Purchase this article with an account.
W.J. Donnelly, III, R.A. Applegate; One–and–a–Half–Pass versus One–Pass in Shack–Hartmann Wavefront Sensing – Are They the Same? . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1218.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
To test whether a Shack–Hartmann wavefront sensor (SHWS) will produce the same wavefront data in a single–pass as it does in the standard one–and–a–half pass configuration.
A physical eye model eye (7mm pupil) with and without cataract was mounted to a SHWS. The model eye had two configurations, ‘1.5–pass’ and ‘1–pass.’ The 1.5–pass configuration was the standard configuration where a small diameter SHWS probe beam passes through the eye’s ocular media to form a retinal guide star that is reflected back out of the eye and into the SHWS. The 1–pass configuration was such that the retinal guide star originated from the retina by illuminating a 50µm pinhole from behind the eye. Six different conditions of simulated nuclear cataract were injected into a volume of water behind the pupil using 2.6% 1µm microsphere solutions in 1.6µl increments. This scattering medium approximated a range of nuclear cataract of 0.1 to 6.9 using the LOCSIII system. Three exposures times were used 100, 200, and 300ms.
There were significant (ANOVA, p = 0.05) differences between total RMS 1.5–pass (1.587 mean, 0.022 SD) and 1–pass (1.557 mean, 0.036 SD) and high order 1.5–pass (0.561 mean, 0.013 SD) and 1–pass (1.557 mean, 0.036 SD) measurements; however, none of the differences were visually significant. The 1.5–pass S/H data had significantly less measurement variation than 1–pass data under variable cataract and exposure conditions.
Under various exposure and nuclear cataract conditions the difference in RMS wavefront error between a 1.5–pass S/H image and a 1–pass S/H image is statistically different. However, the differences in measured wavefront error are too small to be of visual consequence.
This PDF is available to Subscribers Only