Keratoconus: diagnosis and management

Systemic and Ocular Associations of Keratoconus

Introduction

Keratoconus (KC) is the most prevalent corneal ectasia in the world and its pathogenesis is influenced by both ocular and systemic factors. This review explores the multifaceted associations between keratoconus and systemic health conditions, ocular characteristics, and various other environmental/exogenous factors, aiming to illuminate how these relationships influence the pathophysiology of the disease.

Areas Covered

This review will summarize the fundamental attributes of KC, review and discuss the systemic and ocular association of KC including molecular biomarkers, and provide an organized overview of the parallel alterations occurring within various biological pathways in KC.

Expert Opinion

Despite the substantial volume of research on keratoconus, the precise etiology of the disease remains elusive. Further studies are necessary to deepen our understanding of this intricate disorder and improve its management.

Topographic Keratoconus Incidence in Greece Diagnosed in Routine Consecutive Cataract Procedures: A Consecutive Case Series of 1250 Cases over 5 Years

Background: Scheimpflug tomography has for many years been an integral part of our pre-operative assessment in cataract extraction. We retrospectively reviewed the incidence of topographic keratoconus and keratoconus suspicion in our routine cataract surgery population over 5 years. Setting: The Laservision Clinical and Research Institute, Athens, Greece. Methods: In 1250 consecutive cataract surgery cases in otherwise naïve eyes, accounting for years 2017 to 2021, we retrospectively evaluated preoperative Pentacam HR imaging. The cases already classified as keratoconus were included in group A. The residual cases were assessed by five different experienced evaluators (two ophthalmic surgeons and three optometrists) for topographic and tomographic keratoconus suspicion based on irregular pachymetry distribution, astigmatism truncation, and/or astigmatic imaging irregularity and included in group B. Regular corneas, by this assessment, were included in group C; irregular corneas, as determined by the evaluators but unrelated to keratoconus, were included in group D. Results: Based on the above, 138 cases (11.08%) were classified by Pentacam tomography as keratoconus and by default were included in group A. Of the residual cases, 314 or 25.12% were classified as suspect keratoconus and included in group B; 725 cases (58%) were classified as normal and non-keratoconus and included in group C; and 73 cases or 5.84% were placed in group D as non-keratoconus but abnormal. There was no disagreement between the five evaluators over any of the cases in groups C and D, and little variance among them for cases included in group B (less than 5% by ANOVA). Conclusions: The incidence of keratoconus and corneas suspicious for keratoconus in Greece appears to be much higher than respective reports from other regions: one in ten Greeks appear to have topographic keratoconus, most not diagnosed even by the age of cataract surgery, and almost an additional one in four may have suspicious corneal imaging for keratoconus. These data strongly imply that routine screening for disease should be promoted among Greeks, especially during puberty, to halt possible progression; moreover, careful screening should be performed when laser vision correction is being considered.

Five-year results of iontophoresis-assisted transepithelial corneal cross-linking for keratoconus

PURPOSE

To assess long-term efficacy and safety of iontophoresis-assisted transepithelial corneal cross-linking (I-CXL) for keratoconus.

PATIENTS AND METHODS

Twenty-seven eyes of 21 patients (15 M, 6F) affected by progressive keratoconus were evaluated. All subjects were treated with iontophoresis-assisted transepithelial CXL. The patients were examined at baseline and each 6 months after the CXL procedure. Only subjects who completed the follow-up of 5 years were considered in this study. The main outcome measures were uncorrected visual acuity (UCVA), corrected visual acuity (CDVA), corneal transparency and corneal parameters such as K-max, central corneal thickness (CCT) and at the thinnest point, and high-order ocular aberrations (HOAs). The ABCD system was used to determine the progression and re-progression of ectasia.

SETTING

Ophthalmology Clinic, University Hospital of Messina, Messina, Italy.

RESULTS

At 5 years, significant improvements of UCVA from 0.53 ± 0.33 logMAR to 0.4 ± 0.33 logMAR (p = 0.001) and HOAs (p = 0.01) were registered. No significant changes of CDVA (p = 0.4), K-max (p = 0.75), CCT (p = 0.5) were observed at the end of follow-up period. The ABCD system showed re-progression in 25.9% of eyes after 5 years. No adverse events such as corneal opacities and infections were reported.

CONCLUSIONS

Iontophoresis-assisted transepithelial CXL resulted to be safe and effective to stabilize progressive keratoconus in adults at a long-term follow-up.

Systemic Associations with Keratoconus

Keratoconus is a disease of the cornea that results in progressive steepening and thinning of the cornea and subsequent vision loss. It nearly always presents as a bilateral disease, suggesting that there is an underlying abnormality of the corneas that becomes manifest with time. However, the mechanisms underlying the development of keratoconus are largely unknown. Associations reported between keratoconus and systemic diseases are abundant in the literature, and the list of possible associations is very long. We found that atopy, Down syndrome, and various connective tissue diseases were the most frequently cited associations in our broad literature search. Additionally, Diabetes Mellitus has been increasingly studied as a possible protective factor against keratoconus. In this review, we have summarized the evidence for and against these particular systemic conditions and keratoconus and have discussed some of the implications of keratoconus patients having these conditions.

Revisiting the oil droplet sign in keratoconus: Utility for early keratoconus diagnosis and screening

PURPOSE

An annular dark shadow (ADS) reflex has been observed while performing direct ophthalmoscopy on subjects with keratoconus. This study describes a method that may serve as a diagnostic technique for early keratoconus and may be used as a quantitative measure of severity.

METHODS

Healthy keratoconic subjects and keratoconus suspects underwent corneal tomography and a full ocular examination. Keratoconus severity was graded based on Belin ABCD criteria. An iPhone camera was connected to a direct ophthalmoscope to take a picture of the eye. The height of the ASD was measured using the AutoCAD software. Differences between subject groups were evaluated by chi-squared and Mann-Whitney tests. Spearman correlation compared ocular parameters and the height of the ADS. A multiple stepwise linear regression was used to predict the height of the ADS based on clinical parameters.

RESULTS

Fifty-eight subjects participated in this study: 37 healthy controls (37 eyes) and 21 keratoconics or keratoconus suspects (37 eyes). The ADS was present in all keratoconic and keratoconus-suspect eyes but in none of the controls. The height of the ADS was significantly correlated with keratoconus severity. Front corneal surface root mean square of higher order aberrations, sphere and anterior radius of curvature from the front apex curve are significant predictors of the height of the ADS.

CONCLUSIONS AND RELEVANCE

The ADS may be a useful method to diagnose keratoconus and keratoconus-suspect cases and serve as a grading and follow-up method for tracking disease severity.

A Comparison Between Cross-Linking Protocols in Patients With Progressive Keratoconus: A Review

Keratoconus (KC) is a noninflammatory cornea disease leading to progressive thinning, causing it to change from its normal dome shape to a cone shape. One of the novel treatments of KC is corneal collagen cross-linking (CXL). Due to its importance, many studies have been conducted to compare corneal cross-linking protocols; this review article aims to discuss corneal cross-linking and compare its different treatment options, including Dresden, accelerated, and customized protocols in patients with progressive KC and their respective long-term outcomes. A search was performed in PubMed and Google Scholar with no language, dates, or study type restriction. Most of the results showed almost no difference between protocols over traditional cross-linking. However, published data are limited, long-term outcomes of novel age groups remain unclear, and further studies are needed.

Keratoconus Epidemiology Presentations at Najran Province, Saudi Arabia

AIM

Our study aims to produce an estimation of the keratoconus disease epidemiology and important demographic factors in disease presentation in Najran city in the south of Saudi Arabia.

METHODS

Keratoconus patients between 9 and 29 years of age at the eye clinic of King Khaled General Hospital in Najran Province with a confirmed diagnosis of keratoconus were recruited over one year period. Visual acuity, keratometry, corneal thickness and demographic data were collected and analysed.

RESULTS

The keratoconus prevalence in Najran Province was found to be 87.3 cases per 100,000 people with an incidence of 28.47 per 100,000 cases. The disease presented more frequently in male patients (67.9%) with a statistically significant difference in the mean age between genders (p=0.014). Most cases presented at a moderate stage, and almost half of the cases reported a family history of the disease. There were statistically significant differences in best visual acuity and corneal thickness between genders (p<0.05). The majority of the cases were managed with contact lenses (56.08%).

CONCLUSION

Genetic and environmental factors could have a substantial role in the increased rate of keratoconus presentation in Najran Province. Screening programmes should dedicate more attention to late presentation to improve prevention and early detection. More studies on keratoconus epidemiology in Saudi Arabia are needed.

Impact of contact lens wear on epithelial alterations in keratoconus

PURPOSE

The purpose of this study was to characterize the central epithelial thickness (CET) of penetrating keratoplasty corneal specimens obtained from patients with keratoconus (KC) and correlate the histological patterns with their clinical history.

METHODS

Ex vivo histological imaging was performed to measure CET and total corneal thickness (TCT) in 56 patients with KC. Microscopic slides from penetrating keratoplasty corneal specimens, stained with hematoxylin and eosin were evaluated using bright field microscopy. CET and TCT were measured, and morphological features were studied. Clinical history regarding duration of KC prior to surgery and length of and tolerance to contact lens wear were compared and analyzed.

RESULTS

The microscopic slides of all patients available for follow up (n=48) were analyzed and CET and TCT were measured. The histological evaluation revealed 3 distinctive epithelial patterns. Pattern 1 with central hypertrophic and hydropic changes (n=19) measured 70.89±25.88μm in CET and 308.63±100.74μm in TCT; Pattern 2 (n=14) had not changed, similar to normal epithelium CET and TCT measuring 36.5±7.02μm and 260.14±87.93μm respectively. Pattern 3 (n=15) demonstrated thinner central epithelium characterized by atrophy and focal hydropic changes measuring 19.93±4.60μm and 268.00±79.39μm in CET and TCT respectively (all p<0.0001). The presence of Pattern 2 characterized by similar to normal CET was correlated with the duration of the condition (R=0.600, p=0.030). There was a significant difference in the length of CL wear comparing those with patterns 1 and 2 versus 3 (least no. of CL years) (p=0.05 and p=0.33 respectivelly).

CONCLUSIONS

Patients with advanced disease have various central corneal epithelial changes detected with histology. Although each central epithelial pattern type was distinctive comparing the 3 patterns, there was no correlation with years of CL wear but only with the duration of the condition.

Relationship Among Corneal Stiffness, Thickness, and Biomechanical Parameters Measured by Corvis ST, Pentacam and ORA in Keratoconus

Purpose

To assess the relationship among corneal stiffness, thickness, and biomechanical parameters in keratoconus.

Setting

The EENT Hospital of Fudan University, Shanghai, China.

Design

Comparative study.

Methods

In this cross-sectional prospective study, 75 keratoconic eyes of 44 patients were recruited. Eyes were divided three groups according to the steepest K-readings (Kmax): mild (31 eyes; 42.1-54.5D); moderate (27 eyes, 55.0-61.6D); and severe (17 eyes, 65.2-94.5D). Thirty-one healthy subjects were recruited as the control group. All patients underwent Corvis ST, Pentacam and ORA examinations at the same time. Stiffness parameter A1 (SP-A1) and other dynamic parameters were assessed using the Corvis ST. Kmax and thinnest corneal thickness (TCT) was obtained using the Pentacam. Corneal resistance factor (CRF) and corneal hysteresis (CH) were measured using the ORA. Analysis of correlation was applied to investigate the association between variables.

Results

There was a decrease in SP-A1 in different stages of keratoconus compared with controls (P ≤ 0.001): with increasing severity, the value of SP-A1 became smaller (P < 0.05). A statistically significant linear relationship was noted between SP-A1 and TCT in each subgroup of keratoconus (P ≤ 0.001). In all three groups, SP-A1 was found to be positively correlated with first applanation time (P < 0.01), while negatively correlated with deformation amplitude (P < 0.05). Analysis of SP-A1 with regard to CRF and CH indicated statistically positive correlation in keratoconus (P < 0.05).

Conclusion

Significant decreases in corneal stiffness were noted in kerotoconic eyes compared with normal eyes. The stiffness parameter could be a valuable clinical tool enables biomechanically track progression with keratoconus.

Synopsis

Our study found that corneal thinning and biomechanical decreasing synchronize with one another throughout the progression of the keratoconus, and SP-A1 could be a potential biomarker evaluating disease progression.

Visual acuity in patients with keratoconus: a comparison with matched regular myopic astigmatism

PURPOSE

To compare uncorrected distance visual acuity (UDVA) and best-corrected distance visual acuity (CDVA) between patients with keratoconus (KC) and matched patients with regular myopic astigmatism.

METHODS

This retrospective study included consecutive patients diagnosed with KC between 2008 and 2013 at Care-Vision Laser Centers, Tel-Aviv, Israel, and matched patients with regular myopic astigmatism. Data included were central corneal thickness (CCT), spherical equivalent (SE), cylinder (CYL), mean keratometric power, maximum keratometric power (K_max), UDVA, CDVA, and defocus equivalent (DEQ).

RESULTS

The KC group included 734 patients with a mean age of 33.8 ± 9.5 years. The matched, control group included 1462 patients with a mean age of 33.2 ± 9.7 years (p = 0.14). The mean SE and CYL of the KC group were - 3.34 ± 3.29D and - 3.01 ± 1.99D, respectively, compared to - 3.34 ± 2.92D (p = 0.98) and - 2.97 ± 1.35 (p = 0.58). Mean K (46.8 ± 3.3D versus 44.0 ± 1.8D, p < 0.0001) and K_max (48.4 ± 4.0D versus 45.3 ± 2.0D, p < 0.0001) were statically significant higher in the KC group. CCT was significantly thinner in the KC group (444 ± 49 versus 527 ± 40 μm, p < 0.0001). The KC group had a better UDVA than the non-KC group (1.10 ± 0.68 versus 1.22 ± 0.64 logMAR, p < 0.0001). CDVA was significantly lower in the KC group (p < 0.001).

CONCLUSIONS

For defocus equivalents above 6D, the KC group had better UDVA than the non-KC group in spite of worse CDVA.

Comparative Results in a Combined Procedure of Intrastromal Corneal Rings Implantation and Cross-linking in Patients with Keratoconus: A Retrospective Study

Introduction

Corneal thinning disorders caused by keratoconus often lead to protrusion, irregular astigmatism, and even perforation. Keratoconus, like other corneal ectasia, does not have a known cause. Severe cases of keratoconus may require correction or restoration of tectonic integrity of the cornea by surgical means. Intracorneal ring segments are a new modality in the treatment of corneal ectactic disorders. A new technique of stopping the evolution of keratoconus and strengthening the cornea is combining techniques of intrastromal corneal ring implantation and corneal collagen cross-linking. The objective of the study is to compare the effectiveness of combined procedures: intrastromal corneal ring implantation followed by cross-linking, with cross-linking followed by intrastromal corneal ring implantation.

Methods

The study comprised two groups of patients with different evolutionary stages of keratoconus, which met the eligibility criteria for intrastromal corneal ring segment implantation and corneal collagen cross-linking. Group 1 included patients (41 eyes) who underwent intrastromal corneal ring implantation followed by cross-linking and group 2 (30 eyes) included patients who underwent cross-linking first followed by intrastromal corneal ring implantation.

Results

A decrease in Km values of about 1.5 D and refraction was observed in group 1, compared to a decrease in Km values of about 1 D and refraction in group 2. Recovery of visual acuity was higher in group 1 than group 2.

Conclusions

The sequence of intrastromal corneal ring implantation followed by cross-linking proved to be more effective in reducing Km values, spherical equivalent and cylinder compared with cross-linking followed by intrastromal corneal ring implantation.

Corneal aberration changes after rigid gas permeable contact lens wear in keratokonic patients

Purpose

To determine the short-term effect of rigid gas permeable (RGP) contact lenses on corneal aberrations in keratoconic patients.

Method

Sixteen keratoconic eyes with no history of RGP lens wear were included. They all had corneal aberrometry using Pentacam, and different aberration indices of the anterior and posterior surfaces of the cornea were measured before and 3 months after fitting RGP lenses. The effect of baseline parameters on these changes was tested in univariate and multiple models.

Results

Total aberrations and individual Zernike coefficients did not show statistically significant changes after using RGP lenses. Although not statistically significant, vertical coma decreased in the anterior (p = 0.073) and posterior surface (p = 0.095). Relationships that remained statistically significant in the multiple model were between baseline central corneal thickness and changes in total higher order aberrations and anterior 4th order astigmatism 0°, and between baseline 2nd order astigmatism 45° and its changes.

Conclusion

In this study, corneal aberrations remained unchanged 3 months after wearing RGP contact lens. Further studies with sufficient samples in different groups of keratoconus severity or baseline aberrations are needed to obtain more accurate results.

Cost effectiveness of collagen crosslinking for progressive keratoconus in the UK NHS

BACKGROUND

Keratoconus is a progressive degenerative corneal disorder of children and young adults that is traditionally managed by refractive error correction, with corneal transplantation reserved for the most severe cases. UVA collagen crosslinking is a novel procedure that aims to prevent disease progression, currently being considered for use in the UK NHS. We assess whether it might be a cost-effective alternative to standard management for patients with progressive keratoconus.

METHODS

We constructed a Markov model in which we estimated disease progression from prospective follow-up studies, derived costs derived from the NHS National Tariff, and calculated utilities from linear regression models of visual acuity in the better-seeing eye. We performed deterministic and probabilistic sensitivity analyses to assess the impact of possible variations in the model parameters.

RESULTS

Collagen crosslinking is cost effective compared with standard management at an incremental cost of £ 3174 per QALY in the base case. Deterministic sensitivity analysis shows that this could rise above £ 33,263 per QALY if the duration of treatment efficacy is limited to 5 years. Other model parameters are not decision significant. Collagen crosslinking is cost effective in 85% of simulations at a willingness-to-pay threshold of £ 30,000 per QALY.

CONCLUSION

UVA collagen crosslinking is very likely to be cost effective, compared with standard management, for the treatment of progressive keratoconus. However, further research to explore its efficacy beyond 5 years is desirable.

Success of hydrocone (TORIS-K) soft contact lens for keratoconus and traumatic keratopathy

Objective:

To present success of Toris-K contact lenses in keratoconus and traumatic keratopathy with irregular corneal surface.

Methods:

Toris-K contact lenses were used to treat 7 eyes of 4 patients with traumatic keratopathy (Case 1) or keratoconus (Case 2, Case 3, and Case 4). All cases had a complete eye examination before the contact lens application. The case with traumatic keratopathy was a 32-year-old male who had corneal penetrating injury due to hobnail strike 23 months ago. The other 3 keratoconus cases were females at the age of 14, 16 and 22 years old. They had high myopia and irregular astigmatism due to keratoconus. All patients refused using rigid gas permeable contact lens because of intolerance. Toris-K contact lenses were fitted on all eyes. All patients were followed-up for 28 months with a complete ophthalmic examination and corneal topography every two months.

Results:

Improvement of BCVA of the cases was remarkable. All cases were comfortable with their Toris-K contact lenses for 28 months. There was no significant distortion on the lenses during follow-up period.

Conclusion:

Toris-K lenses may be an effective alternative treatment option for the patients with keratoconus and traumatic keratopathy, especially who cannot tolerate rigid gas permeable contact lenses.

Central and peripheral corneal thinning in keratoconus

PURPOSE

Recent data regarding the mid-peripheral portion of the removed corneal button in transplant surgery indicate histopathologically that keratoconus was present also in the peripheral portion of the button. The intent of this study was therefore to investigate if peripheral changes could also be detected clinically by measuring the central and peripheral corneal thickness of KC patients.

METHODS

Corneal pachymetry was measured with the Visante optical coherence tomography and Orbscan II. Of 52 subjects, 26 were KC subjects and 26 were age- and sex-matched control subjects.

RESULTS

Corneal thickness, in KC patients, was significantly reduced in all areas compared with corneal thickness among controls with both the Visante optical coherence tomography and Orbscan II.

CONCLUSION

The results of the present study have provided clinical evidence that KC is a disease affecting a wider area of the cornea. Although the KC cornea shows the greatest change in thickness in the ectatic region, this attenuation declines toward the periphery. The presence of peripheral thinning indicated that KC may be a "pancorneal" pathology and not limited to the ectatic portion.

Prevalence and associations of steep cornea/keratoconus in Greater Beijing. The Beijing Eye Study

PURPOSE

To evaluate the prevalence and associated factors of steep cornea/keratoconus in the adult Chinese population.

METHODS

The population-based Beijing Eye Study 2011 included 3468 individuals with a mean age of 64.6±9.8 years (range: 50-93 years). A detailed ophthalmic examination was performed including optical low-coherence reflectometry. Steep cornea/keratoconus were defined as an anterior corneal refractive power exceeding 48 diopters.

RESULTS

Mean refractive power of the cornea was 43.16±1.45 diopters (range: 36.51 to 48.46 diopters; flattest meridian) and 43.98±1.52 diopters (range: 37.00 to 52.88 diopters; steepest meridian). A steep cornea/keratoconus defined as corneal refractive power of ≥48 diopters and ≥49 diopters was detected in 27 subjects (prevalence rate: 0.9±0.2%) and 6 (0.2± 0.1%) subjects, respectively. Presence of steep cornea/keratoconus was associated with shorter axial length (P<0.001), smaller interpupillary distance (P = 0.038), lower best corrected visual acuity (P = 0.021), higher cylindrical refractive error (P<0.001) and more myopic refractive error (P<0.001). It was not significantly associated with gender, body height, psychic depression, cognitive function, blood concentrations of glucose, lipids, creatinine and C-reactive protein, blood pressure and quality of life score, nor with intraocular pressure, dry eye feeling, and lens thickness.

CONCLUSIONS

A steep cornea/keratoconus defined as corneal refractive power of 48+ diopters has a prevalence of 0.9±0.2% among Chinese aged 50 years and above. Its prevalence was significantly associated with the ocular parameters of shorter axial length, smaller interpupillary distance, higher cylindrical and myopic refractive error and lower best corrected visual acuity, however, with none of the systemic parameters tested.

Changes in refraction, ocular aberrations, and corneal structure after suspending rigid gas-permeable contact lens wear in keratoconus

PURPOSE

This study reports on changes in visual acuity, ocular higher-order aberrations, and refraction after suspending rigid gas-permeable lens wear for 1 week in 15 patients with moderate to severe keratoconus. Alterations in the anterior surface, central corneal powers and axes, and central corneal thickness were also explored.

METHODS

Scheimpflug photography and Hartmann-Shack aberrometry were performed at 2 visits, 7 days apart, after the patients had removed their habitual contact lenses. Subjective refraction and both high- and low-contrast logarithm of the minimum angle of resolution visual acuities were also recorded at both visits.

RESULTS

Reductions in both high-contrast visual acuity (P = 0.001) and low-contrast visual acuity (P = 0.002), along with an increase in third-order root mean square aberrations (P = 0.008), occurred after rigid gas-permeable lens wear was suspended in these patients with keratoconus. However, no significant changes in subjective refraction were found over the 1-week period (P ≥ 0.10). Significant correlations were observed between third-order coma root mean square aberrations and the measured high-contrast (r(p) ≥ 0.59; P ≤ 0.02) and low-contrast visual acuities (r(P) ≥ 0.61; P ≤ 0.015). In addition to increases in the anterior surface central corneal powers (P ≤ 0.02), a reduction in central corneal thickness also was found between the 2 visits (P = 0.00016).

CONCLUSIONS

Changes in the optical and structural parameters of the keratoconic cornea occur after suspending rigid gas-permeable contact lens wear. This information may be of interest to practitioners concerned with prescribing aberration-controlling soft contact lenses for such patients.

Missing X and Y: a review of participant ages in population-based eye studies

Ophthalmic population-based studies have been used to establish the frequency of eye disease and the associated environmental and genetic factors that cause vision impairment and blindness. Most of these studies have concentrated on the diseases of ageing: cataract, age-related macular degeneration, glaucoma and diabetic retinopathy. Other studies have identified eye diseases in children but few studies of young adult eye disease exist. We conducted a systematic review of the ophthalmic literature to identify potential population-based eye studies and then note the age of participants in the studies. We then summarized the disease specific to young adults to show there is a need for further research to identify eye disease in this important and often-neglected group in the community. Eighty-four large population-based studies have been conducted worldwide: 9 in North America, 2 in South America, 17 in Africa, 35 in Asia, 11 in Australia and the Pacific, 6 in Europe, 4 in the Middle East and 1 that covered 3 continents. No studies specifically examined young adults. Twenty-six per cent of studies included young adults as part of all ages examined but none of these examined a large number of young adults.

Differential epithelial and stromal protein profiles in keratoconus and normal human corneas

The purpose of the study was to identify epithelial and stromal proteins that exhibit up- or down-regulation in keratoconus (KC) vs. normal human corneas. Because previous proteomic studies utilized whole human corneas or epithelium alone, thereby diluted the specificity of the proteome of each tissue, we selectively analyzed the epithelium and stromal proteins. Individual preparations of epithelial and stromal proteins from KC and age-matched normal corneas were analyzed by two independent methods, i.e., a shotgun proteomic using a Nano-Electrospray Ionization Liquid Chromatography Tandem Mass Spectrometry [Nano-ESI-LC-MS (MS)(2)] and two-dimensional-difference gel electrophoresis (2D-DIGE) coupled with mass spectrometric methods. The label-free Nano-ESI-LC-MS (MS)(2) method identified 104 epithelial and 44 stromal proteins from both normal and KC corneas, and also quantified relative changes in levels of selected proteins, in both the tissues using spectral counts in a proteomic dataset. Relative to normal corneal epithelial proteins, six KC epithelial proteins (lamin-A/C, keratin type I cytoskeletal 14, tubulin beta chain, heat shock cognate 71 kDa protein, keratin type I cytoskeletal 16 and protein S100-A4) exhibited up-regulation and five proteins (transketolase, pyruvate kinase, 14-3-3 sigma isoform, phosphoglycerate kinase 1, and NADPH dehydrogenase (quinone) 1) showed down-regulation. A similar relative analysis showed that three KC stromal proteins (decorin, vimentin and keratocan) were up-regulated and five stromal proteins (TGF-betaig h3 (Bigh3), serotransferrin, MAM domain-containing protein 2 and isoforms 2C2A of collagen alpha-2[VI] chain) were down-regulated. The 2D-DIGE-mass spectrometry followed by Decyder software analysis showed that relative to normal corneas, the KC corneal epithelium exhibited up-regulation of four proteins (serum albumin, keratin 5, L-lactate dehydrogenase and annexin A8) and down-regulation of four proteins (FTH1 [Ferritin heavy chain protein 1], calpain small subunit 1, heat shock protein beta 1 and annexin A2). A similar relative analysis of stroma by this method also showed up-regulation of aldehyde dehydrogenase 3A1 (ALDH3A1), keratin 12, apolipoprotein A-IV precursor, haptoglobin precursor, prolipoprotein and lipoprotein Gln in KC corneas. Together, the results suggested that the Nano-ESI-LC-MS(MS)(2) method was superior than the 2D-DIGE method as it identified a greater number of proteins with altered levels in KC corneas. Further, the epithelial and stromal structural proteins of KC corneas exhibited altered levels compared to normal corneas, suggesting that they are affected due to structural remodeling during KC development and progression. Additionally, because several epithelial and stromal enzymes exhibited up- or down-regulation in the KC corneas relative to normal corneas, the two layers of KC corneas were under metabolic stress to adjust their remodeling.

Effect of lens diameter on lens performance and initial comfort of two types of GP lenses for keratoconus: a pilot study

Purpose

The purpose of this pilot study was to determine the effect of varying lens diameter of two types of keratoconic lenses on lens performance and initial comfort with participants with either centered or oval cones.

Methods

Sixteen eyes of ten keratoconic participants were fitted with lenses of five diameters i.e. 8.7, 9, 9.6, 10.1 and 10.4 diameters and two commercially available lens types; “KCGP-1” and “KCGP-2”. Lensmovement, centration and initial comfort were assessed.

Results

Ten subjects (2 female and 8 male, sixteen eyes) were enrolled to participate in the pilot study, themean age was 40.4 ± 14.33 years. Six eyes were in the early centred cone group, five in the early oval cone group and five in the late oval cone group. The lenses with the 9.6 lens diameter (TD) decentered the least for all lenses (p = 0.001). When compared to cone type, the 8.7/9 were more decentered for the late oval and late centred cones (p = 0.009). The movement of the smaller KCGP-1 was greater than the KCGP-2 for the centered early cones (p = 0.001) and the movement decreased for the larger KCGP-2 lenses for all cone types but not significantly (p > 0.05). The KCGP-1 lenses were more significantly comfortable than the KCGP-2 lenses for the centered cones (p = 0.003). Only for the early oval cones, was the larger KCGP-2 lenses more comfortable (p = 0.04).

Conclusions

Lens diameter affects comfort and centration especially for the small (8.7/9) and large (10.4/10.1) diameters in this pilot study. Lens movement was not correlated with comfort.

Prevalence and associations of keratoconus in rural maharashtra in central India: the central India eye and medical study

PURPOSE

To evaluate the prevalence and associated factors of keratoconus in the adult Indian population.

DESIGN

Population-based study.

METHODS

The Central India Eye and Medical Study is a population-based study performed in a rural region close to Nagpur in Central India. It included 4,711 subjects (aged 30 years and above) out of 5,885 eligible subjects (response rate, 80.1%). The participants underwent a detailed ophthalmic and medical examination. This study was focused on the prevalence of keratoconus, defined as an anterior corneal refractive power exceeding 48 diopters (D).

RESULTS

Out of the 4,711 subjects, corneal refractive power measurements were available for 4,667 subjects (99.1%). Keratoconus was detected in 212 eyes (2.3%) of 128 subjects (prevalence rate, 2.3% +/- 0.2%). In multivariate analysis, the presence of keratoconus was significantly associated with lower body height (P < .001), lower level of education (P= .03), higher myopic refractive error (P = .004), and thinner central corneal thickness (P = .006). It was not significantly associated with alcohol consumption (P = .99) or smoking (P = .08) nor with questions relating to the psychiatric status. Defining a keratoconus as corneal refractive power of > or =49 D or of > or =50 D, a keratoconus was detected in 58 eyes (0.6%) and 10 eyes (0.1%), respectively.

CONCLUSIONS

Keratoconus defined as corneal refractive power of 48+ D has a prevalence of 2.3% +/- 0.2% among Indians aged 30 years and above and living in the rural region of Central India. The prevalence of keratoconus was associated with lower body height, lower level of education, myopic refractive error, and thinner central cornea.

2008 Sir Norman McAlister Gregg Lecture: 150 years of practical observations on the conical cornea--what have we learned?

The first detailed descriptions of keratoconus were published exactly 150 years ago in the original work of Dr John Nottingham, bringing a degree of clarity to a previously confusing clinical phenomenon--further supported by observations of other contemporaries in the field such as Sir William Bowman. However, it would be another 100 years before knowledge of keratoconus would grow substantially; indeed, our current level of understanding is primarily a result of extensive clinical and laboratory research conducted over the last 50 years--particularly based upon the enormous technological advances of the last two decades. Large clinical studies have confirmed that keratoconus is a non-inflammatory corneal disease with central or paracentral corneal thinning, which exhibits progressive corneal steepening and protrusion that typically results in increasing regular and thereafter irregular astigmatism. Ultimately, disease progression may lead to corneal scarring, corneal hydrops and loss of best spectacle-corrected visual acuity. Although visual rehabilitation may be effected by expert contact lens fitting, 20% of subjects may require corneal transplantation. This Gregg lecture provides a highly referenced, wide-ranging overview of both historical and contemporary aspects of keratoconus, including diagnostic, phenotypic and prognostic factors revealed by large clinical studies, critical diagnostic advances enabled by Placido and slit-scanning computerized corneal topography, the emerging roles of higher order aberration wave-front analysis and corneal hysteresis in delineating early and subclinical keratoconus, inheritance and genetic predisposition to keratoconus, corneal microstructural changes unveiled by in vivo confocal microscopy, unifying theories to explain associations between keratoconus, atopy, eye rubbing and keratocyte apoptosis, and surgical options for keratoconus, such as corneal transplantation, intrastromal ring segments, collagen cross-linking and keratocyte transplantation. However, 150 years along the path our knowledge of keratoconus remains incomplete, but technological advances should enable us to put together the final pieces of the jigsaw in the foreseeable future.

Iron homeostasis and eye disease

BACKGROUND

Iron is necessary for life, but excess iron can be toxic to tissues. Iron is thought to damage tissues primarily by generating oxygen free radicals through the Fenton reaction.

METHODS

We present an overview of the evidence supporting iron's potential contribution to a broad range of eye disease using an anatomical approach.

RESULTS

Iron can be visualized in the cornea as iron lines in the normal aging cornea as well as in diseases like keratoconus and pterygium. In the lens, we present the evidence for the role of oxidative damage in cataractogenesis. Also, we review the evidence that iron may play a role in the pathogenesis of the retinal disease age-related macular degeneration. Although currently there is no direct link between excess iron and development of optic neuropathies, ferrous iron's ability to form highly reactive oxygen species may play a role in optic nerve pathology. Lastly, we discuss recent advances in prevention and therapeutics for eye disease with antioxidants and iron chelators.

GENERAL SIGNIFICANCE

Iron homeostasis is important for ocular health.

Penetrating Keratoplasty for Keratoconus: The Nexus Between Corneal Wavefront Aberrations and Visual Performance

PURPOSE

To compare the visual and optical performance after penetrating keratoplasty (PK) for keratoconus to normal patients and to examine the relationship between corneal wavefront aberrations and visual performance in patients with PK.

METHODS

Visual performance testing, with optimal refractive correction, included low contrast visual acuity (LCVA) and Pelli-Robson contrast sensitivity with and without glare, and high contrast visual acuity. Corneal first surface wavefront aberrations were calculated from EyeSys topography data using VOL-Pro software v7.00 for a 4.0-mm pupil as a 10th order Zernike expansion and converted into single value metrics. Normal patients were compared to patients with PK using analysis of variance, and linear regression was used to compare wavefront aberration metrics to visual performance.

RESULTS

Patients with PK (n=14, age 41.6 +/- 7.0 years) and normal patients (n=14, age 36.7-9.0 years) were of similar age (F(1, 26) = 2.54, P = .12). Normal patients saw significantly better on all visual performance measures and had better optical performance for total higher order root-mean-square corneal wavefront aberration (mean-SD): PK, 0.67 +/- 0.41 microm; normal, 0.09 +/- 0.02 microm (F(1,26) = 28.41, P < .001) and across all Zernike orders and modes. Wavefront aberrations in PK eyes were dominated by trefoil 0.35 +/- 0.27 microm, coma 0.47 +/- 0.37 microm, spherical aberration 0.17 +/- 0.10 microm, and tetrafoil 0.12 +/- 0.07 microm. The relationships between corneal wavefront aberration and visual performance metrics were strongest for LCVA = 0.30-0.98 Pupil fraction for wavefront (tessellation) -0.04 Half width at half height, R2=0.75.

CONCLUSIONS

In this series, patients with PK had poorer visual performance compared to normal patients, which is due to increased corneal wavefront aberrations. Outcomes research in corneal transplantation should include measurement of wavefront aberrations and visual performance in the contrast domain.

Contrast and glare testing in keratoconus and after penetrating keratoplasty

AIM

To compare the performance of keratoconus, penetrating keratoplasty (PK), and control subjects on clinical tests of contrast and glare vision, to determine whether differences in vision were independent of visual acuity (VA), and thereby establish which vision tests are the most useful for outcome studies of PK for keratoconus.

METHODS

All PK subjects had keratoconus before grafting and no subjects had any other eye disease. The keratoconus (n = 11, age 35.0 (SD 11.1) years), forme fruste keratoconus (n = 6, 33.0 (13.0)), PK (n = 21, 41.2 (7.9)), and control (n = 24, 33.7 (8.6)) groups were similar in age. Vision testing, conducted with optimal refractive correction in place, included low contrast visual acuity (LCVA) and Pelli-Robson contrast sensitivity (PRCS) both with and without glare, as well as VA.

RESULTS

Normal subjects saw better than PK subjects who in turn saw better than keratoconus subjects on all raw measures. However, when adjusted for VA, the normal group only saw significantly better than the keratoconus group on LCVA (low contrast loss 0.05 (0.04) v 0.15 (0.12), F(2,48) = 6.16; p<0.01, post hoc Sheffé p<0.05), and the decrements to glare were no worse than for normals. The forme fruste keratoconus group were indistinguishable from normals on all measures.

CONCLUSIONS

PK subjects have superior vision to keratoconus subjects, but not as good as normal subjects. Including mild keratoconus subjects within a keratoconus group could confound these differences in vision. While VA is an excellent test for comparing normal, keratoconus and PK groups, additional information can be provided by LCVA and PRCS, but not by glare testing. Outcomes research into keratoconus management should include a measure in the contrast domain.

Keratoconus associated with continual eye rubbing due to punctal agenesis

PURPOSE

To highlight a possible causal effect of eye rubbing in the etiology of keratoconus.

METHODS

A 43-year-old man presented to the practice of one of the authors (I.F.G.) with the complaint of gradual onset reading difficulty. History revealed the patient to have experienced constant epiphora in the right eye throughout his life as a result of punctal agenesis, which necessitated frequent wiping of this eye. Vision in the patient's right eye had been reduced for approximately 20 years.

RESULTS

Based on ocular examination, the patient was diagnosed as having unilateral keratoconus in the right eye.

CONCLUSION

It is thought by some that keratoconus is associated with, or indeed caused by, persistent rubbing of the anterior eye. While a number of studies support a genetic basis for keratoconus in some patients, it is possible that mechanical factors play a role in the development of this condition in other patients. This paper presents a case of unilateral keratoconus, where there is a confirmed history of habitual eye rubbing and wiping of excess tears as a result of punctal agenesis in the ipsilateral eye, thereby suggesting a possible causal relationship of eye rubbing in the etiology of keratoconus.

RGP fitting philosophies for keratoconus

Rigid gas permeable (RGP) lenses are the choice of vision correction for most keratoconic patients. Various fitting philosophies and different lens designs are available and the question of which technique is the most appropriate is a controversial issue in the field of contact lens practice. This article reviews the different philosophies with respect to their rationale, optical performance and physiological influence on the cornea. The 'three-point-touch' approach is now the most widely-accepted corneal lens fitting philosophy in clinical practice. It provides a well-distributed pressure between the cone apex and the relatively normal peripheral cornea but other philosophies such as apical bearing and apical clearance also have advantages. Having considered the advantages and disadvantages of each philosophy, a variant of the three-point-touch appears to be a practical solution. Practitioners can fit keratoconic patients with a three-point-touch tending towards apical clearance to allow for disease progression and unexpected lack of follow-up. Wearing time, visual acuity and comfort are also important issues to be considered as all of these are essential to constitute a successful contact lens fitting.

Excimer Laser Lamellar Keratoplasty of Augmented Thickness for Keratoconus

PURPOSE

We describe a modified surgical technique for the treatment of patients in the early stage of keratoconus, when it is still possible to correct the astigmatic ametropia with contact lenses.

METHODS

Excimer laser lamellar keratoplasty of augmented thickness (ELLKAT) is a procedure in which a deep plano excimer laser ablation is done on the host cornea and a donor lamellar button--with or without an excimer laser refractive ablation on the posterior surface--is sutured into the recipient bed. In 12 of 20 eyes, the homoplastic button, which had parallel faces and was devoid of any dioptric power, was treated refractively on its stromal face with a Chiron Keracor 116 excimer laser to correct the axial and/or induced myopia present due to the weakened cornea.

RESULTS

The 8 eyes that received donor buttons without excimer laser ablation had improved spectacle-corrected visual acuity from a mean preoperative value of 20/100 (no eye saw 20/40 or better before surgery) to a mean postoperative value of 20/30 after 18 months. Mean refractive astigmatism was reduced from 4.84 +/- 2.34 D to 1.00 +/- 0.46 D. Mean keratometric power was reduced from 56.75 +/- 8.01 D to 44.21 +/- 2.12 D. The associated mean spherical equivalent refraction was reduced from -4.75 to -3.00 D. Mean corneal thickness increased from 422.25 +/- 83 microns preoperatively to 562.87 +/- 57.81 microns postoperatively. The 12 eyes that received donor lamellar buttons treated with excimer laser also had improved spectacle-corrected visual acuity from a mean preoperative value of 20/100 to a mean postoperative value of 20/30 after 18 months. Astigmatism was reduced from a mean 4.84 +/- 2.77 D to 1.66 +/- 1.30 D; mean keratometric power was reduced from 56.08 +/- 7.00 D to 45.31 +/- 2.08 D; and the associated mean spherical equivalent refraction was reduced from -8.75 to -1.75 D. Corneal thickness increased from a mean 414.25 +/- 64.75 microns preoperatively to 576.75 +/- 28.23 microns postoperatively.

CONCLUSION

Compared to penetrating keratoplasty, excimer laser lamellar keratoplasty of augmented thickness for keratoconus has the advantage of preserving the host endothelium and of reducing the refractive error in keratoconus.

Keratoconus: the clinical experience of a Brisbane ophthalmologist

Keratoconus is a common corneal dystrophy. In order to characterize an Australian experience with this condition, a retrospective study of 295 consecutive cases of keratoconus presenting to one Brisbane ophthalmologist (GR) was performed. The majority (82%) of patients presented before the age of 40 years. Keratoconus was bilateral in 240 (81%) patients and unilateral in 55 (19%) patients. Family history of keratoconus occurred in 43 (15%) patients. A history of atopy and eye rubbing was obtained in 131 (44%) and 30 (10%) patients, respectively. Follow-up after a mean +/- SD of 5 +/- 5 years was obtained in 188 patients. Treatment modalities at follow-up included rigid gas-permeable contact lenses (CL) (48%), PMMA CL (3%), corneal graft (25%), no treatment (13%), spectacles (9%), soft CL (2%). The annual corneal graft rate was 3% per year per eye. With careful contact lens fitting most keratoconus patients will not require a corneal graft.

The results of penetrating keratoplasty for keratoconus

At the Department of Ophthalmology, University Hospital in Lund, Sweden, keratoconus is the most common indication for penetrating keratoplasty. We studied 77 keratoplasties performed on keratoconic eyes between 1989-1991. Postoperative corrected visual acuity was better than or equal to 0.5 in 65 eyes (84.4%), and 30 eyes (39%) had visual acuity of 1.0. The mean postoperative astigmatism was 3.75 D with a range of 0-12.5 D. Eight patients underwent relaxing incision with satisfactory results in 6 patients. Graft rejection was observed in 6 eyes (7.8%). The most serious complication seen in our group of patients was a retrocorneal fibrous membrane that developed in one patient.

Clinical detection of unilateral keratoconus

PURPOSE

To determine the incidence of true unilateral keratoconus on the basis of computerised corneal topography in a group with clinically diagnosed unilateral keratoconus.

METHODS

Retrospective review of 295 patients with keratoconus identified 51 patients with a provisional diagnosis of unilateral keratoconus. Thirty-one of these patients were re-examined clinically and 21 patients met the criteria for a clinical diagnosis of unilateral keratoconus. Computerised corneal topographic analysis (Tomey TMS) was then performed.

RESULTS

In a group of 21 patients with clinically diagnosed unilateral keratoconus, computerised corneal topographic analysis identified 14 (67%) patients with bilateral keratoconus and seven (33%) patients with true unilateral keratoconus. Contact lens wear had no significant influence (P=0.76) on the topographical diagnosis of keratoconus in the clinically unaffected fellow eye. The estimated incidence of true unilateral keratoconus in the cohort of 295 patients was 4%.

CONCLUSIONS

Computerised corneal topography improves sensitivity in detection of true unilateral keratoconus.

Leber congenital amaurosis and its association with keratoconus and keratoglobus

Leber congenital amaurosis has been associated with keratoconus and it has been postulated that this is due to eye rubbing, the oculo-digital sign, because of poor vision. Six schools for the blind were visited, and 174 children with a visual acuity of less than 3/60 examined. Thirty-five children had Leber amaurosis, and 10 of these had keratoconus (29%) and one had keratoglobus (3%). The six pedigrees of the cases with Leber amaurosis and keratoconus are presented in detail. Only 3 of the 139 other blind children had keratoconus (P < .05) and 1 had keratoglobus. Keratoconus seems specifically associated with Leber amaurosis, probably due to genetic factors, rather than poor visual acuity per se.

Contact lens failure in keratoconus management

PURPOSE

Surgery is indicated for keratoconus when management with contact lenses fails. The authors sought to determine the relative contribution of various preoperative patient and ocular factors to the ultimate causes of contact lens failure.

METHODS

The records of unoperated eyes of keratoconus patients whose contact lenses were managed intensively before undergoing penetrating keratoplasty (PK) at the authors' institution between 1981 and 1990 were selected for study. Univariate and multivariate analyses were performed to identify risk factors for early contact lens failure.

RESULTS

The records of 99 keratoconic eyes of 75 patients with an average age of 34 years and average keratometry readings of 57.5 diopters at presentation were studied. Cases had been followed for an average of 27 months before PK. The primary reasons for PK were a best-corrected visual acuity of under 20/40 (despite good contact lens fit) causing disability for the patient (43%), contact lens intolerance (32%), frequent lens displacement (13%), and significant peripheral thinning of the cornea (12%). The referral source of the patient, sex, a history of PK in the fellow eye, or of contact lens wear in either eye did not alter the relative contributions of these parameters to surgery.

CONCLUSION

Poor best-corrected visual acuity at presentation, higher keratometry readings (greater than or equal to 55 D), age (greater than or equal to 40 years), and duration of disease (greater than 5 years) were significantly associated with failure due to poor functional acuity and peripheral thinning, frequently leading to surgery within the first 12 months after presentation.