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  11. In Vivo Changes In The Gradient Of Refractive Index Distribution In The Accommodating Human Lens

In vivo changes in the gradient of refractive index distribution in the accommodating human lens

Alyssa L Lie1, Xingzheng Pan2, Thomas W White3

  • 1Department of Physiology, School of Medical Sciences, Aotearoa New Zealand National Eye Centre, University of Auckland, Auckland, New Zealand; School of Optometry and Vision Science, Aotearoa New Zealand National Eye Centre, University of Auckland, Auckland, New Zealand.

Experimental Eye Research|June 12, 2025

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View abstract on PubMed

Summary

Young human lenses show smoother refractive index gradients during accommodation, contributing significantly to increased lens power. Middle-aged lenses do not exhibit these changes, impacting accommodative ability and supporting an intracapsular mechanism of accommodation.

Area of Science:

  • Ophthalmology
  • Biophysics
  • Optics

Background:

  • Human lens accommodation involves changes in lens shape and refractive index.
  • Previous studies suggest water redistribution influences the lens gradient index (GRIN).
  • In vivo studies on GRIN changes during accommodation are limited and yield mixed results.

Purpose of the Study:

  • To investigate changes in human lens geometry and GRIN during accommodation using MRI.
  • To quantify the contribution of GRIN changes to lens power increase.
  • To compare accommodative mechanisms in young and middle-aged adults.

Main Methods:

  • Magnetic resonance imaging (MRI) to measure lens geometry and GRIN.
  • Zemax OpticStudio software for optical modeling.
  • 10 young (20-27 years) and 14 middle-aged (48-55 years) adults under 3 Diopter (D) accommodation stimulus.

Main Results:

  • Young lenses exhibited significant anterior GRIN smoothing, contributing 1.47-1.59 D to the 3.04 D accommodative power increase.
  • Middle-aged (presbyopic) lenses showed no significant changes in geometry or GRIN.
  • Presbyopic lenses only increased lens power by 0.62 D.

Conclusions:

  • Findings support an intracapsular mechanism of accommodation (ICMA).
  • Internal lens optics, specifically GRIN changes, play a crucial role in accommodation.
  • Considering internal lens optics is vital for developing presbyopia treatments.
Keywords:
AccommodationEye lensGradient refractive indexIn vivoMagnetic resonance imagingOpticsPresbyopia

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