Vertical D

A Case of Early Keratoconus Associated with Eye Rubbing in a Young Child

INTRODUCTION

Keratoconus usually presents during puberty and is considered rare in young children.

METHODS

Case report with clinical findings and computerized corneal tomography.

RESULTS

We report the case of an 8-year-old girl with early bilateral keratoconus who presented with allergic conjunctivitis and persistent eye rubbing. Although our patient did not exhibit steep keratometry, early cones and inferotemporal thinnest corneal thicknesses were detected in both eyes using Scheimpflug imaging (Oculus GmbH Pentacam, Wetzlar, Germany). Belin/Ambrósio total D values were 1.85 on the right and 2.11 on the left. Improvement in best-corrected visual acuity was noted after treatment of allergic eye disease, and corneal tomographic findings remained stable 4 months after initial consult.

CONCLUSION

This is a case of early diagnosed keratoconus in a young patient. Diagnosis of this condition in young children is challenging, as these patients are less likely to report visual complaints, and clinical examination is usually unremarkable. Keratoconus screening should be considered in children with atopy and eye rubbing behavior regardless of age, even in those with no other associated pathology and with negative family history.

A review of keratoconus: Diagnosis, pathophysiology, and genetics

We discuss new approaches to the early detection of keratoconus and recent investigations regarding the nature of its pathophysiology. We review the current evidence for its complex genetics and evaluate the presently identified genes/loci and potential candidate gene/loci. In addition, we highlight current research methodologies that may be used to further elucidate the pathogenesis of keratoconus.

Corneal topography in keratoconus: state of the art

The morphological characterization of the cornea using corneal topographers is a widespread clinical practice that is essential for the diagnosis of keratoconus. The current state of this non-invasive exploratory technique has evolved with the possibility of achieving a great number of measuring points of both anterior and posterior corneal surfaces, which is possible due to the development of new and advanced measurement devices. All these data are later used to extract a series of topographic valuation indices that permit to offer the most exact and reliable clinical diagnosis. This paper describes the technologies in which current corneal topographers are based on, being possible to define the main morphological characteristics that the keratoconus pathology produces on corneal surface. Finally, the main valuation indices, which are provided by the corneal topographers and used for the diagnosis of keratoconus, are also defined.

Template-based correction of high-order aberration in keratoconus

PURPOSE

The common change in corneal morphology that is seen in keratoconus (KC) suggests the presence of common high-order aberration (HOA) structures and the potential for HOA corrections that apply to more than one eye. The purpose of this investigation is to classify a sample of KC eyes into subgroups based on similar HOA characteristics and simulate optical performance of common HOA corrections on members of each subgroup.

METHODS

High-order aberrations were recorded over a 5-mm pupil on 111 KC eyes. The eyes were divided into five subgroups based on observed commonality in HOA structure. From each subgroup, two eyes were removed for later evaluation of corrections. Principal components analysis was performed on the remaining eyes of each subgroup. The first principal component was scaled to form a set of corrections. Simulated optical correction of the test eyes was performed by identifying the magnitude of the inner-group correction providing the lowest level of residual higher order root mean square wavefront error (HORMS). Residual uncorrected HORMS was compared with levels found in uncorrected normal eyes and KC eyes wearing rigid gas-permeable corrections.

RESULTS

Ninety (81%) of the 111 eyes were included in one of the five subgroups. All 10 test eyes experienced a reduction in HORMS with a template correction compared with their uncorrected levels. Median HORMS reduced from uncorrected levels of 2.14 to 0.97 μm. On average, the 10 subjects experienced a 51% reduction in HORMS (minimum, 16%; maximum, 81%; p < 0.01). When scaled to a 4-mm pupil, five of the 10 eyes experienced residual uncorrected HORMS within limits associated with gas-permeable wear.

CONCLUSIONS

Overlap exists across these templates because of the dominance of vertical coma in the HOA structure. All eyes evaluated received reduced HORMS with a template-based correction.

Revisiting keratoconus diagnosis and progression classification based on evaluation of corneal asymmetry indices, derived from Scheimpflug imaging in keratoconic and suspect cases

PURPOSE

To survey the standard keratoconus grading scale (Pentacam®-derived Amsler-Krumeich stages) compared to corneal irregularity indices and best spectacle-corrected distance visual acuity (CDVA).

PATIENTS AND METHODS

Two-hundred and twelve keratoconus cases were evaluated for keratoconus grading, anterior surface irregularity indices (measured by Pentacam imaging), and subjective refraction (measured by CDVA). The correlations between CDVA, keratometry, and the Scheimpflug keratoconus grading and the seven anterior surface Pentacam-derived topometric indices - index of surface variance, index of vertical asymmetry, keratoconus index, central keratoconus index, index of height asymmetry, index of height decentration, and index of minimum radius of curvature - were analyzed using paired two-tailed t-tests, coefficient of determination (r(2)), and trendline linearity.

RESULTS

The average ± standard deviation CDVA (expressed decimally) was 0.626 ± 0.244 for all eyes (range 0.10-1.00). The average flat meridian keratometry was (K1) 46.7 ± 5.89 D; the average steep keratometry (K2) was 51.05 ± 6.59 D. The index of surface variance and the index of height decentration had the strongest correlation with topographic keratoconus grading (P < 0.001). CDVA and keratometry correlated poorly with keratoconus severity.

CONCLUSION

It is reported here for the first time that the index of surface variance and the index of height decentration may be the most sensitive and specific criteria in the diagnosis, progression, and surgical follow-up of keratoconus. The classification proposed herein may present a novel benchmark in clinical work and future studies.

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.

Topographic and Tomographic Indices for Detecting Keratoconus and Subclinical Keratoconus: A Systematic Review

Purpose

To provide an overview of the topographic and tomographic indices developed for detecting keratoconus (KC) and subclinical keratoconus.

Methods

Literature review of studies describing and testing KC indices as well as indices developed for improving the sensitivity of subclinical KC detection.

Results

Several indices, based on anterior and posterior curvature measurements, corneal spatial distribution or posterior corneal elevation have been developed for improving the detection of KC and subclinical KC. However, to date, none of them could reach, alone, sufficient discriminating power for differentiating the mildest forms of the disease from normal corneas. New detection programs, based on a combination of corneal indices, and generated using artificial intelligence emerged recently and helped to significantly improve the subclinical KC detection.

Conclusion

The combination of topographic and tomographic corneal indices has helped to significantly improve the sensitivity of subclinical KC detection. However, combining these morphological indices to wavefront and biomechanical analyses of the cornea will certainly further improve the sensitivity of the future screening tests.

How to cite this article

Smadja D. Topographic and Tomographic Indices for Detecting Keratoconus and Subclinical Keratoconus: A Systematic Review. Int J Kerat Ect Cor Dis 2013;2(2):60-64.

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

Purpose

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

Materials and methods

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

Results

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

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

Conclusion

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

Précis

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

How to cite this article

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

Early onset keratectasia after photorefractive keratectomy in a case showing Vertical D topographic pattern

PURPOSE

We describe a case of early onset keratectasia after photorefractive keratectomy (PRK) in a patient with Vertical D topographic pattern in one eye and suspected keratoconus in the other eye.

METHODS

A 31-year-old woman underwent bilateral PRK: attempted correction was -8.00-2.00 × 30° in her right eye (RE) and -4.50-1.50 × 150° tabo in her left eye (LE). Preoperative corneal thickness was 512 µm in the RE and 520 µm in the LE. Preoperative topography showed an asymmetric bow-tie pattern and skewed axis in RE and a Vertical D pattern in LE. Intended maximum ablation was 91 µm in RE and 66 µm in LE.

RESULTS

Three months postoperatively the patient showed early topographic signs of bilateral keratectasia, evolved to manifest keratectasia after six years.

CONCLUSIONS

Although rare after PRK, keratectasia may occur even following moderate (66 µm) surface ablation in eyes with Vertical D topographic pattern in one eye and controlateral suspected keratoconus.

Keratoconus: a review

Keratoconus is the most common primary ectasia. It usually occurs in the second decade of life and affects both genders and all ethnicities. The estimated prevalence in the general population is 54 per 100,000. Ocular signs and symptoms vary depending on disease severity. Early forms normally go unnoticed unless corneal topography is performed. Disease progression is manifested with a loss of visual acuity which cannot be compensated for with spectacles. Corneal thinning frequently precedes ectasia. In moderate and advance cases, a hemosiderin arc or circle line, known as Fleischer's ring, is frequently seen around the cone base. Vogt's striaes, which are fine vertical lines produced by Descemet's membrane compression, is another characteristic sign. Most patients eventually develop corneal scarring. Munson's sign, a V-shape deformation of the lower eyelid in downward position; Rizzuti's sign, a bright reflection from the nasal area of the limbus when light is directed to the limbus temporal area; and breakages in Descemet's membrane causing acute stromal oedema, known as hydrops, are observed in advanced stages. Classifications based on morphology, disease evolution, ocular signs and index-based systems of keratoconus have been proposed. Theories into the genetic, biomechanical and biochemical causes of keratoconus have been suggested. Management varies depending on disease severity. Incipient cases are managed with spectacles, mild to moderate cases with contact lenses and severe cases can be treated with keratoplasty. This article provides a review on the definition, epidemiology, clinical features, classification, histopathology, aetiology and pathogenesis, and management and treatment strategies for keratoconus.

Corneal ectasia after LASIK despite low preoperative risk: tomographic and biomechanical findings in the unoperated, stable, fellow eye

PURPOSE

To report a case of progressive corneal ectasia after LASIK with no detectable preoperative risk factors and to present three-dimensional corneal tomographic and biomechanical findings on the contralateral unoperated eye that would be considered low risk for ectasia and thereby a good LASIK candidate based on the Randleman Ectasia Risk Score System (ERSS).

METHODS

A case report, literature review, and description of novel screening criteria based on Pentacam (Oculus Optikgeräte GmbH) corneal tomography are presented as well as Ocular Response Analyzer (ORA, Reichert Instruments) corneal biomechanical analysis.

RESULTS

Progressive corneal ectasia after LASIK of the operated left eye was confirmed by corneal topography. Scheimpflug imaging identified a meniscus-shaped LASIK flap with a central thickness of 165 μm and residual stromal bed thickness of 280 μm. Randleman ERSS score was 2 for the ectatic eye before LASIK and 1 for the current status of the unoperated eye, which remained stable with normal topography and no change in refraction for >5 years. Low corneal hysteresis (8.6 mmHg) and corneal resistance factor (7.5 mmHg) were found in the unoperated, nonectatic eye, along with a suspicious waveform sign of a second rebounded peak after second applanation. Pentacam average pachymetric progression was 1.09 (normal is <1.15); the Belin-Ambrósio overall deviation index was 1.99 (normal is <1.9).

CONCLUSIONS

Three-dimensional corneal tomographic and ORA biomechanical measurements provide additional information that may help identify individuals at high risk for naturally occurring or iatrogenic corneal ectasia.

Validation of the Ectasia Risk Score System for preoperative laser in situ keratomileusis screening

PURPOSE

To validate the Ectasia Risk Score System for identifying patients at high risk for developing ectasia after laser in situ keratomileusis (LASIK).

DESIGN

Retrospective case-control study.

METHODS

Fifty eyes that developed ectasia and 50 control eyes with normal postoperative courses after LASIK were analyzed and compared using the previously described Ectasia Risk Score System, which assigns points in a weighted fashion to the following variables: topographic pattern, predicted residual stromal bed (RSB) thickness, age, preoperative corneal thickness (CT), and manifest refraction spherical equivalent (MRSE).

RESULTS

In this series, 46 (92%) eyes with ectasia were correctly classified as being at high risk for the development of ectasia, while three (6%) controls were incorrectly classified as being at high risk for ectasia (P < 1 x 10(-10)). Significantly more eyes were classified as high risk by the ectasia risk score than by traditional screening parameters relying on abnormal topography or RSB thickness less than 250 micro (92% vs 50%; P < .00001). There was no difference in the sensitivity or specificity of the Ectasia Risk Score System in the population from which it was derived and this independent population of ectasia cases and controls.

CONCLUSIONS

The Ectasia Risk Score System is a valid and effective method for detecting eyes at risk for ectasia after LASIK and represents a significant improvement over previously utilized screening strategies.