Multivariate Analysis of the Ocular Response Analyzer's Corneal Deformation Response Curve for Early Keratoconus Detection.

Purpose. To thoroughly analyze corneal deformation responses curves obtained by Ocular Response Analyzer (ORA) testing in order to improve subclinical keratoconus detection. Methods. Observational case series of 87 control and 73 subclinical keratoconus eyes. Examination included corneal topography, tomography, and biomechanical testing with ORA. Factor analysis, logistic regression, and receiver operating characteristic curves were used to extract combinations of 45 corneal waveform descriptors. Main outcome measures were corneal-thickness-corrected corneal resistance factor (ccCRF), combinations of corneal descriptors, and their diagnostic performance. Results. Thirty-seven descriptors differed significantly in means between groups, and among them ccCRF afforded the highest individual diagnostic performance. Factor analysis identified first- and second-peak related descriptors as the most variable one. However, conventional biomechanical descriptors corneal resistance factor and hysteresis differed the most between control and keratoconic eyes. A combination of three factors including several corneal descriptors did not show better diagnostic performance than a combination of conventional indices. Conclusion. Multivariate analysis of ORA signals did not surpass simpler models in subclinical keratoconus detection, and there is considerable overlap between normal and ectatic eyes irrespective of the analysis model. Conventional biomechanical indices seem to already provide the best performance when appropriately considered.

Corneal asymmetry analysis by pentacam scheimpflug tomography for keratoconus diagnosis.

PURPOSE: To evaluate intereye corneal asymmetry in Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany) indices as a diagnostic method between normal patients and patients with keratoconus. METHODS: A retrospective, observational case series of 177 healthy, 44 indeterminate, and 121 patients with keratoconus classified by Pentacam ectasia detection indices, randomized to analysis and validation datasets. Intereye asymmetry in 20 Scheimpflug tomography corneal descriptors was calculated and compared to develop diagnostic models. RESULTS: Intereye asymmetry was not correlated with anisometropia in healthy controls but was correlated with the ectasia grade of the worse eye in patients with keratoconus. Patients with keratoconus had significantly greater intereye asymmetry in all descriptors except for relational thickness indices. Intereye asymmetry in front elevation at the thinnest corneal location afforded the single highest diagnostic performance (71% sensitivity and 85% specificity), whereas the best multivariate model combining intereye asymmetry in anterior and posterior keratometry, corneal thickness, and front and back elevation at the thinnest point provided 65% sensitivity and 97% specificity. Multivariate models upheld their performance in the validation dataset. Most (more than 90%) indeterminate patients, according to conventional Pentacam analysis, showed within-normal-range corneal asymmetry. CONCLUSIONS: Healthy corneas are markedly symmetric irrespective of anisometropia, but corneal asymmetry analysis does not provide sufficient sensitivity to be used alone for detecting keratoconus. However, its remarkable specificity suggests that it could be used combined with conventional single cornea Pentacam analysis to reduce the false-positive rate or in dubious cases.

Agreement between placido topography and Scheimpflug tomography for corneal astigmatism assessment.

PURPOSE: To evaluate inter-device agreement between Placido topography (iTrace; Tracey Technologies, Houston, TX) and Scheimpflug tomography (Pentacam; Oculus Optikgeräte GmbH, Wetzlar, Germany) for measuring corneal power and cylinder and axis of astigmatism. METHODS: Observational case series of 54 eyes from 54 subjects with no ocular disease. Main outcome measures were corneal power, cylinder power, and axis of astigmatism and their agreement was assessed by Bland­Altman analysis. RESULTS: For corneal power and corneal cylinder, 95% limits of agreement (LoA) were considered good (−0.38 to 0.45 diopters [D] and −0.49 to 0.27 D, respectively). In contrast, the 95% LoA for corneal astigmatism axis exceeded the clinically relevant margins (−14.8 to 13.5): 28 eyes (52%) had a greater than 5° difference, 10 eyes (19%) had a greater than 10° difference, and 4 eyes (7%) had a greater than 20° difference between instruments. This absolute difference was significantly correlated with average corneal cylinder (Spearman's r = −0.379, P = .005) but not with average corneal power. In eyes with corneal astigmatism 2 D or greater, the 95% LoA for axis were −8.7° to 6.7°, whereas in those with corneal astigmatism less than 1 D, the 95% LoA for axis were −19.1° to 16.6°. CONCLUSIONS: Placido topography and Scheimpflug tomography show good agreement for corneal power and cylinder, but not for corneal astigmatism axis. These instruments could be used interchangeably only in eyes with corneal astigmatism of 2 D or greater.

Pentacam Scheimpflug tomography findings in topographically normal patients and subclinical keratoconus cases.

PURPOSE: To evaluate Pentacam ectasia detection indices in topographically normal patients and in subclinical keratoconus cases. DESIGN: Prospective, observational case series. METHODS: setting: Institutional. patients: Group 1 comprised 1 eye from 189 patients with unremarkable topography and Groups 2 and 3 included the better and worse eyes, respectively, of 55 keratoconic patients. Group 2 eyes with normal topography (n = 37) were considered subclinical keratoconus cases. observation procedure: Pentacam Scheimpflug tomography. main outcome measures: Eleven Pentacam ectasia detection indices. RESULTS: All Pentacam ectasia indices significantly differed between Groups 1 and 2 and were correlated with keratoconus grade. Only 99 eyes (52%) in Group 1 had normal values for every index, whereas 7 subclinical keratoconus eyes (19%) showed 2 or fewer abnormal indices. Standardized relational thickness and overall deviation indices had 73% and 89% sensitivity for subclinical keratoconus, respectively. Both average and maximum pachymetric progression indices offered 84% sensitivity while maximum relational thickness index showed 78% sensitivity for subclinical keratoconus. Optimized cutoff values for subclinical keratoconus increased the sensitivity of the standardized and maximum relational thickness indices. CONCLUSION: Pentacam Scheimpflug tomography can detect most subclinical keratoconus cases with unremarkable topography, but performance is not as good as reported and varies considerably for each index. The overall deviation, average and maximum pachymetric progression, and maximum relational thickness indices offer the highest sensitivity, which can be improved by using optimized cutoff values. Specificity constitutes an issue for some indices and up to 10% of subclinical keratoconus cases may go undetected by this technology.

Combining ocular response analyzer metrics for corneal biomechanical diagnosis.

PURPOSE: To evaluate corneal biomechanical properties in non-keratoconic myopic eyes and to identify descriptors for improving the specificity of the Ocular Response Analyzer (ORA) (Reichert Ophthalmic Instruments, Depew, NY) testing for subclinical keratoconus detection. METHODS: Observational case series of 52 non-keratoconic non-myopic eyes and 97 non-keratoconic myopic eyes (spherical equivalent < -5 diopters [D]) in dataset 1 and 87 non-keratoconic eyes and 73 eyes with subclinical keratoconus in dataset 2. Examination included corneal topography, tomography, and biomechanical testing with the ORA. Receiver operating characteristic curves and logistic regression were used to identify optimal combinations of biomechanical indices for keratoconus detection. Main outcome measures were corneal thickness-corrected hysteresis (DifCH) and resistance factor (DifCRF), the difference between these two (CH-CRF), and the diagnostic performance of their combinations. RESULTS: Compared to non-keratoconic non-myopic eyes, non-keratoconic myopic eyes with flat corneas (average corneal power < 44.0 D) had reduced DifCH (mean ± standard deviation, 0.11 ± 1.27 vs -0.79 ± 1.50, P < .01) and DifCRF (0.24 ± 1.16 vs -0.70 ± 1.59, P < .01) values, whereas non-keratoconic myopic eyes with steep corneas showed no difference. Keratoconic eyes exhibited lower DifCH and DifCRF values than non-keratoconic myopic eyes. Combinations of DifCH, DifCRF, and CH-CRF had increased specificity (> 80%) for subclinical keratoconus compared to the DifCRF index alone (71%). CONCLUSIONS: In biomechanical keratoconus screening, some non-keratoconic myopic eyes show altered ocular biomechanical properties and are identified as false-positive cases. The low specificity of DifCRF when dealing with these non-keratoconic eyes could be improved by considering additional biomechanical descriptors such as DifCH and CH-CRF, which seem to be indicative of the aforementioned biomechanical profile.

Corneal power is correlated with anterior chamber diameter.

PURPOSE: Although corneal power and axial length are known to be inversely correlated, the biological determinants of corneal power are unknown. To elucidate this correlation further, study authors investigated the relationships among corneal power, corneal diameter, anterior chamber diameter, and axial length in a sample of human adults. METHODS: The eyes of 61 subjects seen consecutively in an eye clinic were studied with a high-resolution optimal coherence tomography (OCT) pachymetry device and ophthalmic optical biometer. The relationships between corneal power, white-to-white (WTW) corneal diameter, anterior chamber diameter, and axial length were assessed with Pearson correlations. RESULTS: The mean age of the 61 subjects was 48.7 ± 19.4 years. Corneal power was negatively correlated with axial length (r = -0.303, P < 0.01); WTW corneal diameter (r = -0.399, P < 0.001); and most interestingly, anterior chamber diameter (r = -0.646, P < 0.001). There was also a positive correlation between anterior chamber diameter and axial length (r = 0.489, P < 0.001). CONCLUSIONS: Greater anterior chamber diameters were associated with flatter corneas and, conversely, smaller anterior chamber diameters with steeper corneas. The growth patterns of the anterior segment may be determinants of corneal power.

Improved keratoconus detection by ocular response analyzer testing after consideration of corneal thickness as a confounding factor.

PURPOSE: To compare corneal hysteresis (CH) and corneal resistance factor (CRF) between normal eyes and eyes with keratoconus correcting for the effect of central corneal thickness (CCT) and to estimate keratoconus detection sensitivity and specificity of these parameters. METHODS: Observational case series of 102 normal eyes (control group) and 77 eyes with keratoconus (keratoconus group). Examination included corneal topography, tomography, and biomechanical testing with the Ocular Response Analyzer (Reichert Technologies). The confounding effect of CCT was controlled by stratification (20-µm CCT intervals) and linear transformation. Receiver operating characteristic curves were used to identify optimal CH and CRF cutoff points for keratoconus detection. Main outcome measures were CCT, CH, CRF, and diagnostic performance of CH and CRF. RESULTS: Corneal hysteresis and CRF were positively correlated to CCT in both groups. In the control versus keratoconus group, CH was 9.79 ± 1.51 vs 8.49 ± 1.48 (P<.0001) and CRF was 9.55 ± 1.64 vs 7.24 ± 1.43 (P<.0001), respectively. Only CRF remained significantly lower in eyes with keratoconus after CCT stratification in 20-µm intervals, and keratoconus grade influenced CH and CRF. Transformed CH and CRF data confirmed these results. Sensitivity and specificity of CRF cutoff points ranged between 83% and 94% and 69% and 83%, respectively. True positive rate for CRF in eyes with keratoconus with normal topography was 84%. CONCLUSIONS: Corneal resistance factor was better than CH for detecting keratoconic corneas once the effect of CCT on ORA measurements was considered, even for topographically unaffected fellow eyes of patients with keratoconus. The CCT-corrected CRF cutoff values and transformed indices may be of clinical use.

Family history of myopia is not related to the final amount of refractive error in low and moderate myopia.

BACKGROUND: Previous research has found an association between family history and presence of myopia. It is possible that family history also could be related to the final amount of refractive error developed. If that were true, then family history of myopia could have predictive value for the amount of refractive error a child or young adult would develop after first lens prescription. METHODS: Consecutive myopic adult outpatients were enrolled during the year 2003. They received a refractive examination and a questionnaire concerning age of onset of lens use, academic achievement, and parental history of myopia. RESULTS: In the group of 271 mild and moderate myopes (myopia lower than -6 D) there were 157 subjects with at least one myopic parent and 114 subjects without family history. The presence or absence of a family history of myopia was not associated with either the final myopic refractive error (-3.2 +/- 1.5 D and -2.9 +/- 1.3 D, respectively, P = 0.08) or the age of onset of lens use (17.0 +/- 6.2 years vs 18.1 +/- 6.7 years, respectively, P = 0.15). CONCLUSIONS: In the present retrospective study of a clinical sample of mild and moderate myopic subjects, family history of myopia did not show predictive value for either the age of first prescription, or the final refractive error developed in adulthood.

Family history and reading habits in adult-onset myopia.

PURPOSE: A retrospective study was developed to evaluate risk factors in adult-onset myopia. METHODS: Subjects included were 25 to 35 years old. There were 116 non-myopic subjects in the control group and 66 myopic subjects with first lens prescription at age 17 or later. Subjects received a questionnaire about academic achievement, daily hours of reading during years of study, and family history of myopia. RESULTS: The level of academic achievement was similar for myopic and non-myopic groups in this sample. Myopia was associated with family history (chi(2) = 6.131, p