Evaluation of corneal topography, pachymetry and higher order aberrations for detecting subclinical keratoconus.

PURPOSE: To compare corneal topography, pachymetry and higher order aberrations in keratoconic and normal eyes; to investigate their association in keratoconic eyes; and to determine their diagnostic ability for detecting subclinical keratoconus in a Nepalese population. METHODS: Ninety-six eyes of 48 keratoconus patients and 50 normal eyes of 50 control subjects were included in this study. The eyes of keratoconus patients were classified into four different study groups: subclinical, stage 1, stage 2 and advanced stage keratoconus. In each eye, corneal topography, pachymetry and corneal aberrometry indices were measured using a Sirius corneal tomographer. The study parameters of keratoconic eyes were compared with normal eyes, and the possible association of corneal aberrometry with topography and pachymetry indices was investigated. The area under curve (AUC) of receiver operating characteristic (ROC) curves along with optimal cutoff values with best sensitivity and specificity were also determined for each index to detect subclinical keratoconus. RESULTS: All the indices except average keratometry measurements (Kavg and mmavg ) and spherical aberration (SA) were found to be significantly different in subclinical keratoconus compared to the control group (p < 0.05). In keratoconic eyes, all corneal aberrations were significantly correlated with the topography and pachymetry indices (range of ρ: -0.25 to 0.96; all p < 0.05) except for trefoil and minimum corneal thickness (Thkmin ). All the indices except Kavg , mmavg and SA showed excellent diagnostic ability (AUC > 0.90) in detecting subclinical keratoconus. The cutoff values proposed for the asymmetry index of the corneal back surface (SIb ), Strehl ratio of point spread function (PSF), coma and Baiocchi-Calossi-Versaci index of corneal back surface (BCVb ) each showed excellent sensitivity (100%) and specificity (≥97%). CONCLUSIONS: Corneal higher order aberrations were found to be significantly elevated in subclinical keratoconus compared to healthy controls. SIb , PSF, coma and BCVb were identified as the most powerful Sirius indices for the detection of subclinical keratoconus.

SubFoveal Choroidal Imaging in High Myopic Nepalese Cohort.

Purpose: Evidence suggests that choroid is thinner in myopes as compared to nonmyopes. However, choroidal thickness varies with the refractive error, age, axial length, and ethnicity. The purpose of this study was to determine the subfoveal choroidal thickness (SFCT) in high myopic Nepalese subjects and to investigate its association with the mean spherical equivalent refractive error (MSE), axial length, and age. Methods: Ninety-two eyes of 92 high myopic subjects (MSE ≤ -6 diopters) and 83 eyes of 83 emmetropic subjects (MSE: 0.00 Diopters) were included in the study. SFCT was assessed using spectral domain optical coherence tomography, and the axial length was measured using partial coherence interferometry. SFCT was measured manually using the inbuilt tool within the imaging software. Results: SFCT in the high myopic subjects was significantly thinner (mean ± SD: 224.17 ± 68.91 µm) as compared to the emmetropic subjects (353.24 ± 65.63 µm) (mean difference, 127.76 ± 130.80 µm, and p < 0.001). In high myopic subjects, there was a significant negative correlation of choroidal thickness with the axial length (rho = -0.75; p < 0.001) and MSE (rho = -0.404; p < 0.01). Regression analysis demonstrated a decrease of choroidal thickness by 40.32 µm (p < 0.001) for every 1 millimeter increase in the axial length and by 11.65 µm (p < 0.001) for every 1 diopter increase in the MSE. Conclusion: High myopic Nepalese subjects had significantly thinner choroid as compared to emmetropes. The MSE and axial length were inversely correlated with the SFCT. Age had no effect on SFCT in this study. These findings may have implications in interpreting choroidal thickness values in clinical and epidemiological studies in myopes, especially in the south Asian population.

Sub-Foveal Choroidal Thickness In Healthy Nepalese Population.

PURPOSE: This study was conducted primarily to measure sub-foveal choroidal thickness (SFCT) in healthy Nepalese population. Also, the correlation of SFCT with age, inter-eye difference of SFCT, inter-gender variation and inter-ethnic variation of SFCT was observed. MATERIALS AND METHODS: A cross-sectional, hospital based study in 162 participants (324 eyes) of six ethnic groups (Brahmin, Chhetri, Newar, Tamang, Muslim, and Gurung) was conducted. The mean age of participants was 37.37 ± 15.02 years. All the participants underwent SFCT measurement using Spectral Domain Optical Coherence Tomography (Spectralis HRA+OCT, Heidelberg Engineering, Germany) with the help of in-built caliber. Age, inter-gender, inter-eye and inter-ethnic differences in SFCT were recorded and analyzed. RESULTS: The average SFCT of right eye (RE) and left eye (LE) was 307.98 ± 74.64 µm and 312.63 ± 76.90 µm respectively, with average SFCT of 310.31 ± 75.70 µm for both eyes. SFCT of only the RE was selected for further calculation due to insignificant inter-eye difference of SFCT (p = 0.128). There was a significant negative correlation of SFCT with age (r = -0.705, p = 0.01). A regression analysis showed thinning of SFCT by 3.50 ± 0.278 µm per year. In another context, SFCT of male and female was 305.49 ± 79.72 µm and 313.55 ± 70.76 µm respectively. However, there was no significant inter-gender difference (p = 0.51). Similarly, inter-ethnic variations of SFCT was also statistically non -significant (p = 0.74). CONCLUSION: SFCT was negatively correlated with the age of participants, implying a decrease in choroidal thickness (CT) with an increase in age. Age can be considered as an important factor in the measurement of SFCT. Gender and ethnic groups did not have a significant role in the measurement and comparison of SFCT.