ABSTRACT.Purpose: Previous studies of optical blur in perimetry have measured the effect of foveal refractive error on peripheral perimetric detection thresholds. Since peripheral refractive error can be significantly different from that of the fovea we wished to remove the ambiguity of previous results by correcting the actual peripheral refractive error first before adding blur. Methods: We measured detection thresholds in the fovea and at 30 degrees in the horizontal temporal field in two trained observers. Peripheral refractive error was determined at each location and thresholds measured at the same locations for stimuli ranging in size from 0.2 to 6.4 degrees and refractive errors between ∫4.00 diopters. Results: Foveal thresholds increased immediately with increasing refractive error, particularly for smaller stimulus sizes. At 30 degrees, thresholds for smaller stimuli were less affected by defocus initially and then increased more sharply. Larger stimuli were relatively unaffected by defocus such that when stimulus size reached 1.6 degrees there was little or no increase in threshold for refractive error between ∫4.00 diopters. Conclusions: Peripheral refractive error, largely forgotten by perimetrists, has a significant effect on performance, particularly for smaller stimuli. Differences in foveal vs peripheral viewing can be explained by differences in ganglion cell receptive field sizes.

Aims-To evaluate visual function and vision specific health status in patients undergoing penetrating keratoplasty for keratoconus. Methods-A prospective longitudinal study measuring logMAR visual acuity, contrast sensitivity, disability glare, binocular visual field, stereoacuity, and subjective visual function (VF-14) was conducted on 18 patients with keratoconus undergoing penetrating keratoplasty (PK), including six patients who had already had PK in the fellow eye. Data were collected preoperatively and at 3, 9, and 18 months after surgery. Results-Within 3 months of surgery there was significant improvement in aided visual acuity, contrast sensitivity, and stereoacuity (p<0.05); disability glare (p<0.05) no longer had a significant detrimental eVect on these variables. VF-14 score improved significantly throughout the postoperative period (p<0.05). There was significant correlation of the VF-14 score with aided visual acuity, binocular visual field, and stereoacuity. Postoperative astigmatism (<4D v >4D) did not aVect the VF-14 score significantly. Conclusions-There is substantial and rapid improvement in visual function and vision specific health status in keratoconic patients as a result of uncomplicated penetrating keratoplasty. (Br J Ophthalmol 2000;84:60-66) Keratoconus is the principal indication for penetrating keratoplasty in young adults and graft survival in this condition has been used as a yard stick against which to measure the outcome of corneal transplantation for other conditions. 1 Snellen visual acuity has long served as the primary visual function test of surgical success. However, some patients report limitations to vision despite a clear graft and good corrected visual acuity. Over the past two decades there has been mounting evidence that aspects of visual function other than acuity are impaired in those who have media opacities (corneal scarring and cataracts) and irregularities of the cornea. 2-5At the same time, detailed visual function assessments, which measure self rated disability, have been developed for patients with cataract and their response to surgery. [6][7][8][9] Very few such studies have been reported on patients who have undergone penetrating keratoplasty; most are retrospective and use a single point of time for assessment.5 8-11 The purpose of this study was to undertake a prospective longitudinal evaluation of visual function and vision specific health status in patients undergoing penetrating keratoplasty for keratoconus. MethodsKeratoconic patients undergoing penetrating keratoplasty from January 1996 to March 1996 under the care of two corneal surgeons (AT and AR) were invited to participate in this study. The diagnosis of keratoconus was based on slit lamp examination, computerised video keratotopography, and refraction. The study had approval from the local ethics committee and all subjects gave informed consent. Patients were eligible for the study if they were over the age of 16 years, willing to attend assessments in addition to the routine clin...

Peripheral monocular grating resolution has been shown to be limited by the sampling density of the underlying retinal ganglion cells. We wanted to determine if peripheral resolution is also sampling limited binocularly; and, if so, how great is any improvement in either detection or resolution when viewing binocularly? We measured detection and resolution acuity for sinusoidal gratings in foveal and peripheral vision both monocularly and binocularly. Detection and resolution acuity were very similar in foveal vision and displayed a binocular improvement of 5% over best monocular acuity. However, in peripheral vision, while detection acuity improved by 6% binocularly, resolution acuity improved by 16%, with a subsequently smaller aliasing zone. This improvement was greater than predicted by probability summation and implies that the two monocular ganglion cell sampling arrays combine at a higher level resulting in a higher binocular sampling density.

Increased arousal ("stress") provoked more intense nystagmus eye movements. As seen in other studies, stress did not reduce VA despite the shorter FPs. Although VA and FP can correlate across subjects, there would appear to be little correlation, if any, within a subject. However, RTs did increase with stress and shorter FPs, which may have an adverse impact on the visual performance of those with INS.

We measured detection and resolution acuity for vanishing optotype tumbling E stimuli in both the fovea and at 30 degrees in the periphery to determine if peripheral resolution is sampling limited for this stimulus. In the fovea, where acuity is optically limited, detection and resolution were the same. At 30 degrees, however, detection was markedly better than resolution indicating that peripheral resolution is sampling limited for this stimulus. Detection acuity was higher when contrast was 90% rather than 40%, but resolution did not change with contrast. The vanishing optotype is a legitimate perimetric stimulus to measure retinal ganglion cell density provided the task is resolution and not detection.