The point-spread function of the eye from 0 degrees to 100 degrees and the pattern electroretinogram

In studies on the pattern electroretinogram the quality of the retinal image is a major concern. The use of contact lens electrodes was rejected since a good pattern could not be recorded. This is believed to be due to blurring of the retinal image. As indicator of image quality the patient's visual acuity is often used. We wondered whether this is a sufficient criterion. The retinal image is the product of the whole optical point-spread function of the eye whereas visual acuity refers only to the central portion of this function. On the basis of existing reports it can be estimated that for the young normal eye the outer edges of this function (straylight) causes considerable loss of contrast. The strength of the straylight can be much greater in older eyes. We studied the relation between the point-spread function including straylight and the pattern electroretinogram in normal eyes and some pathological cases. The measurements proved to follow the calculated contrasts on the basis of a local luminance model, with the exception of enhancement (tuning) around 60' checksize for the young normal eye. Because of the considerable differences in straylight in an older population one has to take into account that loss of pattern electroretinogram can be suffered in patients with otherwise good visual acuity.