Classification of normal corneal topography based on computer-assisted videokeratography

Repeatability and Agreement of 4 Biometers Measuring Corneal Astigmatism in Eyes With Irregular Corneal Astigmatism Component

PURPOSE

To investigate the repeatability and agreement of corneal astigmatism measurements in eyes with irregular corneal astigmatism component (ICAC) using four devices: IOLMaster 700 biometer, Lenstar 900 biometer, iTrace, and Pentacam.

DESIGN

Prospective cross-sectional reliability analysis.

METHODS

Sixty-four eyes (52 patients) with ICAC were examined three times using the four devices. The eye with ICAC in this study is defined as the cornea has a certain degree of irregular astigmatism (asymmetric and/or skewed bowtie pattern of corneal topography according to corneal topography classification), accompanied with total corneal higher-order aberrations in the 4 mm zone of 0.3 µm or greater. Corneal astigmatism was evaluated using three categories: anterior corneal astigmatism (ACA), posterior corneal astigmatism, and total corneal astigmatism (TCA). The repeatability was determined using the ∆Ast (arithmetic mean of vector differences among three repeated corneal astigmatism measurements). Bland-Altman plots and astigmatism vector analyses were employed to assess agreement.

RESULTS

The IOLMaster 700 (∆Ast = 0.27 ± 0.20 D) showcased higher repeatability in ACA measurements compared to iTrace (∆Ast = 0.37 ± 0.38 D, P = .040) and Pentacam (∆Ast = 0.50 ± 0.22 D, P < .001), and paralleled the performance of Lenstar 900 (∆Ast = 0.31 ± 0.26 D, P = .338). The Pentacam (∆Ast = 0.09 ± 0.07 D, P < .001) demonstrated superior repeatability in posterior corneal astigmatism, whereas the IOLMaster 700 (∆Ast = 0.33 ± 0.23 D, P < .001) excelled in TCA. The IOLMaster 700 exhibited good agreement with either Lenstar 900 or iTrace, characterized by narrow 95% limits of agreement and clinically acceptable vector differences. Conversely, vector differences between Pentacam and the other three devices in ACA and TCA measurements were clinically significant, exceeding 0.50 D (all P < .05).

CONCLUSIONS

In terms of repeatability of corneal astigmatism measurements in eyes with ICAC, the IOLMaster 700 and Lenstar 900 outperformed iTrace and Pentacam. While the IOLMaster 700 can be used interchangeably with either Lenstar 900 or iTrace, the Pentacam is not interchangeable with the other three devices.

Effectiveness of toric intraocular lens implantation for correcting irregular corneal astigmatism in cataract eyes

A retrospective cohort study was conducted to observe the correction effect of Toric intraocular lens (IOL) implantation in cataract eyes with specific types of irregular corneal astigmatism. Thirty-four eyes with either the "asymmetric bow-tie" pattern (Type I) or the "angled bow-tie" pattern (Type II) were included. Corneal topography was assessed using Pentacam HR, and changes in preoperative corneal astigmatism, visual acuity, manifest refraction, and objective visual quality were measured and compared. The average uncorrected distance visual acuity improved significantly from 0.86 ± 0.40 logMAR to 0.22 ± 0.15 logMAR (P < 0.001). Preoperative corneal astigmatism of 2.05 ± 0.90 D was corrected to a postoperative residual astigmatism of 0.78 ± 0.57 D (P < 0.001), with 32% of eyes within 0.50 D. The residual astigmatism prediction errors in Type I and Type II cases were (0.97 ± 0.68 D) and (0.66 ± 0.37 D), respectively (P = 0.100). The mean spherical equivalent prediction error in Type II cases (0.07 ± 0.36 D) was significantly smaller than that in Type I cases (- 0.29 ± 0.52 D) (P = 0.030). This study concludes that Toric IOL implantation effectively corrects specific types of irregular corneal astigmatism in cataract surgery. Eyes with the "angled bow-tie" pattern show higher accuracy in refractive predictions compared to eyes with the "asymmetric bow-tie" pattern.

Artificial Tear Instillation-Induced Changes in Corneal Topography

This study aims to compare changes of corneal topography (Galilei G4) before and after the instillation of artificial tears in patients with dry eye disease (DED). Corneal topography was performed in patients 1 min before and after artificial tear instillation. Two types of artificial tears were used: 1% polysorbate 80 (PSB) and 0.5% carboxymethylcellulose (CMC). Of 135 patients, PSB and CMC were instilled in 101 and 34 eyes, respectively. The average value of Sim K increased significantly after instillation (44.07 ± 2.26 diopter (D)) compared to before (43.90 ± 2.02 D, p = 0.006) the instillation of artificial tears. Mean Sim K astigmatism was statistically increased after PSB instillation (1.48 ± 2.17 D) compared to before instillation (1.31 ± 2.10 D, p = 0.049). An axis change of astigmatism 10° or more after artificial tear instillation was found in 51.9% of patients, and 30° or more in 20.0% of patients. Increased Sim K value and significant changes in the astigmatic axis in the corneal topography were observed after instillation of artificial tears in DED patients. PSB instillation had a greater effect on corneal keratometry values than CMC instillation.

Correction of high astigmatism with toric intraocular lens in eyes with corneal transplant

OBJECTIVES

To evaluate the results of toric intraocular lens (IOL) implantation during cataract surgery in eyes with high regular astigmatism associated with prior penetrating keratoplasty (PK).

METHODS

A retrospective data analysis of patients with prior PK, who underwent uncomplicated cataract surgery with hydrophobic toric single piece IOL (EyeCryl Toric®, Biotech Vision Care, Luzern, Switzerland).

RESULTS

A total of 18 eyes of 18 patients were included in the study. The mean age was 53.4 ± 12.4 (25-70) years. The mean follow-up period was 15.5 (4-24) months. The mean best corrected visual acuity (BCVA) significantly increased from 1.36 ± 1.0 logMAR to 0.31 ± 0.17 logMAR (p < .001) pre- and post-operative 4 weeks, respectively. There was no significant change in mean BCVA during follow-up; mean BCVA was 0.32 ± 0.17 logMAR at the last visit. The mean pre-operative topographic astigmatism was 6.52 ± 1.80 diopters (D). The mean manifest refraction astigmatism was decreased from 6.55 ± 1.62 D to 2.80 ± 1.43 D (p˂0.001). The mean Surgically induced astigmatism (SIA) was 3.74 ± 0.77 D according to vector analysis. There was no patient with graft rejection or failure, the mean endothelial cell loss rate was 12.75 ± 3.76% (7-17%). There was no patient requiring IOL reposition.

CONCLUSIONS

Toric IOL implantation during cataract surgery provides an option to correct astigmatism in post-PK eyes with high regular astigmatism. When appropriate patients are selected it is a safe method to achieve significant improvements in visual acuity and astigmatism.

Prevalence of Corneal Topographic Patterns in Ectatic Corneal Diseases

SIGNIFICANCE

The article highlights various topographic patterns and their prevalence in a large spectrum of ectatic corneal diseases (ECDs). Knowledge of these patterns can help clinicians for quicker diagnosis and selection of appropriate contact lens design.

PURPOSE

This study aimed to determine various corneal topography patterns and their prevalence in patients with ECDs who visited a tertiary eye hospital in western India.

METHODS

Keratoconus, pellucid marginal degeneration, keratoglobus, and post-refractive surgery progressive corneal ectasia are considered under ECDs. This cross-sectional retrospective study reviewed records of 632 consecutive patients with clinical ECDs at their first presentation. The right eye was considered for pattern analysis. In cases with suspected or forme fruste ectasia in the right eye, the fellow eye was considered. A sagittal map with standard scale of Atlas 9000 topographer (Carl Zeiss Meditec AG, Jena, Germany) was used for pattern analysis. They were classified into 18 categories and grouped under five groups. The prevalence of these patterns was calculated and assessed with 95% confidence interval (CI).

RESULTS

The mean ± SD age of patients was 23.6 ± 8.2 years. The highest prevalence was of asymmetric patterns (39.6% [95% CI, 35.7 to 43.5%]; asymmetric bowtie [AB] with steepest radial axis index [SRAX], 18.8%; AB with inferior steep, 16.0%; AB with superior steep [SS], 3.2%; symmetric bowtie with SRAX, 1.6%) and of central or paracentral patterns (28.6% [95% CI, 25.1 to 32.3%]; inferior steep, 12.2%; heart, 7.4%; oval, 4.1%; symmetric bowtie, 2.4%; round, 1.6%; irregular, 0.9%) followed by advanced patterns (17.3% [95% CI, 14.4 to 20.4%; nonmeasurable, 5.4%; globus, 4.9%; indiscriminate, 7.0%). The peripheral patterns were 11.7% (95% CI, 9.3 to 14.4%) (claw, 6.3%; junctional, 3.2%; butterfly, 1.9%; SS, 0.3%). Rare patterns were 2.8% (95% CI, 1.7 to 4.5%) (superior [junctional, claw, and heart], AB with SS with SRAX, and AB with SRAX located temporally).

CONCLUSIONS

Asymmetric and central or paracentral are the most common patterns in our study. The higher prevalence of advanced patterns indicates the need for earlier diagnosis of ECDs in our population. The peripheral patterns also have significant prevalence.

Clinical Spectrum and Geographic Distribution of Keratitis Fugax Hereditaria Caused by the Pathogenic Variant c.61G>C in NLRP3

PURPOSE

To chart clinical findings in individuals with keratitis fugax hereditaria (KFH) and the geographic distribution of their ancestors.

DESIGN

A prospective cross-sectional study.

METHODS

This study took place in a tertiary referral center with a cohort of 84 Finnish patients (55% female) from 25 families with the pathogenic nucleotide-binding domain, leucine-rich repeat (NLR) family pyrin domain containing 3 (NLRP3) variant c.61G>C. Observation procedures and main outcome measures were Sanger sequencing, clinical examination, corneal imaging, and a questionnaire regarding symptoms, quality of life, treatment, and comorbidities.

RESULTS

The oldest members in each family were born in Ostrobothnia in Western Finland or in Southwestern Finland with historical ties to Sweden. One carrier was asymptomatic. Most (77%, 46/60) experienced their first attack between age 6 and 20 years. Three-quarters had unilateral attacks 3 to 5 times annually, primarily triggered by cold wind or air, or stress. Eighty percent (48/60) reported ocular pain (median, 7 on scale 1-10), conjunctival injection, photophobia, foreign body sensation, and tearing during attacks. Visual blur occurred in 75% (45/60) and 91% (55/60) during and after the attack, respectively, for a median of 10 days (range, 1 day-2 months). Forty-seven percent (39/60) had corneal oval opacities with irregular tomography patterns and mild to moderate decrease (20/60 or better) in best-corrected visual acuity that improved with scleral contact lenses. Except for headache in 40%, systemic symptoms were absent during the attacks.

CONCLUSIONS

Symptoms and signs of KFH are restricted to the anterior segment of the eye and vary widely between individuals. We recommend scleral contact lenses as the first-line treatment for reduced vision. Allele frequencies suggest that KFH goes unrecognized in Sweden and populations with Scandinavian heritage.

Refractive changes during off-the-axis retinoscopy in myopia

Purpose:

To analyze the refractive shift during off-the-axis retinoscopy under cycloplegic drugs in myopic patients during ocular examination.

Methods:

Prospective cross-sectional study was carried out among 10 myopic patients having refractive errors of −3.00 D or less. All the subjects underwent cycloplegic refraction by a single examiner at 0°, 10°, and 20°. Descriptive data were analyzed as mean and standard deviation. Paired t-test was used to compare the mean differences between on-axis (0°) and off-axis (10° and 20°) retinoscopy.

Result:

The mean spherical equivalent refraction of 10 myopic patients showed an increase in myopic shift with approximately 7% and 18% for 10° and 20° of eccentricity, respectively. Similarly, the mean spherical equivalent measure on axis (0°) and off axis (10° and 20°) were -2.5495, −2.737, and −3.0265, respectively. The mean spherical equivalent differences between on-axis (0°) and off-axis (10° and 20°) showed statistically significant differences with P < 0.05.

Conclusion:

This study concluded that a greater degree of eccentricity will induce a greater amount of errors in retinoscopy.

Interocular Symmetry Analysis of Corneal Elevation Using the Fellow Eye as the Reference Surface and Machine Learning

Unilateral corneal indices and topography maps are routinely used in practice, however, although there is consensus that fellow-eye asymmetry can be clinically significant, symmetry studies are limited to local curvature and single-point thickness or elevation measures. To improve our current practices, there is a need to devise algorithms for generating symmetry colormaps, study and categorize their patterns, and develop reference ranges for new global discriminative indices for identifying abnormal corneas. In this work, we test the feasibility of using the fellow eye as the reference surface for studying elevation symmetry throughout the entire corneal surface using 9230 raw Pentacam files from a population-based cohort of 4613 middle-aged adults. The 140 × 140 matrix of anterior elevation data in these files were handled with Python to subtract matrices, create color-coded maps, and engineer features for machine learning. The most common pattern was a monochrome circle (“flat”) denoting excellent mirror symmetry. Other discernible patterns were named “tilt”, “cone”, and “four-leaf”. Clustering was done with different combinations of features and various algorithms using Waikato Environment for Knowledge Analysis (WEKA). Our proposed approach can identify cases that may appear normal in each eye individually but need further testing. This work will be enhanced by including data of posterior elevation, thickness, and common diagnostic indices.

Pellucid marginal degeneration classification development based on investigation of relationship between functional and refractive changes

BACKGROUND: One of the problems in the diagnosis and treatment of pellucid marginal degeneration of the cornea is the difficulty of systematizing its manifestations due to the lack of classification. This is due to the low frequency of pellucid marginal degeneration in the structure of primary keratectasia, the main type of which is keratoconus. The developed classifications of keratoconus cannot be fully applied to pellucid marginal degeneration. AIM: The aim was to develop a classification of pellucid marginal degeneration based on investigation of relationship between functional and refractive changes. MATERIALS AND METHODS: The study included 42 people (42 eyes) with pellucid marginal degeneration. Keratometry and refractometry were performed, uncorrected and best corrected visual acuity, as well as cylindrical and spherical components of subjective refraction were studied, and retinal visual acuity was determined. The 1st group 12 patients (12 eyes) with fully corrected induced ametropia (best corrected visual acuity 0.8), the 2nd group 17 patients (17 eyes) with partially corrected induced ametropia (0.8 and 0.3), the 3rd group 13 patients (13 eyes) with uncorrected induced ametropia (0.3). RESULTS: To develop a clinical classification of pellucid marginal degeneration by stages, we selected: the values of corneal astigmatism, best corrected visual acuity and Index of difference between the values of maximum and minimum keratometry (K), all of which had good separation of obtained data, and their demarcate values in groups. CONCLUSION: The study showed the presence of relationship between functional and refractive changes indices of eyes with pellucid marginal degeneration. The leading parameters of refractive status, objectively determining the value of best corrected visual acuity, are induced corneal astigmatism and K. The developed classification of pellucid marginal degeneration is easy to use and makes it possible to determine the stage of keratectasia even if there is only induced corneal astigmatism or K values.

Proposing an ensemble learning model based on neural network and fuzzy system for keratoconus diagnosis based on Pentacam measurements

PURPOSE

The present study was done to evaluate efficiency of an ensemble learning structure for automatic keratoconus diagnosis and to categorize eyes into four different groups based on a combination of 19 parameters obtained from Pentacam measurements.

METHODS

Pentacam data from 450 eyes were enrolled in the study. Eyes were separated into training, validation, and testing sets. An ensemble system was used to analyze corneal measurements and categorize the eyes into four groups. The ensemble system was trained to consider indices from both anterior and posterior corneal surfaces. Efficiency of the ensemble system was evaluated and compared in each group.

RESULTS

The best accuracy was achieved by the ensemble system with both multilayer perceptron and neuro-fuzzy system classifiers alongside the Naïve Bayes combination method. The accuracy achieved in KC versus N distinction task was equal to 98.2% with 99.1% of sensitivity and 96.2% of specificity for KC detection. The global accuracy was equal to 98.2% for classification of 4 groups, with an average sensitivity of 98.5% and specificity of 99.4%.

CONCLUSION

In this study, authority of an ensemble learning system to work out intricate problems was presented. Despite using fewer parameters, herein, comparable or, in some cases, better results were obtained than methods reported in the literature. The proposed method demonstrated very good accuracy in discriminating between normal eyes and different stages of keratoconus eyes. In some cases, it was not possible to directly compare our results with the literature, due to differences in definitions of KC group as well as differences in selection of items and parameters.

Clinical Validation of the Automated Characterization of Cone Size and Center in Keratoconic Corneas

PURPOSE

To evaluate an automated method for detecting the cone shape characteristics and to assess the cornea specialists' subjective variability of these measures using different maps.

METHODS

Topographic images of the anterior and posterior surface of each eye were presented to 12 clinicians in two different types of map: tangential curvature and relative elevation to the best-fit sphere. They were asked to mark the cone center and its boundaries in the two maps without knowing that they belonged to the same patient. The results between the maps were compared to assess the subjective variability dependent on the map type and the automated method was compared against both estimations to assess its accuracy.

RESULTS

Considering the results of anterior and posterior surfaces, there was low agreement between the cone center estimations using different types of maps for 10 of the 12 cases (P < .05), whereas the comparison between the automated method and the two map estimations did not show differences in 11 of the 12 cases (P > .05). There was high variability, up to 55%, among clinicians' estimations of the cone area. The results of the automated method were within the range of the expert's estimations.

CONCLUSIONS

An objective, mathematically derived method of determining morphological dimensions of the cone was consistent with clinicians' evaluations. Although there was high variability among the experts' subjective estimates, which were highly influenced by the type of map, the objective method provided a reliable evaluation of the keratoconus shape independent of maps or color scale. [J Refract Surg. 2021;37(6):414-421.].

Correlation between Corneal Topographic Patterns and Refractive Status of the Eye in an Adult Iranian Population: Tehran Study

Purpose

To evaluate the corneal topographic patterns in an adult Iranian population and investigate its correlation with the refractive status of the eye.

Methods

In a cross-sectional study named "Tehran Study," 1023 samples were selected by the cluster sampling method from the downtown area of Tehran. Eight hundred and forty-nine adults aged over 15 years participated. All selected participants were refracted and underwent topography imaging.

Results

The patients' ages ranged from 15 to 91 years with a mean of 40.33 ± 16 years. The most frequent topographic patterns were symmetric bowtie (SB) (34%), SB with inferior steepening (SB-IS) (14.1%), and round (10.5%). The orders changed in categorization by refractive status: The most frequent pattern in all subgroups (emmetropia, myopia, and hyperopia) was SB with frequencies 32.7%, 35.8%, and 22.5%, respectively. Although the second order was asymmetric bowtie (AB) with AB-IS in the emmetropic and myopic subgroups, in the hyperopic subgroup, round pattern had the second place. The third place was different in all groups. The rarest patterns in the whole were SB with skewed radial axis (SRAX) and AB with SRAX. The first prevalent topographic pattern was SB in all age groups and in both genders. The prevalence of round pattern, irregular pattern, and SRAX significantly increased in older ages, and the prevalence of SB decreased in older ages. The first observed prevalent pattern was SB in both sexes, but the second most prevalent pattern was AB-IS and round in females and males, respectively.

Conclusions

Corneal topographic pattern might be related to the refractive status of the eye. The information about normal topographic patterns provides a reference for comparison with diseased corneas.

The prevalence of corneal abnormalities in first-degree relatives of patients with keratoconus: a prospective case-control study

PURPOSE

Although there is a high prevalence of keratoconus in the Middle East including Israel, limited data is available describing first-degree relatives of patients with sporadic keratoconus (KC) using Scheimpflug imaging. The purpose of this study is to accurately phenotype first-degree relatives of patients with sporadic KC in Israel using corneal tomography, which may help determine the genetic aetiology of KC.

METHODS

First-degree relatives (N = 56) of 16 KC probands participated in this prospective case-control study. Healthy controls (N = 96) were from a previous study. Autorefraction, visual acuity, slit lamp biomicroscopy, retinoscopy, subjective refraction and Scheimpflug imaging (CSO Sirius Topographer) of keratoconus patients and their first-degree relatives were evaluated. The worse eye was used for KC and KC suspects. The main outcome measure was prevalence of abnormal corneal topography and tomography parameters, which was compared between first-degree relatives vs controls. p values < 0.05 were considered significant.

RESULTS

KC (N = 2) or KC suspect (N = 8) was diagnosed in 18% (95% CI 8-28%) of the first-degree relatives. At least one abnormal corneal parameter was evident in 34% of first-degree relatives, while this was significantly lower for controls (14%, χ2(1,N = 152)  = 8.8, p = 0.01). Qualitative analysis showed KC first-degree relatives had significantly more abnormal anterior corneal topography patterns than controls (34% vs 17%, χ2(1,N = 152)  = 5.9, p = 0.02). For first-degree relatives, sex was not a factor influencing prevalence of corneal abnormalities (18% for both men and women, χ2(1,N = 56)  = 0.0, p = 1.0). A significant correlation was found for first-degree relatives between age and most corneal parameters, while this was not evident for the control group.

CONCLUSIONS AND RELEVANCE

Eye care practitioners should consider first-degree relatives of patients with KC at moderate risk for the disease and/or corneal abnormalities.

Management of Cataract in Patients with Irregular Astigmatism with Regular Central Component by Phacoemulsification Combined with Toric Intraocular Lens Implantation

Purpose

To evaluate visual acuity (VA) and refractive status in patients with cataract and irregular astigmatism with a regular central component after phacoemulsification with implantation of a toric intraocular lens (IOL).

Methods

Patients with cataract associated with irregular astigmatism with a regular central component were enrolled. All patients underwent phacoemulsification and toric IOL implantation. Postoperative visual acuity, residual astigmatism, toric IOL rotation, higher-order aberration, and objective and subjective visual quality were measured 3 months after surgery.

Results

Twenty-three eyes were included in the study. The logMAR corrected and uncorrected distance visual acuity values were decreased at 3 months postoperatively (p  <  0.005). The preoperative average corneal astigmatism and postoperative residual astigmatism were 1.15–6.97 D (1.99 ± 1.26 D) and 0–2.75 D (0.65 ± 0.57 D), respectively. The average IOL rotation was 3.17 ± 2.01°. Some objective indicators of visual quality, including the modulation transfer function (p  <  0.05), Strehl ratio (p  <  0.005), 100% VA (p  <  0.005), 20% VA (p  <  0.005), and 9% VA (p  <  0.005), were significantly higher than the corresponding preoperative values. The objective scatter index (p  <  0.005) was significantly lower than that before surgery. The postoperative VF-14 scale score was 83.99 ± 14.58.

Conclusion

Toric IOL implantation has a good corrective effect on certain specific types of corneal irregular astigmatism with cataract. This effect can be attributed to its ability to correct the regular component of irregular astigmatism. The indications for toric IOL implantation could be expanded to some extent, thereby bringing benefit to more patients.

Corneal Topographical Changes After Müller's Muscle-conjunctival Resection Surgery

PURPOSE

To evaluate corneal refractive and topographical changes after Müller's muscle conjunctival resection surgery on patients with mild ptosis.

METHODS

A total of 28 eyes of 28 patients with mild ptosis underwent Müller's muscle conjunctival resection. Visual acuity, margin reflex distance, and cycloplegic refraction were analyzed preoperatively and at first, third, and sixth months postoperatively. Change in corneal topography was analyzed with Sirius System using parameters including corneal astigmatism (CYL), average simulated keratometry value (simK), apical keratometry front (AKf), symmetry index front (SIf), and central corneal thickness (CCT) at the same intervals.

RESULTS

Best-corrected visual acuity and cycloplegic refraction did not change significantly at all controls postoperatively. The mean change in corneal astigmatism, simK, SIf, and CCT did not show significant differences. Apical keratometry front showed a significant decrease at 3 and 6 months.

CONCLUSION

The pressure of upper eyelid in patients with ptosis appeared to have resulted in steepening of the superior cornea along this axis. The surgical correction of ptosis induces flattening of superior cornea as shown by significant decrease in apical keratometry front value postoperatively and restores corneal topography to a more regular state.

Distribution of Different Corneal Topography Patterns in Iranian Schoolchildren: The Shahroud Schoolchildren Eye Cohort Study

OBJECTIVES

To determine the distribution of corneal topography patterns (CTPs) in children aged 6 to 12 years and its association with the central corneal thickness (CCT), axial length (AL), mean corneal power (MCP), and corneal astigmatism (CA).

METHODS

In this population-based study, 5,620 children selected through random stratified cluster sampling were examined. After applying the inclusion criteria, 4,655 right eyes were analyzed. The Pentacam was used to determine the CTP and measure CA and MCP, and the BioGraph was used to measure the AL. Corneal topography patterns were classified based on the 10 patterns proposed by Rabinowitz et al. RESULTS:: The most common pattern in the right eye was the oval pattern [32.7%, 95% confidence interval (CI): 30.9-34.5] followed by asymmetric bowtie with superior steepening (AB-SS) (14.5%, 95% CI: 13.3-15.7), whereas the rarest patterns were AB with skewed radial axis (AB-SRAX) (0.1%, 95% CI: 0.0-0.2) and irregular pattern (0.2%, 95% CI: 0.1-0.4). The similarity between the two eyes was 23.2% (95% CI: 20.9-25.7). The mean CCT was significantly higher in AB-SS than inferior steepening (IS) (P=0.023), symmetric bowtie with SRAX (SB-SRAX) (P=0.030), and AB with IS (AB-IS) (P=0.015). Corneal astigmatism was higher in SB-SRAX compared with round and oval patterns (P value for both <0.001). The AL was greater, and the MCP was lower in the oval versus the SB-SRAX pattern (P value for both <0.001).

CONCLUSION

The distribution of CTP was different in children and adults, and the oval and AB-SS patterns were the most common CTPs in the current study.

The Role of Ocular Response Analyzer in Differentiation of Forme Fruste Keratoconus From Corneal Astigmatism

PURPOSE

To determine the diagnostic accuracy of corneal biomechanical factors in differentiating patients with forme fruste keratoconus (FFKC) from astigmatic and normal cases.

METHODS

A total of 50 eyes with FFKC, 50 with astigmatism and 50 normal eyes, were included in this study. All patients had a detailed ophthalmologic examination including slit-lamp evaluation, Goldmann tonometry, indirect fundoscopy, topography by Scheimpflug imaging biomicroscopic anterior and posterior segment examination, and corneal biomechanical and intraocular pressure evaluation with ocular response analyzer (ORA).

RESULTS

All topographic findings were statistically significant among the three groups (P>0.05). Although there was no statistically significant difference in the corneal-compensated intraocular pressure (IOPcc) among the three groups, the Goldmann-correlated intraocular pressure (IOPg), corneal hysteresis (CH), and corneal resistance factor (CRF) were statistically significantly lower in the FFKC group, compared with the other groups (P<0.001). There were no statistically significant difference in the IOPg, CH, and CRF between astigmatism and control groups (P=0.99, 0.79, and 0.86, respectively). The area under the receiver operating characteristic (AUROC) curve was greater than 0.85 for IOPg (0.80), CH (0.85), and CRF (0.90) for discriminating between FFKC and controls; whereas the AUROC was greater than 0.85 for IOPg (0.80), CH (0.79), and CRF (0.85) for discriminating between FFKC and astigmatism groups.

CONCLUSION

Based on our study results, in differentiation of patients with FFKC from normal control cases or astigmatic patients, corneal biomechanical parameters play a role particularly in patients with suspicious results. We suggest using ORA in combination with corneal topography for better and more accurate diagnosis of FFKC.

Patterns of Corneal Topography after Penetrating Keratoplasty

Background

The topography of corneas after penetrating keratoplasty is highly variable. We classify the topography into five groups.

Methods

We performed videokeratography on 45 clear compact penetrating keratoplasties, with all sutures removed. Three ophthalmologists classified the keratographs independently into five previously defined topographic groups, based on the pattern of the normalized color-coded videokeratograph.

Results

The five topographic patterns included: prolate bow tie, 14 (30%); oblate bow tie, 14 (30%); mixed prolate and oblate bow tie, 8 (17%); asymmetric, 3 (9%); and steep/flat, 6 (14%). The three ophthalmologists agreed in their initial classification in 87% of the cases and after discussion, in 96%.

Conclusion

The topography of the cornea after penetrating keratoplasty can be classified into five qualitative groups by trained observers, with good clinical reliability.

Optical System Design for Noncontact, Normal Incidence, THz Imaging of in vivo Human Cornea

Reflection mode Terahertz (THz) imaging of corneal tissue water content (CTWC) is a proposed method for early, accurate detection and study of corneal diseases. Despite promising results from ex vivo and in vivo cornea studies, interpretation of the reflectivity data is confounded by the contact between corneal tissue and dielectric windows used to flatten the imaging field. Herein, we present an optical design for non-contact THz imaging of cornea. A beam scanning methodology performs angular, normal incidence sweeps of a focused beam over the corneal surface while keeping the source, detector, and patient stationary. A quasioptical analysis method is developed to analyze the theoretical resolution and imaging field intensity profile. These results are compared to the electric field distribution computed with a physical optics analysis code. Imaging experiments validate the optical theories behind the design and suggest that quasioptical methods are sufficient for designing of THz corneal imaging systems. Successful imaging operations support the feasibility of non-contact in vivo imaging. We believe that this optical system design will enable the first, clinically relevant, in vivo exploration of CTWC using THz technology.

Validity of autorefractor based screening method for irregular astigmatism compared to the corneal topography- a cross sectional study

AIM

To present a method of screening for irregular astigmatism with an autorefractor and its determinants compared to corneal topography.

METHODS

This cross-sectional validity study was conducted in 2013 at an eye hospital in Spain. A tabletop autorefractor (test 1) was used to measure the refractive status of the anterior surface of the cornea at two corneal meridians of each eye. Then corneal topography (test 2) and Bogan's classification was used to group eyes into those with regular or no astigmatism (GRI) and irregular astigmatism (GRII). Test 1 provided a single absolute value for the greatest cylinder difference (Vr). The receiver operating characteristic (ROC) were plotted for the Vr values measured by test 1 for GRI and GRII eyes. On the basis a Vr value of 1.25 D as cut off, sensitivity, specificity were also calculated.

RESULTS

The study sample was comprised of 260 eyes (135 patients). The prevalence of irregular astigmatism was 42% [95% confidence interval (CI): 36, 48]. Based on test 2, there were 151 eyes in GRI and 109 eyes in GRII. The median Vr was 0.75 D (25% quartile, 0.5 D) for GRI and 1.75 D (25% quartile, 1.25 D) for GRII. The area under curve was 0.171 for GRI and 0.83 for GRII. The sensitivity of test I was 78.1% and the specificity was 76.1%.

CONCLUSION

A conventional autorefractor can be effective as a first level screening method to detect irregular corneal astigmatism in places where corneal topography facilities are not available.

Corneal Nerve Regeneration after Self-Retained Cryopreserved Amniotic Membrane in Dry Eye Disease

Purpose

To evaluate the efficacy of self-retained cryopreserved amniotic membrane (CAM) in promoting corneal nerve regeneration and improving corneal sensitivity in dry eye disease (DED).

Methods

In this prospective randomized clinical trial, subjects with DED were randomized to receive CAM (study group) or conventional maximum treatment (control). Changes in signs and symptoms, corneal sensitivity, topography, and in vivo confocal microscopy (IVCM) were evaluated at baseline, 1 month, and 3 months.

Results

Twenty subjects (age 66.9 ± 8.9) were enrolled and 17 completed all follow-up visits. Signs and symptoms were significantly improved in the study group yet remained constant in the control. IVCM showed a significant increase in corneal nerve density in the study group (12,241 ± 5083 μm/mm² at baseline, 16,364 ± 3734 μm/mm² at 1 month, and 18,827 ± 5453 μm/mm² at 3 months, p = 0.015) but was unchanged in the control. This improvement was accompanied with a significant increase in corneal sensitivity (3.25 ± 0.6 cm at baseline, 5.2 ± 0.5 cm at 1 month, and 5.6 ± 0.4 cm at 3 months, p < 0.001) and corneal topography only in the study group.

Conclusions

Self-retained CAM is a promising therapy for corneal nerve regeneration and accelerated recovery of the ocular surface health in patients with DED. The study is registered at clinicaltrials.gov with trial identifier: NCT02764814.

Comparison between corneal elevation maps using different reference surfaces with Scheimpflug-Placido topographer

The purpose of this study was to compare the anterior and posterior elevation measurements using different reference surfaces (spheric, aspheric, and aspherotoric) with Scheimpflug-Placido topography in simple myopic and keratoconus patients. 600 eyes of 600 patients undergoing screening for keratorefractive surgery (500 simple myopic, 100 keratoconus stage 1 and 2) in Sohag refractive center, Egypt, were examined by Scheimpflug-Placido topography (Sirius, CSO, Italy) for both the anterior and posterior corneal elevation maps using the spheric, aspheric, and aspherotoric reference surfaces. 100 keratoconic eyes showed higher discriminating power using the aspherotoric reference surface in both the anterior and posterior elevation maps. The use of aspherotoric reference surface gives more data for eyes with keratoconus and its use is more informative in screening.

Evaluation of corneal higher order aberrations in normal topographic patterns

Purpose

This study reports the characteristics of corneal higher order aberrations (HOAs) in eyes with normal topographic pattern using the Pentacam scheimpflug system.

Methods

In this prospective, observational, comparative study, 165 eyes of 97 patients separated into five groups based on corneal topographic patterns were enrolled. All eyes received a comprehensive ophthalmologic examination including corneal tomographic analysis with the Pentacam system. Keratometry, corneal cylinder, and corneal aberrometric data were recorded and analyzed. Root mean square values (RMS) were calculated for corneal HOAs up to the 6th order, total coma, total trefoil, total spherical aberration, total tetrafoil, and higher order astigmatism. Evaluation of these data to discriminate between the five groups was assessed using the analysis of variance test by Generalized Estimation Equation Linear Model.

Results

Corneal HOAs were found to be significantly higher for Asymmetric Bow Tie and Irregular groups than other groups (p = <0.001). RMS of total coma aberration (Z3−1, Z31, Z5−1, Z51) were significantly greater in the Asymmetric Bow Tie pattern than others, and RMS of total Spherical aberration (Z40, Z60) was significantly higher in the Irregular pattern than other groups (p = <0.001). The results of our study demonstrate that a tendency toward significant higher values of trefoil, tetrafoil, and higher order astigmatism in Irregular pattern (all p < 0.05). Significantly higher amounts of 3rd order RMS in Asymmetric Bow Tie group and 4th to 6th order RMS in Irregular pattern group were other outcomes of our study (p = <0.001).

Conclusions

Based on results in this study, there were a good correlation between corneal topographic pattern and corneal HOAs in normal eyes. These results indicate that the corneal HOAs values are largely determined by the topographic patterns. A larger sample size would perhaps have been beneficial to yield in more accurate outcomes.

[Safety of the automated microkeratome for Sub-Bowman's Keratomileusis on the flat cornea]

INTRODUCTION

Use of the One Use-Plus SBK (Sub-Bowman's Keratomileusis) automated microkeratome (Moria, Antony, France) has been shown to be safe, predictable and comfortable for the creation of thin corneal flaps with a smooth and regular stromal bed.

PURPOSE

To evaluate the use of the Moria One Use-Plus SBK (Moria, Antony, France) automated microkeratome on corneas with 180°-keratometry under 40 diopters (D).

METHODS

We retrospectively studied cases that underwent SBK whose 180°-keratometry was under 40 D. We separated the cases between 39 and 40 D and those less than 39 D. The preoperative data, the procedure and the postoperative outcomes were analyzed. The Moria One Use-Plus SBK microkeratome with the 90-micron head was used for all cases.

RESULTS

Among the 2883 eyes that underwent SBK LASIK over the past six years, 80 eyes (2.77%) had a preoperative topographical 180°-keratometry of less than 40 D: 63 eyes (2.19%) between 39 and 40 D and 17 eyes (0.59%) between 38 and 39 D (38.13-38.97 D). The spherical equivalent was between -3.50 D (-2.25 sph -2.50 cyl. at 175°) and+6.00 D (+5.50 sph +1.00 cyl. at 85°). Fifty-eight eyes (72.5%) had hyperopia and/or hyperopic astigmatism; 18 eyes (22.5%) had mixed astigmatism; and 4 eyes (5%) had myopia and/or myopic astigmatism. Twenty-six eyes (32%) had a history of strabismus. Thirteen patients (27.66%) had a history of amblyopia. The "-1" ring was used in all cases, with a 7.5 stop (14%) or 8 stop (86%). The procedure went uneventfully in all cases with a stable vacuum between 117 and 123 mm Hg. The nasal hinge and the stromal bed were normal in size in all cases and sufficient to perform the photoablation laser safely with an optical zone between 6.00 and 7.00 millimeters. There were no intraoperative nor immediate postoperative complications: free cap 0%; incomplete flap 0%; button hole 0%; epithelial erosion 0%; bleeding 0%; irregular stromal bed 0%. Postoperative complications: flap displacement 0%; punctate keratitis: 8%; LASIK retreatments: 12%; safety: 100% (no loss of lines of visual acuity).

DISCUSSION

Corneas with a topographical 180°-keratometry under 40 D are a very small percentage of the total eyes that undergo LASIK (SBK). Those with a 180°-keratometry under 39 D are even more infrequent. Due to the characteristics of the flat cornea, the percentage of hyperopia is much larger in than in the general LASIK group. In addition, the percentage with a history of strabismus and amblyopia is higher.

CONCLUSION

The Moria One Use-Plus SBK microkeratome is an excellent device that allows the easy creation of thin corneal flaps and regular and smooth corneal beds, safely and predictably even in extremely flat corneas without complications. The safety, efficacy and predictability are quite comparable to the general LASIK group.

Using LaserSight Astrapro Planner 2.2 Z software in corneal topography-guided laser in situ keratomileusis for myopia with asymmetric corneal shape

AIM

To determine the clinical outcomes of laser in situ keratomileusis (LASIK) treatments using LaserSight AstraPro Planner 2.2 Z software for myopia with asymmetric corneal shape.

METHODS

Four hundred and eighty-five eyes [243 patients; spherical equivalent (SE), -5.93±1.88 diopters (D)] were treated with asymmetric ablations using LaserSight SLX laser (version 5.3, 300Hz) were retrospectively analyzed and LaserSight AstraPro Planner 2.2 Z software. Preoperative and postoperative uncorrected visual acuities (UCVA), spherical equivalent (SE) refraction, pachymetry, and corneal asphericity (Q value) and decentration were evaluated.

RESULTS

At 12mo postoperatively, the decimal UCVA was 1.0 or better in 449 (92.6%) eyes. Two eyes (0.4%) lost 1 line of the decimal best spectacle-corrected visual acuity (BCVA), 316 (65.2%) did not change, 149 (30.7%) gained 1 line, and 18 (3.7%) gained 2 lines or more after surgery. Three hundred and thirty-two eyes (68.5%) were within 0.5 D in SE. The mean tissue saving ablation depth was 4.28±2.86 (0-16) µm (median, 4 µm). The mean attempted remaining central corneal thickness was 435.79±29.56 µm, the mean postoperative pachymetry was 444.94±28.93 µm. The mean preoperative Q value was -0.19±0.18, the postoperative was 0.30±0.48 (P=0.000). The mean postoperative decentration was 0.39±0.19 mm.

CONCLUSION

Topography-guided LASIK with AstraPro Planner 2.2 Z custom ablation planning software in an asymmetric ablation mode was an effective, safe, predictable, and stable refractive procedure for the myopia with asymmetric corneal topography.

Corneal topography patterns in the Tehran eye study: warning about the high prevalence of patterns with a skewed radial axis

Purpose:

The purpose of this study is to determine the distribution of corneal topography patterns in Tehran.

Materials and Methods:

In this population-based study, a total of 442 individuals were randomly selected by cluster sampling for complete ophthalmologic examination. A total of 404 (788 eyes) met the inclusion criteria and were enrolled in this study. Orbscan II (Bausch and Lomb Surgical, Salt Lake City, USA) was used to determine the anterior segment indices and axial power maps for each eye.

Results:

On the basis of the axial power maps, the symmetric bowtie (SB) (29.0%) and asymmetric bowtie with inferior steepening (16.7%) patterns were the most prevalent and the irregular (3.3%) and superior steepening (1.5%) patterns the least prevalent. Asymmetric bowtie pattern with a skewed radial axis (AB-SRAX) was seen in 7.6% of eyes. These cases had both thinner and steeper corneas compared with round and SB ones (P < 0.014 and P < 0.006). Maximum anterior elevation in 5 mm zone, of AB-SRAX corneas were higher than other patterns (P < 0.01) except for superior steepened and inferior steepened ones.

Conclusions:

The distribution of corneal topographic patterns in Iranians seems like other Asian population on the whole. The 7.6% prevalence of AB-SRAX patterns may be a warning on keratoconus prevalence in our population. This is in line with recent regional reports.

Classification of posterior polymorphous corneal dystrophy as a corneal ectatic disorder following confirmation of associated significant corneal steepening

IMPORTANCE

The identification of steep corneal curvatures in a significant percentage of patients with posterior polymorphous corneal dystrophy (PPCD) confirms this previously reported association and suggests a role for the ZEB1 protein in keratocyte function.

OBJECTIVE

To determine whether PPCD is characterized by significant corneal steepening.

DESIGN, SETTING, AND PARTICIPANTS

Cross-sectional study at university-based and private ophthalmology practices of 38 individuals (27 affected and 11 unaffected) from 23 families with PPCD.

EXPOSURE

Slitlamp examination and corneal topographic imaging were performed for individuals with PPCD and unaffected family members. Saliva or blood samples were obtained from each individual for DNA isolation and ZEB1 sequencing. Corneal ZEB1 expression was measured using immunohistochemistry.

MAIN OUTCOMES AND MEASURES

Percentage of individuals affected with PPCD and controls with an average keratometric value greater than 48.0 diopters (D) in each eye; the mean keratometric value averaged for both eyes of individuals with PPCD and controls; and the correlation of ZEB1 mutation with keratometric value.

RESULTS

ZEB1 coding region mutations were identified in 7 of the 27 affected individuals. Ten of the 38 individuals (26.3%) had average keratometric values greater than 48.0 D OU: 10 of 27 individuals with PPCD (37.0%; 6 of 7 individuals with ZEB1 mutations [85.7%] and 4 of 20 individuals without ZEB1 mutations [20.0%]) and 0 of 11 unaffected individuals (P = .04 for unaffected vs affected individuals; P = .004 for individuals with PPCD with vs without ZEB1 mutation). The mean keratometric value of each eye of affected individuals (48.2 D) was significantly greater than that of each eye of unaffected family members (44.1 D) (P = .03). Affected individuals with ZEB1 mutations demonstrated a mean keratometric value of 53.3 D, which was significantly greater than that of affected individuals without ZEB1 mutations (46.5 D; P = .004). Fluorescence immunohistochemistry demonstrated ZEB1 expression in keratocyte nuclei.

CONCLUSIONS AND RELEVANCE

Abnormally steep corneal curvatures are identified in 37% of all individuals with PPCD and 86% of affected individuals with PPCD secondary to ZEB1 mutations. ZEB1 is present in keratocyte nuclei, suggesting a role for ZEB1 in keratocyte function. Therefore, ZEB1 may play a role in both corneal stromal and endothelial development and function, and PPCD should be considered both an endothelial dystrophy and an ectatic disorder.

Corneal topography and corneal thickness in children

PURPOSE

To evaluate the corneal topography, thickness, and elevation (anterior and posterior corneal surface) in children.

METHODS

One hundred eyes of 100 patients with a mean ± standard deviation age of 10.6 ± 2.7 years (range: 5 to 15 years) were imaged. The corneal elevation maps were classified into regular ridge, irregular ridge, incomplete ridge, island, and unclassified patterns.

RESULTS

Mean simulated keratometry (Sim K) astigmatism was -0.69 ± 0.35 diopters (D) with mean maximum and minimum keratometry (K) of 44.26 ± 1.55 and 43.56 ± 1.57 D, respectively. Mean astigmatism and refractive power in the 3- and 5-mm zones was 0.64 ± 0.36, 43.85 ± 1.53 and 0.78 ± 0.5, 43.41 ± 1.48, respectively. The thinnest site on the cornea had an average thickness of 540 ± 34.03 μm. This site was most commonly located in the inferotemporal quadrant in 61% of eyes, followed by the superotemporal quadrant in 31%. Among the nine regions of the cornea evaluated, the central cornea had the lowest average thickness of 540 ± 34.03 μm and the superonasal cornea had the greatest average thickness of 628 ± 38.94 μm. The most common anterior corneal elevation pattern was the incomplete ridge (52%), followed by the island pattern. The incomplete ridge was most commonly observed on the posterior corneal elevation map (35%).

CONCLUSIONS

These results provide normal standards for elevation and curvature topography and corneal thickness in children. These data may prove useful as a reference for future comparative studies of different corneal diseases in children.

Topography-guided laser refractive surgery

PURPOSE OF REVIEW

Topography-guided laser refractive surgery seeks to correct vision by altering the major refractive surface of the eye. Whereas results are not significantly different from current treatment options for primary surgery, topography-guided treatment is uniquely effective in eyes with corneal irregularity. This review highlights topography-guided ablations, emphasizing recent advances in treating highly aberrated eyes, including treatment for corneal ectasia in conjunction with collagen cross-linking (CXL).

RECENT FINDINGS

Studies continue to document similar outcomes between topography-guided and wavefront-guided customized corneal ablations while exploring the indications for each modality. Topography-guided ablations demonstrate good outcomes for the correction of astigmatism after penetrating keratoplasty, laser-assisted in-situ keratomileusis (LASIK) flap or interface complications, post-radial keratotomy eyes, and other highly aberrated corneas, many of which are poor candidates for wavefront-guided therapy. The use of topography-guided ablations with CXL seeks to address both the refractive and structural abnormalities of corneal ectasias. This combination therapy has shown promising results for keratoconus, post-LASIK ectasia, and pellucid marginal degeneration.

SUMMARY

Topography-guided customized corneal ablation is well tolerated and effective. Recent attention has been focused on the unique therapeutic benefits of this treatment for highly irregular and ectatic corneas with encouraging results.

Posterior polymorphous dystrophy associated with nonkeratoconic steep corneal curvatures

PURPOSE

To report a case series of eyes with posterior polymorphous corneal dystrophy and steep nonkeratoconic corneas.

METHODS

Retrospective, descriptive, nonrandomized case series.

RESULTS

Thirty-five eyes of 18 patients (14 cases from 6 families and 4 isolated cases) with diffuse posterior polymorphous corneal dystrophy had mean topographic simulated keratometry readings of 52.21 diopters (D), with a range of 46.47 D to 59.86 D and an SD of 3.69 D, with no slit-lamp or topographic findings suggestive of keratoconus.

CONCLUSIONS

The patients in this series demonstrate diffuse posterior polymorphous corneal dystrophy and nonkeratoconic steep corneas.

Excimer laser refractive correction of myopia after episcleral buckling for rhegmatogenous retinal detachment

PURPOSE

To evaluate the long-term effects of excimer laser treatment for ametropia after surgical treatment of rhegmatogenous retinal detachment (RRD) with scleral buckles.

SETTING

Helsinki University Eye Hospital, Helsinki, Finland.

METHODS

Ten patients (10 eyes) who had 1 or more surgeries for RRD followed by refractive surgery for myopia were retrospectively enrolled in this study and were examined after excimer laser refractive surgery. Photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK) was performed using a Star S2 excimer laser system (Visx). The best spectacle-corrected visual acuity (BSCVA), refraction, degree of anisometropia, and topographical changes were evaluated before and after the surgeries.

RESULTS

All patients were free of asthenopic symptoms after refractive surgery. At the end of the follow-up, a mean of 67 months +/- 14 (SD) after refractive surgery, 6 patients were within +/-1.0 diopter of the intended correction. Compared with previously reported cohorts of myopic patients, the achieved refraction in patients who previously had a scleral buckling procedure was worse. The postoperative refraction was stable, and corneal topography did not show induced scar formation, keratectasia, or irregular astigmatism. After refractive surgery, the BSCVA improved 1 Snellen line in 3 patients and 2 lines in 1 patient. One patient lost 1 Snellen line and another patient lost 2 lines. Four patients showed no changes. New retinal complications were not observed.

CONCLUSIONS

In the long-term, PRK and LASIK were safe methods for the treatment of myopia in RRD patients after scleral buckling. The predictability of myopic LASIK/PRK may be worse than generally reported in myopic cohorts.

Heritability of Corneal Curvature and Astigmatism

PURPOSE

To study child-parent similarities and the heritability of corneal shape by applying a variance component model to videokeratographic data.

METHODS

Sixteen astigmatic (keratometric cylinder >/= 1.0 D) and 18 nonastigmatic (keratometric cylinder < 1.0 D) children, 7-14 years of age (mean age, 9.5 years), were enrolled with their parents. Corneal curvature, corneal astigmatism (axis and magnitude), asphericity, corneal uniformity index, and Rabinowitz McDonnell inferior-superior dioptric asymmetry value (I-S value), as well as spherical and astigmatic topographic patterns, were determined by a corneal topographer. Child-parent comparisons were assessed through a 1-way analysis of variance and the chi test. For corneal curvature, corneal astigmatism, and asphericity, heritability was estimated by a variance component model after adjustments were made for age and sex.

RESULTS

Both astigmatic and nonastigmatic children showed steeper keratometric values than their parents (P < 0.05). The axis values of corneal astigmatism showed no statistically significant difference (P = 0.684) between astigmatic offspring and their parents, whereas the magnitude values were significantly higher (P < 0.001) in astigmatic children. Altogether, 68% (95% confidence interval [CI], 66%-72%) of child-parent comparisons showed the same topographic pattern between parents and their offspring. Heritability values (48%; 95% CI, 36%-57%) were statistically significant for corneal curvature (P < 0.00001) and <30% for corneal astigmatism and asphericity.

CONCLUSIONS

The application of a variance component model to videokeratographic child-parent comparisons suggests that the genetic contribution to corneal shape affects corneal curvature rather than corneal astigmatism.

Corneal topographic features in a family with nanophthalmos

PURPOSE

To characterize the corneal topographic features in a family with nanophthalmos.

METHODS

Two observational case reports and a review of the literature. Corneal shape was analyzed using a topographic modeling system (TMS) and an Orbscan topographic system, with further analysis based on Fourier series and Zernicke polynomials. A control group was used for comparison.

RESULTS

Two female family members with nanophthalmos belonging to the same generation showed significant irregular corneal astigmatism and corneal steepening.

CONCLUSION

Topographic corneal steepening and irregular astigmatism seems to be associated in 1 family with inherited nanophthalmos. Higher degrees of irregular astigmatism, which were not evident without a topographic analysis, may account, in part, for the unexplained visual reduction.

Astigmatism and the Impact of Relaxing Incisions After Penetrating Keratoplasty

PURPOSE

To determine the impact of relaxing incisions for correcting postoperative astigmatism following penetrating keratoplasty.

METHODS

Data were collected through the Swedish Corneal Transplant Register. Of the 1161 grafts with complete 2-year follow-up, 131 underwent relaxing incisions. Stepwise multiple regression was used to determine the factors that influenced the extent of astigmatism in diopters (D) (square root transformed). The change in astigmatism brought about by relaxing incisions was evaluated both by subtraction (ie, ignoring angle) and vector analysis.

RESULTS

The overall mean astigmatism was 4.56 D (95% confidence interval [CI]: 4.40-4.73, n = 1161). The final regression model explained only a small proportion of the overall variability of the data (< 5%). There was a slight increase in postoperative astigmatism with recipient age (P = .025), and two of the seven participating clinics achieved lower levels of astigmatism (P = .001 and P = .036, respectively). In patients who underwent relaxing incisions, astigmatism was reduced from 8.40 D (95% CI: 8.0-9.0, n = 131) to 3.80 D (95% CI: 3.5-4.3). The mean difference by subtraction was 4.50 D (95% CI: 4.0-5.0, P < .001, paired t test). Vector analysis showed the overall reduction of astigmatism due to surgery to be 7.90 D (95% CI: 7.2-8.7). Compared with grafts with no refractive surgery, a trend was noted that suggested corrected visual acuity was improved following relaxing incisions.

CONCLUSIONS

Relaxing incisions were found to be a safe and effective method for reducing postoperative astigmatism and may improve visual acuity.

3D average human corneal models

In this paper we propose a method of building an average model or atlas of the cornea based on topographic data. Specific models can be constructed for the left or right eye, gender, age, or ametropia, to assess differences and similarities. An application of this atlas construction methodology to the study of corneal shape evolution with age is presented. Results show significant differences between age groups. This numerical atlas could also be helpful in the design of algorithms targeting the detection of corneal shape abnormalities, such as keratoconus or previous laser surgery.