[Development of a new evaluation system for visual function].

Abstract

Visual deterioration is caused principally by media opacity, by retinal damage, or by disorders of the higher visual system posterior to the optic nerve. In this article, we focused on media and retinal disorders and clinically evaluated a newly developed system for visual function. The decrease in visual function in cataract is subjectively well evaluated by contrast sensitivity, but is difficult to evaluate objectively. Recently, a wavefront sensor has been developed and ocular higher-order aberration (HOA) can now be measured objectively. We studied the relationship between age and HOA by wavefront sensor and found that HOA, especially spherical aberration in the lens, increased abruptly at the presbyopic age. We also found that the against-the-rule astigmatism in the lens increased at this age. Next, we investigated monocular diplopia which was presumably caused by HOA. Nine eyes with monocular triplopia and with mild nuclear cataract showed significant increase of trefoil aberration and negative spherical aberration (p<0.001). The simulated retinal Landolt's image from these two aberrations showed a triple configuration. Thus we confirmed that triplopia is caused by the combination of trefoil aberration and negative spherical aberration in early nuclear cataract. Next, we investigated whether Area under Log Contrast Sensitivity Function (AULCSF) can be predicted by HOA and light scattering. Backward light scattering (BLS) was evaluated by Schei mpflug image and the forward light scattering (FLS) by a spot size of the Hartmann image compensated for the effect of HOA. HOA was evaluated by root mean square (RMS) value from Hartmann image in a 4 mm pupil. Multiple linear regression revealed that AULCSF could be predicted from BLS, FLS, and HOA, in which each parameter contributed to the prediction significantly (p<0.01). By using this predicted value of AULCSF, the improvement of vision after cataract surgery can be predicted in cataract complicated by retinal disease. It has been reported that by fundus camera equipped with adaptive optics (AO), which is an application of wavefront analysis, photoreceptors could be visualized 2-dimensionally. We developed a compact AO fundus camera and demonstrated that cones were separately analyzed at retinal loci 1 degree temporal to the fovea centralis when the ocular aberration was reduced to less than 0.1 microm RMS in a 6 mm pupil. We are going to use this apparatus for eyes with retinal disease. The functional evaluation of residual retinal ganglion cells (RGCs) in the retina with damage to the photoreceptors is critically important for selecting candidates for artificial retina or regenerative therapy. Transcorneal electrical stimulation (TES) of the retina via contact lens electrodes evokes phosphene and indirect pupillary reflex. The threshold current for evoking phosphene in severely degenerated retinas with visual acuity worse than counting fingers showed a wide distribution, which suggested that TES was useful to evaluate residual RGCs functionally. TES also showed a neuroprotective effect. We suggest that the activation of glial cells by TES up-regulates the production of IGF-1, which eventually protects RGCs. The peripheral retina is important for walking even though the spatial resolution is not high. We developed an apparatus to measure stereopsis in the peripheral retina using a wide screen, and evaluated the peripheral stereopsis of 12 patients after macular translocation surgery and squint surgery. All three patients who showed peripheral stereopsis had only a small amount of squint angle. This method may be useful to evaluate stereopsis in patients with a central scotoma.