Topographic Patterns in Refractive Surgery Candidates

Logistic Regression Model Using Scheimpflug-Placido Cornea Topographer Parameters to Diagnose Keratoconus

Purpose

Diagnose keratoconus by establishing an effective logistic regression model from the data obtained with a Scheimpflug-Placido cornea topographer.

Methods

Topographical parameters of 125 eyes of 70 patients diagnosed with keratoconus by clinical or topographical findings were compared with 120 eyes of 63 patients who were defined as keratorefractive surgery candidates. The receiver operating character (ROC) curve analysis was performed to determine the diagnostic ability of the topographic parameters. The data set of parameters with an AUROC (area under the ROC curve) value greater than 0.9 was analyzed with logistic regression analysis (LRA) to determine the most predictive model that could diagnose keratoconus. A logit formula of the model was built, and the logit values of every eye in the study were calculated according to this formula. Then, an ROC analysis of the logit values was done.

Results

Baiocchi Calossi Versaci front index (BCV_f) had the highest AUROC value (0.976) in the study. The LRA model, which had the highest prediction ability, had 97.5% accuracy, 96.8% sensitivity, and 99.2% specificity. The most significant parameters were found to be BCV_f (p=0.001), BCV_b (Baiocchi Calossi Versaci back) (p=0.002), posterior rf (apical radius of the flattest meridian of the aspherotoric surface in 4.5 mm diameter of the cornea) (p=0.005), central corneal thickness (p=0.072), and minimum corneal thickness (p=0.494).

Conclusions

The LRA model can distinguish keratoconus corneas from normal ones with high accuracy without the need for complex computer algorithms.

Topographic, elevation, and keratoconus indices for diagnosis of keratoconus by a combined Placido and Scheimpflug topography system

PURPOSE

To determine the accuracy of various corneal parameters in keratoconus diagnosis using Scheimpflug camera combined with Placido disk corneal topography (Sirius, CSO).

METHODS

One hundred and fifteen keratoconic eyes (group1) and a 111 normal eyes (group2) were assessed prospectively between March 2018 and July 2019 for: corneal keratometric indices (K1, K2, sim K, apex curvature) at different corneal rings of both corneal surfaces, central corneal thickness (CCT), thinnest corneal thickness (TL), corneal asphericity (Q), elevation at thinnest point, root mean square (RMS), and root mean square per area (RMS/A) in spherical, aspheric and aspherotoric reference for both corneal surfaces and keratoconus summary parameters; surface asymmetry index of front and back (SIf, SIb respectively), elevation at keratoconus vertex front and back (KVf, KVb respectively), Baiocchi Calossi Versaci front and back index (BCVf, BCVb) and its vector summation (BCV) and convergence radius and cutoff value for each was calculated.

RESULTS

All studied indices were significantly different between the two groups. The highest predictive accuracy "Area under receiver operating characteristic curve (AUROC)" of 0.999 was observed for BCVf, KVb, RMS and RMS/A at 6 mm aspherotoric reference posterior surface. Keratoconus summary indices had high AUROC (0.986, 0.984, 0.948, 0.999, 0.999, 0.998 respectively). Curvature indices had lower AUROC than elevation indices, except for curvature of corneal apex at anterior (0.98) and posterior surface (0.99). Higher AUROC was noted with elevation at thinnest point especially at aspherotoric reference surface.

CONCLUSION

Sirius topography showed high predictive accuracy in detection of keratoconus. Elevation indices and keratoconus summary parameters have the highest diagnostic ability.

Evaluation of corneal topography and tomography in fellow eyes of unilateral keratoconus patients for early detection of subclinical keratoconus

Purpose:

To analyse topographic and tomographic changes in fellow eyes of unilateral keratoconus patients by comparing them with normal eyes.

Methods:

This five-year retrospective observational comparative case study included 15 advanced keratoconus eyes of unilateral keratoconus (KCN group), 15 normal fellow eyes of unilateral keratoconus (Fellow eye group) and 34 eyes of normal refractive surgery candidates (Normal group). Topographic and tomographic data, data from enhanced elevation maps, and keratoconus indices were measured in all study eyes using Pentacam. Receiver operating characteristic (ROC) curves were used to evaluate the area under the curve (AUC), sensitivity and specificity of each parameter and identify cut-off points in discriminating between the fellow and normal eyes.

Results:

Corneal thickness at the apex (CTA, P = 0.001) and at the thinnest point (CTT, P < 0.001), corneal volume (CV, P = 0.007), Belin/Ambrosio Enhanced Ectasia Display (BAD) - thinnest point (Dt, P = 0.002) and thinnest point displacement (Da, P = 0.002) were significantly lower in the fellow group compared to eyes of normal subjects. On ROC curve analysis, the most efficient distinguishing indices between the fellow group and normal controls were BAD - overall D value (AUC = 0.859), Dt (AUC =0.827), Da (AUC = 0.789) followed by pachymetric progression index maximum (AUC = 0.741).

Conclusion:

BAD-D value and pachymetric progression index could be useful in detecting the earliest form of subclinical keratoconus. However, every single parameter alone is not enough to detect early changes; a combination of different data is required to distinguish subclinical keratoconus.

Laser in situ keratomileusis (LASİK) in patients with superior steepening on corneal topography: Is it safe and predictable?

BACKGROUND

Attention is usually given to inferior steepening on corneal topography in the evaluation of a patient's suitability for LASIK surgery. The aim of this study is to investigate long-term refractive results with superior steepening.

METHODS

Patients who underwent LASIK surgery between 2015 and 2019 in our refractive surgery department were retrospectively reviewed. The patients with a ≥ 1.0 D superior-inferior (S-I) quadrant difference in the tangential map, using a Scheimpflug camera with a Placido disc topographer (Sirius), were included in the study. Preoperative and postoperative best-corrected and uncorrected visual acuity (Snellen), cylindrical refraction values, and spherical equivalent (SE) values were compared. Adverse events were recorded.

RESULTS

Fifty eyes of 28 patients participated in the study. The mean age of the patients was 27.5 ± 8.0 (19-59). Sixteen patients were female (57.1%), and 12 (42.8%) patients were male. The average follow-up time was 29.8 ± 11.1 months (12-61). Average central corneal thickness was 549.4 ± 26.0 (498-602) μm. Average minimal corneal thickness was 549.1 ± 26.9 (497-598) μm. Preoperative S-I quadrant difference (D) was 1.87 ± 0.7 (1.0-3.99). Posterior elevation (Kvb) was 11.2 ± 1.9 (9-17) μm. The preoperative SE value was - 1.7 ± 2.1 (- 6.25-3.25) and improved to - 0.3 ± 0.44 D (- 1.25-0.75) (p < 0.001). Preoperative cylindrical refraction values were - 2.04 ± 1.7 (- 6.25-0), and postoperative values were - 0.47 ± 0.4 (- 2-0) D (p < 0.001). Uncorrected visual acuity was median 1.0 (0.4-1.0) with 38 eyes (76%) having 20/20 postoperative uncorrected visual acuity. No sight threatening complications or ectasia findings were observed during the 2 years postoperative follow-up time.

CONCLUSIONS

Abnormal corneal topographies with (S-I) asymmetry result in predictable results after LASIK.

Gonadotropins in Keratoconus: The Unexpected Suspects

Keratoconus (KC) is the most common ectatic corneal disease with a significant visual acuity burden. The actual burden is intangible given that KC can disrupt daily activities (reading, driving, and various career paths). Despite decades of research and clinical studies, the etiology, onset, and pathobiology of KC remain a mystery. The purpose of this study was to investigate the role of gonadotropins in KC. We recruited 86 KC patients (63 males, 23 female), and 45 healthy controls (22 male, 23 female). Plasma samples were collected and analyzed using an enzyme-linked immunosorbent assay. Corneal stromal cells from KC and healthy controls, and human epithelial corneal cells, were also investigated for gonadotropin-related markers. Our results show significant alterations of LH/FSH in KCs, compared to healthy controls. Our data also reveals, for the first time, the existence of gonadotropins and their receptors in KC. Our study is the first to demonstrate the role of LH/FSH in KCs, and expand the list of organs known to express gonadotropins, or their receptors, to include the human cornea. Our findings suggest that the human cornea is capable of responding to gonadotropins, and propose an intriguing mechanism for the onset and/or progression of KC.

Increased Corneal Ectasia Risk in Patients with Familial Mediterranean Fever

PURPOSE

To evaluate the corneal tomographic parameters in patients with familial Mediterranean fever (FMF) and to compare data with those of healthy control subjects.

MATERIALS AND METHODS

Forty eyes of 40 patients with FMF (FMF group) and 35 eyes of 35 healthy subjects (control group) were included to this prospective study. All participants underwent complete ophthalmological examination and tomographic analysis with Pentacam HR. Maximum keratometry, front and back astigmatism, thinnest pachymetry, maximum anterior and posterior elevation best-fit-sphere (BFS) at the 5.0 mm zone, front and back difference elevation, final D, average and maximum pachymetric progression index, and maximum Ambrósio relational thickness parameters were noted.

RESULTS

Groups were similar in terms of age and gender (p = 0.77 and 0.35). Maximum keratometry, thinnest pachymetry, front and back astigmatism, and maximum anterior elevation BFS at the 5.0 mm values were similar between groups (p = 0.22, 0.52, 0.49, 0.29, and 0.31, respectively). Maximum posterior elevation BFS at the 5.0 mm and back difference elevation values were higher than control group in FMF group (p = 0.001 and 0.04). The mean values of final D, average and maximum pachymetric progression index were higher, and Ambrósio relational thickness was lower in FMF group compared to control group (p = 0.03, 0.002, 0.006, and 0.01, respectively).

CONCLUSIONS

FMF patients carry increased corneal ectasia risk compared to healthy subjects. The corneal tomographic characteristics and the association of keratoconus with FMF may be important in a detailed refractive surgery work-up.

Prevalence of Keratoconus in a Refractive Surgery Population

Objective

This study examined the prevalence of keratoconus among patients who were interested in undergoing refractive surgery. Corneal tomography measurements were used to help detect keratoconus.

Methods

Adult subjects who presented to the private hospital Cataract and Refractive Surgery Unit (Abha, Saudi Arabia) for refractive surgery evaluation were considered for inclusion in this cross-sectional, retrospective study. All subjects were from the Aseer province, a southern, high-altitude region in Saudi Arabia, and presented between January and December 2017. The incidence of keratoconus and other refractive surgery contraindications were examined.

Results

A total of 2931 patients were considered for inclusion in analyses. Of these, 2280 patients (77.8%) were not candidates for refractive surgery. These 2280 patients had a mean age of 24.1 ± 6.6 years and 1231 patients (54.0%) were male. Of the subjects who did not undergo refractive surgery, 548 (24%) had keratoconus, 400 (17.5%) were keratoconus suspects, 344 (15.1%) had thin corneas, 321 (14.1%) had high myopia, and 52 (2.3%) had a high astigmatism. An additional 479 subjects (21%) were candidates for refractive surgery, but chose not to undergo a procedure.

Conclusion

The incidence of keratoconus in Saudi Arabian refractive surgery prospects was 18.7%. Keratoconus was the most common reason for not performing refractive surgery and accounted for 24.0% of cases in which surgery was not performed.

Mean Posterior Corneal Power and Astigmatism in Normal Versus Keratoconic Eyes

Purpose:

To compare mean posterior corneal power and astigmatism in normal versus keratoconus affected eyes and determine the optimal cut-off points to maximize sensitivity and specificity in discriminating keratoconus from normal corneas.

Methods:

A total of 204 normal eyes and 142 keratoconus affected eyes were enrolled in this prospective comparative study. Mean posterior corneal power and astigmatism were measured using a dual Scheimpflug camera. Correlation coefficients were calculated to assess the relationship between the magnitudes of keratometric and posterior corneal astigmatism in the study groups. Receiver operating characteristic curves were used to compare the sensitivity and specificity of the measured parameters and to identify the optimal cut-off points for discriminating keratoconus from normal corneas.

Results:

The mean posterior corneal power was −6.29 ± 0.20 D in the normal group and −7.77 ± 0.87 D in the keratoconus group (P < 0.001). The mean magnitudes of the posterior corneal astigmatisms were −0.32 ± 0.15 D and −0.94 ± 0.39 D in the normal and keratoconus groups, respectively (P < 0.001). Significant correlations were found between the magnitudes of keratometric and posterior corneal astigmatism in the normal (r=−0.76, P < 0.001) and keratoconus (r=−0.72, P < 0.001) groups. The mean posterior corneal power and astigmatism were highly reliable characteristics that distinguished keratoconus from normal corneas (area under the curve, 0.99 and 0.95, respectively). The optimal cut-off points of mean posterior corneal power and astigmatism were −6.70 D and −0.54 D, respectively.

Conclusion:

Mean posterior corneal power and astigmatism measured using a Galilei analyzer camera might have potential in diagnosing keratoconus. The cut-off points provided can be used for keratoconus screening.

Keratoconus Screening Indices and Their Diagnostic Ability to Distinguish Normal From Ectatic Corneas

PURPOSE

To compare the diagnostic ability of 3 Scheimpflug devices in differentiating normal from ectatic corneas.

DESIGN

Comparison of diagnostic instrument accuracy.

METHODS

This study included 42 normal, 37 subclinical keratoconic, and 51 keratoconic eyes seen in a tertiary eye care institute. Keratoconus screening indices were evaluated using the Pentacam (Oculus, Wetzlar, Germany), Galilei (Ziemer, Biel, Switzerland), and Sirius (Costruzione Strumenti Oftalmici, Florence, Italy). Sensitivity, specificity, and area under receiver operating characteristic curve (AUC) were calculated.

RESULTS

Highest sensitivity (100%) to diagnose keratoconus was seen for 6 parameters on Pentacam and 1 on Galilei. None of the indices in Sirius reached 100% sensitivity. For subclinical keratoconus, the highest sensitivity (100%) was seen for 2 parameters on Pentacam but for none of them on Galilei and Sirius. All parameters were strong enough to differentiate keratoconus (AUC > 0.9). On comparing the best parameters of all 3 machines, the AUC of the Belin/Ambrosio enhanced ectasia total derivation (BAD-D) and the inferior-superior value (ISV) of Pentacam were statistically similar to that of the keratoconus prediction index (KPI) and keratoconus probability (Kprob) of Galilei (P = .27) and 4.5 mm root mean square per unit area (RMS/A) back of Sirius (P = .55). When differentiating subclinical from normal corneas, BAD-D was similar to the surface regularity index (SRI) of Galilei (P = .78) but was significantly greater than the 8 mm RMS/A back of Sirius (P = .002).

CONCLUSION

Keratoconus indices measured by all 3 machines can effectively differentiate keratoconus from normal corneas. However, new cutoff values might be needed to differentiate subclinical from normal corneas.

Topographic typology in a consecutive series of refractive surgery candidates

PURPOSE

The term 'keratoconus (KC) suspect' is used as a blanket term to refer to any deviation of virgin cornea shape toward KC features. We intend to subclassify such topographies in meaningful and informative designations.

METHODS

Pentacam corneal topographies of 199 consecutive refractive surgery candidates (398 eyes) are examined. Features of steepness, inferior-superior asymmetry, focal steepening, thinning, and bounded anterior or posterior elevations are observed in the quad map. Scissoring on retinoscopy, loss of best spectacle-corrected visual acuity, and iron ring deposition were looked for. Through iterative observation and refinement of classification criteria-partly taken from the literature-all eyes were designated a specific topographic diagnosis, i.e., circumventing the usage of the expression KC 'suspect'.

RESULTS

Topographies of 308, 48, 21, 13, 6, 1, and 1 (collectively 398 eyes) were designated: normal, 'atypical normal,' forme fruste KC, posterior KC, subclinical/mild KC, superior KC, and pseudo-KC, respectively.

CONCLUSION

Current imaging modalities of the cornea and our accumulated experience in refractive science allow assignment of distinctive designations for abnormal corneal shapes along the topography spectrum. We devised and used the expressions: normal, atypical normal, forme fruste (arrested-incomplete) KC, posterior KC, subclinical (active latent) KC, superior KC, and pseudo-keratoconus. Identification of 1.5% (mild) KC highlights the importance of screening for ultraviolet cross-linkage candidacy in refractive surgery referrals.

Accuracy of machine learning classifiers using bilateral data from a Scheimpflug camera for identifying eyes with preclinical signs of keratoconus

PURPOSE

To describe the topographic and tomographic characteristics of normal fellow eyes of unilateral keratoconus cases and to evaluate the accuracy of machine learning classifiers in discriminating healthy corneas from the normal fellow corneas.

SETTING

Department of Ophthalmology, Semmelweis University, Budapest, Hungary.

DESIGN

Retrospective case-control study.

METHODS

Patients with bilateral keratoconus (keratoconus group), clinically and according to the keratoconus indices of the Pentacam HR Scheimpflug camera; normal fellow eyes of patients with unilateral keratoconus (fellow-eye group); and eyes of refractive surgery candidates (control group) were compared. Tomographic data, topographic data, and keratoconus indices were measured in both eyes using the Scheimpflug camera. Receiver operating characteristic (ROC) analysis was used to assess the performance of automated classifiers trained on bilateral data as well as individual parameters to discriminate fellow eyes of patients with keratoconus from control eyes.

RESULTS

Keratometry, elevation, and keratoconus indices values were significantly higher and pachymetry values were significantly lower in keratoconus eyes than in fellow eyes of unilateral keratoconus cases (P < .001). These fellow eyes had significantly higher keratometry, elevation, and keratoconus index values and significantly lower pachymetry values than control eyes (P < .001). Automated classifiers trained on bilateral data of index of height decentration had higher accuracy than the unilateral single parameter in discriminating fellow eyes of patients with keratoconus from control eyes (area under ROC 0.96 versus 0.88).

CONCLUSION

Automatic classifiers trained on bilateral data were better than single parameters in discriminating fellow eyes of patients with unilateral keratoconus with preclinical signs of keratoconus from normal eyes.

FINANCIAL DISCLOSURE

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

Predictive Ability of Galilei to Distinguish Subclinical Keratoconus and Keratoconus from Normal Corneas

Purpose:

To determine the predictive ability of different data measured by the Galilei dual Scheimpflug analyzer in differentiating subclinical keratoconus and keratoconus from normal corneas.

Methods:

This prospective comparative study included 136 normal eyes, 23 eyes with subclinical keratoconus, and 51 keratoconic eyes. In each eye, keratometric values, pachymetry, elevation parameters and surface indices were evaluated. Receiver operating characteristic (ROC) curves were calculated and quantified by using the area under the curve (AUC) to compare the sensitivity and specificity of the measured parameters and to identify optimal cutoff points for differenciating subclinical keratoconus and keratoconus from normal corneas. Several model structures including keratometric, pachymetric, elevation parameters and surface indices were analyzed to find the best model for distinguishing subclinical and clinical keratoconus. The data sets were also examined using the non-parametric “classification and regression tree” (CRT) technique for the three diagnostic groups.

Results:

Nearly all measured parameters were strong enough to distinguish keratoconus. However, only the radius of best fit sphere and keratometry readings had an acceptable predictive accuracy to differentiate subclinical keratoconus. Elevation parameters and surface indices were able to differentiate keratoconus from normal corneas in 100% of eyes. Meanwhile, none of the parameter sets could effectively discriminate subclinical keratoconus; a 3-factor model including keratometric variables, elevation data and surface indices provided the highest predictive ability for this purpose.

Conclusion:

Surface indices measured by the Galilei analyzer can effectively differentiate keratoconus from normal corneas. However, a combination of different data is required to distinguish subclinical keratoconus.

Keratoconus in Inflammatory Bowel Disease Patients: A Cross-sectional Study

BACKGROUND AND AIMS

Increasing evidence suggests that keratoconus may have an inflammatory component. The possible association of keratoconus with inflammatory bowel disease (IBD) has yet to be determined. The aim of this study was to determine the prevalence of keratoconus and suspect keratoconus in patients with IBD.

METHODS

All consecutive adult IBD patients seen in the Department of Gastroenterology, Nancy, University Hospital, France, between March 2014 and June 2014 were included. Pregnant women, rigid lens wearers, patients with a family history of keratoconus and patients with a history of refractive surgery were excluded. A control group of healthy subjects was included. All included patients underwent a corneal topography (OPD-Scan III, Nidek) to detect keratoconus or suspect keratoconus. Rabinowitz videokeratographic indices were the basis of corneal topography interpretation.

RESULTS

Two hundred and one IBD patients were included, 150 with Crohn's disease and 51 with ulcerative colitis. Mean age was 38.7 years and 121 were women. Mean disease duration was 10.8 years. Two IBD patients were diagnosed with keratoconus (1%) and 38 with suspect keratoconus (18.9%). Overall prevalence of keratoconus and suspect keratoconus was 19.9% (95% confidence interval [CI] 17.5-22.0). None of the 100 healthy subjects had keratoconus, while three were diagnosed with suspect keratoconus (p = 0.0002 versus IBD patients). Only smoking was identified as a risk factor (p = 0.029), especially in Crohn's disease.

CONCLUSION

Inflammatory bowel disease patients may carry an increased risk of keratoconus and suspect keratoconus, smoking further increasing this risk. This supports the hypothesis of an inflammatory origin of keratoconus.

Keratoconus: an inflammatory disorder?

Keratoconus has been classically defined as a progressive, non-inflammatory condition, which produces a thinning and steepening of the cornea. Its pathophysiological mechanisms have been investigated for a long time. Both genetic and environmental factors have been associated with the disease. Recent studies have shown a significant role of proteolytic enzymes, cytokines, and free radicals; therefore, although keratoconus does not meet all the classic criteria for an inflammatory disease, the lack of inflammation has been questioned. The majority of studies in the tears of patients with keratoconus have found increased levels of interleukin-6 (IL-6), tumor necrosis factor-α(TNF-α), and matrix metalloproteinase (MMP)-9. Eye rubbing, a proven risk factor for keratoconus, has been also shown recently to increase the tear levels of MMP-13, IL-6, and TNF-α. In the tear fluid of patients with ocular rosacea, IL-1α and MMP-9 have been reported to be significantly elevated, and cases of inferior corneal thinning, resembling keratoconus, have been reported. We performed a literature review of published biochemical changes in keratoconus that would support that this could be, at least in part, an inflammatory condition.

Sensitivity and specificity of posterior and anterior corneal elevation measured by orbscan in diagnosis of clinical and subclinical keratoconus

PURPOSE

To determine the sensitivity and specificity of anterior and posterior corneal elevation parameters as determined by Orbscan II (Bausch and Lomb, Rochester, NY, USA) in discriminating between (sub) clinical keratoconus (KCN) and normal corneas.

METHODS

This prospective case-control study included 28 eyes with subclinical KCN, 65 with clinical KCN and 141 normal corneas. Anterior and posterior corneal elevation was measured and compared in the central 5-mm corneal zone using Orbscan II.

RESULTS

Receiver operating curves (ROC) curve analyses for posterior corneal elevation showed predictive accuracy in both KCN and subclinical KCN with an area under the curve (AUC) of 0.97 and 0.69, respectively while optimal cutoff points were 51 μm for KCN and 35 μm for subclinical KCN. These values were associated with sensitivity and specificity of 89.23% and 98.58%, respectively, for KCN; and 50.00% and 88.65% for subclinical KCN. ROC curve analyses for anterior corneal elevation showed predictive accuracy in both KCN and subclinical KCN with AUC of 0.97 and 0.69, respectively while optimal cutoff points were 19 μm for KCN and 16 μm for subclinical KCN. These values were associated with sensitivity and specificity of 93.85% and 97.16%, respectively, for KCN; and 60.71% and 87.94% for subclinical KCN.

CONCLUSION

Anterior and posterior corneal elevation data obtained by Orbscan II can well discriminate between KCN and normal corneas, however the reliability of their indices is lower in differentiating subclinical KCN from normal cases.

Comparison of stromal corneal nerves between normal and keratoconus patients using confocal microscopy

OBJECTIVE

To evaluate the differences in stromal corneal nerves between normal patients and keratoconus patients.

MATERIAL AND METHODS

A total of 140 eyes of 70 normal patients (group A) and 122 eyes of 87 keratoconus patients (group B) were examined with the confocal microscope, with a central scan of the total corneal thickness being taken. The morphology and thickness of the corneal stromal nerves were evaluated by using the Navis v. 3.5.0. software. Nerve thickness was obtained from the mean between the widest and the narrowest portions of each stromal nerve.

RESULTS

Corneal stromal nerves were observed as irregular linear hyper-reflective structures with wide and narrow portions in all cases. Mean corneal stromal nerves thickness in group A was 5.7±1.7 (range from 3.3 to 10.4 μ), mean corneal stromal nerves thickness in group B was 7.2±1.9 (range from 3.5 to 12.0 μ). There was a statistical significant difference (P<.05) in stromal corneal nerves thickness between group A and group B.

CONCLUSION

Stromal corneal nerves morphology was similar in both groups, but stromal nerves were thicker in keratoconus patients.

Keratoconus diagnosis with optical coherence tomography–based pachymetric scoring system

PURPOSE

To develop an optical coherence tomography (OCT) pachymetry map–based keratoconus risk scoring system.

SETTINGS

Doheny Eye Institute, University of Southern California, Los Angeles, California, and Brass Eye Center, New York, New York, USA; Department of Ophthalmology, Affiliated Eye Hospital of Wenzhou Medical College, Wenzhou, China.

DESIGN

Cross-sectional study.

METHODS

Fourier-domain OCT was used to acquire corneal pachymetry maps in normal and keratoconus subjects. Pachymetric variables were minimum, minimum−median, superior–inferior (S–I), superonasal–inferotemporal (SN–IT), and the vertical location of the thinnest cornea (Ymin). A logistic regression formula and a scoring system were developed based on these variables. Keratoconus diagnostic accuracy was measured by the area under the receiver operating characteristic (ROC) curve.

RESULTS

One hundred thirty-three eyes of 67 normal subjects and 82 eyes from 52 keratoconus subjects were recruited. The keratoconus logistic regression formula = 0.543 × minimum + 0.541 × (S–I) − 0.886 × (SN–IT) + 0.886 × (minimum–median) + 0.0198 × Ymin. The formula gave better diagnostic power with the area under the ROC than the best single variable (formula = 0.975, minimum = 0.942; P<.01). The diagnostic power with the area under the ROC of the keratoconus risk score (0.949) was similar to that of the formula (P=.08).

CONCLUSION

The OCT corneal pachymetry map–based logistic regression formula and the keratoconus risk scoring system provided high accuracy in keratoconus detection. These methods may be useful in keratoconus screening.

Risk Assessment for Ectasia after Corneal Refractive Surgery

PURPOSE

To analyze the epidemiologic features of ectasia after excimer laser corneal refractive surgery, to identify risk factors for its development, and to devise a screening strategy to minimize its occurrence.

DESIGN

Retrospective comparative and case-control study.

PARTICIPANTS

All cases of ectasia after excimer laser corneal refractive surgery published in the English language with adequate information available through December 2005, unpublished cases seeking treatment at the authors' institution from 1998 through 2005, and a contemporaneous control group who underwent uneventful LASIK and experienced a normal postoperative course.

METHODS

Evaluation of preoperative characteristics, including patient age, gender, spherical equivalent refraction, pachymetry, and topographic patterns; perioperative characteristics, including type of surgery performed, flap thickness, ablation depth, and residual stromal bed (RSB) thickness; and postoperative characteristics including time to onset of ectasia.

MAIN OUTCOME MEASURES

Development of postoperative corneal ectasia.

RESULTS

There were 171 ectasia cases, including 158 published cases and 13 unpublished cases evaluated at the authors' institution. Ectasia occurred after LASIK in 164 cases (95.9%) and after photorefractive keratectomy (PRK) in 7 cases (4.1%). Compared with controls, more ectasia cases had abnormal preoperative topographies (35.7% vs. 0%; P<1.0x10(-15)), were significantly younger (34.4 vs. 40.0 years; P<1.0x10(-7)), were more myopic (-8.53 vs. -5.09 diopters; P<1.0x10(-7)), had thinner corneas before surgery (521.0 vs. 546.5 microm; P<1.0x10(-7)), and had less RSB thickness (256.3 vs. 317.3 microm; P<1.0x10(-10)). Based on subgroup logistic regression analysis, abnormal topography was the most significant factor that discriminated cases from controls, followed by RSB thickness, age, and preoperative corneal thickness, in that order. A risk factor stratification scale was created, taking all recognized risk factors into account in a weighted fashion. This model had a specificity of 91% and a sensitivity of 96% in this series.

CONCLUSIONS

A quantitative method can be used to identify eyes at risk for developing ectasia after LASIK that, if validated, represents a significant improvement over current screening strategies.

Topographic Indications of Emerging Keratoconus in Teenage New Zealanders

PURPOSE

To screen a population of teenagers for emerging topographic signs of keratoconus (KC), with particular reference to ethnicity.

METHODS

Corneal topography, visual acuity, and an environmental risk factor analysis were included in a screening program designed to identify early indications of potential KC in teenagers. Two schools from central North Island, New Zealand, were invited to participate: one with predominantly Maori/Polynesian students and the other with students of mainly European descent.

RESULTS

A total of 198 Maori/Polynesian, 16.8 +/- 1.05 years of age, and 243 European students, 16.2 +/- 1.3 years of age, participated in the study. Corneal topography suggestive strongly of KC was evident in 3 Maori/Polynesian [1.2%; 95% confidence interval (CI): 0.3-4.3] and no European students (0%; 95% CI, 0%-1.5%). Anomalous corneal topography reminiscent of emerging KC in at least 1 eye were found in 19% (95% CI, 15.6%-22.9%). A significant difference (P = 0.0014) in the percentage of suspected KC was found between European students (12.9%; 95% CI, 9.2%-17.9%) and Maori/Polynesian students (26.9%; 95% CI, 21.0%-33.7%). In multivariate analyses, the significant independent predictors of probable or suspected KC included being Maori/Polynesian [odds ratio (OR) = 2.1; 95% CI, 1.25-3.54; P = 0.0052], increasing age (OR = 1.4; 95% CI, 1.10-1.80; P = 0.0067), and a history of hayfever (OR = 2.0; 95% CI, 1.16-3.59; P = 0.013). Topographical indicators that were associated significantly with suspected KC included central keratometry (P < 0.0001), astigmatism (P = 0.014), and inferior-superior asymmetry (P < 0.0001).

CONCLUSIONS

Although only a longitudinal study will determine the proportion of true KC candidates, these data provide evidence of ethnicity-related differences in corneal topography in teenage New Zealanders.

Penetrating keratoplasty versus intrastromal corneal ring segments to correct bilateral corneal ectasia: Preliminary study

PURPOSE

To describe the outcomes over time in patients with corneal ectasia pathology treated with intrastromal corneal ring segments (Intacs, Addition Technology, Inc.) in 1 eye and penetrating keratoplasty (PKP) in the other eye.

SETTING

Clinica de Cornea, Centro Medico Docente La Trinidad, Caracas, Venezuela.

METHODS

A nonrandomized comparative study and analysis of retrospective data comprised 17 patients who had PKP in 1 eye and Intacs implantation in the other eye. Patients were classified into 2 groups: asymmetric (different grade of keratoconus in each eye) and symmetric (same grade of keratoconus in both eyes). Parameters analyzed included uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), and keratometry (flat and steep values and astigmatism readings). Follow-up after PKP was at 24 hours and 6 and 24 months and after Intacs implantation, at 24 hours and 3 and 10 months.

RESULTS

In both groups, UCVA improved and the corneal shape was normal. No patient lost a line of acuity, and BCVA improved in both groups.

CONCLUSIONS

Eyes with Intacs had a shorter recovery time than eyes having PKP. The eyes with Intacs had no complications. Complications in eyes with PKP included cataract, graft rejection, and elevated intraocular pressure. Thus, Intacs segments may delay or prevent the need for a corneal graft, although longer follow-up is needed.

Post-laser in-situ keratomileusis ectasia: current understanding and future directions

PURPOSE OF REVIEW

The aim of this article is to review the causes, risk factors, management, and future research directions for corneal ectasia after laser in situ keratomileusis.

RECENT FINDINGS

Complex corneal biomechanical processes influence the integrity of the normal and postoperative cornea, and developing an understanding of these processes facilitates recognition of risk factors for ectasia after laser in-situ keratomileusis. Currently identified risk factors include keratoconus, high myopia, low residual stromal bed thickness from excessive ablation or thick flap creation, and defined topographic abnormalities such as forme fruste keratoconus and pellucid marginal corneal degeneration. Ectasia can also rarely occur in patients without currently identifiable risk factors, and future identification of at-risk patients may be facilitated by corneal interferometry and corneal hysteresis measurements. Utilization of intraoperative pachymetry measurements at the time of surgery and confocal microscopy prior to enhancement to measure residual stromal bed thickness should avoid unanticipated low residual stromal bed thickness. Management options for ectasia after laser in situ keratomileusis include intraocular pressure reduction, rigid gas permeable contact lenses, and intracorneal ring segments, in addition to corneal transplantation. In the future, collagen cross-linking may reduce corneal steepening and improve refractive error.

SUMMARY

When ectasia develops, early recognition and proper management are essential to prevent progression, to promote visual rehabilitation, and to reduce the need for corneal transplantation for these patients.