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Daniel R Neal, Thomas Daniel Raymond, Wei Xiong, Kavita Dhamdhere; Estimation of visual acuity from dynamic wavefront tear film measurement. Invest. Ophthalmol. Vis. Sci. 2018;59(9):3278.
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© ARVO (1962-2015); The Authors (2016-present)
Several methods have been used for tear film measurement. Most common is the use of fluorescein to measure tear film break up time (TBUT) with slit lamp observation. But TBUT does not predict the actual optical performance of the eye. It would advantageous if we could quantify tear film quality the same way we quantify other visual performances, like visual acuity (VA). This would provide a method for directly interpreting the degradation of the patient’s vision with changes in the tear film and help us compare the effectiveness of various therapeutic approaches.
A combined aberrometer/topographer was used to acquire simultaneous images of both the transmitted wavefront and the anterior topography dynamically at 7-10 Hz. The residual wavefront surface after Zernike decomposition was used to calculate the far-field intensity distribution. The width of this distribution can be computed across multiple spatial scales including higher order and micro-aberrations. The distribution width was estimated using the 2nd moment integral, which produces values that can be represented in minutes of arc. Using the Rayleigh criteria the effective VA could then be computed based on the known Snellen letter sizes.
A pilot study was conducted with 5 subjects ages 35-61. These subjects were measured using a stare 40 second stare test and simultaneous anterior corneal topography (CT) and wavefront (WF) aberrometry were measured at 7 fps, with both WF and CT measured simultaneously. The residual RMS wavefront and topography values increased progressively with time until the tear film broke up and the subject blinked. The VA was estimated from the far-field calculated WF data. Analysis of the WF shows two different scattering scales (full pupil FP) and micro scattering (lenslet). Both of these correlate well with the other metrics and provide a way to quantify the effect of the tear film on VA. The full pupil WF is the dominate contributor to reduction in VA until the tear film breaks up.
This method of quantifying tear film VA provides reasonable results and provides a method for comparing the optical performance of the tear film to other optical phenomena such as scattering, aberrations or refractive error. Initial results show good sensitivity to the dynamic tear film changes and correlate well with other tear film metrics.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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