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A. Y. Zhang, H. Saheb, T. Jayasundera, M. Khuthaila, O. Fontaine, M. R. Lesk, J. C. Chen; Development of a Manometric Device for the Measurement of Scleral Rigidity in AMD: Rabbit Experimental Data. Invest. Ophthalmol. Vis. Sci. 2010;51(13):6147.
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Scleral rigidity is an important parameter in a number of diseases, including glaucoma, myopia, and age-related macular degeneration (AMD). In AMD, Friedman proposes a vascular model, postulating that increased scleral rigidity, caused by accumulation of lipids in the sclera and Bruch’s membrane, leads to hemodynamic changes resulting in AMD. Our objective was to design, build, and test a device to measure human eye scleral rigidity in vivo.
We have designed a direct manometric measurement device which can be used to measure human eye scleral rigidity in a sterile environment. The device is capable of continuous injection of sterile saline into the eye, through an anterior chamber paracentesis, up to a maximum pressure of 75mmHg. Using the principle of compressibility of air and noncompressibility of liquid within a closed system, the relative displacement of air to the amount of volume displaced allows the device to generate a calculated pressure curve. The constant of scleral rigidity is derived from the change in pressure over change in volume. Using the measurement device, we performed measurements in 12 freshly euthanized rabbit eyes.
Each of the 12 rabbit measurements demonstrates a reproducible biphasic curve of pressure over volume. As volume is injected into the eye at a constant rate, pressure increases until a plateau pressure is reached, the mean being 23 mmHg, and then resumes the increase at a similar rate. The mean of the pre-plateau slope is 0.28 +/- 0.11; the mean of the post-plateau slope is 0.57 +/- 0.18.
The direct manometric measurement results in a reproducible biphasic curve in euthanized rabbit eyes. We hypothesize that this biphasic curve results from filling of the intraocular space until it reaches intravascular pressure of the choroid. At this point, an isovolumetric exchange occurs, where injected saline displaces blood contents outward.In order to validate this finding, living animal eyes will be tested where we would expect to see the lack of the biphasic curve. This manometric measurement device can be used to measure in vivo human eye scleral rigidity in a sterile environment.
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