Biomechanical properties of early keratoconus: Suppressed deformation signal wave.

PURPOSE: To examine the diagnostic validity of different corneal biomechanical parameters for the detection of early keratoconus METHODS: Sixty-one eyes with a diagnosis of early keratoconus and 61 topographically normal eyes were enrolled in the study. All participants underwent testing with the Ocular Response Analyzer (ORA), and 40 indices from each cornea were included in the analysis. RESULTS: The mean (standard deviation: SD) of keratometry and central corneal thickness in keratoconic corneas was 46.9 (2.5) diopter (D) and 473 (31) µm, respectively. Of the 40 evaluated indices, 32 showed a significant difference between the two groups using t-test (p<0.05). According to the results of logistic regression, the indices of height from the lowest to the highest point in peak 2 (H21) and corneal resistance factor (CRF) with R2=0.79 were the best predictors of early keratoconus (p<0.001). H21 ≤190 with a sensitivity and specificity of 87% and 91.8%, respectively, and CRF≤8.6 with sensitivity and specificity of 87% and 85.3%, respectively, yielded an overall diagnostic accuracy of 97.3%. CONCLUSION: This study results point to the important role of novel waveform-derived indices measured by ORA, along with conventional biomechanical indices, for the early diagnosis of keratoconus. The best predictors of keratoconus in its early stages are H21 and CRF which showed very high sensitivity and specificity for the detection of early keratoconus.

Pentacam top indices for diagnosing subclinical and definite keratoconus.

PURPOSE: To determine pachymetric, aberrometric, and topometric indices in patients with definite and subclinical keratoconus and the validity of these indices in the diagnosis of keratoconus. METHODS: We evaluated 262 keratoconic and 97 healthy eyes in this study. Pentacam HR examination was performed for all participants, and the data of all pachymetric, aberrometric, and topometric indices was extracted for the study population. RESULTS: The average of all evaluated pachymetric and topometric indices and the 3rd and 5th order vertical coma aberrations showed a significant difference between the study groups (p < 0.001). Belin/Ambrosio Deviation Display (BAD_D), Index of Vertical Asymmetry (IVA), Index of Surface Variance (ISV), and 5th order vertical coma aberration were identified as the best diagnostic criteria for the diagnosis of subclinical keratoconus (R (2) = 0.65, p <0.001), and BAD_D, mean keratometry and 3rd order vertical coma aberration were identified as the best diagnostic criteria for the diagnosis of definite keratoconus (R (2) = 0.91, p <0.001). The sensitivity and specificity of the above-mentioned models were 83.6% and 96.9%, and 97.9% and 96.9%, respectively. CONCLUSION: Simultaneous evaluation of BAD_D, 5th order vertical coma aberration, IVA, and ISV, especially when the pattern of the corneal curvature is normal, can detect subclinical keratoconus with high sensitivity and specificity. As for definite keratoconus, each of the BAD_D, mean keratometry, and 3rd order vertical coma aberration indices has a desirable diagnostic validity. However, the aforementioned indices do not negate the importance of widely recognized and acceptable indices like keratometry and central corneal thickness.

Corneal elevation and keratoconus indices in a 40- to 64-year-old population, Shahroud Eye Study.

PURPOSE: To determine the corneal elevation values and keratoconus indices in the 40- to 64-year-old population and their changes with aging. METHODS: The 6311 invitees of this study were selected through random cluster sampling, and 5190 of them participated in the study (response rate = 82.2%). Here, we analyzed results of Pentacam acquisitions in 4148 respondents. Cases of keratoconus and forme fruste keratoconus (FFKC) were determined using topography and clinical data. Studied variables included keratoconus indices, central corneal thickness readings, maximum elevations on the anterior and posterior surfaces, and elevation values at the thinnest point, anterior steepest point, and posterior steepest point in healthy, FFKC, and keratoconus groups. RESULTS: In all subjects, the mean maximum elevations were 6.80 ± 5.0 µm and 16.60 ± 7.7 µm on the anterior and posterior corneal surfaces, respectively. Maximum elevation values on the anterior and posterior corneal surfaces showed significant correlations in the keratoconus, FFKC, and healthy groups (P < 0.002). Maximum anterior elevation correlated with age (r = 0.11, P < 0.001), but maximum posterior elevation showed no such correlation (P = 0.476). Keratoconus indices demonstrated significant changes with age (P < 0.001). CONCLUSION: Anterior elevation values slightly increase with age, and keratoconus indices change as well. Elevation readings and keratoconus indices in the keratoconus group and FFKC cases are higher than the healthy corneas although their values could be compared with other studies on younger participants.

Prevalence of Refractive Errors among High School Students in Western Iran.

PURPOSE: To determine the prevalence of refractive errors among high school students. METHODS: In a cross-sectional study, we applied stratified cluster sampling on high school students of Aligoudarz, Western Iran. Examinations included visual acuity, non-cycloplegic refraction by autorefraction and fine tuning with retinoscopy. Myopia and hyperopia were defined as spherical equivalent of -0.5/+0.5 diopter (D) or worse, respectively; astigmatism was defined as cylindrical error >0.5 D and anisometropia as an interocular difference in spherical equivalent exceeding 1 D. RESULTS: Of 451 selected students, 438 participated in the study (response rate, 97.0%). Data from 434 subjects with mean age of 16±1.3 (range, 14 to 21) years including 212 (48.8%) male subjects was analyzed. The prevalence of myopia, hyperopia and astigmatism was 29.3% [95% confidence interval (CI), 25-33.6%], 21.7% (95%CI, 17.8-25.5%), and 20.7% (95%CI, 16.9-24.6%), respectively. The prevalence of myopia increased significantly with age [odds ratio (OR)=1.30, P=0.003] and was higher among boys (OR=3.10, P<0.001). The prevalence of hyperopia was significantly higher in girls (OR=0.49, P=0.003). The prevalence of astigmatism was 25.9% in boys and 15.8% in girls (OR=2.13, P=0.002). The overall prevalence of high myopia and high hyperopia were 0.5% and 1.2%, respectively. The prevalence of with-the-rule, against-the-rule, and oblique astigmatism was 14.5%, 4.8% and 1.4%, respectively. Overall, 4.6% (95%CI, 2.6-6.6%) of subjects were anisometropic. CONCLUSION: More than half of high school students in Aligoudarz had at least one type of refractive error. Compared to similar studies, the prevalence of refractive errors was high in this age group.

Corneal topography patterns in the Tehran eye study: warning about the high prevalence of patterns with a skewed radial axis.

PURPOSE: The purpose of this study is to determine the distribution of corneal topography patterns in Tehran. MATERIALS AND METHODS: In this population-based study, a total of 442 individuals were randomly selected by cluster sampling for complete ophthalmologic examination. A total of 404 (788 eyes) met the inclusion criteria and were enrolled in this study. Orbscan II (Bausch and Lomb Surgical, Salt Lake City, USA) was used to determine the anterior segment indices and axial power maps for each eye. RESULTS: On the basis of the axial power maps, the symmetric bowtie (SB) (29.0%) and asymmetric bowtie with inferior steepening (16.7%) patterns were the most prevalent and the irregular (3.3%) and superior steepening (1.5%) patterns the least prevalent. Asymmetric bowtie pattern with a skewed radial axis (AB-SRAX) was seen in 7.6% of eyes. These cases had both thinner and steeper corneas compared with round and SB ones (P < 0.014 and P < 0.006). Maximum anterior elevation in 5 mm zone, of AB-SRAX corneas were higher than other patterns (P < 0.01) except for superior steepened and inferior steepened ones. CONCLUSIONS: The distribution of corneal topographic patterns in Iranians seems like other Asian population on the whole. The 7.6% prevalence of AB-SRAX patterns may be a warning on keratoconus prevalence in our population. This is in line with recent regional reports.

Prevalence of keratoconus in a population-based study in Shahroud.

PURPOSE: To determine the prevalence of keratoconus in the 40- to 64-year-old population of Shahroud, Iran. METHODS: This study was done cross sectionally based on the data from the first phase of the Shahroud Eye Cohort Study. In this study, 6311 patients were selected using random cluster sampling, and 5190 patients (response rate = 82.2%) participated in the study. Here, the analysis was done on data pertaining to those whose topographic map (with Pentacam) had no errors. These patients were categorized as keratoconus, forme fruste keratoconus, and non-keratoconus. RESULTS: After applying the exclusion criteria, data from 4592 patients with a mean age of 50.83 ± 0.12 years were analyzed. Of these, 35 patients (0.76%) were diagnosed with keratoconus in at least 1 eye, and 47 patients (1.02%) were identified as having forme fruste keratoconus. The prevalence of keratoconus was 0.72% (95% confidence interval, 0.35-1.09) in men, and 0.79% (95% confidence interval, 0.43-1.15) in women (P = 0.793). The mean age of the keratoconic patients was 47.6, which was significantly lower than 50.9 of normal individuals (P < 0.001). The mean maximum keratometry and central corneal thickness in patients with keratoconus were 48.67 ± 3.6 diopters and 470 ± 29 µm, respectively. Keratoconus was associated with an 8.1 greater odds of visual impairment (P < 0.001). CONCLUSIONS: The prevalence of keratoconus in the Shahroud population is far higher than in western populations. Because of the high odds of visual impairment in this population, it can be a serious warning for the need to assess the prevalence and causes of keratoconus in the Middle Eastern region.