Estimation of the refractive index of the human cornea in vivo by non-invasive optical pachymetry

Session Details

Session Title: Imaging Anterior Segment

Session Date/Time: Sunday 08/10/2017 | 16:00-18:00

Paper Time: 16:06

Venue: Meeting Center Room I

First Author: : L.Tutchenko UKRAINE

Co Author(s): :    O. Horak   V. Sanin   S. Kosuba   S. Patel           

Abstract Details

Purpose:

To estimate the average refractive index (RI) of the cornea along the antero-posterior direction within the central optical zone using a modification of traditional optical pachymetry.

Setting:

National Medical Academy of Postgraduate Education named after P. L. Shupyk, Kyiv, Ukraine

Methods:

The ratio of the corneal optical section widths (OSW) observed during routine slit lamp biomicroscopy using different but fixed optical arrangements on the same cornea depends directly on the corneal RI. Corneal RI could be estimated using a calibration curve equating OSW ratios with known RI values. The OSW was measured for: [I]rigid contact lenses of various refractive RI(1.415-1.453) for calibration (1 investigator); [II]patients (50 right eyes only) by two operators for estimating inter-operator agreement; [III]104 patients to estimate effects of age on RI, using two fixed optical setups for a standard pachymeter.

Results:

[I] Calibrated RI=1.3592+0.0426x(r=0.9674,p=0.0016,n=6). 95% confidence intervals (CI) for the mean and slope were 1.428-1.438 and 0.027- 0.058 respectively. [II] Mean(±sd) corneal RI for operator one and two: 1.381±0.092 and 1.376±0.099 respectively,(p=0.824). ΔRI(±sd) between individual pairs of measurements of two operators: 0.004±0.045;95% CI=±0.001. There was no relationship between ΔRI and the mean of each pair of measurements (r=-0.1088,n=50,p=0.452). RMS difference between measurements obtained by operators was 0.007. [III] Mean(±sd) age was 44.96±20.87 (19-84). There was no significant association between RI and age (r=-0.0532,n=104,p=0.2976) or between genders (p=0.4177). The mean RI was 1.366±0.103.

Conclusions:

The refractive index of the human cornea along the antero-posterior axis can be reliably estimated using a modified application of traditional optical pachymetry. Inter-operator error was small and the mean values we observed were equivalent to those reported in the contemporary literature. However, we did not find any clear association between corneal refractive index and patient age.

Financial Disclosure:

NONE