The Effects of Primary Pterygium on Contrast Sensitivity Preoperatively and Postoperatively

Pterygium is the growth of conjunctival tissue onto the cornea, usually from the nasal quadrant of the cornea.Visual acuity may be reduced due to direct invasion of the visual axis or astigmatism induced by the pterygium. Contrast sensitivity measures two variables, size, and contrast which could comprehensively reflect the visual quality of the primary pterygium patients. In this study, we would investigate the the effects of primary pterygium on contrast sensitivity preoperatively and on the 1st, 3rd and 6th month postoperatively, moreover, the related parameters on the contrast sensitivity in the primary pterygium patients would be analyzed.

There would have two groups included in our study, which are primary pterygium group(40 patients) and the normal group (20 volunteers). The inclusion criteria for the primary pterygium group were: 1) more than 18 and less than 60 years old; 2)diagnosed as primary pterygium by the professional doctor; 3)0.0 or better logMAR BCVA; 4) absence of other ocular disorders and no history of eye surgery and other systemic diseases. The inclusion criteria for the normal group were: 1) between 18 and 60 years old; 2) 0.0 or better logMAR BCVA;3) no history of any ocular pathology, and normal physical and mental health. All the subjects would receive the ophthalmic examination and contrast sensitivity test (quick contrast sensitivity function, quick CSF), in which the pterygium group would achieve the pterygium surgery by the same surgeon (Jin Yuan) and then be performed the contrast sensitivity test on the 1st, 3rd and 6th month postoperatively. The quick CSF method, implemented in a 10 alternative forced-choice digit identification task, was used to assess the contrast sensitivity function34, 38. Stimuli were displayed on a gamma-corrected 46 inch LCD monitor (Model: NEC LCD P463) with a 1920×1080 pixel resolution, 50 cd/m2 mean luminance and 60 Hz vertical refresh rate. Observers viewed the display monocularly from a distance of 4 m in a dark room. For each trial, they were asked to verbally report the identities of three digits presented on the screen to the experimenter, who used the computer keyboard to enter their responses. The stimuli disappeared after all the responses were entered. Observers were given the option to report ''I don't know'' upon which the response was coded as incorrect. No feedback was provided. All three responses were used to update the posterior distribution of the CSF parameters, which in turn was used to adaptively choose the most informative combination of spatial frequency and contrast for the next trial. A new trial started 500 ms after the responses. There were 30 trials in approximately 5 min. The quick CSF data were scored to generate the cutoff spatial frequency, defined as the spatial frequency corresponding to a perceptual sensitivity of 1, and the area under the log CSF (AULCSF), a summary measure of the window to spatial vision