Abstract
Purpose :
The refractive index of the crystalline lens in the human eye is a critical parameter to determine the refractive performance of the eye during accommodation. The accommodative changes in the lens refractive index, however, have not been well characterized because of the difficulties to access the lens refractive index in vivo. Recently an anterior segment OCT (AS-OCT) equipped ray-traceable Scheimpflug imaging (RTSI) system was successfully developed to measure the lens refractive index in vivo. The purpose of this study was to measure accommodative changes of the lens refractive index for a group of young adults by using the new system.
Methods :
An AS-OCT equipped RTSI system was used to measure the refractive index of the lens in the right eyes for 12 subjects (aged 22 to 26 yrs old; Rx from -4.25 to +0.50D) during accommodation from 0.00D to 4.00D. The accommodation was induced by a Badal
system, with which the refractive error for myopic subjects was corrected also. The pupil was dilated with two doses of phenylephrine for RTSI imaging. The AS-OCT and RTSI images were processed by using a self-developed MatLab program to trace the light
ray and calculate the lens refractive index. The derived lens refractive index represents the average refractive index (Nav ) along the light ray pathway within the lens.
Results :
From 0D to 4D accommodation, the mean Nav along the central ray for this group of subjects was found to change from 1.397±0.010 to 1.414 ±0.016, while the mean central lens thickness was increased from 3.613±0.294mm to 3.834±0.340mm. Substantial individual variation in the accommodative changes in lens N av was observed among this group of subjects with a range from 0.001 to 0.022. For off-axis rays, the Nav decreases with the distance of the ray from the lens axis and forms a function across the
pupil diameter. As the eye accommodates, the mean Nav function becomes more curved.
Conclusions :
The Nav of the lens increases with accommodation, and the amount of Nav increase varies from individual eye to individual eye. The accommodative change of the lens refractive index needs to be taken into account for optically measuring lens shape and axial length of the whole eye. The results provide basic information for characterizing the accommodative performance of the human eye and also designing an accommodative intraocular lens.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.