Digital mini-shadowphotogrammetric system for morphometric analysis of ex-vivo crystalline lenses: Pilot study on human lenses

Abstract

 

Purpose

 

To examine the morphometry of human crystalline lenses using a miniature shadowphotogrammetric system.

 

Methods

 

Crystalline lenses (n = 41, aged 10 months-88 years, median post-mortem time 25 hours (interquartile range, 19-34 hours)) were isolated from eyes received from the Ramayamma International Eye Bank, Hyderabad, India. The sagittal and coronal profiles of the lenses were imaged using a custom-built digital optical system based on the principle of shadowphotogrammetry. The experimental setup is an improvement on the study by Augusteyn et al (Mol Vis 2006) which used an industrial optical comparator. Analysis of the coronal and sagittal images was performed using custom MATLAB-based software. The sagittal lens contour was fit to a 10^th order even Fourier series (Urs et al Vis Res 2010) and thickness and diameter measurements were made. Conic and spherical functions were applied to anterior and posterior lens surfaces for central 6mm and 3mm zones, respectively.

 

Results

 

The system’s ~6.4 µm/pixel resolution of images enabled accurate fits of the detected lens contours. Analysis took ~5 minutes/lens. Rapid changes were observed in the young lenses in all dimensions obtained from the lens profiles, but at this time insufficient data are available to permit detailed analyses. Adult lens diameter, thickness (T), anterior T and posterior T increased at 0.013mm, 0.009mm, 0.003mm and 0.006mm per year, respectively. The relationship between age and cross-sectional area (mm²), surface area (mm²) & volume (mm³) for adult lenses were described using the following power equations: y = 14.51x^0.2, y = 100.35x^0.16 & y = 67.42x^0.27 respectively. After age 18 years, the anterior radii (R) of curvature for the central 6mm and 3mm zones were 8.05±2.45mm and 8.78±2.21mm respectively, whereas the posterior R ranged between 4.52-6.99mm and 4.70-7.58mm respectively. The shape factors for anterior and posterior surfaces were 9.94±8.76 and 0.14±1.09 respectively.

 

Conclusions

 

All lens parameters increased as a function of age, consistent with continuous lens growth. The information obtained from morphometric analysis of a large number of isolated human lenses over a wide age range will be valuable in the development of biomechanical simulation and optical modeling of natural and artificial crystalline lenses.

 

 

Mini-Shadowgraph System

 

 

Representative Sagittal and Coronal Images

 

Keywords: 413 aging • 551 imaging/image analysis: non-clinical • 419 anatomy