Esther G. González

Fixation characteristics of patients with macular degeneration recorded with the mp-1 microperimeter.

Purpose: The authors examined the fixation stability patterns of people with age-related macular degeneration (AMD) using the MP-1 microperimeter and describe a method to bypass some calibration artifacts that can influence the fixation results. Method: The preferred retinal locus (PRL) and fixation patterns of 37 eyes with AMD and the foveas location relative to the middle of the optic disc of 10 experienced controls were measured. For the patients, fixation characteristics such as the former foveas location, PRL distance, and fixation stability were analyzed. Results: For the controls, the mean foveal distance temporal to the middle of the optic disc was 15.5 deg ± 0.86 deg horizontally and –1.33 deg ± 0.71 deg vertically. Thirty-one out of 37 PRLs occurred in the upper and right quadrants of the retina. There were significant positive correlations between fixation stability and PRL distance from the former fovea. Time since diagnosis and acuity also showed positive correlations with fixation stability and PRL distance from the fovea. Conclusions: The authors recommend that fixation stability recorded with the MP-1 be analyzed based on the raw data. Most of the fixation parameters obtained agree with those reported in the literature, if proper calibration is used.

Eye Position Stability in Amblyopia and in Normal Binocular Vision

PURPOSE We investigated whether the sensory impairments of amblyopia are associated with a decrease in eye position stability (PS). METHODS The positions of both eyes were recorded simultaneously in three viewing conditions: binocular, monocular fellow eye viewing (right eye for controls), and monocular amblyopic eye viewing (left eye for controls). For monocular conditions, movements of the covered eye were also recorded (open-loop testing). Bivariate contour ellipses (BCEAs), representing the region over which eye positions were found 68.2% of the time, were calculated and normalized by log transformation. RESULTS For controls, there were no differences between eyes. Binocular PS (log(10)BCEA = -0.88) was better than monocular PS (log(10)BCEA = -0.59) indicating binocular summation, and the PS of the viewing eye was better than that of the covered eye (log(10)BCEA = -0.33). For patients, the amblyopic eye exhibited a significant decrease in PS during amblyopic eye (log(10)BCEA = -0.20), fellow eye (log(10)BCEA = 0.0004), and binocular (log(10)BCEA = -0.44) viewing. The PS of the fellow eye depended on viewing condition: it was comparable to controls during binocular (log(10)BCEA = -0.77) and fellow eye viewing (log(10)BCEA = -0.52), but it decreased during amblyopic eye viewing (log(10)BCEA = 0.08). Patients exhibited binocular summation during fellow eye viewing, but not during amblyopic eye viewing. Decrease in PS in patients was mainly due to slow eye drifts. CONCLUSIONS Deficits in spatiotemporal vision in amblyopia are associated with poor PS. PS of amblyopic and fellow eyes is differentially affected depending on viewing condition.

Vision with one eye: a review of visual function following unilateral enucleation.

What happens to vision in the remaining eye following the loss of vision in the fellow eye? Does the one-eyed individual have supernormal visual ability with the remaining eye in order to adapt and compensate for the loss of binocularity and the binocular depth cue, stereopsis? There are subtle changes in visual function following the complete loss of one eye from unilateral enucleation. Losing binocularity early in life results in a dissociation in form perception and motion processing: some aspects of visual spatial ability are enhanced, whereas motion processing and oculomotor behaviour appear to be adversely affected suggesting they are intrinsically linked to the presence of binocularity in early life. These differential effects may be due to a number of factors, including plasticity through recruitment of resources to the remaining eye; the absence of binocular inhibitory interactions; and/or years of monocular practice after enucleation. Finally, despite this dissociation of spatial vision and motion processing, research that has examined visual direction and performance on monocular tasks shows adaptive effects as a result of the loss of one eye. Practically speaking, one-eyed individuals maintain perfectly normal lives and are not limited by their lack of binocularity.

Human optokinetic nystagmus in response to moving binocularly disparate stimuli.

Physiological and behavioral evidence shows that the directionally preponderant subcortical control of optokinetic nystagmus (OKN) in lower mammals is supplemented in higher mammals by bidirectional cortical control. It is hypothesized that this cortical control allows higher mammals to cope with the parallactic movement of the scene produced by linear motion of the body. In particular, it is hypothesized that a coupling between OKN and stereopsis allows higher mammals to stabilize the images of objects within the plane of fixation while ignoring motion signals from objects at other distances. According to this hypothesis the gain of the slow phase of OKN should be highest for binocularly fused moving stimuli and attenuated for binocularly disparate displays. The results of Experiment 1 confirmed this prediction although the effects of accommodation were not ruled out completely. In Experiment 2 a display moving in one direction was presented across the central retina at the same time as one moving in the opposite direction was presented in the upper and lower periphery. It was found that subjects do not show OKN in the direction of the peripheral display unless it is binocularly fused and the central display is disparate. In Experiment 3 a stationary display of dots was superimposed on a moving display. It was found that OKN is not inhibited by the stationary display when it has a horizontal disparity and the moving display is fused. Experiment 4 found that horizontal OKN is disrupted by the sudden introduction of a vertical disparity in the stimulus. Since accommodative state was kept constant in the last three experiments, the data show that binocular disparities can help a person to stabilize selectively the image of one moving display while ignoring conflicting motion signals from another display.

Fixation stability using radial gratings in patients with age-related macular degeneration

BACKGROUND The fixation stability of patients with macular atrophy is generally worse than that of people without pathology. METHODS The effects of 2 types of high-contrast fixation stimuli on fixation stability were compared between patients with longstanding age-related macular degeneration (AMD) and control subjects with normal vision. One stimulus was a 9-cycle square-wave radial grating measuring 5 degrees in diameter and the other a white 0.5 degrees disc. A video-based infrared eye tracker with remote optics was used to record eye position while participants fixated the stimuli in primary position of gaze for 6 to 7 s. Fixation stability was measured with a bivariate contour ellipse area (BCEA). RESULTS For patients with AMD, fixation stability for the radial grating was largely independent of visual acuity, whereas fixation stability for the disc diminished with acuity. For the control observers, there were no differences in fixation stability for the 2 kinds of stimuli. INTERPRETATION In clinical and research settings, radial gratings can be useful targets for fixation for patients with macular disease since they provide enough visual information to help maintain fixation stability. These findings have important implications for the design of clinical tests and procedures such as perimetry, multifocal electroretinography, and optical coherence tomography for patients with macular atrophies.

Fixation stability during binocular viewing in patients with age-related macular degeneration.

PURPOSE The authors examined the fixation stability of patients with age-related macular degeneration (AMD) and large interocular acuity differences, testing them in monocular and binocular viewing conditions. The relationship between fixation stability and visual performance during monocular and binocular viewing was also studied. METHODS Twenty patients with AMD participated. Their monocular and binocular distance acuities were measured with the ETDRS charts. Fixation stability of the better and worse eye were recorded monocularly with the MP-1 microperimeter (Nidek Technologies Srl., Vigonza, PD, Italy) and binocularly with an EyeLink eye tracker (SR Research Ltd., Mississauga, Ontario, Canada). Additional recordings of monocular fixations were obtained with the EyeLink in viewing conditions when one eye viewed the target while the fellow eye was covered by an infrared filter so it could not see the target. RESULTS Fixation stability of the better eye did not change across viewing conditions. Fixation stability of the worse eye was 84% to 100% better in the binocular condition than in monocular conditions. Fixation stability of the worse eye was significantly larger (P < 0.05) than that of the better eye when recorded monocularly with the MP-1 microperimeter. This difference was dramatically reduced in the binocular condition but remained marginally significant (95% confidence interval, -0.351 to -0.006). For the better eye, there was a moderate relationship between fixation stability and visual acuity, both monocular and binocular, in all conditions in which this eye viewed the target. CONCLUSIONS Fixational ocular motor control and visual acuity are driven by the better-seeing eye when patients with AMD and large interocular acuity differences perform the tasks binocularly.

Fixation Stability, Fixation Location, and Visual Acuity after Successful Macular Hole Surgery

PURPOSE This study examined whether changes in fixation stability and fixation location are good predictors of visual acuity after successful macular hole surgery. METHODS Ten patients with macular hole were tested before surgery and at 1 and 3 months after surgery. Visual acuity was measured with the ETDRS; fixation stability and fixation location were assessed with the MP-1 Microperimeter (Nidek Technologies Srl., Vigonza, PD, Italy). The quantitative measure of fixation stability was calculated with a bivariate contour ellipse area (BCEA). Fixation location shift was evaluated using the differential map analysis feature of the MP-1 Microperimeter. RESULTS There was a significant improvement in visual acuity after macular hole closure. Fixation location shifted an average of 0.55 deg and 0.87 deg at 1 month and 3 months after surgery, respectively. The fixation shift was not a good predictor of visual outcome. Fixation stability improved from an average of 0.35 deg(2) before surgery to 0.29 deg(2) at 3 months after surgery. The change in fixation stability (DeltaBCEA = BCEA before - BCEA after surgery) correlated highly with visual outcome. The regression model showed that DeltaBCEA accounted for a significant proportion of the variance in visual acuity both 1 and 3 months after surgery. CONCLUSIONS Some changes in ocular motor function explain the visual outcome after the anatomic success of macular hole surgery. Fixation location shift has no influence on visual acuity post-operatively; however, change in fixation stability is a strong predictor of visual outcome after successful closure of the macular hole.

Fixation Control before and after Treatment for Neovascular Age-Related Macular Degeneration

PURPOSE We studied changes in visual acuity (VA), fixation stability, and location of the preferred retinal locus (PRL) after treatment for unilateral neovascular age-related macular degeneration (AMD) for previously untreated eyes. Concomitant changes in fixation stability, PRL, and VA in the untreated fellow eye were also analyzed. METHODS Pre- and posttreatment tests of visual acuity, fixation stability, and PRL location in both the treated and the untreated eyes were performed on 13 patients undergoing three monthly intravitreal injections of ranibizumab in one eye. RESULTS For the treated eyes there were improvements in VA and fixation stability but no changes in the location of the PRL. No significant changes in any of the three variables were found in the untreated eye. CONCLUSIONS For previously untreated eyes, the improvement in visual acuity after intravitreal ranibizumab injections was accompanied by improvement in fixation stability.

Binocular interactions in patients with age-related macular degeneration: acuity summation and rivalry.

This study examined two aspects of binocular function in patients with age-related macular degeneration (AMD): summation/inhibition of visual acuity and rivalry. The performance of 17 patients with AMD was compared with that of 17 elderly controls and 21 young people. Monocular and binocular acuities were measured using a multiple-E optotype test. Binocular ratios, defined as the better-eye acuity divided by the binocular acuity, were calculated. We also measured eye dominance during rivalry (proportion of time the participants reported perceiving the input to each eye) and rivalry rates (number of alternations per minute). The results showed that while overall binocular ratios were similar for the three groups, the frequency distributions of people who experienced inhibition, equality or summation were different for the young and AMD groups. In the rivalry test, patients experienced more piecemeal perception than the elderly and young controls, but time dominance from the better-seeing eye was comparable for the three groups. Rivalry rates decreased with age and further with pathology. Moreover, rivalry time dominance of the worse-seeing eye was negatively correlated with interocular acuity differences for the AMD group.

Reading training with threshold stimuli in people with central vision loss: a feasibility study.

Purpose To evaluate the effectiveness of a perceptual learning technique for improving reading performance of patients with central vision loss and to explore whether this learning generalizes to other visual functions. Methods Ten patients with central vision loss were trained binocularly, in four consecutive sessions, with serially presented words printed at each patient’s reading acuity limit. Patients read 10 blocks of 100 words in each session. They were encouraged to read the whole word and were discouraged to read letter by letter. Assessment sessions before and after training measured fixation stability, monocular and binocular visual acuity, as well as reading acuity, critical print size, and maximum reading speed with continuous text. Another six patients with central vision loss were included in a test-retest control group and were tested twice, 1 week apart, with no intervention. Results The average time required to read a block of trials decreased significantly with each training session. After training, continuous text reading improved in terms of reading acuity (p = 0.017) and maximum reading speed (p = 0.01), but critical print size did not change. Binocular acuity improved significantly from an average of 0.54 logMAR before training to 0.44 logMAR after training. Binocular ratio (better eye acuity/binocular acuity) increased from an average of 1.0 before training to 1.17 after training. There was a 62% improvement in fixation stability in the better eye and 58% in the worse eye. There were no changes in the outcome measures for the test-retest control group. Conclusions The technique described in this article can be used for vision rehabilitation of patients with central vision loss. When training is done with size threshold stimuli, learning generalizes to visual acuity, continuous text reading, and fixation stability.