Comparison of Placido disc and Scheimpflug image-derived topography-guided excimer laser surface normalization combined with higher fluence CXL: the Athens Protocol, in progressive keratoconus

Merging Photorefractive Keratectomy and Collagen Crosslinking: An Analysis of Literature and a Guide to Prevalent Protocols

PURPOSE

The purpose of this review was to summarize the different surgical approaches combining photorefractive keratectomy (PRK) and corneal crosslinking (CXL), present each protocol template in a simple format, and provide an overview of the primary outcomes and adverse events.

METHODS

A literature review was conducted as outlined by the Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines. Eight different databases were searched. Papers were included if PRK was immediately followed by CXL.

RESULTS

Thirty-seven papers met the inclusion criteria of a total yield of 823. The latest research into simultaneous PRK and CXL has been shown to not only stabilize the cornea and prevent keratoconus progression but also improve the visual acuity of the patient. Improvements in uncorrected distance visual acuity and (spectacle) corrected distance visual acuity were found to be significant when considering all protocols. There were also significant reductions in K1, K2, mean K, Kmax, sphere, cylinder, and spherical equivalent. Random-effects analysis confirmed these trends. Corrected distance visual acuity was found to improve by an average of 0.18 ± 1.49 logMAR (Cohen's D [CD] 0.12; P <0.02). There was also a significant reduction of 2.57 ± 0.45 D (CD 5.74; P <0.001) in Kmax. Cylinder and spherical equivalent were also reduced by 1.36 ± 0.26 D (CD 5.25; P <0.001) and 2.61 ± 0.38 D (CD 6.73; P <0.001), respectively.

CONCLUSIONS

Combining the 2 procedures appears to be of net benefit, showing stabilization and improvement of ectatic disease, while also providing modest gains in visual acuity. Since customized PRK and CXL approaches appear superior, a combination of these would likely be best for patients.

Ray-Tracing Customization in Myopic and Myopic Astigmatism LASIK Treatments for Low and High Order Aberrations Treatment: 2-Year Visual Function and Psychometric Value Outcomes of a Consecutive Case Series

Purpose

The safety and long-term efficacy of automated ray-tracing customized myopic and myopic astigmatic femtosecond laser-assisted LASIK.

Methods

This consecutive case series retrospective analysis, of 20 subjects (40 eyes) treated with automated raytracing named Wavelight Plus, to include low and high order aberrations based on a three-dimensional custom virtual eye for each case-calculated from interferometry data-obtained from a single diagnostic device that also provides Hartman-Shack Wavefront and Scheimpflug tomography data. We evaluated before and after the customized LASIK procedure: visual acuity, refractive error, high order aberrations, contrast sensitivity, and psychometric post-operative visual function data.

Results

At 24 months, the comparison of the pre-operative to the post-operative refractive and visual function value changes in average were: subjective manifest refraction from -4.38 ± 2.54 diopters (D) (range -9.75 to -1.25 D) to +0.11 ± 0.19 D; subjective manifest refractive astigmatism from -0.76 ± 0.91 D (range -2.75 to 0 D) to -0.13 ± 0.16 D, corneal astigmatism from -1.16 ± 0.64 D (range -0.2 to -2.8) to -0.47 ± 0.11 D. 65% of the eyes studied demonstrated an increase of at least one line of vision, while from the same group 38% demonstrated 2 lines of increase. High order aberrations, contrast sensitivity as well as the subjective psychometric input based on the VFQ-25 questionnaire demonstrated actual improvement.

Conclusion

This longer-term follow-up, single-arm retrospective consecutive case series documents LASIK treatment customization that appears to be safe and effective in the correction of myopia and myopic astigmatism. Markedly improved objective and subjective visual function post-operatively, underlying the potential importance of simultaneously attempting to correct high order aberrations and improving the spatial alignment of total, measured human eye optics.

Short- and long-term safety and efficacy of corneal collagen cross-linking in progressive keratoconus: A systematic review and meta-analysis of randomized controlled trials

PURPOSE

The purpose of the study is to evaluate the safety and outcomes of corneal collagen cross-linking (CXL) and different CXL protocols in progressive keratoconus (PK) population at short and long-term.

MATERIALS AND METHODS

A systematic review and meta-analysis was conducted. A total of eight literature databases were searched (up to February 15, 2022). Randomized controlled trials (RCTs) comparing CXL versus placebo/control or comparing different CXL protocols in the PK population were included. The primary objective was assessment of outcomes of CXL versus placebo and comparison of different CXL protocols in terms of maximum keratometry (Kmax) or Kmax change from baseline (Δ), spherical equivalent, best corrected visual acuity (BCVA), and central corneal thickness (CCT) in both at short term (6 months) and long term (1^st, 2^nd, and 3^rd year or more). The secondary objective was comparative evaluation of safety. For the meta-analysis, the RevMan5.3 software was used.

RESULTS

A total of 48 RCTs were included. Compared to control, CXL was associated with improvement in Δ Kmax at 1 year (4 RCTs, mean difference [MD], -1.78 [-2.71, -0.86], P = 0.0002) and 2 and 3 years (1 RCT); ΔBCVA at 1 year (7 RCTs, -0.10 [-0.14, -0.06], P < 0.00001); and Δ CCT at 1 year (2 RCTs) and 3 years (1 RCT). Compared to conventional CXL (C-CXL), deterioration in Δ Kmax, ΔBCVA and endothelial cell density was seen at long term in the transepithelial CXL (TE-CXL, chemical enhancer). Up to 2 years, there was no difference between TE-CXL using iontophoresis (T-ionto) and C-CXL. At 2 and 4 years, C-CXL performed better compared to accelerated CXL (A-CXL) in terms of improving Kmax. Although CCT was higher in the A-CXL arm at 2 years, there was no difference at 4 years. While exploring heterogeneity among studies, selection of control eye (fellow eye of the same patient vs. eye of different patient) and baseline difference in Kmax were important sources of heterogeneity.

CONCLUSION

CXL outperforms placebo/control in terms of enhancing Kmax and CCT, as well as slowing disease progression over time (till 3 years). T-ionto protocol, on the other hand, performed similarly to C-CXL protocol up to 2 years.

Current Developments in Corneal Topography and Tomography

Introduction: Accurate assessment of the corneal shape is important in cataract and refractive surgery, both in screening of candidates as well as for analyzing postoperative outcomes. Although corneal topography and tomography are widely used, it is common that these technologies are confused. The aim of this study was to present the current developments of these technologies and particularly distinguish between corneal topography and tomography. Methods: The PubMed, Web of Science and Embase databases were the main resources used to investigate the medical literature. The following keywords were used in various combinations: cornea, corneal, topography, tomography, Scheimpflug, Pentacam, optical coherence tomography. Results: Topography is the study of the shape of the corneal surface, while tomography allows a three-dimensional section of the cornea to be presented. Corneal topographers can be divided into large- and small-cone Placido-based devices, as well as devices with color-LEDs. For corneal tomography, scanning slit or Scheimpflug imaging and optical coherence tomography may be employed. In several devices, corneal topography and tomography have been successfully combined with tear-film analysis, aberrometry, optical biometry and anterior/posterior segment optical coherence tomography. Conclusion: There is a wide variety of imaging techniques to obtain corneal power maps. As different technologies are used, it is imperative that doctors involved in corneal surgery understand the science and clinical application of devices for corneal evaluation in depth.

Sensitivity and Specificity of Belin Ambrosio Enhanced Ectasia Display in Early Diagnosis of Keratoconus

Purpose

Early diagnosis of keratoconus disease (KCN) is the first priority in the preoperative evaluations of refractive surgery (RS).The aim of this study was to investigate the correlation between findings of Belin Ambrosio enhanced ectasia display (BAD) software and conventional corneal imaging (Orbscan and topography) in the early diagnosis of KCN.

Methods

For conducting this cross-sectional study, a total of 1000 eyes were selected from 500 patients that underwent the myopic photorefractive keratectomy surgery and were compared in four study groups during the years 2017-2018. In group 1, all topography, Orbscan, and BAD criteria were normal (65.8%).In contrast, in Group 2, at least one of the topography or Orbscan criteria as well as at least one BAD criterion (12.6%) were abnormal. In Group 3, the eyes had normal Orbscan and topography criteria with at least one abnormal BAD criterion (18.5%). Also, in Group 4, the patients had at least one abnormal Orbscan or topography criterion, but all BAD criteria (3.1%) were normal. Thickness of the thinnest point (TP) of cornea was compared in Pentacam and topography. Data analysis was done by SPSS software (version 21).

Results

BAD criteria were normal in 78.5% of all eyes with normal topography and Orbscan criteria (specificity). BAD criteria were also abnormal in 80.2% of eyes (sensitivity). There was also no significant difference between TP in Orbscan and Pentacam.

Conclusions

BAD criteria had a relatively acceptable sensitivity and specificity, compared with conventional Orbscan and topography criteria. Thus, BAD criteria can be more effective in the early diagnosis of KCN.

Initial Outcomes with Customized Myopic LASIK, Guided by Automated Ray Tracing Optimization: A Novel Technique

Purpose

Safety and efficacy of a novel automated ray tracing optimization in customization of excimer ablation in myopic LASIK.

Methods

In a consecutive case series, 25 patients (50 eyes) undergoing femtosecond-laser-assisted myopic LASIK were evaluated. The novel, artificial-intelligence platform initially calculates the ablation profile based on a model eye for each case, based on interferometry axial length data. Low- and high-order aberration calculation is performed by raytracing based on wavefront and Scheimpflug tomography measurements, all from a single diagnostic device. Visual acuity, refractive error, keratometry, topography, high-order aberrations and contrast sensitivity were evaluated, over six months follow-up.

Results

Change from pre- to 6 months post-operative: mean refractive error improved from −5.06 ± 2.54 diopters (D) (range −8.0 to −0.50 D) to −0.11 ± 0.09 D (range −0.25 to + 0.25); refractive astigmatism from −1.07 ± 0.91 D (range −4.25 to 0 D) to −0.15 ± 0.04 D (range −0.25 to 0); and topographic astigmatism from −1.65 ± 0.85 D to −0.26 ± 0.11 D (range −0.60 to 0). About 65% of eyes gained one line of vision and 38% 2 lines. Pre- to post-operative high-order aberration average: RMSh changed from 0.25 um to 0.35 um. Contrast sensitivity improved post-operatively.

Conclusion

We report safe and effective preliminary outcomes with a novel excimer laser customization by ray tracing optimization, for myopic LASIK treatments, employing several independent up-till-now diagnostics and a customized eye model reference for each case. It bears the potential advantage through total eye aberration data and ray tracing refraction calculation to offer improved and more predictable visual outcomes.

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Scheimpflug vs Scanning-Slit Corneal Tomography: Comparison of Corneal and Anterior Chamber Tomography Indices for Repeatability and Agreement in Healthy Eyes

Purpose

To evaluate and compare the repeatability and agreement of Scheimpflug vs scanning-slit tomography of the cornea and the anterior chamber in terms of keratometric and tomographic indices in healthy eyes.

Methods

The 20 eyes of 10 healthy participants underwent 3 consecutive measurements using both Scheimpflug-tomography and scanning-slit tomography, diagnostic devices. Multiple corneal and anterior chamber tomographic parameters were recorded and evaluated to include corneal keratometry and its axis; corneal best-fit sphere (BFS), pachymetry mapping, angle kappa, anterior chamber depth (ACD), pupil diameter, and location. Repeatability for each device was assessed using the within each subject standard deviation of sequential exams, the coefficient variation (CV) and the intraclass correlation coefficient (ICC). Agreement between the two devices was assessed using Bland-Altman plots with 95% limits of agreement (LoA) and correlation coefficient (r).

Results

Both devices were found to have high repeatability (ICC>0.9) both in keratometric and other tomographic measurements. Scheimpflug tomography's repeatability though appeared superior in the average keratometry values, anterior and posterior BFS, thinnest corneal pachymetry value and location (p<0.05). Agreement: Statistically significant inter-device differences were noted in the mean values of K1, K2, BFS, ACD and thinnest corneal pachymetry (p<0.05). Despite the agreement differences noted, the two devices were well correlated (r>0.8) in respective measurements with Scheimpflug delivering consistently lower values than the scanning-slit tomography device.

Conclusion

Scheimpflug-tomography repeatability was found to be superior to that of scanning-slit tomography in this specific study, in most parameters evaluated. Inter-device agreement evaluation suggests that reading from the two devices may not be used interchangeably in absolute values, yet they are well correlated with Scheimpflug delivering consistently lower values in most.

Combined Protocols for Corneal Collagen Cross-Linking with Photorefractive Surgery for Refractive Management of Keratoconus: Update on Techniques and Review of Literature

With the development and gradual dissemination of corneal collagen cross-linking (CXL) in the twenty-first century as an early treatment for keratoconus, the management paradigm has shifted to include a greater focus on complete refractive correction for these patients. Though supplemental hard contact lens therapy remains a mainstay of visual rehabilitation in keratoconus, there has been increasing appeal in a completely surgical approach by combining CXL with adjuvant refractive procedures to both halt the ectatic process and enhance functional visual outcomes. Collectively termed "CXL plus" procedures, several combined protocols have been studied to various degrees in conjunction with CXL, involving photorefractive keratectomy (PRK), transepithelial phototherapeutic keratectomy (PTK), conductive keratoplasty (CK), intrastromal corneal ring segments (ICRS) implantation, phakic intraocular lens (PIOL) implantation, or multiple of these techniques together. The scope of this review aims to encompass a summary of current CXL protocols and present the current status of studies involving adjunctive keratorefractive procedures combined with CXL. By discussing the results to date of these CXL plus protocols, we can assess what further areas of investigation are necessary within this field as the next step to optimizing treatment modalities and outcomes for our keratoconus patients, regardless of disease severity.

Management of progressive keratoconus with partial topography-guided PRK combined with refractive, customized CXL - a novel technique: the enhanced Athens protocol

Purpose

To report a novel application of partial topography-guided photorefractive keratectomy combined with topographically customized, higher fluence, and variable pattern corneal cross-linking applied on the same day of the treatment of keratoconus.

Methods

A topography-guided partial photorefractive keratectomy treatment of maximum 30 µm over the thinnest cone area was applied initially followed by a 7 mm, 50 µm phototherapeutic keratectomy treatment to address epithelial removal. 0.02% Mitomycin C was applied for 20 seconds and then the exposed stroma was soaked with 0.1% riboflavin solution for 5 minutes. The cornea was then treated with a customized, variable-pattern and 20 mW/cm² fluence for a total of 5-10 J, and up to 15 J of energy was delivered with the KXL-II device employing an active tracker. The center of the pattern that received the 15 J was topography-matched with the thinnest area of the cone. Visual acuity, refractive error, cornea clarity, keratometry, topography, pachymetry with a multitude of modalities and endothelial cell density were evaluated over 36 months.

Results

Keratoconus was stabilized in all cases. The severity of keratoconus stage by Amsler- Krumeich criteria improved from an average of 3.2 (1-4) to 1.8 (0-3). Uncorrected distance visual acuity changed from preoperative 20/80 to 20/25 at 6 months. A maximum astigmatic reduction of 7.8 D (5.3-15.6), and a significant cornea surface normalization (an index of height decentration improvement from 0.155 [±0.065] to 0.045 [±0.042]) were achieved by 1 month and remained relatively stable for 36 months postoperatively. Two cases delayed full reepithelialization for up to 9 days.

Conclusion

This paper introduces a novel technique in order to maximize the refractive normalization effect along with ectasia stabilization in young keratoconus patients. This may facilitate the use of less tissue ablation, in comparison to utilizing a homogeneous UV light beam for corneal cross-linking in Athens Protocol cases. It broadens the number of potential candidate cases that would have been limited to employ this technique due to tissue thickness limitations.

Effects of single-segment Intacs implantation on visual acuity and corneal topographic indices of keratoconus

PURPOSE

To assess the changes in visual acuity and topographic indices after implantation of single-segment Intacs.

METHODS

Forty-two keratoconic eyes received Femtosecond-assisted single-segment Intacs. Uncorrected distance visual acuity (UDVA) and best spectacle corrected visual acuity (BSCVA), refractive error, keratometry (K1, K2, Km, and KMax.), and seven Pentacam measured topographical indices; index of surface variance (ISV), index of vertical asymmetry (IVA), keratoconus index (KI), central keratoconus index (CKI), index of height asymmetry (IHA), index of height decentration (IHD), and minimum radius of curvature (R Min) were assessed 4 months after surgery. Correlations between changes of visual acuity and topographical indices changes were evaluated.

RESULTS

UDVA increased from 0.92 ± 0.35 to 0.49 ± 0.31 logMAR (P < 0.001), and BSCVA increased from 0.39 ± 0.15 to 0.23 ± 0.11 logMAR (P < 0.001). Subjective refraction spherical equivalent (SRSE) decreased from -3.92 ± 1.66 diopters (D) to -2.00 ± 1.51 D (P < 0.001). Mean central Keratometry decreased 2.16 ± 1.09 D from the preoperative readings (P < 0.001). All Pentacam topographical indices except CKI significantly improved (for IHA P = 0.046, for five others P < 0.001). The correlation between improvement in topographical indices and visual acuity improvements was not week.

CONCLUSION

Intacs implantation in keratoconic eyes increased visual acuity and made corneal shape less irregular. However, the improvements of visual acuity and corneal shape were not strongly correlated.

Occupational safety measures and morbidity among welders in Vellore, Southern India

BACKGROUND

Welders in the unorganized occupational sector in the economically developing world are exposed to respiratory, skin, eye, ear, and neurological problems exacerbated by non-usage of personal protective equipment (PPE).

OBJECTIVE

To study the frequency of health problems and the usage of PPE among welders in unorganized welding units in Vellore, India.

METHODS

A cross-sectional survey was conducted among 150 welders to determine the frequency of skin, ear, eye, and respiratory morbidity and the usage of PPE. A group of 150 non-welders were chosen for comparison.

RESULTS

Significant differences in the frequency of skin burns, redness, hyper pigmentation, itching, eye injuries, and sensorineural deafness were observed among the welders and non-welders (P < 0.001). Hypertension was noted in 12.6% of the welders as compared to 0.7% among the non-welders. None of the welders used appropriate PPE. For welders, low educational attainment was associated with an increased risk of eye injury (P < 0.05, OR = 0.29). There was also a significant difference between sensorineural deafness and a welder having less than 10 years of welding work experience (P < 0.001, OR = 18.18) which could probably be accounted for by the healthy worker effect.

CONCLUSION

Welders in this sample experienced a significant skin, eye, and ear morbidity accentuated by the non-usage of PPE. All worked without formal training and were unaware of the safe working guidelines that exist, but are not implemented for the welders in India.

Strategies for improving the early diagnosis of keratoconus

To diagnose keratoconus at its earliest stage is meaningful in order to avoid refractive surgery in the eye, which may lead to further damage in the abnormal cornea structure and consequently cause iatrogenic ectasia. In this article, the following aspects of detecting earliest stage of keratoconus were reviewed: 1) nomenclature of the earliest forms of keratoconus; 2) diagnosis of keratoconus using curvature-based topography (also known as Placido-based topography, ie, videokeratography) as a traditional method and elevation-based topography as a new method which has gained popularity in recent years; and 3) other methods analyzing keratoconus cornea like corneal biomechanics and wavefront sensing. Elevation-based topography using either Scheimpflug imaging techniques or slit-scanning imaging techniques has shown to be advantageous over the curvature-based topography in detecting keratoconus at its earliest stage. Posterior elevation of the cornea is notified to enhance the sensitivity and specificity of detection if used along with the measurements of anterior surface of the cornea. Cornea biomechanics analysis and wavefront sensing also revealed differences between normal eyes and keratoconic eyes in their earliest stage. Combining the latest technology and the traditional techniques will be the future trend to improve early diagnosis of keratoconus.

Higher incidence of steroid-induced ocular hypertension in keratoconus

BACKGROUND

To compare intraocular pressure (IOP) changes following topical dexamethasone administration for 1 month in keratoconic versus normal eyes.

METHODS

This is a retrospective, single-center, non-randomized case series evaluation of 350 eyes. Two groups were formed: normal/control Group A (nA =73), eyes that underwent excimer laser photorefractive keratectomy; and keratoconic (KCN) Group B (nB =277), eyes that were subjected to partial laser photorefractive keratectomy combined with collagen cross-linking (The Athens Protocol). All eyes received the same post-operative regimen of topical dexamethasone 0.1 % for at least 1 month. Goldmann applanation tonometry IOP readings and central corneal thickness (CCT) measurements were monitored. Cases with induced ocular hypertension (OHT, defined as post-operative IOP higher than 21 mmHg), were identified and correlated to refractive procedure, gender, and corneal thickness.

RESULTS

At 4 weeks postoperatively, OHT was noted on 27.4 % (20 /73 eyes) in Group A, and 43.7 % (121 /277 eyes) in KCN Group B, (p <0.01). Six months post-operatively (following 5-months of discontinuing topical dexamethasone treatment and commencing treatment of IOP-lowering medications), OHT rate was 1.8 % in Group A and 3.9 % in the KCN Group B.

CONCLUSION

This study demonstrates a potentially significant pre-disposition of keratoconic eyes to the development of steroid-induced OHT.

Distribution and Repeatability of Corneal Astigmatism Measurements (Magnitude and Axis) Evaluated With Color Light Emitting Diode Reflection Topography

Purpose:

To evaluate and investigate the distribution and repeatability of anterior corneal surface astigmatism measurements (axis and magnitude) using a novel corneal topographer.

Methods:

Anterior corneal surface astigmatism was investigated in a total of 195 eyes using a novel multicolored spot reflection topographer (Cassini; i-Optics). Two patient groups were studied, a younger-age group A and an older-age group B. Three consecutive acquisitions were obtained from each eye. The repeatability of measurement was assessed using Bland–Altman plot analysis and is reported as the coefficient of repeatability.

Results:

Group A (average age 34.3 years) had on average with-the-rule astigmatism, whereas the older-age group B (average age 72.3 years) had on average against-the-rule astigmatism. Average astigmatism magnitude measurement repeatability in group A was 0.4 diopters (D) and in group B 0.4 D. Average astigmatism axis measurement repeatability in group A was 5.4 degrees and in group B 5.5 degrees. The axis measurement repeatability improved with increasing magnitude of astigmatism: in the subgroups with astigmatism between 3.0 and 6.0 D, the axis repeatability was 1.4 degrees (group A) and 1.2 degrees (group B), whereas in the subgroups with astigmatism larger than 6.0 D, the repeatability was 1.1 and 0.6 degrees, respectively.

Conclusions:

This novel corneal topography device seems to offer high precision in reporting corneal astigmatism. This study reaffirms the established trend of a corneal astigmatism shift from an average “with-the-rule” to “against-the-rule” with aging.

Pentacam topographic changes after collagen cross-linking in patients with keratoconus

Background:

Corneal cross-linking (CXL) with riboflavin and ultra-violet A is less invasive in comparison with other procedures such as penetrating keratoplasty. Hence, we planned this study to evaluate the efficacy of CXL in disease progression and to compare keratoconus indices before and 1 year after cross-linking by Pentacam.

Materials and Methods:

In this prospective clinical trial, we enrolled 37 eyes of 37 patients suffering from keratoconus who were candidates for CXL. All eyes were examined before and one 1 year after surgery with a slit lamp and Pentacam for corneal topography. To compare the mean of each Pentacam parameter and index before and 1 year after the surgery, we used paired t-test.

Results:

There were 23 males and 14 females. The mean age was 21.5 years 18-30 years). At the 12^th month examination, the corneal thickness had decreased (P = 0.0068) and the Index of Height Decentration (IHD) had increased (P = 0.016). There were no statistically significant differences in other indices and parameters 1 year after CXL.

Conclusion:

Most of the parameters and indices had not changed during 1 year after CXL. The procedure seems to be effective in stopping the disease progression at least for 12 months after surgery.

Color light-emitting diode reflection topography: validation of keratometric repeatability in a large sample of wide cylindrical-range corneas

Purpose

To investigate repeatability of steep and flat keratometry measurements, as well as astigmatism axis in cohorts with normal range and regular astigmatic such as: eyes following laser-assisted in situ keratomileusis (LASIK) and normal population, as well as cohorts of high and irregular astigmatism such as keratoconic eyes, and keratoconic eyes following corneal collagen cross-linking, employing a novel corneal reflection topography device.

Methods

Steep and flat keratometry and astigmatism axis measurement repeatability was investigated employing a novel multicolored-spot reflection topographer (Cassini) in four study groups, namely a post myopic LASIK-treated Group A, a keratoconus Group B, a post-CXL keratoconus Group C, and a control Group D of routine healthy patients. Three separate, maps were obtained employing the Cassini, enabling investigation of the intra-individual repeatability by standard deviation. Additionally we investigated in all groups,the Klyce surface irregularity indices for keratoconus, the SAI (surface asymmetry index) and the SRI (surface regularity index).

Results

Flat keratometry repeatability was 0.74±0.89 (0.03 to 5.26) diopters (D) in the LASIK Group A, 0.88±1.45 (range minimum to maximum, 0.00 to 7.84) D in the keratoconic Group B, and 0.71±0.94 (0.02 to 6.23) D in the cross-linked Group C. The control Group D had flat keratometry repeatability 0.36±0.46 (0.00 to 2.71) D. Steep keratometry repeatability was 0.64±0.82 (0.01 to 4.81) D in the LASIK Group A, 0.89±1.22 (0.02 to 7.85) D in the keratoconic Group B, and 0.93±1.12 (0.04 to 5.93) D in the cross-linked Group C. The control Group D had steep keratometry repeatability 0.41±0.50 (0.00 to 3.51) D. Axis repeatability was 3.45±1.62° (0.38 to 7.78°) for the LASIK Group A, 4.12±3.17° (0.02 to 12.13°) for the keratoconic Group B, and 3.20±1.99° (0.17 to 8.61°) for the cross-linked Group C. The control Group D had axis repeatability 2.16±1.39° (0.05 to 5.86°). The SAI index measurement repeatability was 0.33±0.40 (0.01 to 2.31) in the post-LASIK Group A, 0.39±0.75 (0.00 to 7.15) in the keratoconic Group B, and 0.43±0.56 (0.05 to 3.50) in the keratoconus post-CXL Group C. The control group had SAI measurement repeatability of 0.26±0.30 (0.00 to 2.39). The SRI index repeatability was 0.22±0.17 (0.01 to 0.96) for post-LASIK Group A, 0.20±0.18 (0.00 to 1.07) in keratoconic Group B, and 0.13±0.09 (0.00 to 0.45) in the keratoconus post-CXL Group C. The control Group D had SRI measurement repeatability of 0.23±0.16 (0.00 to 0.75).

Conclusion

This novel corneal topography device appears to offer very high specificity in estimating corneal keratometry and specific corneal irregularity indices, even in topographically challenging corneas such as LASIK treated, keratoconic, and cross-linked.

OCT corneal epithelial topographic asymmetry as a sensitive diagnostic tool for early and advancing keratoconus

PURPOSE

To investigate epithelial thickness-distribution characteristics in a large group of keratoconic patients and their correlation to normal eyes employing anterior-segment optical coherence tomography (AS-OCT).

MATERIALS AND METHODS

The study group (n=160 eyes) consisted of clinically diagnosed keratoconus eyes; the control group (n=160) consisted of nonkeratoconic eyes. Three separate, three-dimensional epithelial thickness maps were obtained employing AS-OCT, enabling investigation of the pupil center, average, mid-peripheral, superior, inferior, maximum, minimum, and topographic epithelial thickness variability. Intraindividual repeatability of measurements was assessed. We introduced correlation of the epithelial data via newly defined indices. The epithelial thickness indices were then correlated with two Scheimpflug imaging-derived AS-irregularity indices: the index of height decentration, and the index of surface variance highly sensitive to early and advancing keratoconus diagnosis as validation.

RESULTS

Intraindividual repeatability of epithelial thickness measurement in the keratoconic group was on average 1.67 μm. For the control group, repeatability was on average 1.13 μm. In the keratoconic group, pupil-center epithelial thickness was 51.75±7.02 μm, while maximum and minimum epithelial thickness were 63.54±8.85 μm and 40.73±8.51 μm. In the control group, epithelial thickness at the center was 52.54±3.23 μm, with maximum 55.33±3.27 μm and minimum 48.50±3.98 μm epithelial thickness. Topographic variability was 6.07±3.55 μm in the keratoconic group, while for the control group it was 1.59±0.79 μm. In keratoconus, topographic epithelial thickness change from normal, correlated tightly with the topometric asymmetry indices of IHD and ISV derived from Scheimpflug imaging.

CONCLUSION

Simple, OCT-derived epithelial mapping, appears to have critical potential in early and advancing keratoconus diagnosis, confirmed with its correlation with established Scheimpflug-derived asymmetry topometric indices.

Clinical Correlation between Placido, Scheimpflug and LED Color Reflection Topographies in Imaging of a Scarred Cornea

This case report aims to evaluate safety, efficacy and feasibility of anterior surface imaging by a novel point-source reflection topographer, in comparison to four other corneal imaging modalities. A 17-year-old female patient, clinically diagnosed with chronic herpetic keratitis in her left eye was imaged by a novel multicolored-spot reflection topography system. We comparatively investigated elevation and curvature maps between the novel topographer and established Placido disk topography and Scheimpflug tomography systems. Pachymetry maps were compared between the Scheimpflug system and anterior-segment optical coherence tomography system. The Placido system failed to properly register the abnormal anterior surface due to incomplete mire registration, while the Scheimpflug topometry device imaged the anterior surface properly, but not the posterior (due to media opacity), and thus pachymetry was highly irregular and erroneous in this case. Imaging of corneas infected with herpes simplex virus keratitis has been rare; we have not identified any such documentation in the peer review literature in the last 10 years. This novel multicolored-spot reflection topography imaging may offer successful corneal imaging in cases where established clinical topography systems may fail to produce accurate reconstruction of the corneal shape. This is an important case demonstrating exceptional clinical feasibility in such rare cases offered by a newly introduced technology in ophthalmic imaging.

Management of residual refractive error after laser in situ keratomileusis and photorefractive keratectomy

PURPOSE OF REVIEW

To review the various steps and methods in managing residual refractive error after laser in situ keratomileusis and photorefractive keratectomy (PRK).

RECENT FINDINGS

Past studies have shown the efficacy and safety of flap relifts over recuts and for surface ablation over the flap. Other previous and also more recent studies show the use of a femtosecond laser for side cuts only. Recently, the creation of a femtosecond mini flap has been described. New studies also demonstrate the use of collagen cross-linking in postrefractive surgery ectasia.

SUMMARY

Residual refractive error is a known complication after both laser in situ keratomileusis and PRK. A systematic approach should be taken to manage this complication starting with a thorough evaluation to determine if an enhancement is indicated and if so, which method will be the safest and most efficacious for the patient.

Toric topographically customized transepithelial, pulsed, very high-fluence, higher energy and higher riboflavin concentration collagen cross-linking in keratoconus

Purpose

To report a novel application of toric topographically customized transepithelial collagen cross-linking (CXL) aiming to achieve refractive astigmatic changes in a keratoconic cornea.

Methods

Specially formulated riboflavin transepithelial administration and delivery of high-fluence UVA in a topographically customized pattern was applied in an eye with progressive keratoconus. Visual acuity, cornea clarity, keratometry, topography, and pachymetry with a multitude of modalities, as well as endothelial cell counts were evaluated for >6 months.

Results

Uncorrected distance visual acuity changed from preoperative 20/40 to 20/25 at 6 months. A mean astigmatic reduction of 0.8 D, and significant cornea surface normalization was achieved 6 months postoperatively. There was some mild change in the epithelial distribution, with the treated area having a slight normalization in the average epithelial thickness.

Conclusions

We introduce herein the novel application of a topographically customizable transepithelial CXL in progressive keratoconus in order to achieve an astigmatic refractive effect and ectasia stabilization. This novel technique offers a nonablative and nonincisional approach to treat irregular astigmatism in ectatic cornea with rapid visual rehabilitation.

In vivo Confocal Microscopy Report after Lasik with Sequential Accelerated Corneal Collagen Cross-Linking Treatment

We report the first pilot qualitative confocal microscopic analysis of a laser in situ keratomileusis (Lasik) treatment combined with sequential high-fluence accelerated corneal collagen cross-linking, denominated Lasik XTra, by means of HRT II laser scanning in vivo confocal microscopy after a 6-month follow-up. After obtaining approval from the Siena University Hospital Institutional Review Board, a 33-year-old female patient underwent a Lasik XTra procedure in her left eye. Confocal analysis demonstrated induced slight corneal microstructural changes by the interaction between UV-A, riboflavin and corneal stromal collagen, beyond the interface to a depth of 160 µm, without adverse events at the interface and endothelial levels. This application may be considered a prophylactic biomechanical treatment, stiffening the intermediate corneal stroma to prevent corneal ectasia and stabilizing the clinical results of refractive surgery. According to our preliminary experiences, this combined approach may be useful in higher-risk Lasik patients for hyperopic treatments, high myopia and lower corneal thicknesses.

Comparison of high-resolution Scheimpflug and high-frequency ultrasound biomicroscopy to anterior-segment OCT corneal thickness measurements

Background

The purpose of this study was to compare and correlate central corneal thickness in healthy, nonoperated eyes with three advanced anterior-segment imaging systems: a high-resolution Scheimpflug tomography camera (Oculyzer II), a spectral-domain anterior-segment optical coherence tomography (AS-OCT) system, and a high-frequency ultrasound biomicroscopy (HF-UBM) system.

Methods

Fifty eyes randomly selected from 50 patients were included in the study. Inclusion criteria were healthy, nonoperated eyes examined consecutively by the same examiner. Corneal imaging was performed by three different methods, ie, Oculyzer II, spectral-domain AS-OCT, and FH-UBM. Central corneal thickness measurements were compared using scatter diagrams, Bland-Altman plots (with bias and 95% confidence intervals), and two-paired analysis.

Results

The coefficient of determination (r²) between the Oculyzer II and AS-OCT measurements was 0.895. Likewise, the coefficient was 0.893 between the Oculyzer II and HF-UBM and 0.830 between the AS-OCT and HF-UBM. The trend line coefficients of linearity were 0.925 between the Oculyzer II and the AS-OCT, 1.006 between the Oculyzer II and HF-UBM, and 0.841 between the AS-OCT and HF-UBM. The differences in average corneal thickness between the three pairs of CCT measurements were −6.86 μm between the Oculyzer II and HF-UBM, −12.20 μm between the AS-OCT and Oculyzer II, and +19.06 μm between the HF-UBM and AS-OCT.

Conclusion

The three methods used for corneal thickness measurement are highly correlated. Compared with the Scheimplug and ultrasound devices, the AS-OCT appears to report a more accurate, but overally thinner corneal pachymetry.

Forme Fruste Keratoconus Imaging and Validation via Novel Multi-Spot Reflection Topography

Background/Aims

This case report aims to evaluate safety, efficacy and applicability of anterior surface imaging in a patient with forme fruste keratoconus (FFKC) based on a novel multi-spot, multicolor light-emitting-diode (LED) tear film-reflection imaging technology

Case Description

A 45-year-old male patient, clinically diagnosed with FFKC, with highly asymmetric manifestation between his eyes, was subjected to the multicolor-spot reflection topography. We investigated elevation and sagittal curvature maps comparatively with the multicolor-spot reflection topographer, a Placido topographer and a Scheimpflug imaging system. For the right eye, steep and flat keratometry values were 41.92 and 41.05 D with the multicolor spot-reflection topographer, 42.30 and 42.08 D with the Placido, and 41.95 and 41.19 D with the Scheimpflug system. For the left eye, steep and flat keratometry values were 41.86 and 41.19 D with the multicolor spot-reflection topographer, 42.06 and 41.66 D with the Placido topographer, and 41.96 and 41.66 D with the Scheimpflug camera. Average repeatability of the keratometry measurements was ±0.35 D for the multicolor spot-reflection topographer, ±0.30 D for the Placido, and ±0.25 D for the Scheimpflug camera. Very good agreement between the instruments was demonstrated on the elevation and curvature maps.

Conclusion

The ease of use and the comparable results offered by the multicolor spot-reflection topographer, in comparison to established Placido and Scheimpflug imaging, as well as the increased predictability that may be offered by the multicolor spot-reflection topographer, may hold promise for wider clinical application, such as screening of young adults for early keratoconus and, in a much wider perspective, potential candidates for laser corneal refractive surgery.

Evaluation of Visual Acuity, Pachymetry and Anterior-Surface Irregularity in Keratoconus and Crosslinking Intervention Follow-up in 737 Cases

Purpose

To investigate visual acuity, corneal pachymetry, and anterior-surface irregularity indices correlation with keratoconus severity in a very large pool of clinically-diagnosed untreated keratoconic eyes, and in keratoconic eyes subjected to crosslinking intervention.

Materials and methods

Total of 737 keratoconic (KCN) cases were evaluated. Group A was formed from 362 untreated keratoconic eyes, and group B from 375 keratoconic eyes subjected to partial normalization via topography-guided excimer laser ablation and high-fluence collagen crosslinking. A control group C of 145 healthy eyes was employed for comparison. We investigated distance visual acuity, uncorrected (UDVA), best-spectacle corrected (CDVA), and Scheimpflug-derived keratometry, pachymetry (central corneal thickness, CCT and thinnest, TCT), and two anterior-surface irregularity indices, the index of surface variance (ISV) and the index of height decentration (IHD). The correlations between these parameters vs topographic keratoconus classification (TKC) were investigated.

Results

Keratometry for group A was K1 (flat) 46.67 ± 3.80 D and K2 (steep) 50.76 ± 5.02 D; for group B K1 44.03 ± 3.64 D and K2 46.87 ± 4.61 D; for group C, K1 42.89 ± 1.45 D and K2 44.18 ± 1.88 D. Visual acuity for group A was UDVA 0.12 ± 0.18 and CDVA 0.59 ± 0.25 (decimal), for group B, 0.51 ± 0.28 and 0.77 ± 0.22, and for group C, 0.81 ± 0.31 and 0.87 ± 0.12.

Correlation between ISV and TKC (r2) was for group A 0.853, and for group-B 0.886. Correlation between IHD and TKC was for group A r2 = 0.731, and for group B 0.701. The ROC analysis ‘area under the curve’ was for CDVA 0.550, TCT 0.596, ISV 0.876 and IHD 0.887.

Conclusion

Our study indicates that the traditionally employed metrics of visual acuity and corneal thickness may not be robust indicators nor provide accurate assessment on either keratoconus severity or postoperative evaluation. Two anterior surface irregularity indices, derived by Scheimpflug-imaging, ISV and IHD, may be more sensitive and specific tools.

Précis

Visual acuity, Scheimpflug-derived pachymetry and anterior-surface irregularity correlation to keratoconus severity in untreated cases (A), treated with crosslinking (B), and in a control group (C) reveals that visual acuity and pachymetry do not correlate well with keratoconus severity.

How to cite this article

Kanellopoulos AJ, Moustou V, Asimellis G. Evaluation of Visual Acuity, Pachymetry and Anterior-Surface Irregularity in Keratoconus and Crosslinking Intervention Follow-up in 737 Cases. J Kerat Ect Cor Dis 2013;2(3):95-103.