Computer-assisted corneal topography in family members of patients with keratoconus

Keratoconus Diagnosis: From Fundamentals to Artificial Intelligence: A Systematic Narrative Review

The remarkable recent advances in managing keratoconus, the most common corneal ectasia, encouraged researchers to conduct further studies on the disease. Despite the abundance of information about keratoconus, debates persist regarding the detection of mild cases. Early detection plays a crucial role in facilitating less invasive treatments. This review encompasses corneal data ranging from the basic sciences to the application of artificial intelligence in keratoconus patients. Diagnostic systems utilize automated decision trees, support vector machines, and various types of neural networks, incorporating input from various corneal imaging equipment. Although the integration of artificial intelligence techniques into corneal imaging devices may take time, their popularity in clinical practice is increasing. Most of the studies reviewed herein demonstrate a high discriminatory power between normal and keratoconus cases, with a relatively lower discriminatory power for subclinical keratoconus.

Recurrent keratoconus: an analysis of breaks in Bowman's layer in corneal grafts

OBJECTIVE

To study in a masked fashion whether an objective histological feature associated with keratoconus (KCN) occurs in donor corneas in eyes originally receiving a corneal graft for KCN.

METHODS

Two ocular pathologists performed a retrospective masked histological analysis of slides from donor buttons recovered from 21 eyes with a history of KCN undergoing repeat penetrating keratoplasty (failed-PK-KCN), 11 eyes that underwent their first PK due to KCN (primary KCN), and 11 eyes without history of KCN which underwent PK for other conditions (failed-PK-non-KCN). Breaks/gaps in Bowman's layer served as the pathological feature indicative of recurrent KCN.

RESULTS

Breaks in Bowman's layer were present in 18/21 (86%) of the failed-PK-KCN group, 10/11 (91%) of the primary KCN group, and in 3/11 (27%) of the failed-PK-non-KCN group. Pathological evidence suggests that the prevalence of breaks is significantly higher in grafted patients with a history of KCN than non-KCN controls (OR: 16.0, 95% CI 2.63 to 97.2, Fisher's exact test p=0.0018) with a conservative Bonferroni criterion of p <0.017 to account for multiple group comparisons. There was no statistically significant difference found between the failed-PK-KCN and primary KCN groups.

CONCLUSIONS

This study provides histological evidence that breaks and gaps in Bowman's layer, consistent with those found in primary KCN, may develop within the donor tissue in eyes with a history of KCN.

The Evolution of Diagnostics for Keratoconus: From Ophthalmometry to Biomechanics

PURPOSE

To enumerate the various diagnostic modalities used for keratoconus and their evolution over the past century.

METHODS

A comprehensive literature search including articles on diagnosis on keratoconus were searched on PUBMED and summarized in this review.

RESULTS

Initially diagnosed in later stages of the disease process through clinical signs and retinoscopy, the initial introduction of corneal topography devices like Placido disc, photokeratoscopy, keratometry and computer-assisted videokeratography helped in the earlier detection of keratoconus. The evolution of corneal tomography, initially with slit scanning devices and later with Scheimpflug imaging, has vastly improved the accuracy and detection of clinical and sub-clinical disease. Analyzing the alteration in corneal biomechanics further contributed to the earlier detection of keratoconus even before the tomographic changes became evident. Anterior segment optical coherence tomography has proven to be a helpful adjuvant in diagnosing keratoconus, especially with epithelial thickness mapping. Confocal microscopy has helped us understand the alterations at a cellular level in keratoconic corneas.

CONCLUSION

Thus, the collective contribution of the various investigative modalities have greatly enhanced earlier and accurate detection of keratoconus, thus reducing the disease morbidity.

Evaluation of Ocular Higher-Order Aberrations in First-Degree Relatives of Patients With Keratoconus

PURPOSE

The aim of this study was to evaluate the corneal higher-order aberrations (HOAs) in first-degree relatives of patients with keratoconus (KCN) and compare with the normal population.

METHODS

In this prospective comparative study, 210 eyes from 105 family members of 28 patients with KCN and 210 normal eyes of 105 controls were enrolled. In each eye, corneal topography, tomography, and aberrometry were performed and compared between the 2 groups.

RESULTS

This study included 61 female (58.1%) and 44 male participants (41.9%) and 105 age-matched and sex-matched controls with normal topographic cornea. In 14 of 105 first-degree relatives (13.33%) of patients with KCN, KCN was diagnosed with a male preponderance (71.5% male, 28.5% female). Tomographic indices and irregularity indices in 3 and 5 mm zone in Orbscan were significantly higher in the relative group. In addition, other irregularity indices of TMS-4 topography including surface regularity index, surface asymmetry index, difference sector index, SDP, and irregular astigmatism index were significantly higher in family members of patients with KCN. The most prevalent topographic pattern in the control group was the symmetric bowtie (57.1%) and in the relative group was the asymmetric bowtie (39.5%). In addition, significantly thinnest corneal pachymetry was detected in the relative group. Root mean square of all HOAs including vertical trefoil, vertical coma, horizontal coma, horizontal trefoil, quadrifoil, and fourth-order spherical aberrations were significantly greater in the relative group than controls.

CONCLUSIONS

Owing to the high prevalence of undiagnosed KCN susceptibility in family members with KCN, keratorefractive surgery should be considered cautiously in these individuals. In addition, comprehensive preoperative examination should be considered to detect subtle topographic and HOAs in these individuals.

KeratoScreen: Early Keratoconus Classification With Zernike Polynomial Using Deep Learning

PURPOSE

We aimed to investigate the usefulness of Zernike coefficients (ZCs) for distinguishing subclinical keratoconus (KC) from normal corneas and to evaluate the goodness of detection of the entire corneal topography and tomography characteristics with ZCs as a screening feature input set of artificial neural networks.

METHODS

This retrospective study was conducted at the Affiliated Eye Hospital of Wenzhou Medical University, China. A total of 208 patients (1040 corneal topography images) were evaluated. Data were collected between 2012 and 2018 using the Pentacam system and analyzed from February 2019 to December 2021. An artificial neural network (KeratoScreen) was trained using a data set of ZCs generated from corneal topography and tomography. Each image was previously assigned to 3 groups: normal (70 eyes; average age, 28.7 ± 2.6 years), subclinical KC (48 eyes; average age, 24.6 ± 5.7 years), and KC (90 eyes; average age, 25.9 ± 5.4 years). The data set was randomly split into 70% for training and 30% for testing. We evaluated the precision of screening symptoms and examined the discriminative capability of several combinations of the input set and nodes.

RESULTS

The best results were achieved using ZCs generated from corneal thickness as an input parameter, determining the 3 categories of clinical classification for each subject. The sensitivity and precision rates were 93.9% and 96.1% in subclinical KC cases and 97.6% and 95.1% in KC cases, respectively.

CONCLUSIONS

Deep learning algorithms based on ZCs could be used to screen for early KC and for other corneal ectasia during preoperative screening for corneal refractive surgery.

Performances of Corneal Topography and Tomography in the Diagnosis of Subclinical and Clinical Keratoconus

Aim

The purpose of the study was to assess the efficacy of topographical and tomographical indices given by the Pentacam (pachymetric, tomopetric, and aberometric) in clinical and subclinical keratoconus (KCN) diagnosis.

Material and Methods

In this observational analytic retrospective study, patients with abnormal findings in topography and tomography maps but with no signs on clinical examination (subclinical KCN group, sKCN), patients with clinical keratoconus (KCN group), and healthy subjects (Control group) were evaluated.

Results

The KCN group proved significantly different (p < 0.001) values of the investigated parameters than the Control group. Eleven out of 28 investigated parameters proved significantly different in the sKCN group compared to controls (p < 0.001). Two topographic measurements, namely I-S (cut-off = 1.435, a large value indicates the presence of KCN) and CCT (cut-off = 537, a small value indicates the presence of KCN), showed AUCs equal to 1 [0.999 to 1]. Six other Pentacam measurements, including Back maximum keratometry (Back Kmax) proved to be excellent parameters for case-finding and screening. In distinguishing sKCN from normal eyes, Pentacam index of vertical asymmetry (IVA), inferior-superior difference (I-S) value, thinnest point (TP), Belin Ambrosio Enhanced Ectasia Display (BAD_D) and root mean square total (RMS total) performed best.

Conclusions

In distinguishing sKCN from normal eyes, Back Kmax, IVA, I-S, and RMS total values demonstrated higher accuracy and utility. Six indices, namely ISV, IVA, KISA, PRC, RMS-HOA, and Back Kmax demonstrate excellent utility in case-finding and screening for clinical KCN.

Clinical Study on the Differential Diagnosis of High Myopia Astigmatism and Subclinical Keratoconus in Adolescents by Pentacam Anterior Segment Analyzer

To explore the clinical value of Pentacam anterior segment analyzer in differential diagnosis of high myopia astigmatism and subclinical keratoconus in adolescents. The study included 100 teenagers with ophthalmic diseases treated at our hospital between July 2015 and August 2021, including 58 individuals with simple high myopia astigmatism (73 eyes in the simple high myopia astigmatism group) and 42 teenagers with subclinical keratoconus (51 eyes in the subclinical keratoconus group). The corneal parameters of the two groups were measured with a Pentacam anterior segment analyzer, and we compared the thinnest corneal thickness, anterior (posterior) vertex height of the thinnest point of the cornea, index of vertical asymmetry (IVA), index of height descent (IHD), and the average corneal pachymetric progression index. The receiver operating characteristic curve (ROC) was drawn to evaluate the value of various parameters and combined diagnostic factor Y in the differential diagnosis of high myopia astigmatism and subclinical keratoconus. The thinnest region of the cornea in the subclinical keratoconus group was less than that in the simple high myopia astigmatism group, while the anterior (posterior) vertex height of the thinnest point of the cornea, index of vertical asymmetry (IVA), index of height decentration (IHD), and average corneal pachymetric progression index were higher than those in the simple high myopia astigmatism group (P < 0.05). For the differential diagnosis of high myopia astigmatism and subclinical keratoconus, the combined diagnostic factor Y, anterior (posterior) vertex height, IVA, IHD, and mean corneal progression index were 0.808, 0.833, 0.868, 0.847, 0.684, and 0.926 (P < 0.05). The AUC of the combined diagnostic factory was the largest, which was significantly different from that of the anterior vertex height of the thinnest point of the cornea (Z = 3.280), the posterior vertex height of the thinnest point of the cornea (Z = 3.205), IVA (Z = 2.764), IHD (Z = 2.237), and the average corneal progression index (Z = 4.125) (P < 0.05). Using the Pentacam anterior segment analyzer, differential diagnoses can be made for high myopia, astigmatism, and subclinical keratoconus.

Between eye asymmetry in keratoconus in an Indian population

PURPOSE

The purpose of this study was to assess the clinical as well as topographic asymmetry between the eyes in keratoconus.

METHODS

Clinical examination including retinoscopy, distant direct ophthalmoscopy, manual keratometry (Bausch & Lomb), slitlamp biomicroscopy and topography (Nidek ARK10000) was carried out on 44 eyes of 22 subjects. At least four high quality topographical images, which were within 0.25 D of one another as measured by simulated keratometry (SimK), were obtained for each eye. Of these, the one with the best alignment and at least six digitised rings was selected for analysis.

RESULTS

The visual acuity (logMAR), and spherical and cylindrical errors showed marked asymmetry with means of 0.3 +/- 0.3 (SD),-5.2 +/- 6.2 D,-3.1 +/- 2.5 D in the better eyes and 0.5 +/- 0.3,-9.8 +/- 8.5 D,-5.0 +/- 2.5 D in the worse eyes (p = 0.01, 0.05, 0.01, respectively). Scissoring retinoscopy reflex, oil droplet sign, Munson's sign, Vogt's striae, scarring and keratometry readings were significantly greater in the more affected eyes. The inferior-superior steepening, central corneal power and apex power as deduced from topography were significantly greater in the more affected eyes with values of 20.3 +/- 15.7 D, 51.4 +/- 10.1 D, 56.7 +/- 11.0 D in the better eyes and 30.4 +/- 18.6 D, 60.1 +/- 10.9 D, 68.7 +/- 19.6 D in the worse eyes (p = 0.05, 0.01, 0.02).

CONCLUSION

Keratoconus is essentially a bilateral but asymmetric corneal degeneration. Seven of our patients had clinically unilateral keratoconus but on topography, based on KISA% index, six of the unaffected eyes were diagnosed as keratoconus though much milder than in the other eye.

Transepithelial versus epithelium-off corneal crosslinking for progressive keratoconus

BACKGROUND

Keratoconus is the most common corneal dystrophy. It can cause loss of uncorrected and best-corrected visual acuity through ectasia (thinning) of the central or paracentral cornea, irregular corneal scarring, or corneal perforation. Disease onset usually occurs in the second to fourth decade of life, periods of peak educational attainment or career development. The condition is lifelong and sight-threatening. Corneal collagen crosslinking (CXL) using ultraviolet A (UVA) light applied to the cornea is the only treatment that has been shown to slow progression of disease. The original, more widely known technique involves application of UVA light to de-epithelialized cornea, to which a photosensitizer (riboflavin) is added topically throughout the irradiation process. Transepithelial CXL is a recently advocated alternative to the standard CXL procedure, in that the epithelium is kept intact during CXL. Retention of the epithelium offers the putative advantages of faster healing, less patient discomfort, faster visual rehabilitation, and less risk of corneal haze.

OBJECTIVES

To assess the short- and long-term effectiveness and safety of transepithelial CXL compared with epithelium-off CXL for progressive keratoconus.

SEARCH METHODS

To identify potentially eligible studies, we searched the Cochrane Central Register of Controlled Trials (CENTRAL) (which contains the Cochrane Eyes and Vision Trials Register) (2020, Issue 1); Ovid MEDLINE; Embase.com; PubMed; Latin American and Caribbean Health Sciences Literature database (LILACS); ClinicalTrials.gov; and World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP). We did not impose any date or language restrictions. We last searched the electronic databases on 15 January 2020.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) in which transepithelial CXL had been compared with epithelium-off CXL in participants with progressive keratoconus.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methodology.

MAIN RESULTS

We included 13 studies with 723 eyes of 578 participants enrolled; 13 to 119 participants were enrolled per study. Seven studies were conducted in Europe, three in the Middle East, and one each in India, Russia, and Turkey. Seven studies were parallel-group RCTs, one study was an RCT with a paired-eyes design, and five studies were RCTs in which both eyes of some or all participants were assigned to the same intervention. Eleven studies compared transepithelial CXL with epithelium-off CXL in participants with progressive keratoconus. There was no evidence of an important difference between intervention groups in maximum keratometry (denoted 'maximum K' or 'Kmax'; also known as steepest keratometry measurement) at 12 months or later (mean difference (MD) 0.99 diopters (D), 95% CI -0.11 to 2.09; 5 studies; 177 eyes; I² = 41%; very low certainty evidence). Few studies described other outcomes of interest. The evidence is very uncertain that epithelium-off CXL may have a small (data from two studies were not pooled due to considerable heterogeneity (I² = 92%)) or no effect on stabilization of progressive keratoconus compared with transepithelial CXL; comparison of the estimated proportions of eyes with decreases or increases of 2 or more diopters in maximum K at 12 months from one study with 61 eyes was RR 0.32 (95% CI 0.09 to 1.12) and RR (non-event) 0.86 (95% CI 0.74 to 1.00), respectively (very low certainty). We did not estimate an overall effect on corrected-distance visual acuity (CDVA) because substantial heterogeneity was detected (I² = 70%). No study evaluated CDVA gain or loss of 10 or more letters on a logarithm of the minimum angle of resolution (logMAR) chart. Transepithelial CXL may result in little to no difference in CDVA at 12 months or beyond. Four studies reported that either no adverse events or no serious adverse events had been observed. Another study noted no change in endothelial cell count after either procedure. Moderate certainty evidence from 4 studies (221 eyes) found that epithelium-off CXL resulted in a slight increase in corneal haze or scarring when compared to transepithelial CXL (RR (non-event) 1.07, 95% CI 1.01 to 1.14). Three studies, one of which had three arms, compared outcomes among participants assigned to transepithelial CXL using iontophoresis versus those assigned to epithelium-off CXL. No conclusive evidence was found for either keratometry or visual acuity outcomes at 12 months or later after surgery. Low certainty evidence suggests that transepithelial CXL using iontophoresis results in no difference in logMAR CDVA (MD 0.00 letter, 95% CI -0.04 to 0.04; 2 studies; 51 eyes). Only one study examined gain or loss of 10 or more logMAR letters. In terms of adverse events, one case of subepithelial infiltrate was reported after transepithelial CXL with iontophoresis, whereas two cases of faint corneal scars and four cases of permanent haze were observed after epithelium-off CXL. Vogt's striae were found in one eye after each intervention. The certainty of the evidence was low or very low for the outcomes in this comparison due to imprecision of estimates for all outcomes and risk of bias in the studies from which data have been reported.

AUTHORS' CONCLUSIONS

Because of lack of precision, frequent indeterminate risk of bias due to inadequate reporting, and inconsistency in outcomes measured and reported among studies in this systematic review, it remains unknown whether transepithelial CXL, or any other approach, may confer an advantage over epithelium-off CXL for patients with progressive keratoconus with respect to further progression of keratoconus, visual acuity outcomes, and patient-reported outcomes (PROs). Arrest of the progression of keratoconus should be the primary outcome of interest in future trials of CXL, particularly when comparing the effectiveness of different approaches to CXL. Furthermore, methods of assessing and defining progressive keratoconus should be standardized. Trials with longer follow-up are required in order to assure that outcomes are measured after corneal wound-healing and stabilization of keratoconus. In addition, perioperative, intraoperative, and postoperative care should be standardized to permit meaningful comparisons of CXL methods. Methods to increase penetration of riboflavin through intact epithelium as well as delivery of increased dose of UVA may be needed to improve outcomes. PROs should be measured and reported. The visual significance of adverse outcomes, such as corneal haze, should be assessed and correlated with other outcomes, including PROs.

Corneal epithelial thickness analysis of forme fruste keratoconus with optical coherence tomography

AIM

To explore the significance of corneal epithelial thickness analysis in diagnosing early keratoconus.

METHODS

There were 26 clinical keratoconus, 21 forme fruste keratoconus, 40 high corneal astigmatism (ΔK) and 40 low ΔK eyes involved in the study. Fourier-domain optical coherence tomography was used to measure the corneal epithelial thickness of four groups. The morphological features of topographic map and the thickness of corneal epithelial thinnest point were analyzed. The distribution curve of corneal epithelial thickness at 45°, 90°, and 135° axial directions that are through the pupil center was also analyzed. One-way ANOVA was performed to compare the data.

RESULTS

The topographic map of forme fruste keratoconus corneal epithelial thickness was uniformity shape; crater shape existed only in clinical keratoconus group; and central island shape mainly existed in high ΔK group. The thinnest point of corneal epithelial thickness of forme fruste keratoconus group was significantly lower than that of low ΔK group (P=0.022). The thickness of corneal epithelium in the forme fruste keratoconus at 90° was thinner than that in the low astigmatism group at -1, and -2 mm points (P _{-1 mm}=0.015, P _{-2 mm}=0.036).

CONCLUSION

The analysis of the thinnest point in forme fruste keratoconus corneal epithelium appears earlier than corneal epithelial remodeling. The topographic map of corneal epithelium in high ΔK eyes appears in central island shape, and can be used for the differential diagnosis of early keratoconus.

Update on the genetics of keratoconus

In the past few years we have seen a great acceleration of discoveries in the field of keratoconus including new treatments, diagnostic tools, genomic and molecular determinants of disease risk. Recent genome-wide association studies (GWAS) of keratoconus cases and population wide studies of variation in central corneal thickness and in corneal biomechanical properties confirmed already identified genes and found many new susceptibility variants and biological pathways. Recent findings in genetic determinants of familial keratoconus revealed functionally important variants and established first mouse model of keratoconus. Latest transcriptomic and expression studies started assessing novel non-coding RNA targets in addition to identifying tissue specific effects of coding genes. First genomic insights into better prediction of treatment outcomes are bringing the advent of genomic medicine into keratoconus clinical practice.

Genetics vs chronic corneal mechanical trauma in the etiology of keratoconus

Both genetic and environmental factors have been considered to play a role in the etiology keratoconus. Eye rubbing, and more recently eye compression due to sleeping position, have been identified to be highly related to the condition, and are present in a high percentage of patients. Today, the predominant model is that these factors can provide the "second hit" necessary to generate the condition in a genetically susceptible individual. In addition, the extremely high prevalence in Arab populations, where endogamy could play a role, the high concordance rate in monozygotic twins, and the presence of family history of the condition between 5 and 23% of cases, support a genetic influence. Segregation analysis studies suggest that keratoconus is a complex non-Mendelian disease. Results from linkage analysis, next generation sequencing studies and genome-wide association studies also have suggested that genetic factors are involved in the condition. Recently, it has been proposed that mechanical trauma (i.e. eye rubbing or eye compression at night), is a sine quanon condition for the onset of keratoconus, and quite possibly its only cause. There are various arguments for and against this hypothesis. Indeed, it is possible, as initially suggested around 55 years ago, that the term "keratoconus" include diverse phenotypically similar conditions, which are actually of different etiology.

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.

Pediatric keratoconus: a review of the literature

PURPOSE

To describe the epidemiology and prevalence, rates of progression, difference between adult and pediatric populations, and therapeutic approaches to pediatric keratoconus from documented literature.

METHODS

A literature search was done on PubMed using key words including pediatric keratoconus, children with keratoconus, adult keratoconus, penetrating keratoplasty, corneal cross-linking and intracorneal ring segments. The literature was reviewed and reported to explore the key epidemiological differences between the pediatric and adult population with regards to presentation and treatment options.

RESULTS

Pediatric keratoconus is more aggressive than adult keratoconus, which has been explained by structural differences in the cornea between both populations. High rates of progression were documented in pediatric populations. While corneal collagen cross-linking, intracorneal ring segments and penetrating keratoplasties have been used as therapies in the pediatric population, the literature overwhelmingly shows higher rates of failure and progression despite these measures as compared to adults.

CONCLUSION

Pediatric keratoconus is more aggressive than adult keratoconus, and current therapies used in adults may not be sufficient for the pediatric population.

Comparative proteome analysis of the tear samples in patients with low-grade keratoconus

PURPOSE

To elucidate the metabolic processes playing roles in the formation of keratoconus (KC).

METHODS

Tears samples were collected using capillary glass tubes without stimulation and without prior anesthesia from 17 patients and 16 controls. Proteomic analysis by fluorescent 2D gel electrophoresis (DIGE) coupled with MALDI-TOF/TOF was performed. The identified proteins that were differentially regulated were subjected to Ingenuity Pathway Analysis (IPA). Corneal topography analyses with Sirius topography system (Costruzioni Strumenti Oftalmici, Florence, Italy) were performed on all participants. The steepest keratometry index was lower than 50 diopters in all keratoconus patients.

RESULTS

DIGE analysis showed changes in abundance of nine proteins. Six of these proteins, namely serum albumin, Keratin Type II Cytoskeletal 1, IgG gamma chain-1, GAPDH, alpha-1 antitrypsin and ApoA-I, were down-regulated in the KC samples in comparison with the controls. In addition, we detected up-regulation of lysozyme C, keratin type I cytoskeletal 10 and lipocalin. The subsequent IPA predicted that NADH repair pathway is activated in the KC patients. This pathway involves generation of NADHX as a by-product via catalysis by GAPDH. NADHX is an inhibitor of several dehydrogenases and must be removed.

CONCLUSION

The involvement of NADHX repair pathway in KC should be investigated, since preliminary clues obtained in this study point to that direction. In particular, showing the presence of ATP-dependent NAD(P)H-hydrate dehydratase that eliminates NADHX would strengthen our findings and would be a major step toward understanding KC.

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.

Clinical Profile of Omani Keratoconus Patients: An Experience from a tertiary referral centre in Muscat

OBJECTIVE:

To determine the demographics and associated clinical features of Omani keratoconus patients presenting to the Ministry of Defence Hospital (MODH) in Muscat.

METHODS:

This is a retrospective, descriptive study whereby the electronic medical records of all Omani keratoconus patients presenting to the MODH between January 2011 and December 2015 were reviewed. Demographic details, corrected distance visual acuity, refraction, corneal topography, pachymetry, and treatment received were all documented.

RESULTS:

There were 458 new keratoconus patients (257 males, 201 females) comprising a total of 893 eyes with a mean age of 20 years ± 5.6 (standard deviation) (range 6–46 years). On their first visit, 35% of eyes had spectacle-corrected distance visual acuity <0.5 logarithm of the minimum angle of resolution (LogMAR), 38% had central corneal thickness <450 um, and 25% had a mean keratometry more than 53 Diopter (D). According to the Amsler-Krumeich classification, 37%, 30%, 18%, and 16% of eyes classified into stages I, II, III, and IV, respectively. The severity of keratoconus did not correlate with the age of patients (rs = −0.13, P < 0.05). Over the 5-year period of the study, 502 eyes were fitted with rigid gas permeable lenses with 91% achieving the vision of 0.1 LogMAR or better, 22% of eyes underwent collagen cross linking, 3% underwent intracorneal ring segments implantation, and 4% underwent corneal grafting.

CONCLUSION:

A significant proportion of Omani keratoconus patients seen in the MODH showed advanced disease on their first visit. There was no correlation between severity and age suggesting that keratoconus can progress quickly in our pediatric group. Population-based studies are an important next step. Meanwhile, early detection and timely interventions to limit the burden of the disease are crucial.

Effects of Atopic Syndrome on Keratoconus

PURPOSE

To evaluate the effects of atopic syndrome on manifestations of keratoconus.

METHODS

In this retrospective study, we reviewed patient files and data generated by Scheimpflug imaging of 670 eyes of 434 keratoconus patients. Patients were divided into a study group consisting of patients suffering from atopic syndrome (110 eyes of 75 patients), namely allergic asthma, atopic dermatitis, and/or allergic rhinitis, and a control group of patients without known atopic syndrome (560 eyes of 359 patients).

RESULTS

We found a significant difference with the mean age being 36.1 ± 11.7 for the control group, 32.8 ± 9.6 for the atopic group (P = 0.002) with 1 atopic trait, and 30.4 ± 7.5 for patients with 2 or more atopic traits (P = 0.002). No statistically significant differences were found in the mean corrected distance visual acuity, corneal pachymetry, minimum relative pachymetric progression (RPImin), mean refraction, keratoconus index, anterior chamber depth and volume, Kmax, and location of Kmax in relation to the corneal apex. However, we found a significantly higher corneal density for the anterior 120 μm of the cornea in the atopic group (control: 20.74 ± 4.68, atopic group: 21.92 ± 4.65 P = 0.016).

CONCLUSIONS

Keratoconus patients suffering from atopic syndrome were significantly younger but showed no topographical changes except in corneal densitometry compared with keratoconus patients without an atopic disease. This suggests atopic syndrome is a factor, which can trigger earlier manifestation of keratoconus.

The Long-term Clinical Outcome after Corneal Collagen Cross-linking in Korean Patients with Progressive Keratoconus

Purpose

To evaluate the long-term clinical effectiveness and safety of corneal collagen cross-linking (CXL) in progressive keratoconus compared with untreated contralateral eyes.

Methods

In this retrospective study, nine eyes of nine patients with progressive keratoconus who received CXL (treatment group) and nine untreated contralateral eyes with keratoconus (control group) were included. All patients were followed for at least 5 years and assessed with best-corrected visual acuity, maximum keratometry, mean keratometry, corneal astigmatism, and corneal thickness. Clinical data were collected preoperatively and at 1, 3, 6, 12, 24, 36, 48, and 60 months, postoperatively.

Results

Mean best-corrected visual acuity improved significantly from 0.58 ± 0.37 logarithm of minimum angle of resolution preoperatively to 0.39 ± 0.29 logarithm of minimum angle of resolution at 5 years after corneal CXL (p = 0.012). There was significant flattening of the maximum keratometry and mean keratometry from preoperative values of 63.39 ± 10.89 and 50.87 ± 6.27 diopter (D) to postoperative values of 60.89 ± 11.29 and 49.54 ± 7.23 D, respectively (p = 0.038, 0.021). Corneal astigmatism decreased significantly from 7.20 ± 1.83 D preoperatively to 5.41 ± 1.79 D postoperatively (p = 0.021). The thinnest corneal thickness decreased from 434.00 ± 54.13 to 365.78 ± 71.58 µm during 1 month after treatment, then increased to 402.67 ± 52.55 µm at 5 years, which showed a statistically significant decrease compared to the baseline (p = 0.020). In the untreated contralateral eyes, mean keratometry increased significantly at 2 years compared with the baseline (p = 0.043).

Conclusions

CXL seems to be an effective and safe treatment for halting the progression of keratoconus over a long-term follow-up period of up to 5 years in progressive keratoconus.

Ectasia risk factors in refractive surgery

This review outlines risk factors of post-laser in situ keratomileusis (LASIK) ectasia that can be detected preoperatively and presents a new metric to be considered in the detection of ectasia risk. Relevant factors in refractive surgery screening include the analysis of intrinsic biomechanical properties (information obtained from corneal topography/tomography and patient’s age), as well as the analysis of alterable biomechanical properties (information obtained from the amount of tissue altered by surgery and the remaining load-bearing tissue). Corneal topography patterns of placido disk seem to play a pivotal role as a surrogate of corneal strength, and abnormal corneal topography remains to be the most important identifiable risk factor for ectasia. Information derived from tomography, such as pachymetric and epithelial maps as well as computational strategies, to help in the detection of keratoconus is additional and relevant. High percentage of tissue altered (PTA) is the most robust risk factor for ectasia after LASIK in patients with normal preoperative corneal topography. Compared to specific residual stromal bed (RSB) or central corneal thickness values, percentage of tissue altered likely provides a more individualized measure of biomechanical alteration because it considers the relationship between thickness, tissue altered through ablation and flap creation, and ultimate RSB thickness. Other recognized risk factors include low RSB, thin cornea, and high myopia. Age is also a very important risk factor and still remains as one of the most overlooked ones. A comprehensive screening approach with the Ectasia Risk Score System, which evaluates multiple risk factors simultaneously, is also a helpful tool in the screening strategy.

Contemporary Treatment Paradigms in Keratoconus

The past 20 years have witnessed an explosion in our knowledge of keratoconus, accompanied by a radical transformation of management options. A 2-hit hypothesis proposes an underlying genetic predisposition coupled with external environmental factors, including eye rubbing and atopy. The variable prevalence and natural history have been better defined including significant cone progression in middle age. Therefore, current management must include early diagnosis, regular monitoring, and treatment of environmental cofactors. Spectacles and contact lenses remain fundamental to the optical management of keratoconus. Intrastromal corneal ring segments have been increasingly used, providing improvement in the corneal shape, corrected visual acuity, and contact lens wear. However, like contact lenses, intrastromal corneal ring segments do not treat the underlying disease process. Therefore, current approaches must also consider treatments to minimize keratoconus progression. Fortunately, there is increasing evidence that corneal collagen crosslinking will halt or slow progression in most cases. Until relatively recently, penetrating keratoplasty was the preferred intervention for advanced keratoconus, with long-term success in the region of 90%; however, the greatest risk of failure remains endothelial allograft rejection. Deep anterior lamellar keratoplasty has emerged in the new millennium as a preferred approach to conserve the host endothelium and avoid rejection. Nonetheless, the overall superiority of deep anterior lamellar keratoplasty compared with penetrating keratoplasty, in terms of optical and survival benefits, is still debated. This perspective provides an overview of our current knowledge of keratoconus and current management options. A step-ladder approach to managing keratoconus is outlined to provide the practitioner with a contemporary management paradigm.

Tear Film and Serum Prolidase Activity and Oxidative Stress in Patients With Keratoconus

PURPOSE

To determine and compare the serum and tear film prolidase activity (PA) between patients with keratoconus and healthy subjects. Also, we aimed to evaluate the serum oxidative stress level and the correlation with serum PA in patients with keratoconus.

METHODS

This prospective, comparative clinical study included 31 patients with keratoconus and 33 age-matched and sex-matched control subjects. All participants underwent a detailed ophthalmologic examination. Serum and tear samples were obtained from all participants. Tears and serum PA and serum oxidative stress markers were measured.

RESULTS

No significant differences in demographic characteristics were detected between groups (P > 0.05). The serum PA was significantly lower in the keratoconus group than in the control group (895.6 ± 198.7 vs. 1145.9 ± 285.4 U/L, P < 0.001). A tear film comparison showed that PA was lower in the keratoconus group than in the control group; however, this difference was not significant (3075.4 ± 672.2 vs. 3225.8 ± 903.2 U·L⁻¹·g⁻¹ protein, P = 0.45). Oxidative stress markers, such as total oxidant status and oxidative stress index, were found to be significantly higher in the keratoconus group (P < 0.001).

CONCLUSIONS

The serum PA was found to be lower in patients with keratoconus than in the controls. Additionally, serum oxidative stress markers were found to be higher than those of the controls. Thus, prolidase and systemic oxidative stress may have a role in the pathogenesis of keratoconus.

Presence of Fleischer ring and prominent corneal nerves in keratoconus relatives and normal controls

AIM

To examine the occurrence of commonly known clinical signs of keratoconus (KC), i.e. Fleischer ring, prominent corneal nerves and thinning, among unaffected family members of KC patients and healthy control individuals.

METHODS

Data of both eyes of 117 relatives of KC patients having no manifest disease based on videokeratography indices (KC relatives), and 142 controls were used for Pearson correlation and t-test statistics. Correlation of Fleischer ring, prominent corneal nerves and central pachymetry data were tested with each other and with videokeratography indices (KSI, KISA, 3 and 6 mm Fourier asymmetry, and I-S).

RESULTS

A moderate correlation was found between Fleischer ring and all examined topographical indices. Most important correlation was present with 6 mm Fourier asymmetry, and corneal pachymetry (r=0.272, P<0.001; r=-0.234, P=0.027, respectively). Similar correlations were found with prominent corneal nerves (r=0.234, P<0.001 for 6 mm Fourier asymmetry and r=-0.235, P=0.0265 for pachymetry). KC family members who exhibited Fleischer ring or prominent nerves had thinner and more asymmetric corneas than those without Fleischer ring or prominent corneal nerves (P<0.05 for pachymetry and topographic indices with t-test and Mann-Whitney rank sum test). Though rarely, Fleischer ring and prominent corneal nerves occurred among normal controls, indicating the existence of forme fruste cases in the normal population. Control subjects, who had corneal Fleischer ring or prominent nerves had corneas more similar to KC than other controls (t-test: increased KSI and KISA, P=0.048 and 0.012, respectively).

CONCLUSION

In KC family members and healthy individuals, Fleischer ring and prominent corneal nerves are associated with features of KC and may suggest a possibility of forme fruste KC. Searching for the possible presence of Fleischer ring or prominent nerves on the cornea may help in the decision whether or not to diagnose subclinical KC in a borderline case.

An Update on the Safety and Efficacy of Corneal Collagen Cross-Linking in Pediatric Keratoconus

Keratoconus is a degenerative disease that affects adolescents and young adults and presents with variable thinning and conical deformation of the corneal apex. The resultant irregular astigmatism can progress to levels that can significantly affect everyday activities and overall quality of life. Therefore, stopping the progression of the disease is an essential part in managing patients with keratoconus. Corneal collagen cross-linking is a minimally invasive procedure that stiffens the anterior corneal stroma by creating strong covalent bonds between collagen fibrils. Over the past decade, many studies have proved its safety and efficacy in halting keratoconus progression in adults. This review of the literature highlights the growing trend towards using this treatment in pediatric keratoconic patients. In children, keratoconus tends to be more severe and fast progression is often encountered requiring closer follow-up intervals. Standard cross-linking shows comparable results in children with a good safety-efficacy profile during follow-up periods of up to three years. Further research is needed to standardize and evaluate transepithelial and accelerated cross-linking protocols as these could be of tremendous help in a population where cooperation and compliance are major issues.

Segregation analysis suggests that keratoconus is a complex non-mendelian disease

PURPOSE

Complex segregation analysis of 60 unrelated sporadic keratoconus (KC) families was performed to reveal the presumed mode of inheritance in our dataset.

METHODS

Sixty probands, 212 family members and 212 age and gender matched healthy controls underwent clinical and videokeratographic examination. Family aggregation and distribution of videokeratography parameters were examined. Segregation of KSI, KISA and 6mm Fourier asymmetry alone or in covariate analysis with gender or the presence of Fleischer ring, exploring mendelian and non-mendelian models of inheritance was tested using complex segregation analysis with the S.A.G.E. program package.

RESULTS

In 145 relatives of probands, the estimated prevalence of manifest KC was 7.6% (95% CI: 3.3-11.9) based on KISA index, indicating strong familial aggregation. All examined videokeratography indices were able to differentiate between KC and non-KC family members as well as normal controls (anova p < 0.001). Hypotheses accepted as most parsimonius models of inheritance (p > 0.1) for all indices indicated the presence of a non-mendelian major gene effect (MG). Inclusion of Fleischer ring as covariate improved the fit of MG models. Mendelian, Sporadic and polygenic models were consistently rejected.

CONCLUSIONS

Complex segregation analysis indicates a strong genetic contribution to the transmission of keratoconus. Inheritance is most probably due to a non-mendelian major gene effect. Low genotype-phenotype correlation in sporadic KC families can make linkage studies difficult, thus genome wide association studies, epigenetic and pathway analyses may provide more information on disease pathogenesis in non-familial keratoconus.

Keratoconus: tissue engineering and biomaterials

Keratoconus (KC) is a bilateral, asymmetric, corneal disorder that is characterized by progressive thinning, steepening, and potential scarring. The prevalence of KC is stated to be 1 in 2000 persons worldwide; however, numbers vary depending on size of the study and regions. KC appears more often in South Asian, Eastern Mediterranean, and North African populations. The cause remains unknown, although a variety of factors have been considered. Genetics, cellular, and mechanical changes have all been reported; however, most of these studies have proven inconclusive. Clearly, the major problem here, like with any other ocular disease, is quality of life and the threat of vision loss. While most KC cases progress until the third or fourth decade, it varies between individuals. Patients may experience periods of several months with significant changes followed by months or years of no change, followed by another period of rapid changes. Despite the major advancements, it is still uncertain how to treat KC at early stages and prevent vision impairment. There are currently limited tissue engineering techniques and/or "smart" biomaterials that can help arrest the progression of KC. This review will focus on current treatments and how biomaterials may hold promise for the future.

Optical coherence tomography combined with videokeratography to differentiate mild keratoconus subtypes

PURPOSE

To develop parameters using a combination of optical coherence tomography (OCT) and videokeratography to detect early keratoconus.

METHODS

Videokeratography, wavefront analysis, and measured OCT indices were performed on 180 normal eyes, 46 eyes with moderate keratoconus, 54 eyes with early keratoconus, 7 eyes with forme fruste keratoconus, and 16 eyes with keratoconus "suspect" to determine the most sensitive parameters for separating these groups.

RESULTS

A combination of videokeratography and OCT indices (inferior-superior [I-S] value and minimum pachymetry) was statistically the most significant in separating the keratoconus groups from normal eyes (P < .001). Using a newly derived index, the minimum pachymetry divided by the I-S value (pachymetry/asymmetry [PA]/I-S index) with a cut-off of 100, 100% of early and forme fruste keratoconus could be identified as being abnormal with 7 normals misclassified (misclassification rate 2.7%). By adding keratoconus "suspect" to the analysis and an I-S value of 1.2 as a cut-off point, 5 "suspects" were classified as normal and 11 normals as abnormal (misclassification rate 7.8%). The PA/I-S index, with a cut-off point of 100, reduced this misclassification rate to 4.4%.

CONCLUSIONS

These results suggest that OCT combined with videokeratography may be more useful for differentiating mild forms of keratoconus than videokeratography alone.

Investigation of the Efficacy of the Cone Location and Magnitude Index in the Diagnosis of Keratoconus

PURPOSE

The aim of this study was to investigate the sensitivity, specificity, and accuracy of The Cone Location and Magnitude Index (CLMI) in keratoconus diagnosis.

METHODS

301 eyes of 159 keratoconus patients and 394 eyes of 265 refractive surgery candidates as a control group were enrolled in this retrospective clinical study. CLMI was compared with keratometric corneal topography parameters, wavefront aberrations, and pachymetry data derived from optical coherence tomography using independent sample t-tests and ROC curves. Logistic regression analysis was applied to determine the most accurate parameter in keratoconus diagnosis. Pearson's correlation analysis was used to determine the correlation between CLMI and the other measurements.

RESULTS

Average axial CLMI (aCLMI) was 8.19 ± 6.15 D in the keratoconus group and 0.83 ± 0.62 D in the control group (p = 0.001). aCLMI had the greatest sensitivity (89%), specificity (94%), and accuracy (92%) for the keratoconus diagnosis at the best cut-off point of 1.82 according to the ROC curve. Logistic regression analysis selected aCLMI as the most accurate measurement among the other parameters (accuracy 92.8%). aCLMI showed strongest correlations with coma-like aberrations (r = 0.881), total high-order aberrations (r = 0.858), and vertical coma (r = -0.814), respectively.

CONCLUSION

CLMI is a robust index for screening keratoconus with high sensitivity, specificity, and accuracy.

The genetics of keratoconus

Keratoconus is a bilateral, non-inflammatory corneal ectasia characterized by progressive conical thinning and protrusion of the cornea. Its etiology has long been believed to be multifactorial, with environmental, behavioral, and genetic factors all contributing to the disease process. This review focuses specifically on examining the evidence that supports a genetic basis for keratoconus.

Independent Population Validation of the Belin/Ambrósio Enhanced Ectasia Display: Implications for Keratoconus Studies and Screening

With advances in technology and imaging, finding diagnostic criteria that are both sensitive and specific for keratoconus while using the latest corneal imaging modalities is paramount. The Belin/Ambrósio enhanced ectasia display final ‘D’ index, tested on an independent population, illustrated excellent false positive rates for refractive screening while eliminating 99% of keratoconus corneas. A false positive rate of 0% is achieved with a final ‘D’ of 2.69, meeting the more stringent criteria for treatment studies.

How to cite this article

Villavicencio OF, Gilani F, Henriquez MA, Izquierdo L Jr, Ambrósio RR Jr, Belin MW. Independent Population Validation of the Belin/Ambrósio Enhanced Ectasia Display:Implications for Keratoconus Studies and Screening. Int J Kerat Ect Cor Dis 2014;3(1):1-8.

Evaluation of corneal microstructure in keratoconus: a confocal microscopy study

PURPOSE

To compare the corneal microstructure in patients with manifest keratoconus (KCN), subclinical KCN, and topographically normal relatives of patients with KCN and in healthy controls.

DESIGN

Prospective and cross-sectional study.

METHODS

We enrolled 145 subjects in the study. The participants were divided into 4 groups, based on clinical and topographical evaluation: the manifest KCN group (n = 30), the subclinical KCN group (n = 32), the KCN relatives group (n = 53), and the control group (n = 30). Corneal microstructure was assessed by corneal in vivo confocal microscopy in all of the individuals. Mean outcome measures were basal epithelial cell density, endothelial cell density, anterior keratocyte density, posterior keratocyte density, sub-basal nerve density, sub-basal nerve diameter, and stromal nerve diameter.

RESULTS

The mean basal epithelial cell density, endothelial cell density, and sub-basal nerve diameter were not significantly different among the 4 groups (P = 0.057, P = 0.592, and P = 0.393, respectively). The mean anterior and posterior stromal keratocyte densities were significantly lower in the manifest group, in the subclinical group, and in the relatives group when compared with the control group (for both parameters; P < 0.001, P < 0.001, and P< 0.001, respectively). The mean stromal nerve diameter in the manifest group, subclinical group, and relatives group was significantly higher than in the control group (P = 0.001, P = 0.049, and P = 0.004, respectively).

CONCLUSION

The anterior and posterior stromal keratocyte densities were statistically lower and stromal nerve diameter was statistically higher in patients with manifest KCN, subclinical KCN, and topographically normal KCN relatives compared with controls. Confocal microscopy may be useful for the determination of early corneal microstructural changes before manifestation of typical or subtle topographic signs.

Genetic association of COL5A1 variants in keratoconus patients suggests a complex connection between corneal thinning and keratoconus

PURPOSE

Single nucleotide polymorphisms (SNPs) located near or within the COL5A1 gene, at 9q34.2-q34.3 chromosomal region have been reported in association with central corneal thickness (CCT). Using family linkage analysis, we identified a keratoconus susceptibility locus at 9q34. These findings led us to perform an association study between COL5A1 variation and keratoconus susceptibility.

METHODS

A Caucasian case-control cohort of 222 keratoconus patients and 3324 controls was selected as the discovery panel. An independent case-control panel of 304 cases and 518 controls and a family panel of 186 subjects were replicated for genotyping and association. Forty-four SNPs (21 for discovery and 23 for fine-mapping) spanning 300 kilobases in and around COL5A1 were genotyped and tested for genetic association. Logistic regression models implemented in PLINK were used to test for association in case controls. Generalized estimating equation models accounting for familial correlations implemented in genome-wide interaction analyses with family data were used for association testing in families.

RESULTS

Two CCT associated SNPs (rs1536482 and rs7044529 near and within COL5A1) were identified in the keratoconus discovery cohort (P values of 6.5 × 10(-3) and 7.4 × 10(-3)). SNP rs1536482 was replicated in the second case-control sample (P = 0.02), and SNP rs7044529 was replicated in a keratoconus family panel (P = 0.03). Meta P values of rs1536482 and rs7044529 in the keratoconus cohorts were 1.5 × 10(-4) (odds ratio [OR] = 1.30) and 2.9 × 10(-3) (OR = 1.39). After Bonferroni correction, the association of SNP rs1536482 remained significant (P = 6.5 × 10(-3)).

CONCLUSIONS

SNPs in the COL5A1 region, which regulate normal variation in CCT, may play a role in the thinning associated with keratoconus.

Characterization of corneal structure in keratoconus

The increasing volume of patients interested in refractive surgery and the new treatment options available for keratoconus have generated a higher interest in achieving a better characterization of this pathology. The ophthalmic devices for corneal analysis and diagnosis have experienced a rapid development during the past decade with the implementation of technologies such as the Placido-disk corneal topography and the introduction of others such as scanning-slit topography, Scheimpflug photography, and optical coherence tomography, which are able to accurately describe not only the geometry of the anterior corneal surface but also that of the posterior surface, as well as pachymetry and corneal volume. Specifically, anterior and posterior corneal elevation, corneal power, pachymetry maps, and corneal coma-like aberrometry data provide sufficient information for an accurate characterization of the cornea to avoid misleading diagnoses of patients and provide appropriate counseling of refractive surgery candidates.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Keratoconus: overview and update on treatment

Keratoconus is a non-inflammatory, progressive thinning process of the cornea. It is a relatively common disorder of unknown etiology that can involve each layer of the cornea and often leads to high myopia and astigmatism. Computer- assisted corneal topography devices are valuable diagnostic tools for the diagnosis of subclinical keratoconus and for tracking the progression of the disease. The traditional conservative management of keratoconus begins with spectacle correction and contact lenses. Several newer, more invasive, treatments are currently available, especially for contact lens-intolerant patients. Intrastromal corneal ring segments can be used to reshape the abnormal cornea to improve the topographic abnormalities and visual acuity. Phakic intraocular lenses such as iris-fixated, angle-supported, posterior chamber implantable collamer and toric lenses are additional valuable options for the correction of refractive error. Corneal cross-linking is a relatively new method of stiffening the cornea to halt the progression of the disease. The future management of keratoconus will most likely incorporate multiple treatment modalities, both simultaneous and sequential, for the prevention and treatment of this disease.