Purchase this article with an account.
Janice Dias, Chi Yat Ben Yau, Vincent Moy, Jean-Marie A. Parel, Noel Ziebarth; Feasibility of Bulk Corneal Elasticity Measurement with Atomic Force Microscopy. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4198.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
To test the feasibility of measuring bulk corneal elasticity of fully hydrated samples in a non-destructive manner.
We have designed an indentation system based on Atomic Force Microscopy (AFM). To combat the limitation of commercial AFM systems, the developed system can indent samples a few nanometers up to several microns. This enables measurement of bulk mechanical properties instead of localized, single-layer measurements. The system was used to measure corneal bulk mechanical properties, corresponding to the stroma, without removing Bowman’s membrane. The tips of traditional AFM cantilevers were modified with glass microbeads (diameter: 60-75µm) to enable higher indentation. Measurements were performed on three human eyes (age: 45, 87, 91 years, <18 days postmortem) retrieved from the eye bank. The corneal epithelium was removed using a cotton swab. The cornea was then excised leaving a generous sclera rim and placed in 20% Dextran for 24 hours to restore corneal thickness to physiological levels. The excised cornea was placed in a custom holder and the elasticity was measured with the custom-built AFM. The anterior corneal surface was probed with the modified cantilever tips at gradually increasing indentation. Sample hydration was maintained during the measurements by submerging the samples in 15% Dextran. Young’s modulus was calculated from the scans at all indentation depths using the Hertz model for a spherical indenter.
The dehydration protocol was validated by measuring the thickness of 3 samples 10 days postmortem using OCT. The thickness was 486±67µm after 24 hours in 20% Dextran. Young’s modulus was graphed as a function of indentation, revealing an increasing trend until reaching an asymptote. The asymptote most likely represents the elasticity of the corneal stroma. Young’s modulus was 19.6kPa, 215kPa, and 103kPa for the 45, 87, and 91 year old corneal samples, respectively.
The custom AFM system and modified tips can be used to measure bulk corneal elasticity of fully hydrated samples.
This PDF is available to Subscribers Only