Retinal sensitivity and spatial summation in amblyopia

The retinal sensitivity and the spatial summation function in the foveal and parafoveal regions of unilaterally amblyopic patients with eccentric fixation were studied psychophysically by means of a refined fundus perimeter; the device made possible continuous and simultaneous monitoring of the subject's fundus, fixation behavior and location of the stimulus on the retina, and enabled us to obtain selectively reliable data. In 9 out of 10 amblyopic eyes, the retinal sensitivity was the highest at the subject's eccentric fixation locus, demonstrating central relative scotoma. In the fovea of amblyopic eyes, the spatial summation curve showed an abnormal gradient when tested with small stimuli, suggesting an enlarged spatial summation area at the amblyopic fovea. On the other hand, the spatial summation curve at the eccentric fixation locus was comparable to that at the corresponding eccentric locus of the nonamblyopic fellow eye, suggesting the spatial summation function at the peripheral retina was normal in the amblyopic eye.