Effects of Sildenafil Citrate on Optical Properties of the Eye

Abstract

Abstract: : Purpose: To determine if the vasoactive phosphodiesterase inhibitor sildenafil citrate may produce optical shifts consistent with choroidal engorgement. Any agent capable of modulating ocular perfusion might be of therapeutic value in the treatment of a range of choroidal, retinal and axonal disorders. There have been mixed reports regarding changes in ocular blood flow as measured by laser Doppler flowmetry and tonometric ocular pulse wave analyses after administration of sildenafil. We hypothesized that if the choroid engorges, there may be a small hyperopic shift due to potential changes in retinal location that would be reflected in the Zernike mode for defocus Z₀₂. Methods: An IRB-approved double-masked randomized study was conducted on 6 healthy subjects (4 sildenafil/ 2 placebo) to determine if optical properties of the eye, as measured by SHACK-HARTMAN wavefront sensing, changed following administration of 50mg oral sildenafil citrate. 1% Cyclogyl was instilled every 2 hr to stabilize refraction and eliminate accommodation. Four baseline measurements were taken on each cyclopleged eye prior to dosing. Measurements were continued at 30 minute intervals for 3-5 hr after dosing. On a separate test day, static NeuroScientific contrast sensitivities were obtained with the same subjects, prior to and from 1-3 hr after dosing, without cycloplegia. Results: The RMS wavefront error for Z₀₂ was normalized for each subject to the mean of their pre-dose measurements. In the subjects given sildenafil, the normalized RMS error for Z₀₂ significantly (p=0.01) shifted 0.104 microns in the hyperopic direction. This is equivalent to a 0.059 D hyperopic shift in defocus. Assuming that a 3 D shift in defocus is equivalent to a 1mm shift in retinal location, the hyperopic change is consistent with a 19.6 micron anterior movement of the retina. In these 4 subjects, there was an 80% increase in contrast sensitivity comparing 3 baseline and 3 post-sildenafil measurements using 5.5 cpd static sine-wave testing (from 98 +/- 8 (mean +/- sem) before, to 168 +/- 28 after sildenafil). Among subjects receiving placebo, no uniform trends or significant changes from baseline were noted in any measured variable. Conclusion: There was a significant shift in defocus consistent with a 19.6 micron anterior movement in retinal location, with attendant increase in contrast sensitivity at 5.5 cycles/degree. If the observed optical shift was indeed attributable to anterior displacement of the retina, simple refractive optics and chromatic aberration might explain the blurring and blue-shift noted (see product insert) among presbyopes taking sildenafil.

Keywords: 500 optical properties • 331 blood supply • 368 contrast sensitivity