Abnormal tear film dynamics lead to reduced visual quality due to time-varying wavefront aberrations

Purpose: Due to abnormal tear film dynamics, the wavefront aberration (WFA) of the eye changes over time. For 13 eyes with different diopters, we used a simulation method to investigate changes in the visual quality of wavefront aberrations over time.

METHODS: The WFA of 13 normal eyes of 13 subjects was measured once every second for 10 seconds. First, we simulated the WFA after traditional corneal excimer refraction by removing the second-order aberrations of the least-significant measurement in consecutive WFA measurements. Second, we simulated the WFA after personalized excimer refractive surgery by removing the second-order to sixth-order aberrations of the least-significant measurement in the continuous WFA measurement. We calculated Strehl Ratios and retinal images from these corrected consecutive WFAs.

RESULTS: In one eye, after blinking at the same time point, it was found that the root mean square (RMS) of the second-order corrected WFA was sometimes smaller than the root mean square of the WFA corrected from the second to the sixth order. However, in the other 12 eyes, the root mean square of the second-order to sixth-order correction is smaller than the root mean square only after the second-order correction. In 8 eyes, the Strehl ratio after the second-order to sixth-order correction is larger than the second-order corrected Strehl ratio. In the remaining 5 eyes, the Strel ratios from the second-order to the sixth-order corrections are sometimes smaller than the second-order corrections.

Conclusion: In the simulations, the correction of time-invariant higher-order aberrations usually reduces the RMS value, but it does not always result in higher Strehl ratio than the Strehl ratio obtained by second-order correction alone. Jpn J Ophthalmol 2007;51:258-264 © Japanese Ophthalmological Society 2007

Keywords: Aberration, Retina Image, Shack-Hartmann Aberrometer, Strehlby, Tear Film


Studies of human eye wavefront aberration (WFA) have clearly revealed that monochromatic aberrations reduce visual quality. 1,2 The reason for the decrease is not only the static phenomenon but also the dynamics of the whole eye. 3,4 Typical full eye dynamics that reduce visual quality are tear film dynamics, 5-7 total eye adjustment, 8, 9 and cardiovascular activity. 10

Studies have been carried out on the tear film dynamics, ie continuous measurements using a Plassido disc corneal imager. 11–14 Nemeth et al.11 measured changes in surface rules, surface asymmetry, and corneal power. Goto et al. 12 and Kojima et al. 13 calculated the change in rupture zone and rupture time based on the Placido disc image. Montes-Mico et al.14 evaluated corneal WFA calculated based on Prussian disk images of dry eye patients. Recently, people have investigated aberration changes after blinking, namely the measurement point spread function (PSF) 5 and the total eye WFA. 6,7 The total WFA increase in the blink of an eye after a few seconds. 5-7 Tutt et al.15 studied the visual quality of abnormal tear film dynamics.

In order to investigate changes in visual quality caused by tear film dynamics, we continuously measured the blinking post-WFA. Then use the simple calculation model described below to simulate the WFA of the following eye: once subjected to conventional corneal laser refractive surgery or refractive correction through glasses, and once subjected to personalized corneal laser refractive surgery or through personalized contact lenses Refractive correction. Based on these continuous computerized WFA results, we modeled the temporal changes in PSF, Strehlbi, and Landolt ring retinal images.