2000 to 2020

OBJECTIVES

To estimate global and regional trends from 2000 to 2020 of the number of persons visually impaired by glaucoma and their proportion of the total number of vision-impaired individuals.

METHODS

A systematic review and meta-analysis of published population studies and grey literature from 2000 to 2020 was carried out to estimate global and regional trends in number of people with vision loss due to glaucoma. Moderate or severe vision loss (MSVI) was defined as visual acuity of 6/60 or better but <6/18 (moderate) and visual acuity of 3/60 or better but <6/60 (severe vision loss). Blindness was defined as presenting visual acuity <3/60.

RESULTS

Globally, in 2020, 3.61 million people were blind and nearly 4.14 million were visually impaired by glaucoma. Glaucoma accounted for 8.39% (95% uncertainty intervals [UIs]: 6.54, 10.29) of all blindness and 1.41% (95% UI: 1.10, 1.75) of all MSVI. Regionally, the highest proportion of blindness relating to glaucoma was found in high-income countries (26.12% [95% UI: 20.72, 32.09]), while the region with the highest age-standardized prevalence of glaucoma-related blindness and MSVI was Sub-Saharan Africa. Between 2000 and 2020, global age-standardized prevalence of glaucoma-related blindness among adults ≥50 years decreased by 26.06% among males (95% UI: 25.87, 26.24), and by 21.75% among females (95% UI: 21.54, 21.96), while MSVI due to glaucoma increased by 3.7% among males (95% UI: 3.42, 3.98), and by 7.3% in females (95% UI: 7.01, 7.59).

CONCLUSIONS

Within the last two decades, glaucoma has remained a major cause of blindness globally and regionally.

Comparison of corneal biomechanical parameters in healthy corneas with symmetric and asymmetric bow-tie topographic pattern with inferior and superior steepening

PURPOSE

To compare the corneal biomechanical parameters in healthy corneas with symmetric and asymmetric bow-tie topographic patterns.

METHODS

In this cross-sectional study, 144 eyes were divided based on inferior-superior asymmetry value (I-S) into symmetric (zero I-S: - 0.50 to + 0.50 D) and asymmetric bow-tie topographic patterns with inferior (positive I-S: + 0.51 to + 1.4 D) or superior (negative I-S: - 2.5 to - 0.51 D) steepening. The biomechanical assessment was performed using Corvis ST and ocular response analyzer (ORA). A general linear model univariate analysis was used to compare the parameters, while the central corneal thickness, intraocular pressure, and age were considered covariates.

RESULTS

Only the peak distance (PD) at the highest concavity phase (P = 0.007) and tomographic biomechanical index (TBI, P = 0.001) showed statistically significant differences between the three groups. For TBI, this difference was statistically significant between the positive I-S group separately with the zero I-S group (P < 0.001), and with the negative I-S group (P = 0.022). For PD, the significant difference was between the negative I-S group separately with zero I-S (P = 0.019), and positive I-S groups (P = 0.018). There was a statistically significant correlation between the I-S value with PD (r = 0.281, P = 0.001) and TBI (r = 0.170, P = 0.044).

CONCLUSIONS

Most corneal biomechanical parameters are not statistically significant compared to the zero I-S group. However, superior steepening is associated with a stiffer response based solely on the shorter PD values seen in this group, and the group with the inferior steepening shows the highest or more suspicious values based on TBI.

Peripapillary vessel density in healthy people, primary open-angle glaucoma, and normal-tension glaucoma

OBJECTIVE

To compare peripapillary vessel density using optical coherence tomography angiography (OCT-A) in eyes of healthy people, primary open-angle glaucoma (POAG), and normal-tension glaucoma (NTG).

METHODS

Thirty patients with POAG, 27 patients with NTG, and 29 healthy individuals in the control group were assessed. Capillary vessels in peripapillary retinal nerve fiber layer (RNFL) represented by whole image RPC (radial peripapillary capillary) density in an AngioDisc scan 4.5 × 4.5 mm centered on the optic disc, and ONH morphological variables (disc area, rim area, cup to disc area ratio (CDR)), and average peripapillary RNFL thickness were measured.

RESULTS

Differences in mean RPC, RNFL, disc area, rim area, and CDR between the groups were statistically significant (P < 0.05). The difference in RNFL thickness and rim area was not significant between NTG and healthy groups, while RPC and CDR showed a statistically significant difference between all pairs. The vessel density in the POAG group was 8.25% and 11.7% lower compared to the NTG and healthy groups, respectively; while the mean difference was less (2.97%) for the NTG and healthy group. In the POAG group, 67.2% of the variation in RPC can be explained by a model containing CDR and RNFL thickness, and in normal eyes 38.8% of the changes using a model containing RNFL.

CONCLUSION

The peripapillary vessel density is reduced in both types of glaucoma. The vessel density in NTG was significantly lower than in the healthy eyes, despite the lack of significant difference in RNFL thickness and neuroretinal rim area between them.

Impact of a 50bp insertion/deletion polymorphism of the superoxide dismutase-1 on oxidative stress status and risk of keratoconus

Keratoconus (KC) is characterized by the predominant primary ectatic disease, affecting the cornea, necessitating corneal transplants in some cases. While some loci associated with KC risk have been identified, the understanding of the disease remains limited. Superoxide dismutase (SOD) enzymes play a crucial role in countering the reactive oxygen species and providing protection against oxidative stress (OS). Accordingly, the objective of this study was to investigate a potential association of a 50 nucleotide base pairs (bp) insertion/deletion (I/D) within the SOD1 promoter, and the located 1684 bp upstream of the SOD1 ATG, with KC in the Iranian population. Additionally, an assessment was conducted on SOD activity and the total antioxidant capacity (TAC), as determined by the ferric reducing-antioxidant power assay, along with malondialdehyde (MDA) levels. In this case-control study, genomic DNA was extracted from the blood cells of KC (n = 402) and healthy (n = 331) individuals. The genotype of this gene was determined using the PCR technique. Furthermore, the amount of SOD enzyme activity and the MDA and TAC levels were measured in the serum of the study groups. The (I/I) genotype was present in 84.23%, the (I/D) genotype in 15.06%, and the (D/D) genotype in 0.69% of both groups. A statistically significant relationship was seen between different genotypes and TAC, MDA, and SOD1 activity indices (P < 0.05). Individuals with the D/D genotype exhibited a decrease in total antioxidant capacity, an increase in the amount of MDA, and a decrease in SOD1 enzyme activity (P < 0.05). Moreover, the logistic regression analysis of KC development indicated that elevated levels of MDA increased the risk of KC incidence in the patient group compared to the healthy group, while a higher activity of SOD1 and greater values of TAC decreased the KC risk. The removal of the 50 bp fragment reduced SOD1 activity and elevated OS levels, thereby impacting the oxidant-antioxidant balance. This could potentially play a significant role in individuals afflicted by KC.

Changes in corneal biomechanical parameters in keratoconus eyes with various severities after corneal cross-linking (CXL): A comparative study

OBJECTIVES

To compare changes in corneal biomechanical parameters one year after corneal cross-linking (CXL) in keratoconus (KCN) eyes of different severities.

METHODS

Seventy-five eyes with mild, moderate, and severe grades of KCN (n = 24, 31, and 20 eyes, respectively) that were treated with CXL, based upon the standard Dresden protocol, were included. The corneal biomechanical assessment was performed using Corvis ST and Ocular Response Analyzer (ORA). Changes in Corvis's dynamic corneal response (DCR) parameters and ORA's derived parameters (corneal hysteresis (CH), and corneal resistance factor (CRF)) were assessed whilst the corneal thickness and intraocular pressure were considered as covariates.

RESULTS

There was no statistically significant difference in the corneal biomechanical parameters obtained using both devices after surgery separately in different KCN grades, except for the deformation amplitude (DA) in the severe KCN group (P = 0.017). Changes in the classic parameters of the highest concavity phase of Corvis ST (peak distance, radius, and DA) were more positive and in the newer parameters (integrated inverse radius (IIR), deformation amplitude ratio (DAR)) more negative in the severe group compared to the other groups. Also, the mean change in CH (P = 0.710), and CRF (P = 0.565), showed a negative shift in higher grades of KCN; however, there was no significant difference in the mean changes of all parameters between different groups. (P > 0.05).

CONCLUSIONS

Similar changes in the Corvis ST and ORA parameters in mild, moderate, and severe KCN indicate biomechanical stability and the effective role of CXL in stopping the progressive nature of keratoconus in eyes of varying severities one year after CXL.

After-effect on tear film quality and quantity of reading on laptop computer screen versus hardcopy

CLINICAL RELEVANCE

Electronic displays, including laptops, tablets, and smartphones, have dramatically altered the way information is accessed and become significant factors in human daily life. They interfere with the blink rate and increase dry eye symptoms, which lead to more discomfort compared to hard copy while reading.

BACKGROUND

Digital eye strain occurs when an individual suffers from symptoms, or they are exacerbated, while performing a task requiring digital screen viewing. This study assessed the tear film status immediately following reading on a laptop computer screen versus an identical hard copy.

METHODS

Thirty young adults with normal ocular health and reporting no significant symptoms of dry eye (ocular surface disease index (OSDI) score < 13 and non-invasive tear break-up time (NITBUT) > 10 seconds) read a text as hard copy and on a laptop computer screen for 30 min on separate days in a random sequence in a controlled reading experimental condition. The texts were matched in size and contrast and presented at a viewing distance of 40 cm. The NITBUT and strip meniscometry tube tests were administered at baseline and after reading in both conditions.

RESULTS

The median baseline NITBUT decreased from 13.0 s to 10.0 s (P < 0.001) after hardcopy reading and to 7.0 (P < 0.001) after reading from a laptop computer screen, with a significant difference between the task medium (P = 0.001). The baseline strip meniscometry tube results decreased from 6.7 mm to 5.0 mm (P < 0.001) after hardcopy reading and to 5.0 mm (P < 0.001) after reading from a laptop computer screen, but there was no significant difference with the task medium (P = 0.085).

CONCLUSION

Reading in both conditions led to tear film instability in terms of the tear film quality and quantity. Additionally, the computer screen has a greater impact on the TBUT compared to hardcopy reading, while these two reading mediums had a similar effect on the tear volume.

Detection ability of corneal biomechanical parameters for early diagnosis of ectasia

PURPOSE

To assess the detection ability of corneal biomechanical parameters for early diagnosis of ectasia.

METHODS

This retrospective descriptive-analytical study included 134 normal eyes (control group) from 134 healthy subjects and 128 eyes with asymmetric contralateral corneal ectasia with normal topography (ACE-NT, study group) from 128 subjects with definite keratoconus in the opposite eye. Placido-disk-based corneal topography with TMS-4, Scheimpflug corneal tomography with Pentacam HR, and corneal biomechanical assessment with Corvis ST and ocular response analyzer (ORA) were performed. A general linear model was used to compare Corvis ST and ORA biomechanical parameters between groups, while central corneal thickness (CCT) and biomechanically corrected intraocular pressure (bIOP) were considered covariates. Receiving operator sensitivity curve (ROC) analysis was used to determine the cut-off point with the highest sensitivity and specificity along with the area under the curve (AUC) for each parameter.

RESULT

All parameters of Corvis ST and ORA showed a statistically significant difference between the two groups except for the first (P = 0.865) and second (P = 0.226) applanation lengths, and deformation amplitude (P = 0.936). The discriminative analysis of corneal biomechanical showed that the highest accuracy for the classic, new, and combined parameters of Corvis ST was related to HCR (AUC: 0.766), IR & DAR (0.846), and TBI (0.966), respectively. Using ORA, the corneal resistance factor (0.866) had a higher detection ability than corneal hysteresis (0.826).

CONCLUSIONS

TBI has the best accuracy and the highest effect size for differential diagnosis of normal from ACE-NT eyes with a cut-off point of 0.24.

The Combined Utilization of Epithelial Thickness Mapping and Tomography in Keratorefractive Surgery Screening: One Imaging Modality is Not Sufficient

Increasing popularity and utility of epithelial thickness mapping (ETM) in keratorefractive surgery screening may begin to inappropriately devalue the use of tomography. An increasing body of research suggests that the interpretation of ETM based solely on the corneal resurfacing function may be insufficient to screen and select patients for refractive surgery. ETM and tomography are complementary and, when used together, may provide the safest and most optimal tools for keratorefractive surgery screening.

Comparison of corneal biomechanical properties in healthy thin corneas with matched keratoconus eyes

PURPOSE

To compare corneal biomechanical parameters of normal thin corneas with matched keratoconus eyes.

SETTING

Eye Research Center, Mashhad University of Medical Sciences, Mashhad, Iran.

DESIGN

Cross-sectional comparative study.

METHODS

Dynamic corneal response parameters of Corvis ST were compared in 61 eyes with keratoconus with 61 matched healthy thin corneas (corneal thinnest point <500 μm), while corneal thickness, biomechanically corrected intraocular pressure, and age were considered covariates. The receiving operator sensitivity curve analysis was used to determine the cutoff point with the highest sensitivity and specificity, and the area under the curve (AUC) for each parameter.

RESULTS

All biomechanical parameters were statistically significant between the 2 groups except for the first ( P = .947) and second ( P = .582) applanation length, first ( P = .783) and second ( P = .301) applanation velocity, and deformation amplitude in the highest concavity phase ( P = .106). The highest mean difference between groups (12.89 ± 2.03 mm Hg/mm) was related to the stiffness parameter at the first applanation (SPA1). Although the Corvis biomechanical index and tomographic biomechanical index had the highest detection ability based on their AUC (0.912 and 0.959, respectively), among the standard and combined biomechanical parameters except for keratoconus screening parameters, the highest discriminative ability was related to SPA1 with AUC, sensitivity, and specificity of 0.793, 60.66%, and 90.16%, respectively.

CONCLUSIONS

Keratoconus corneas were significantly softer compared with healthy thin corneas of matched thickness. Optimal cutoff points close to the maximum value defined for screening parameters limit their clinical use for differentiation purposes in these particular types of cases.

Changes in Stress-Strain Index and Corneal Biomechanics in Granular Corneal Dystrophy

Background: The aim of this study was to assess stress-strain index (SSI) and corneal biomechanical parameters in eyes with granular corneal dystrophy (GCD). Methods: This case-control study included 12 eyes of 12 patients with GCD (mean age 45.2 ± 18.7 years) and 20 eyes of 20 healthy individuals (mean age 54.4 ± 3.8 years). In addition to SSI, dynamic corneal response (DCR) parameters were assessed at the first and second applanation, including length (AL1, AL2), velocity (AV1, AV2), time (AT1, AT2), and deformation amplitude (DA A1, DA A2), and at the highest concavity (HC) phase, including DA, peak distance (PD), radius (HCR), and DA ratio (DAR 1 and 2 mm), by Corvis ST. Central corneal thickness (CCT) and biomechanically corrected intraocular pressure (bIOP) were considered covariates in comparing DCR parameters between the two groups. Results: SSI was statistically significantly lower in eyes with GCD than in normal eyes (p = 0.04). The corneal velocity towards the first applanation was 0.02 m/s faster in the GCD eyes AV1 (0.15 ± 0.02 vs. 0.13 ± 0.02 m/s, p < 0.001) and IR (7.48 ± 1.01 vs. 6.80 ± 1.22 mm, p = 0.003) parameters were significantly higher in the GDC group, while AT1 (7.33 ± 0.66 vs. 7.47 ± 0.36 ms, p = 0.002) and HCR (7.42 ± 0.76 vs. 8.20 ± 1.08 mm, p = 0.014) were significantly lower in the normal group. Conclusions: GCD led to a change in biomechanical properties of the cornea. SSI refers to fewer stiff corneas in GDC than normal.

Visual outcomes of photorefractive keratectomy in non-children with anisometropic amblyopia: One-year Follow-up Outcomes

OBJECTIVE

To evaluate the safety, efficiency, short term stability, and sensory results of photorefractive keratectomy (PRK) in anisometropic in non-compliant children with correction.

METHODS

Twelve eyes of 12 children with an age range: 6-17 years and anisometropic amblyopia who underwent PRK under general anesthesia to correct the dioptric difference between the eyes were included in this study. A complete ophthalmic assessment including refractive status, uncorrected and corrected distance visual acuity (UDVA & CDVA), and binocular vision status using the Worth 4-dot test and stereopsis were performed before and 1, 3, 6, and 12 months after PRK.

RESULTS

The mean preoperative CDVA was 0.34 ± 0.24 LogMAR which showed a statistically significant improvement at 12 months (0.20 ± 0.19, p = 0.024) after surgery compared to the preoperative assessment. (p = 0.003) The mean preoperative UDVA was 0.63 ± 0.24 LogMAR that increased to 0.44 ± 0.24, 0.32 ± 0.16, 0.25 ± 0.19, and 0.25 ± 0.19 LogMAR at 1, 3, 6, and 12 months after PRK, respectively. One to three lines improvement in UDVA and CDVA was seen in 10 (83.4%) and 8 eyes (66.7%); while one line UDVA and CDVA loss was seen in one (8.3%) and one (8.3%) eye and unchanged UDVA and CDVA was seen in 1 (8.3%) and 3 eyes (25%), respectively. The mean preoperative stereoacuity was 341.9 ± 245.7 s of arc, which significantly improved to 166.6 ± 87.5 s of arc 12 months after PRK. (p = 0.012).

CONCLUSION

PRK was an effective surgical alternative to improve visual acuity and stereopsis in anisometropic children who did not cooperate with conventional methods of amblyopia therapy.

Agreement of wavefront-based refraction, dry and cycloplegic autorefraction with subjective refraction

PURPOSE

To evaluate the agreement of dry, and cycloplegic autorefraction and wavefront-based refraction with subjective refraction.

METHOD

83 subjects aged 19-57 years were included in this cross-sectional study. Refractive status was determined using four methods including subjective refraction, wavefront-based refraction, dry and cycloplegic autorefraction. Refractive data were recorded as sphere, cylinder and spherical equivalent (SE). Power vector components were used to compare the astigmatism obtained using the different methods of refraction.

RESULTS

The more negative spherical, cylindrical and SE components were obtained using dry autorefraction, wavefront-based refraction and dry autorefraction, respectively. The less negative spherical, cylindrical and SE components were obtained using cycloplegic autorefraction, subjective refraction and cycloplegic autorefraction, respectively. Considering the spherical component, there was a statistically significant hyperopic shift (0.12 ± 0.29 D, p = 0.001) with cycloplegic autorefraction and a significant myopic shift (-0.17 ± 0.32 D, p < 0.001) with dry autorefraction compared to subjective refraction, while the difference between wavefront-based and subjective refraction was not significant statistically (p = 0.145). The calculated cylindrical component using subjective refraction showed statistically significant difference with dry auto-refraction (p < 0.001), cycloplegic auto-refraction (p = 0.041) and wavefront refraction (p < 0.001). The highest correlation with subjective refraction in sphere, cylinder and SE was observed for cycloplegic auto-refraction (rs = 0.967), dry auto-refraction (rs = 0.983) and cycloplegic auto-refraction (rs = 0.982), respectively.

CONCLUSIONS

As subjective refraction is gold standard in our study, sphere in cycloplegic auto-refraction and astigmatism in dry auto-refraction showed better agreement and correlation.

Distribution pattern of total corneal thickness in keratoconus versus normal eyes using an optical coherence tomography

Purpose:

To evaluate the total corneal thickness distribution pattern using a high-resolution spectral-domain optical coherence tomography (HR SD-OCT) for distinguishing normal eyes from keratoconus (KCN).

Methods:

One hundred and forty-four patients were enrolled in three groups (55 normal, 45 mild KCN, and 44 moderate-to-severe KCN eyes) in this prospective diagnostic test study. Total corneal thickness was measured in 8 semi-meridians using HR SD-OCT (Heidelberg Engineering, Heidelberg, Germany) in 5 and 7 mm zones. The central corneal thickness (CCT), corneal focal thinning (minimum thickness [Min], min minus median and maximum [Min-Med, Min-Max]), and asymmetry indices (inferior minus superior [I-S] and supranasal minus infratemporal [SN-IT]) were calculated. One-way analysis of variance and the area under the receiver operating characteristic curve (AUC) were used for the analysis.

Results:

Thinner CCT, lower Min thickness, more negative Min-Max, Min-Med, and greater I-S and SN-IT were found in KCN eyes compared to the control group (P < 0.001). The inferior and IT semi-meridians were the thinnest locations in KCN cases in the 5 mm central zone (P < 0.001). CCT followed by Min-Med had the highest discriminative ability for differentiating mild KCN (AUC, sensitivity and specificity: 0.822, 87.0%, 60.37% and 0.805, 82.93%, 66.0%, respectively) and moderate-to-severe KCN (0.902, 87.82%, 73.08% and 0.892, 85.37%, and 78.85%, respectively) from normal corneas.

Conclusion:

The inferior and IT sectors of the cornea with the largest thickness changes in the 5 mm zone are the most common thinning sites in keratoconic corneas, and CCT and Min-Med are the most sensitive indices for the diagnosis of KCN.

Corneal Stability and Visual Acuity 1 Year After Corneal Cross-linking Assessed Using the ABCD Keratoconus Staging System

PURPOSE

To assess corneal stability and corrected distance visual acuity (CDVA) 3, 6, and 12 months following corneal cross-linking (CXL) using the ABCD keratoconus staging system.

METHODS

This prospective longitudinal study included 31 eyes with keratoconus receiving CXL based on the standard Dresden protocol. CDVA, refraction, and Scheimpflug tomography with the Pentacam HR (Oculus Optikgeräte GmbH) were evaluated before and after surgery. Geometric and functional changes were assessed using the actual values and staging of each element of the ABCD keratoconus staging system. A, B, C, and D refer to the anterior and posterior radii of curvature in a 3-mm zone centered on the cor-neal thinnest point, minimum corneal thickness, and CDVA, respectively.

RESULTS

There were no significant changes in the actual values of anterior radius of curvature (P = .497) and CDVA (P = .082), whereas posterior radius of curvature (P = .007) and corneal thinnest point (P < .001) showed significant changes statistically. Pairwise comparison showed only a statistically significant steepening in posterior radius of curvature at 3 months after CXL compared to the preoperative radius (P = .002) and a significant decrease in corneal thinnest point at 3 (P < .001) and 6 (P = .028) months after CXL compared to baseline assessment. Staging of each element of the ABCD keratoconus staging system indicated no change between baseline and 3, 6, and 12 months after CXL.

CONCLUSIONS

The geometric and functional parameters included in the ABCD keratoconus staging system showed stability of corneal status and CDVA 1 year after CXL. [J Refract Surg. 2021;37(10):700-706.].

Comparison of Keratoconus Cone Location of Different Topo/tomographical Parameters

Purpose: To compare the corneal cone location on different maps and instruments, and their agreements, with elevation maps.Methods: In 90 left eyes with bilateral keratoconus, the apex of cone location was determined based on the maximum simulated keratometry (Kmax) location on the anterior sagittal curvature map by Pentacam HR, the maximum curvature on the mean curvature map by ATLAS 9000, most elevated point of the island of positive elevation relative to the best fit sphere on the front and back corneal elevation maps by Pentacam HR, and thinnest point on the thickness map by Pentacam HR and Orbscan, and the thinnest points on pachymetry and epithelial thickness maps by RTVue OCT.Results: There was a significant difference among the location on different maps along the x- and y-axes (p < .001). The lowest agreement with the cone apex on both front and back elevation maps was for the anterior sagittal curvature map and the highest agreement for the Pentacam thickness map. The majority of keratoconus cone apexes were displaced in the inferotemporal direction on the different maps except for the epithelial thickness maps.Conclusions: Despite the variability between different devices and methods; the thickness map on the Pentacam HR showed the highest correlation with the front and back elevation maps, while the RTVue epithelial thickness map showed the poorest correlation. Based on this study, epithelial thickness maps and anterior curvature maps should be utilized with caution to determine the location of the cone.

Keratoconus detection of changes using deep learning of colour-coded maps

Objective

To evaluate the accuracy of convolutional neural networks technique (CNN) in detecting keratoconus using colour-coded corneal maps obtained by a Scheimpflug camera.

Design

Multicentre retrospective study.

Methods and analysis

We included the images of keratoconic and healthy volunteers’ eyes provided by three centres: Royal Liverpool University Hospital (Liverpool, UK), Sedaghat Eye Clinic (Mashhad, Iran) and The New Zealand National Eye Center (New Zealand). Corneal tomography scans were used to train and test CNN models, which included healthy controls. Keratoconic scans were classified according to the Amsler-Krumeich classification. Keratoconic scans from Iran were used as an independent testing set. Four maps were considered for each scan: axial map, anterior and posterior elevation map, and pachymetry map.

Results

A CNN model detected keratoconus versus health eyes with an accuracy of 0.9785 on the testing set, considering all four maps concatenated. Considering each map independently, the accuracy was 0.9283 for axial map, 0.9642 for thickness map, 0.9642 for the front elevation map and 0.9749 for the back elevation map. The accuracy of models in recognising between healthy controls and stage 1 was 0.90, between stages 1 and 2 was 0.9032, and between stages 2 and 3 was 0.8537 using the concatenated map.

Conclusion

CNN provides excellent detection performance for keratoconus and accurately grades different severities of disease using the colour-coded maps obtained by the Scheimpflug camera. CNN has the potential to be further developed, validated and adopted for screening and management of keratoconus.

Refractive characteristics of keratoconus eyes with corneal Vogt's striae: A contralateral eye study

PURPOSE

The aim of this study was to assess and compare clinical characteristics of bilateral keratoconus patients with unilateral Vogt's striae.

METHODS

In this contralateral eye study, refractive status were evaluated in patients with bilateral keratoconus whose corneas had definite slit-lamp biomicroscopic evidence of unilateral Vogt's striae. All cases underwent a comprehensive ophthalmic examination. Some refractive errors components provided by autorefraction were converted to vectorial notation for power vector analysis. Finally, the outcomes were compared between keratoconus eyes with and without Vogt's striae.

RESULTS

Fifty patients aged 20 to 38 years (27.43±5.5) were recruited in this study. The results showed a significant difference in uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), non-cycloplegic and cycloplegic autorefraction including sphere, cylinder, spherical equivalent, and J₀, between keratoconus eyes with and without Vogt's striae (all P<0.05), except for J₄₅ (P=0.518 in non-cycloplegic autorefraction and P=0.574 in cycloplegic autorefraction). Comparison of cycloplegic and non-cycloplegic autorefraction in both study groups showed significant differences in the sphere and spherical equivalent (all P<0.001), but no significant difference was found in cylinder, J₀, and J₄₅ between the study groups (all P>0.05).

CONCLUSIONS

Comparison of the cycloplegic and non-cycloplegic autorefraction in keratoconus eyes with and without Vogt's striae showed significant differences in UDVA, CDVA, and some refractive errors components provided by autorefraction between the two groups, with a worse condition in KCN eyes with Vogt's striae.

Corneal Biomechanical Properties in Varying Severities of Myopia

Purpose: To investigate corneal biomechanical response parameters in varying degrees of myopia and their correlation with corneal geometrical parameters and axial length.

Methods: In this prospective cross-sectional study, 172 eyes of 172 subjects, the severity degree of myopia was categorized into mild, moderate, severe, and extreme myopia. Cycloplegic refraction, corneal tomography using Pentacam HR, corneal biomechanical assessment using Corvis ST and Ocular Response Analyser (ORA), and ocular biometry using IOLMaster 700 were performed for all subjects. A general linear model was used to compare biomechanical parameters in various degrees of myopia, while central corneal thickness (CCT) and biomechanically corrected intraocular pressure (bIOP) were considered as covariates. Multiple linear regression was used to investigate the relationship between corneal biomechanical parameters with spherical equivalent (SE), axial length (AXL), bIOP, mean keratometry (Mean KR), and CCT.

Results: Corneal biomechanical parameters assessed by Corvis ST that showed significant differences among the groups were second applanation length (AL2, p = 0.035), highest concavity radius (HCR, p < 0.001), deformation amplitude (DA, p < 0.001), peak distance (PD, p = 0.022), integrated inverse radius (IR, p < 0.001) and DA ratio (DAR, p = 0.004), while there were no significant differences in the means of pressure-derived parameters of ORA between groups. Multiple regression analysis showed all parameters of Corvis ST have significant relationships with level of myopia (SE, AXL, Mean KR), except AL1 and AL2. Significant biomechanical parameters showed progressive reduction in corneal stiffness with increasing myopia (either with greater negative SE or greater AXL), independent of IOP and CCT. Also, corneal hysteresis (CH) or ability to dissipate energy from the ORA decreased with increasing level of myopia.

Conclusions: Dynamic corneal response assessed by Corvis ST shows evidence of biomechanical changes consistent with decreasing stiffness with increasing levels of myopia in multiple parameters. The strongest correlations were with highest concavity parameters where the sclera influence is maximal.

Comparative analysis of two different types of intracorneal implants in keratoconus: A corneal tomographic study

OBJECTIVE

To evaluate changes in visual acuity and corneal tomographic outcomes at 6 months after femtosecond-laser assisted implantation of two different types of intracorneal implants in keratoconus.

METHODS

A total of 39 keratoconus eyes implanted with two segments KeraRing (n = 22 eyes) or MyoRing (n = 17 eyes) were enrolled. Tomographic data (Pentacam system, Oculus) were analyzed and correlated with enhancement in uncorrected (UDVA) and corrected distance visual acuity (CDVA). The tomographic indices were front maximum keratometry (Kmax), corneal asphericity (Q-value) on both surfaces, average pachymetric progression indices (PPI), maximum Ambrosio relational thickness (ARTmax), Belin-Ambrósio enhanced ectasia total deviation index (BAD-D), index of surface variance (ISV), vertical asymmetry (IVA), height asymmetry (IHA) and height decentration (IHD).

RESULTS

LogMAR UDVA and CDVA improved 2.1 (p = 0.003) and 0.7 (p = 0.074) lines with KeraRing, and 8 and 2.5 lines with MyoRing (p = 0.001). The highest and lowest mean differences in the tomographic indices between both groups were related to ISV and IHD, respectively. Changes in all indices differed significantly between two groups except for changes in front corneal astigmatism, ARTmax, ISV, IVA, IHD and IHA (p > 0.05). Correlation of changes in CDVA with changes in other parameters was statistically significant only for IHD in the KeraRing group, while changes in in UDVA were significantly correlated with changes in spherical equivalent, back Q-value, ISV, IVA, and IHA only in the MyoRing group.

CONCLUSION

Both implants promote corneal shape regularization and an enhancement in UDVA in keratoconus. A considerable flattening effect and reduction in prolateness in the front corneal surface were observed with MyoRing.

Corneal Epithelial Thickness Mapping After Photorefractive Keratectomy for Myopia

PURPOSE

To evaluate the longitudinal changes in epithelial thickness after photorefractive keratectomy (PRK) and correlate these with refractive changes.

METHODS

This prospective study included 52 eyes of 52 candidates for myopic PRK. Along with standard ophthalmic examinations, corneal epithelial thickness mapping by anterior segment optical coherence tomography was performed. Epithelial thickness maps of 9-mm diameter were divided into 25 sectors, including a central 2-mm zone and eight octants within para-central (2 to 5 mm), midperipheral (5 to 7 mm), and peripheral (7 to 9 mm) annular zones. All PRK treatments were performed using the Technolas Teneo 317 model 2 excimer laser (Bausch & Lomb, Rochester, NY) and an aspheric profile with a 6-mm diameter optical zone. Follow-up was at 1, 3, and 6 months.

RESULTS

Repeated thickness measures before and after PRK at different follow-up times showed a significant difference in thickness separately in various zones (P < .001). A significant decrease in thickness was seen 1 month after PRK in all zones. Afterward, epithelial thickening continued in all zones and reached the preoperative thickness in the midperipheral and peripheral zones 6 months later, whereas the thickness in the central 5-mm zone was significantly thicker than before surgery. There was also a significant correlation between changes in spherical equivalent and epithelial thickness from before to 6 months postoperatively in the paracentral and peripheral zones.

CONCLUSIONS

There was a marked decrease in the epithelial thickening pattern at 1 month after PRK, with gradual thickening at 3 and 6 months. Changes in epithelial thickness and spherical equivalent were significant only for the para-central peripheral zone. [J Refract Surg. 2019;35(10):632-641.].

Masked comparison of two silicone hydrogel bandage contact lenses after photorefractive keratectomy

PURPOSE

To compare the efficiency and safety of two bandage contact lenses after photorefractive keratectomy (PRK).

METHODS

In this double-blind study, 45 patients (90 eyes) received PRK in both eyes and wore bandage contact lenses (BCLs), PureVision (Bausch & Lomb, Rochester, NY, USA) in one eye and PureVision2 (Bausch & Lomb, Rochester, NY, USA) in the other eye, randomly assigned. The medication regimen after surgery was the same for both eyes. The epithelial defect's size, conjunctival hyperemia and lens centration were graded objectively using slit-lamp biomicroscopy on days 1, 3 and 5 after surgery. Also ocular symptoms of discomfort including tearing, photophobia, foreign body sensation and visual fluctuations were assessed subjectively at each visit.

RESULTS

The mean epithelial defect size on the first day after operation was similar in eyes fitted with PureVision (30.08 ± 5.30 mm²) and PureVision2 (30.25 ± 5.72 mm²) lenses. (p = 0.79) Contact lens deposits and bulbar hyperaemia on days 1 and 3 after PRK were similar between the two eyes, but were significantly greater on day 5 for PureVision2 lenses. (p = 0.02; p = 0.04 respectively) There was no difference in contact lens decentration, and discomfort symptoms including pain, tearing, foreign body sensation, photophobia and visual fluctuations between the eyes fitted with PureVision and PureVision2. (p > 0.05) CONCLUSIONS: PureVision and PureVision2 contact lenses are equivalent as bandage lenses in important aspects such as corneal re-epithelialization and subjective comfort., although PureVision2 led to a higher incidence of contact lens deposits and conjunctival hyperemia early post-PRK.

Biomechanically-Corrected Intraocular Pressure Compared To Pressure Measured With Commonly Used Tonometers In Normal Subjects

PURPOSE

To compare the biomechanically-corrected intraocular pressure (bIOP) measured by the Corvis ST (Oculus, Wetzlar, Germany) with IOP measurements made by other commonly used tonometers; and to test the correlations between IOP measures and central corneal thickness.

METHODS

One randomly-selected eye from each of 94 healthy subjects was assessed. The bIOP was determined by the CorVis ST and compared with the IOP measurements made by standard Goldmann Applanation Tonometer (GAT: Haag-Streit AG, Bern, Switzerland), the Icare (Icare Finland Oy, Vantaa, Finland), and the Ocular Response Analyzer (ORA-IOPcc: Reichert, New York, USA). Corneal thickness was assessed by the Oculus Pentacam. The correlation between bIOP and the other devices and between CCT were assessed using the Pearson correlation test or Spearman's rho test accordingly to the distribution of these values. The Bland-Altman method and intraclass correlation coefficients (ICC) were used to assess the agreement of bIOP results with IOP obtained with other techniques. The limits of agreement (LoA) were determined as the mean difference ±1.96 SD of the mean differences. In all tests, the significance level was considered to be 0.05.

RESULTS

Mean and SD of the bIOP were 16.11±1.66 mmHg. Significant differences were found between the bIOP and other IOP measurements (GAT, 3.02±2.60 mmHg, p<0.001, Icare, 1.51±2.95 mmHg, p<0.001, IOPcc, 1.09±1.96 mmHg, p<0.001). The lowest and highest mean differences in IOP were with the IOPcc and GAT, respectively. Interestingly, there were no significant differences in bIOP, GAT-IOP and ORA-IOPcc between the eyes with thin or thick corneal thicknesses, with Icare-IOP being the only exception (p<0.001).

CONCLUSION

The Corvis bIOP has a higher correlation with the IOPcc by ORA, which are also compensated for the effects of corneal biomechanics and have less association with corneal thickness relative to the uncorrected GAT and Icare measurements.

Phacoemulsification in bilateral anterior lenticonus in Alport syndrome: A case report

RATIONALE

To report the visual status and results of phacoemulsification cataract surgery in a young patient with Alport syndrome associated with bilateral anterior lenticonus. The milestone of this report is the use of anterior segment optical coherence tomography (AS-OCT) to confirm the central protrusion of the anterior surface of the crystalline lens.

PATIENT CONCERNS

A 23-year-old young woman presented with severe progressive visual loss in both eyes, which started several years ago.

DIAGNOSES

Refractive status was indicative of high myopia with astigmatism and vision was not improved with optimal correction to better than 0.1 in the right eye and 0.2 in the left eye (visual acuities given in decimal notation). Slit-lamp examination showed transparent cornea, anterior lenticonus and posterior sub-capsular cataract in both eyes. The classical appearance of oil droplet was evident using retro-illumination on the slit lamp.

INTERVENTIONS

The natural lenses were replaced with intraocular lens (IOL).

OUTCOMES

An excellent refractive status achieved associated with an uncorrected distance visual acuity 0.9 and 0.8 in the right and left eye, respectively.

LESSONS

AS-OCT is a valuable device for confirming the budging of the anterior crystalline lens surface.

The Effect of Cycloplegia on the Ocular Biometric and Anterior Segment Parameters: A Cross-Sectional Study

Introduction

To evaluate the effects of cycloplegia on the biometric components and anterior segment parameters of the eye.

Methods

In this cross-sectional study, changes to axial length (AL), anterior chamber depth (ACD) lens thickness, anterior chamber angle (ACA) and volume, corneal thickness in the pupil center (PC), corneal curvature (CC) and white-to-white (WTW) following cycloplegia induced by tropicamide 1% in 42 eyes of patients aged 23–58 years were assessed. Biometric components and anterior segment parameters were measured using an IOLMaster 700 (Carl Zeiss Meditec, Jena, Germany) and a Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany), respectively.

Results

Significant statistical changes in ACD (increased by 0.06 ± 0.05 mm; p < 0.001), anterior chamber volume (increased by 15.19 ± 10.32 mm³; p < 0.001), ACA (decreased by 2.18 ± 10.20°; p = 0.029) and lens thickness (decreased by 0.02 ± 0.03 mm; p < 0.001) were observed post-cycloplegia, while the changes in CC, corneal thickness in the PC, WTW and AL were not statistically different (p > 0.05). Also, a significant inferior displacement of the PC along the vertical axes was seen (p = 0.020).

Conclusion

Cycloplegia resulted in a deeper ACD and thinner lens thickness. These changes should be considered in determining intraocular lens (IOL) power to prevent refractive surprises in cataract surgery and also in the phakic IOL implantation.

Predictors of Successful Outcome following Intrastromal Corneal Ring Segments Implantation

Purpose: To assess the preoperative visual, refractive, corneal topo/tomographic, aberrometric and biomechanical parameters as predictive factors of a successful outcome 6 months following intrastromal corneal ring segments implantation. Methods: Sixty-eight keratoconus eyes implanted with Keraring using femtosecond laser technology were assessed. The preoperative assessed parameters included uncorrected and corrected distance visual acuity (UDVA & CDVA), refraction, placido-disk based topography using TMS-4, Scheimplfug tomography using Pentacam HR, corneal biomechanical assessments using Ocular Response Analyzer (ORA) and the wavefront analysis using i-Trace aberrometer. Other variables were type of astigmatism based on orientation of the steep meridian, keratoconus staging based on the Amsler-Krumeich classification and the difference between the axes of refractive astigmatism, topographic astigmatism and comatic aberration based on a difference less or more than 30°. The success criterion was defined based on CDVA, a post-operative CDVA improvement at least two lines were considered as a success and otherwise were recognized as a failure following Keraring implantation. Results: Only UDVA, coincidence of the most elevated points on the front and back corneal surfaces and the difference between UDVA and CDVA showed significant difference between the eyes with successful outcomes and those with unsuccessful results (P < 0.05). Although corneal curvature and astigmatism were higher and corneal thickness was lower in the unsuccessful group, differences were not statistically significant. Conclusion: It is expected that the greater difference between the preoperative uncorrected and corrected distance visual acuity (Δ UDVA-CDVA) and more coincidence of the most elevated points in the two corneal surfaces on the elevation maps increase the rate of successful outcome following the Keraring implantation. Abbreviations: ICRS: intrastromal corneal ring segments; UDVA: uncorrected distance visual acuity; CDVA: corrected distance visual acuity; logMAR: logarithm of minimum angle of resolution; SE: spherical equivalent; IOP: intra-ocular pressure; Km: mean keratometry; CA: corneal astigmatism; WTR: with-the-rule; ATR: against-the-rule; OBL: oblique; SB: symmetric bow-tie; AB: asymmetric bow-tie; IS: inferior steepening; SRAX: skewed radial axis; Q: asphericity (Q-value); CCT: central corneal thickness; CTP: corneal thinnest point; ORA: ocular response analyzer; CH: corneal hysteresis; CRF: corneal resistance factor; HOAs: higher-orders aberrations; RMS: root mean square; SD: standard deviation; CI: confidence interval.

Four-year changes in corneal biomechanical properties in children

BACKGROUND

To determine four-year changes of corneal biomechanical parameters in Iranian children aged seven to eleven years and their correlation with optical components.

METHODS

In this four-year prospective cohort study, 468 children aged seven to eleven years who were initially evaluated in 2012 were re-evaluated in 2016-2017. Multi-stage stratified cluster sampling was applied. Cycloplegic refraction, biometry using LENSTAR/BioGraph, and corneal biomechanical assessment using Ocular Response Analyzer (ORA) were undertaken for each participant. The corneal biomechanical parameters assessed were corneal hysteresis (CH), corneal resistance factor (CRF), areas under the peaks 1 and 2 (p1 and p2 areas) and irregularity indices (A and B indices).

RESULTS

All biomechanical parameters except A index decreased in phase 2. The mean changes of CH and CRF were 0.68 ± 0.16 mmHg (for both parameters) during four years. The mean difference in CH and CRF was 0.23 ± 0.23 and 0.24 ± 0.23 mmHg in females and 1.03 ± 0.23 and 0.96 ± 0.23 mmHg in males, respectively. Different age groups showed varying amounts of decrease in all parameters except for A index. The age group 'ten years' experienced the smallest decrease in CH (0.02 ± 0.48 mmHg) and CRF (0.20 ± 0.47 mmHg) and the age group 'eleven years' showed the greatest decrease in CH (1.41 ± 0.35 mmHg) and CRF (0.99 ± 0.34 mmHg). According to linear regression analysis, CH and CRF had a significant direct relationship with corneal power and an inverse relationship with axial length (p < 0.001).

CONCLUSION

Age and sex are influencing factors on the ORA parameters. Older age is associated with reduced biomechanical parameters and reductions are more significant in males than females. Axial elongation and corneal flattening decrease CH and CRF.

Long-term Evaluation of Corneal Biomechanical Properties After Corneal Cross-linking for Keratoconus: A 4-Year Longitudinal Study

PURPOSE

To compare the long-term changes in corneal biomechanics, topography, and tomography before and 4 years after corneal cross-linking (CXL) with the Dresden protocol and correlate these changes with visual acuity.

METHODS

In this longitudinal study, 18 eyes of 18 patients with progressive keratoconus who were treated with CXL were included. All patients received a standard ophthalmological examination and were examined by Placido disc-based topography, Scheimpflug tomography, and biomechanical assessments with the Corvis ST (OCULUS Optikgeräte GmbH, Wetzlar, Germany) and Ocular Response Analyzer (ORA; Reichert Ophthalmic Instruments, Buffalo, NY) before and 4 years after CXL. The main outcome measures were dynamic corneal response (DCR) parameters obtained from the Corvis ST, corneal hysteresis (CH), corneal resistance factor (CRF), visual acuity, refraction, corneal curvature, and corneal thickness.

RESULTS

There were no significant differences in mean visual acuity, refraction, intraocular pressure, corneal topography, corneal astigmatism in both corneal surfaces, maximum keratometry, corneal thickness at apical and thinnest points, thickness profile indices, corneal volume, and specular microscopy before and 4 years after CXL (P > .05). Significant changes were observed in many DCR parameters, including radius at highest concavity and integrated inverse radius, both of which were consistent with stiffening. The CH and CRF values after CXL were not statistically significant. The new parameters using the Corvis ST include integrated inverse concave radius, which showed a significant decrease 1.07 ± 0.93 mm^-1, consistent with stiffening. The corneal stiffness parameter at the first applanation, Ambrósio's Relational Thickness to the horizontal profile, deformation amplitude ratio, and Corvis Biomechanical Index as a combined biomechanical screening parameter did not show significant changes.

CONCLUSIONS

CXL is a minimally invasive treatment option to prevent keratoconus progression over 4 years. Pressure-derived biomechanical parameters obtained from the ORA did not show any change following CXL at 4 years of follow-up, whereas the Corvis ST DCR parameters detected changes in corneal biomechanical properties. [J Refract Surg. 2018;34(12):849-856.].

Advances in Biomechanical Parameters for Screening of Refractive Surgery Candidates: A Review of the Literature, Part III

Corneal biomechanical properties have garnered significant interest in their relation to the development of ectatic corneal disease. Alongside the advent of corneal tomography and Scheimpflug imaging such as Pentacam and Galilei, there have been advances in assessing the cornea based on its biomechanical characteristics. Though the aforementioned imaging systems are highly capable of identifying morphologic abnormalities, they cannot assess mechanical stability of the cornea. This article, in contrast to Parts I and II of this article series, will focus on in vivo corneal biomechanical imaging systems. The two most readily available commercial systems include the Corvis ST and the Ocular Response Analyzer. Both of these systems aimed to characterize corneal biomechanics via distinct measurements. While in Parts I and II of this article series the authors focused on elevation, pachymetric, and keratometric data, the purpose of this article was to summarize biomechanical parameters and their clinical use in screening refractive surgery candidates. Moreover, this article explores biomechanical decompensation and its role in the development of corneal ectasia and keratoconus. There is a focus on the diagnostic accuracy of biomechanical indices in the identification of diseases such as keratoconus that may preclude a patient from undergoing refractive surgery.

Galilei Corneal Tomography for Screening of Refractive Surgery Candidates: A Review of the Literature, Part II

Corneal topography is the most widely used technology for examining the anterior corneal surface. Scheimpflug imaging is a newer technique that allows for measurement of both the anterior and posterior corneal surface, which allows for three-dimensional reconstruction of the cornea. This is of particular interest and value in the field of cataract and refractive surgery. The Galilei camera is a commercially available dual Scheimpflug system that combines curvature data from Placido disc-based corneal topography with elevation data from Scheimpflug technology. The addition of Placido disc topography makes the Galilei unique from its more popular counterpart, the Pentacam, which was discussed in Part I. Compared to the Pentacam, and however, the Galilei analyzer is a newer system that has emerged as a valuable screening tool given its dual Scheimpflug capability. In the first article of this series, the authors summarized the refractive indices available on the Pentacam system with the purpose of identifying the best diagnostic parameters for keratoconus. Similarly, the purpose of this article is to summarize corneal surface indices available on the Galilei system and evaluate their use in screening of the refractive surgery candidate. Since post-operative keratectasia is still prevalent, this paper aims to identify the most clinically relevant indices that may be used in pre-operative evaluation.

Pentacam® Corneal Tomography for Screening of Refractive Surgery Candidates: A Review of the Literature, Part I

Corneal tomography and Scheimpflug imaging are frequently used to analyze the corneal surface, especially in the field of cataract and refractive surgery. The Pentacam system is one of the most commonly used commercially available systems for this purpose. Through a rotating Scheimpflug camera, the system is capable of creating a three-dimensional map of the cornea. These advances in tomography have simultaneously enhanced the ability of clinicians to screen surgical candidates and detect subtle corneal changes in diseases such as keratoconus. However, there remains a need to enhance diagnosis in order to recognize mild and early forms of corneal ectasia. As iatrogenic ectasia and keratoconus are dreaded complications of refractive surgery, it is imperative to screen patients appropriately prior to surgery. The Pentacam is one of many systems utilized in the screening process, but the literature has not identified specific protocol nor parameters that are capable of carrying out this process appropriately. Post-operative keratoconus continues to occur despite the advances in technology seen in corneal imaging. Therefore, clear indices for screening are required in order to diagnose early forms of keratoconus and other corneal diseases that may exclude the seemingly asymptomatic patient from undergoing refractive surgery. This article aims to summarize the indices available on the Pentacam system and to identify the most accurate parameters for screening of the refractive surgery candidate.

Comparison of cyclopentolate versus tropicamide cycloplegia: A systematic review and meta-analysis

PURPOSE

The aim of the present meta-analysis is to compare the efficacy of cyclopentolate and tropicamide in controlling accommodation during refraction.

METHODS

A comprehensive literature search was performed in PubMed, Scopus, Science direct and Ovid databases by the key words: "tropicamide"; "cyclopentolate"; "cycloplegia" and "cycloplegic" from inception to April 2016. Methodological quality of the literature was evaluated according to the Oxford Center for Evidence Based Medicine and modified Newcastle-Ottawa scale. Statistical analyses were performed using Comprehensive Meta-Analysis (version 2; Biostat Inc., USA).

RESULTS

The present meta-analysis included six studies (three randomized controlled trials and three case-control studies). Pooled standardized difference in the mean changes in the refractive error was 0.175 D [lower and upper limits: -0.089; 0.438] more plus in the cyclopentolate group compared to the tropicamide group; however, this difference was not statistically significant (p=0.194; Cochrane Q value=171.72 (p<0.05); I²=95.34%). Egger's regression intercept was -5.33 (p=0.170). Considering type of refractive errors; refractive assessment procedure and age group; although cycloplegic effect of cyclopentolate was stronger than tropicamide; however, this effect was only statistically significant in children; hyperopic patients and with retinoscopy.

CONCLUSION

We suggest that tropicamide may be considered as a viable substitute for cyclopentolate due to its rapid onset of action. Although these results should be used cautiously in infants and in patients with high hyperopia or strabismus when using tropicamide as the sole cycloplegic agent especially in situations that the findings are variable or there is no consistency between the examination results and clinical manifestations of the visual problems.

Changes in the ABCD Keratoconus Grade After Intracorneal Ring Segment Implantation

PURPOSE

To assess the changes in the ABCD keratoconus staging system 6 months after intracorneal ring segment implantation.

METHODS

Fifty eyes of 50 patients with keratoconus who were implanted with the Keraring (Mediphacos, Belo Horizonte, Brazil) using the femtosecond laser were assessed. Preoperative and postoperative assessments included determination of distance uncorrected visual acuity and distance corrected visual acuity (DCVA), refraction, and Scheimpflug tomography with the Pentacam HR. In the ABCD keratoconus staging system, the elements A, B, C, and D stand for anterior and posterior radii of curvature in a 3.0-mm zone centered on the thinnest point (TP), corneal thickness at the TP, and DCVA, respectively.

RESULTS

Keraring implantation produced significant flattening changes (preoperatively vs. postoperatively) in the anterior (6.60 ± 0.48 vs. 7.22 ± 0.57 mm, P < 0.001) and posterior (4.99 ± 0.47 vs. 5.16 ± 0.53 mm, P = 0.002) radii of curvature of the 3-mm zone centered on the corneal TP associated with a statistically significant improvement in the DCVA (0.56 ± 0.24 vs. 0.70 ± 0.22 in the decimal notation, P = 0.001) with no significant change in the corneal thickness at the TP (P = 0.285). The most changes occurred in element A of the ABCD keratoconus classification. Also, a 1-stage change was observed for element B, whereas elements C and D did not show changes in their postoperative stages after ring implantation. ABCD keratoconus staging before ring implantation was A2B3C2D1 and changed to A1B2C2D1 6 months after surgery.

CONCLUSIONS

The ABCD staging system provides a more comprehensive guide that better illustrates the structural changes and visual acuity as one aspect of visual function after the implantation of the intrastromal corneal ring segments.

Effect of Induced Vertical Disparity on Horizontal Fusional Reserves

PURPOSE

The aim of this study was to investigate the effects of induced vertical disparity on horizontal fusional reserves at near.

MATERIALS AND METHODS

In 170 healthy subjects wearing best corrective refraction, the negative and positive horizontal fusional reserves were measured with base-in (BI) and base-out (BO) prisms, respectively, in the presence of 0.5 prism diopters (^∆) and 1^∆ vertical prisms placed in trial frames in front of the right eye. The prism power was slowly increased step by step until the subject reported sustained blur, break, and recovery. These were compared to horizontal fusional reserves in the same subjects without a vertical prism. Data were analyzed in SPSS.17 software using a repeated measures ANOVA.

RESULTS

Induced vertical disparity decreased negative fusional reserves (NFR) horizontally and was more significant with 1^∆ vertical disparity (P<0.001). There were significant differences between the blur (P<0.001), break (P<0.001), and recovery (P<0.001) for NFR before and after induced vertical disparity and no significant difference between blur (P=0.173) and recovery points (P=0.261) with a marginal difference for break points (P=0.045) for the positive fusional reserves (PFR).

CONCLUSION

Inducing vertical disparity even with small magnitudes affects all 3 aspects (blur, break, and recovery) of horizontal negative fusional reserves while only break is affected in positive fusional reserves. These changes are statistically significant but do not seem to be clinically significant except for cases accompanied by symptoms.

Corneal hysteresis and corneal resistance factor in pellucid marginal degeneration

Purpose

To evaluate and compare corneal hysteresis (CH) and corneal resistance factor (CRF) in pellucid marginal degeneration (PMD), keratoconus (KCN), and normal eyes using the Ocular Response Analyzer (ORA).

Methods

In this retrospective study, corneal biomechanical parameters were measured in patients with PMD (n = 102) and KCN (n = 202) and normal subjects (n = 208) using the ORA. Data, including full patient history as well as the results of refraction, slit-lamp biomicroscopy, Pentacam HR (Oculus), and ORA (Reichert; Buffalo, New York, USA), were collected from medical records. Also, the data of only one eye per individual were selected for the analysis. The inclusion criteria for PMD and KCN groups were a reliable diagnosis of these ectatic disorders based on the clinical and corneal tomographic findings. CH, CRF, CH–CRF, intraocular pressure (IOP) measurements were assessed for each subject. Data were analyzed with SPSS and MedCalc using the ANOVA, Pearson Correlation, and receiver operating characteristic (ROC) curve analysis.

Results

The mean CH was 8.91 mmHg ± 1.05 [standard deviation (SD)], 8.43 ± 0.78, and 10.89 ± 1.08 in the PMD, KCN, and normal group, respectively. Also, the mean CRF was 8.21 ± 1.35, 7.19 ± 1.11, and 10.69 ± 1.41 in the PMD, KCN, and normal group, respectively. ANOVA showed differences in the mean CH, CRF, and CH–CRF between three groups (P < 0.001). Also, ROC curve analysis showed the cut-off points ≤9.5, ≤9.5, and >1.3 mmHg for CH, CRF, and CH–CRF in the PMD group, respectively. For biomechanical parameters in PMD eyes, CRF had the highest sensitivity (75.49%) while the greatest area under the ROC curve (AUC) was seen for CH (0.903). Moreover, central corneal thickness (CCT) showed no correlation with CH (P = 0.30, r = −0.104) or CRF (P = 0.75, r = 0.033) in the PMD group.

Conclusions

This study presented the values of corneal biomechanics for PMD using the ORA. The results of the ORA were markedly different between PMD, KCN, and normal eyes.

Dysfunctional lens syndrome

PURPOSE

To report the pre- and post-operative findings of a case with dysfunctional lens syndrome.

METHODS

An adult patient was evaluated using iTrace aberrometer, Tomey topographer and slitlamp biomicroscopy to confirm dysfunctional lens syndrome.

RESULTS

A 45-year-old male patient presented with the chief complaint of poor visual quality; uncorrected visual acuity 20/40 in the right eye, best spectacle corrected visual acuity 20/25 in the right eye with refraction Plano/-1.50 × 80 (SE = -0.75D). Pre- and post-operative root-mean-square (RMS) of total higherorder aberrations in the entire eye, the internal optics and the cornea were 0.350 & 0.257, 0.311 & 0.236 and 0.214 & 0.191 micron (μ), respectively. Also, the magnitude of preoperative total, internal and corneal coma was 0.254 μ × 222°, 0.274μ×242° and 0.097μ × 131° and postoperative values were 0.170 μ × 162°, 0.131 μ × 177°, 0.054 μ × 125°, respectively.

CONCLUSION

These results show that sometime the HOAs of the internal optics, mainly crystalline lens, are not compensated by the cornea and this may cause visual discomfort in the absence of any significant cataract, this situation is known as dysfunctional lens syndrome (DLS).

Part-time versus full-time occlusion therapy for treatment of amblyopia: A meta-analysis

PURPOSE

To compare full-time occlusion (FTO) and part-time occlusion (PTO) therapy in the treatment of amblyopia, with the secondary aim of evaluating the minimum number of hours of part-time patching required for maximal effect from occlusion.

METHODS

A literature search was performed in PubMed, Scopus, Science Direct, Ovid, Web of Science and Cochrane library. Methodological quality of the literature was evaluated according to the Oxford Center for Evidence Based Medicine and modified Newcastle-Ottawa scale. Statistical analyses were performed using Comprehensive Meta-Analysis (version 2, Biostat Inc., USA).

RESULTS

The present meta-analysis included six studies [three randomized controlled trials (RCTs) and three non-RCTs]. Pooled standardized difference in the mean changes in the visual acuity was 0.337 [lower and upper limits: -0.009, 0.683] higher in the FTO as compared to the PTO group; however, this difference was not statistically significant (P = 0.056, Cochrane Q value = 20.4 (P = 0.001), I2 = 75.49%). Egger's regression intercept was 5.46 (P = 0.04). The pooled standardized difference in means of visual acuity changes was 1.097 [lower and upper limits: 0.68, 1.513] higher in the FTO arm (P < 0.001), and 0.7 [lower and upper limits: 0.315, 1.085] higher in the PTO arm (P < 0.001) compared to PTO less than two hours.

CONCLUSIONS

This meta-analysis shows no statistically significant difference between PTO and FTO in treatment of amblyopia. However, our results suggest that the minimum effective PTO duration, to observe maximal improvement in visual acuity is six hours per day.

Accommodative amplitude using the minus lens at different near distances

Purpose:

The purpose of this study was to compare the mean findings and the repeatability of the minus lens (ML) amplitude of accommodation (AA) at 33 cm and 40 cm.

Materials and Methods:

AA was measured from the dominant eye of 120 fully corrected subjects using the ML procedure when viewing the target at both 33 and 40 cm. Each measurement was repeated between 24 and 48 hours after the first trial.

Results:

Mean AA when tested at 33 cm and 40 cm was 10.20 diopter (D) (standard deviation [SD] =1.24) and 8.85 D (SD = 1.23), respectively (P < 0.001). The limits of agreement of the measured amplitude calculated with taking into account of the replicates at 33 and 40 cm were − 0.19 (95% confidence interval [CI]: −0.34 to −0.04) and 2.53 (95% CI: 2.38 to 2.68), respectively. The repeatability of testing at the two distances 33 and 40 cm was ± 1.24 and ± 0.99, respectively. In addition, the retest reliability of measured amplitude using the intraclass correlation coefficient was 0.87 (95% CI: 0.789–0.920) at 33 cm and 0.91 (95% CI: 0.872–0.945) at 40 cm.

Conclusion:

There is no agreement in the obtained amplitude at the two measurement distances. Testing the ML AA at 40 cm may be superior given that a lower repeatability coefficient was observed. However, it is unclear whether the larger amplitude measured at 33 cm reflects a larger increase in accommodation (greater proximity effect) or a decrease in the ability to perceive the first slight sustained blur.

Comparing measurement techniques of accommodative amplitudes

Aim and Background:

This study was designed to compare four standard procedures, for determining the monocular accommodative amplitudes.

Materials and Methods:

Fifty-two students participated in this analytical-descriptive study. Accommodative amplitudes were measured using four common clinical techniques, namely: Push-up, push-down, minus lens, and modified push-up.

Results:

The highest amplitude was obtained using the push-up method (11.21 ± 1.85 D), while the minus lens technique gave the lowest finding (9.31 ± 1.61 D). A repeated-measures Analysis of Variance (ANOVA) showed a significant difference between these methods (P < 0.05), further analysis showed that this difference was only between the minus lens and other the three methods (the push-up (P < 0.001), the push-down (P < 0.001) and the modified push-up (P < 0.001)). The highest and the lowest mean difference was related to the push-up with the minus lens, and the push-down with the modified push-up, while the highest and the lowest 95% limits of agreement were related to the push-up with the modified push-up and the push-up with the push-down methods. There was almost a perfect agreement between the push-up and the push-down method, whereas, a poor agreement was present between the modified push-up and the minus lens technique, and a fair agreement existed between the other pairs.

Conclusions:

The quick and easy assessment of the amplitude using the push-up and the push-down methods compared to other methods, and the obtained perfect agreement between these two methods can further emphasize their use as a routine procedure in the clinic, especially if a combination of the two techniques is used to offset their slight over- and underestimation.

The effectiveness of home-based pencil push-up therapy versus office-based therapy for the treatment of symptomatic convergence insufficiency in young adults

Purpose:

To compare the effectiveness of pencil push-up therapy (PPT) versus office-based vision therapy in patients with convergence insufficiency.

Materials and Methods:

In this study, 60 students from Zahedan University of Medical Sciences with convergence insufficiency were selected. After determining their refractive error (with a retinoscope), near point of convergence (by millimeter ruler), near heterophoria (by alternate prism cover test), and positive fusional vergence at near (by prism bar), subjects were divided into two groups to receive PPT (at least three times a day for 5 minutes each time) or office-based therapy (two times each week for 60 minutes each visit) without home reinforcement. Subjects were re-examined 4 and 8 weeks after initiation of treatment. Statistical analysis was performed with the independent samples t-test and the analysis of variance (ANOVA). Statistical significance was indicated by P < 0.05.

Results:

The near point of convergence, phoria, and positive fusional vergence were not statistically different between the two groups before treatment (P > 0.05). After 4 and 8 weeks of therapy, only the positive fusional vergence was statistically significantly different between groups (P = 0.001). Results from ANOVA indicated a considerable difference between the two groups in general but the observed difference was related only to positive fusional vergence.

Conclusion:

PPT and office-based vision therapy are comparable for treatment of convergence insufficiency. While we do not deny the more efficacious nature of office-based therapy, it is not always practical, may be too expensive, and may not be locally available. A home-based therapy offers a cost-effective reasonable alternative.

Stereoacuity as an indicator of prism adaptation

PURPOSE

The purpose of this study was to determine whether stereoacuity can be used as an indicator of prism adaptation. In particular, we wanted to know whether the time required for stereoacuity to return to the initial level after viewing through a prism can be used to determine the degree of adaptation.

MATERIALS AND METHODS

Eighteen subjects participated in this study. Stereoacuity and dissociated phoria were determined using the TNO stereotest and the Maddox rod, respectively. Prism vergences were measured using a prism bar. For each participant, prism power equivalent to the blur point of base-in (BI) and base-out (BO) fusional vergence at 40 cm was divided and placed in front of both eyes. At 0, 3, 6, 9 and 12 min after prism introduction, the stereoacuity was measured, and at 0 and 12 min, the heterophoria was measured.

RESULTS

The repeated measures ANOVA showed a significant difference between the mean stereoacuity for BI and BO prisms at the different measurement times (p < 0.05). For BO prism, the initial value was different between 0 and 3 min after the prism introduction, whereas for BI prism, a difference in stereoacuity was found between the pre-prism value and the value at 0, 3 and 6 min. The size of the heterophoria with BO and BI prisms was different from 0 to 12 min (p < 0.05).

CONCLUSION

The time required for stereoacuity to return to baseline level was more than 3 min for BO, and more than 6 min for BI prism. In addition, the time required to return to baseline values was not similar for the stereoacuity and heterophoria. The recovery of stereoacuity is slower when adapting to divergence, as when looking from near to far. This implies that stereopsis responds faster to near targets than to distant one, and may precede complete phoria adaptation.

Effect of target distance on accommodative amplitude measured using the minus lens technique

BACKGROUND

The aim was to investigate the effect on the measured amplitude of accommodation and repeatability of using the minus lens technique with the target at distance or near.

METHODS

Forty-three students (average age: 21.17 ± 1.50 years, 35 female) had their amplitude of accommodation measured with minus lenses on top of their distance correction in a trial frame with the target at far (6.0 m) or near (0.4 m). The minus lens power was gradually added with steps of 0.25 D. Measurements were taken on two occasions at each distance, which were separated by a time interval of at least 24 hours.

RESULTS

The measured amplitude at six metres was significantly lower than that with the target at 40 cm, by 1.56 ± 1.17 D (p < 0.001) and this varied between individuals (r = 0.716, intraclass correlation coefficient = 0.439). With either target distance, repeated measurement was highly correlated (r > 0.9) but the agreement was better at 6.0 m (±0.74 D) than at 40 cm (± 0.92 D).

CONCLUSION

The measurements of the amplitude of accommodation with the minus lens technique using targets at far or near are not comparable and the difference between the target distances may provide clinically relevant information.

Accommodative response under monocular and binocular conditions as a function of phoria in symptomatic and asymptomatic subjects

BACKGROUND

The neurological linkage of vergence and accommodation is a factor which can affect accuracy of accommodation, is in turn associated with symptoms of near-related visual discomfort. The purpose of this study was to compare the accommodative response under monocular and binocular conditions in symptomatic and asymptomatic participants with different near phorias.

METHODS

Seventy students at Zahedan University of Medical Sciences, Iran (mean age: 21.2 ± 1.7 years; age range: 18 to 25 years) participated. The participants were divided into symptomatic and asymptomatic groups according to the convergence insufficiency symptom survey questionnaire score. The type and magnitude of the near dissociated phoria were determined using the prism neutralised cover test. The accommodative lag was measured by the 'monocular estimate method' (MEM) retinoscopy, at first under binocular and then monocular conditions. Testing distance was 40 cm.

RESULTS

The accommodative lag in exophoric participants was lower under binocular conditions compared to monocular and in esophoric participants greater under binocular than under monocular conditions. The binocular accommodative response (AR) was greatest in participants with high exophoria at near vision and least in participants with esophoria at near vision (p < 0.001; one-way analysis of variance). The difference between binocular lag and monocular lag was significantly greater in symptomatic participants than in asymptomatic participants in both exophoria (p < 0.001) and esophoria (p = 0.009) (independent samples t-test).

CONCLUSION

The near binocular accommodative response was related to near heterophoria. Higher levels of vergence accommodation, resulting in differences in lag under monocular and binocular conditions, may be a factor in near point asthenopia.

Evaluation of fixation disparity curve with the modified near Mallett unit and the wesson fixation disparity card in symptomatic and asymptomatic subjects

PURPOSE

The purpose of this study is the evaluation of fixation disparity curve (FDC) parameters with an instrument that includes a central fusion lock (the modified near Mallett unit) and another without one (the Wesson fixation disparity card) to determine which is useful for diagnosis of symptomatic from asymptomatic subjects.

MATERIALS AND METHODS

In this analytical-descriptive study, 100 students were selected randomly and divided into symptomatic and asymptomatic groups. FDC parameters were determined with the Wesson card and the modified near Mallett unit for each subject and compared in symptomatic and asymptomatic groups. Data were analyzed by Wilcoxon, Mann-Whitney U, Spearman correlation coefficient and Chi-square tests.

RESULTS

The mean slope, y-intercept, and x-intercept with the Mallett unit and the Wesson card were significantly different in the symptomatic and asymptomatic groups (p < 0.001). Significant correlations were obtained between the Mallett unit and the Wesson card in y-intercept, x-intercept and slope (p < 0.001). There was a significant difference in the distributions of fixation disparity curve types in the two symptom groups with the Mallett unit (p = 0.01) and the Wesson card (p = 0.002) by Chi-square test.

CONCLUSIONS

Among symptomatic participants in this study, both Type I and Type III FD are more common than previously thought, but depend upon the method used to measure it. The x-intercepts were on average displaced in the base-in direction, y-intercepts were shifted in the exo direction, and the slopes were steeper with the Wesson FD card compared with the modified near Mallett unit. This may be related to the design of two devices. These differences were more significant in the symptomatic group.

Body mass index and binocular vision skills

INTRODUCTION

Body Mass Index (BMI) is of increasing interest to eye care practitioners. Associations have recently been proven between high BMI and several diseases affecting the eyes, including AMD, intracranial hypertension, optic disc cupping, and glaucoma. The symptoms of dizziness and vertigo have also been associated with high BMI. However, to these authors' knowledge, there has been no study performed comparing BMI to binocular function.

METHODS

In this analytical-descriptive study, 119 randomly selected young subjects had their BMI measured, along with refractive error, dissociated phoria, near point of convergence, vergence ranges and facility, and stereopsis.

RESULTS

In most situations, the subjects classified as normal and overweight, based on their BMI had better performance than those classified as underweight or obese. The worst binocular performance was found in underweight subjects. The one-way ANOVA showed only statistically significant differences between mean of near point of convergence and vergence facility, in different states of BMI.

CONCLUSION

Unlike most ocular diseases that are adversely affected by higher BMI values, most binocular vision skills are adversely affected by lower BMI values. The possible reasons for this are discussed.