Preferred Retinal Locus Research Articles

Spontaneous and training-induced cortical plasticity in MD patients: Hints from lateral masking

Macular degeneration (MD) affects central vision and represents the leading cause of visual diseases in elderly population worldwide. As a consequence of central vision loss, MD patients develop a preferred retinal locus (PRL), an eccentric fixation point that replaces the fovea. Here, our aim was to determine whether and to what extent spontaneous plasticity takes place in the cortical regions formerly responding to central vision and whether a visual training based on perceptual learning (PL) can boost this plasticity within the PRL area. Spontaneous and PL-induced cortical plasticity were characterized by using lateral masking, a contrast sensitivity modulation induced by collinear flankers. This configuration is known to be sensitive to neural plasticity and underlies several rehabilitation trainings. Results in a group of 4 MD patients showed that collinear facilitation was similar to what observed in age- and eccentricity-matched controls. However, MD patients exhibited significantly reduced collinear inhibition, a sign of neural plasticity, consistent with the hypothesis of partial cortical reorganization. Three AMD patients from the same group showed a further reduction of inhibition after training, but not controls. This result suggests that PL might further boost neural plasticity, opening promising perspectives for the development of rehabilitation protocols for MD patients.

Mechanisms of Image Stabilization in Central Vision Loss: Smooth Pursuit.

In addition to understanding the adaptive mechanisms of eccentric viewing during smooth pursuit, the ocular motor adaptations of patients with central vision loss give us a better understanding of the basic mechanisms of smooth pursuit in the healthy visual system. For patients with age-related macular degeneration and controls with normal vision, we examined the closed-loop gain of horizontal and vertical smooth pursuit eye movements as a function of stimulus speed and direction. We hypothesized that pursuit gain functions would be affected by stimulus speed and the location of the preferred retinal locus (PRL) in relation to the scotoma as determined by a fixation stability task using a microperimeter. Specifically, that a PRL on the left of the scotoma in the visual field would decrease the rightward gain relative to the leftward gain and a PRL below the scotoma in the visual field would decrease the upward gain. Ten patients and 15 controls were tested in a step-ramp procedure with direction (left/right for horizontal motion; up/down for vertical motion), speed (5, 10, 15, 20, and 30 deg/s), and five replication conditions randomized and blocked by orientation (horizontal vs. vertical). Horizontal pursuit had a higher gain than vertical pursuit. The two eyes of the patients moved conjugately with similar smooth pursuit gains. For horizontal pursuit, all patients, regardless of PRL location, showed significantly better pursuit of leftward motion. For vertical pursuit, downward pursuit had a higher gain than upward pursuit for most patients. PRL location was not predictive of the directional preponderance of pursuit performance. These results imply that patients may not use the PRL that was initially found during a static fixation task; they may adapt to the task by using a PRL that appears more suitable.

Eccentric fixation patterns, clinical findings, and reading speed in patients with bilateral toxoplasmic macular retinochoroiditis

To study visual acuity, refractive errors, eccentric fixation, and reading performance in patients with toxoplasmic macular retinochoroiditis. Twenty-three participants with bilateral toxoplasmic macular retinochoroiditis and 4 with toxoplasmic macular retinocho-roiditis in their unique eye were evaluated. Participants reported their eye dominance, confirmed by the Portus and Miles test. Best corrected visual acuity, spherical equivalent refraction, magnification need, and reading speed were measured. Microperimetry (MAIA, Centervue - Padova, Italy) recorded the preferred retinal locus and fixation stability by means of the bivariate contour ellipse area. Fourteen eyes from 14 normally sighted subjects served as controls. Mean ± SD best corrected visual acuity was better in the dominant eye than in the nondominant eye: 0.9 ± 0.2 (logMAR 0.5 to 1.4) vs. 1.2 ± 0.3 (logMAR 0.6 to 1.7) (p<0.0001, paired t-test). Spherical equivalent myopia of -4.00 or higher was present in 42% of the eyes. Microperimetry was performed in 42 eyes. Eccentric fixation was observed in all examined eyes. In 14 eyes (33%), the preferred retinal locus was placed (in the retina) superior temporal to the macular lesion, in 10 (24%) superior nasal, in 6 (14%) inferior temporal, and in 12 (28%) inferior nasal. There was no significant difference in the distribution of the preferred retinal locus position between dominant and nondominant eyes (p=0.85, Pearson test). There was no correlation between reading speed and the distance between the preferred retinal locus and the estimated original foveal position (r=-0.09; p=0.73), the bivariate contour ellipse area (r=-0.19; p=0.44), or best corrected visual acuity (r=0.024; p=0.92). Myopia is more prevalent in patients with toxoplasmic macular retinochoroiditis. Reading speed is not dependent on preferred retinal locus position, stability, or visual acuity. Nevertheless, documentation of fixation provides new data on the impact of visual impairment in these patients and may be useful for rehabilitation efforts.

Contrast Sensitivity in Eyes with Central Scotoma: Effect of Stimulus Drift.

In the field of visual rehabilitation of patients with central visual field loss (CFL), knowledge on how peripheral visual function can be improved is essential. This study presents measurements of peripheral dynamic contrast sensitivity (with optical correction) for off-axis viewing angles in subjects with CFL. Subjects with CFL rely on a peripheral preferred retinal locus (PRL) for many visual tasks. It is therefore important to ascertain that contrast sensitivity (CS) is maximized in the PRL. This study evaluates the effect of stimulus motion, in combination with optical correction, on CS in subjects with CFL. The off-axis refractive errors in the PRL of five young CFL subjects were measured with a COAS open-view Hartmann-Shack aberrometer. Low-contrast (25% and 10%) and high-contrast resolution acuity for stationary gratings was assessed with and without optical correction. High-contrast resolution was also measured for gratings drifting at 7.5 Hz (within a fixed Gaussian window). Furthermore, resolution CS was evaluated for both stationary and moving gratings with optical correction for a total of two to three spatial frequencies per subject. High-contrast resolution acuity was relatively insensitive to stimulus drift motion of 7.5 Hz, whereas CS for gratings of 0.5 cycles per degree improved with drift for all subjects. Furthermore, both high- and low-contrast static resolution improved with optical correction. Just as for healthy eyes, stimulus motion of 7.5 Hz enhances CS for gratings of low spatial frequency also in the PRL of eyes with CFL. Concurrently, high-contrast resolution is unaffected by the 7.5-Hz drift but improves with off-axis optical correction. This highlights the importance of providing optimal refractive correction for subjects with CFL and that stimulus motion can be used to further enhance CS at low spatial frequencies.

The Preferred Retinal Locus Used to Watch Videos.

PurposeEccentric viewing is a common strategy used by people with central vision loss (CVL) to direct the eye such that the image falls onto functioning peripheral retina, known as the preferred retinal locus (PRL). It has been long acknowledged that we do not know whether the PRL used in a fixation test is also used when performing tasks. We present an innovative method to determine whether the same PRL observed during a fixation task was used to watch videos and whether poor resolution affects gaze location.MethodsThe gaze of a group of 60 normal vision (NV) observers was used to define a democratic center of interest (COI) of video clips from movies and television. For each CVL participant (N = 20), we computed the gaze offsets from the COI across the video clips. The distribution of gaze offsets of the NV participants was used to define the limits of NV behavior. If the gaze offset was within this 95% degree confidence interval, we presumed that the same PRL was used for fixation and video watching. Another 15 NV participants watched the video clips with various levels of defocus blur.ResultsCVL participants had wider gaze-offset distributions than NV participants (P < 0.001). Gaze offsets of 18/20 CVL participants were outside the NV confidence interval. Further, none of the 15 NV participants watching the same videos with spherical defocus blur had a gaze offset that was decentered (outside the NV confidence interval), suggesting that resolution was not the problem.ConclusionsThis indicates that many CVL participants were using a PRL to view videos that differed from that found with a fixation task and that it was not caused by poor resolution alone. The relationship between these locations needs further investigation.

Transfer of an induced preferred retinal locus of fixation to everyday life visual tasks.

Subjects develop a preferred retinal locus of fixation (PRL) under simulation of central scotoma. If systematic relocations are applied to the stimulus position, PRLs manifest at a location in favor of the stimulus relocation. The present study investigates whether the induced PRL is transferred to important visual tasks in daily life, namely pursuit eye movements, signage reading, and text reading. Fifteen subjects with normal sight participated in the study. To develop a PRL, all subjects underwent a scotoma simulation in a prior study, where five subjects were trained to develop the PRL in the left hemifield, five different subjects on the right hemifield, and the remaining five subjects could naturally chose the PRL location. The position of this PRL was used as baseline. Under central scotoma simulation, subjects performed a pursuit task, a signage reading task, and a reading-text task. In addition, retention of the behavior was also studied. Results showed that the PRL position was transferred to the pursuit task and that the vertical location of the PRL was maintained on the text reading task. However, when reading signage, a function-driven change in PRL location was observed. In addition, retention of the PRL position was observed over weeks and months. These results indicate that PRL positions can be induced and may further transferred to everyday life visual tasks, without hindering function-driven changes in PRL position.

Domain Specificity of Oculomotor Learning after Changes in Sensory Processing.

Humans visually process the world with varying spatial resolution and can program their eye movements optimally to maximize information acquisition for a variety of everyday tasks. Diseases such as macular degeneration can change visual sensory processing, introducing central vision loss (a scotoma). However, humans can learn to direct a new preferred retinal location to regions of interest for simple visual tasks. Whether such learned compensatory saccades are optimal and generalize to more complex tasks, which require integrating information across a large area of the visual field, is not well understood. Here, we explore the possible effects of central vision loss on the optimal saccades during a face identification task, using a gaze-contingent simulated scotoma. We show that a new foveated ideal observer with a central scotoma correctly predicts that the human optimal point of fixation to identify faces shifts from just below the eyes to one that is at the tip of the nose and another at the top of the forehead. However, even after 5000 trials, humans of both sexes surprisingly do not change their initial fixations to adapt to the new optimal fixation points to faces. In contrast, saccades do change for tasks such as object following and to a lesser extent during search. Our findings argue against a central brain motor-compensatory mechanism that generalizes across tasks. They instead suggest task specificity in the learning of oculomotor plans in response to changes in front-end sensory processing and the possibility of separate domain-specific representations of learned oculomotor plans in the brain.SIGNIFICANCE STATEMENT The mechanism by which humans adapt eye movements in response to central vision loss is still not well understood and carries importance for gaining a fundamental understanding of brain plasticity. We show that although humans adapt their eye movements for simpler tasks such as object following and search, these adaptations do not generalize to more complex tasks such as face identification. We provide the first computational model to predict where humans with central vision loss should direct their eye movements in face identification tasks, which could become a critical tool in making patient-specific recommendations. Based on these results, we suggest a novel theory for oculomotor learning: a distributed representation of learned eye-movement plans represented in domain-specific areas of the brain.

Functional changes at the preferred retinal locus in subjects with bilateral central vision loss.

Subjects with bilateral central vision loss (CVL) use a retinal region called the preferred retinal locus (PRL) for performing various visual tasks. We probed the fixation PRL in individuals with bilateral macular disease, including age-related macular degeneration (AMD) and Stargardt disease (STGD), for localized sensitivity deficits. Three letter words at the critical print size were presented in the NIDEK MP-1 microperimeter to determine the fixation PRL and its radial retinal eccentricity from the residual fovea in 29 subjects with bilateral CVL. Fixation stability was defined as the median bivariate contour ellipse area (BCEA) from 3 fixation assessments. A standard 10-2 grid (68 locations, 2° apart) was used to determine central retinal sensitivity for Goldmann size II test spots. Baseline and follow-up supra-threshold screening of the fixation PRL for localized sensitivity deficits was performed using high density (0.2° or 0.3° apart) 0dB Goldmann size II test spots. Custom MATLAB code and a dual bootstrapping algorithm were used to register test-spot locations from the baseline and follow-up tests. Locations where the 0dB test spots were not seen on either test were labeled as micro-scotomas (MSs). Median BCEA correlated poorly with the radial eccentricity of the fixation PRL. Mean (±SD) sensitivity around the PRL from 10-2 testing was 4.93±4.73dB. The average percentage of MSs was similar for patients with AMD (25.4%), STGD (20.3%), and other etiologies of CVL (27.1%). The fixation PRL in subjects with bilateral CVL frequently includes local regions of sensitivity loss.

Sustained visual attention at different retinal eccentricities and its significance for the development of the preferred retinal locus

Sustained visual attention at different retinal eccentricities and its significance for the development of the preferred retinal locus

Can positions in the visual field with high attentional capabilities be good candidates for a new preferred retinal locus?

The sustained component of visual attention lowers the perceptual threshold of stimuli located at the attended region. Attentional performance is not equal for all eccentric positions, leading to variations in perception. The location of the preferred retinal locus (PRL) for fixation might be influenced by these attentional variations. This study investigated the relation between the placement of sustained attention and the location of a developed PRL using simulations of central scotoma. Thirteen normally sighted subjects participated in the study. Monocular sustained attention was measured in discrete eccentric locations of the visual field using the dominant eye. Subsequently, a six degrees macular scotoma was simulated and PRL training was performed during eight ten-minutes blocks of trials. After training, every subject developed a PRL. Subjects with high attentional capabilities in the lower hemifield generally developed PRLs in the lower hemifield (n=10), subjects with high attentional capabilities in the upper hemifield developed PRLs in the upper hemifield (n=2) and one subject with similar attentional capabilities in the upper and lower hemifield developed the PRL on the upper hemifield. Analyzed individually, the results showed that 70% of the subjects had a PRL location in the hemifield where high attentional performance was achieved. These results suggest that attentional capabilities can be used as a predictor for the development of the PRL and are of significance for low vision rehabilitation and for the development of new PRL training procedures, with the option for a preventive attentional training in early macular disease to develop a favorable PRL.

Morphologic and Postoperative Fixation Characteristics of the Macular Epiretinal Membrane in Young Patients Undergoing Surgery.

To describe morphologic characteristics, surgical outcomes, postoperative preferred retinal loci (PRL), and fixation stability of epiretinal membranes (ERMs) in young patients. This retrospective study analyzed 43 eyes of 41 young patients (age range: 0.8 years to 28 years) with ERMs, which were divided into two groups: secondary ERMs (SERMs; n = 28) and idiopathic ERMs (IERMs; n = 13). All 43 eyes underwent 25-gauge vitrectomy and membrane peeling. Spectral-domain optical coherence tomography scans and microperimetry were used to analyze morphologic and fixation characteristics, respectively. Premacular fibrosis was more common in SERMs group (P = .006). SERMs were also associated with less external limiting membrane (ELM) (P = .008) and ellipsoid zone visibility (P = .008) compared with IERMs. Best-corrected visual acuity (BCVA) improved in 20 eyes (69%) with SERMs (P = .005) and in 12 eyes (86%) with IERMs (P = .13). From the analysis of the postoperative fixation characteristics, there was a linear correlation between visual acuity and fixation stability (R2 = 0.495). BCVA improved significantly in young patients with ERM, even in cases with a severely disrupted ELM and ellipsoid zone. More attention should be paid to the postoperative fixation location and stability. [Ophthalmic Surg Lasers Imaging Retina. 2017;48:655-662.].

Blur Adaptation to Central Retinal Disease.

PurposeThe long-term, low-resolution vision experienced by individuals affected by retinal disease that causes central vision loss (CVL) may change their perception of blur through adaptation. This study used a short-term adaptation paradigm to evaluate adaptation to blur and sharpness in patients with CVL.MethodsA variation of Webster's procedure was used to measure the point of subjective neutrality (PSN). The image that appeared normal after adaptation to each of seven blur and sharpness levels (PSN) was measured in 12 patients with CVL (20/60 to 20/320) and 5 subjects with normal sight (NS). Patients with CVL used a preferred retinal locus to view the images. Small control studies investigated the effects of long-term and medium-term (1 hour) defocus and diffusive blur.ResultsAdaptation was reliably measured in patients with CVL and in the peripheral vision of NS subjects. The shape of adaptation curves was similar in patients with CVL and both central and peripheral vision of NS subjects. No statistical correlations were found between adaptation and age, visual acuity, retinal eccentricity, or contrast sensitivity. Long-term blur experience by a non-CVL myopic participant caused a shift in the adaptation function. Conversely, medium-term adaptation did not cause a shift in the adaptation function.ConclusionsBlur and sharp short-term adaptation occurred in peripheral vision of normal and diseased retinas. In most patients with CVL, neither adaptation nor blur perception was affected by long-term attention to peripheral low-resolution vision. The impact of blur/sharp adaptation on the benefit of image enhancement techniques for patients with CVL is discussed.

Dysflective cones: Visual function and cone reflectivity in long-term follow-up of acute bilateral foveolitis

PurposeConfocal adaptive optics scanning laser ophthalmoscope (AOSLO) images provide a sensitive measure of cone structure. However, the relationship between structural findings of diminished cone reflectivity and visual function is unclear. We used fundus-referenced testing to evaluate visual function in regions of apparent cone loss identified using confocal AOSLO images. MethodsA patient diagnosed with acute bilateral foveolitis had spectral-domain optical coherence tomography (SD-OCT) (Spectralis HRA + OCT system [Heidelberg Engineering, Vista, CA, USA]) images indicating focal loss of the inner segment-outer segment junction band with an intact, but hyper-reflective, external limiting membrane. Five years after symptom onset, visual acuity had improved from 20/80 to 20/25, but the retinal appearance remained unchanged compared to 3 months after symptoms began. We performed structural assessments using SD-OCT, directional OCT (non-standard use of a prototype on loan from Carl Zeiss Meditec) and AOSLO (custom-built system). We also administered fundus-referenced functional tests in the region of apparent cone loss, including analysis of preferred retinal locus (PRL), AOSLO acuity, and microperimetry with tracking SLO (TSLO) (prototype system). To determine AOSLO-corrected visual acuity, the scanning laser was modulated with a tumbling E consistent with 20/30 visual acuity. Visual sensitivity was assessed in and around the lesion using TSLO microperimetry. Complete eye examination, including standard measures of best-corrected visual acuity, visual field tests, color fundus photos, and fundus auto-fluorescence were also performed. ResultsDespite a lack of visible cone profiles in the foveal lesion, fundus-referenced vision testing demonstrated visual function within the lesion consistent with cone function. The PRL was within the lesion of apparent cone loss at the fovea. AOSLO visual acuity tests were abnormal, but measurable: for trials in which the stimulus remained completely within the lesion, the subject got 48% correct, compared to 78% correct when the stimulus was outside the lesion. TSLO microperimetry revealed reduced, but detectible, sensitivity thresholds within the lesion. Conclusions and importanceFundus-referenced visual testing proved useful to identify functional cones despite apparent photoreceptor loss identified using AOSLO and SD-OCT. While AOSLO and SD-OCT appear to be sensitive for the detection of abnormal or absent photoreceptors, changes in photoreceptors that are identified with these imaging tools do not correlate completely with visual function in every patient. Fundus-referenced vision testing is a useful tool to indicate the presence of cones that may be amenable to recovery or response to experimental therapies despite not being visible on confocal AOSLO or SD-OCT images.

Multimodal analysis of the Preferred Retinal Location and the Transition Zone in patients with Stargardt Disease.

The purpose of our study was to investigate morpho-functional features of the preferred retinal location (PRL) and the transition zone (TZ) in a series of patients with recessive Stargardt disease (STGD1). Fifty-two STGD1 patients with at least one ABCA4 mutation, atrophy of the central macula (MA) and an eccentric PRL were recruited for the study. Microperimetry, fundus autofluorescence (FAF), spectral-domain optical coherence tomography (SD-OCT) were performed. The location and stability of the PRL along with the associated FAF pattern and visual sensitivities were determined and compared to the underlying retinal structure. The mean visual sensitivity of the PRLs for the 52 eyes was 10.76 +/- 3.70 dB. For the majority of eyes, PRLs were associated with intact ellipsoid zone (EZ) bands and qualitatively normal FAF patterns. In 17 eyes (32.7%) the eccentric PRL was located at the edge of the MA. In 35 eyes (67.3%) it was located at varying distances from the border of the MA with a TZ between the PRL and the MA. The TZ was associated with decreased sensitivity values (5.92 +/- 4.69 dB) compared to PRLs (p<0.05), with absence/disruption of the EZ band and abnormal FAF patterns (hyper or hypo-autofluorescence). In STGD1 eccentric PRLs are located away from the border of MA and associated with intact EZ bands and normal FAF. The TZ is characterized by structural and functional abnormalities. The results of multimodal imaging of the PRL and TZ suggest a possible sequence of retinal and functional changes with disease progression that may help in the planning of future therapies; RPE dysfunction appears to be the primary event leading to photoreceptor degeneration and then to RPE loss.

FMRI with Central Vision Loss: Effects of Fixation Locus and Stimulus Type.

In patients with central visual field scotomata, a large part of visual cortex is not adequately stimulated. Patients often use a new eccentric fixation area on intact peripheral retina ("preferred retinal locus"-PRL) that functions as a pseudo-fovea. We used functional magnetic resonance imaging (fMRI) to examine whether stimulating this pseudo-fovea leads to increased activation or altered activation patterns in visual cortex in comparison to stimulating a comparable peripheral area in the opposite hemifield (OppPRL). Nineteen patients with binocular central scotomata caused by hereditary retinal dystrophies and an age-matched control group were tested. The center of the visual field, PRL, and OppPRL were stimulated with flickering checkerboard stimuli and object pictures during fMRI measurement. Results show that stimulation with pictures of everyday objects led to overall larger BOLD (blood oxygen level dependent) responses in visual cortex compared to that evoked by stimulation with flickering checkerboards. Patients showed this enhancement as early as in V1. When the PRL was directly stimulated with object pictures, the central representation area in early visual cortex was coactivated in the patients but not in the controls. In higher visual areas beyond retinotopic cortex, BOLD responses to stimulation of the PRL with object pictures were significantly enhanced in comparison to stimulation of the OppPRL area. Highly stable eccentric fixation with the PRL was associated with a higher BOLD signal in visual cortex in patients, and this effect was most pronounced in the conditions with object picture stimulation. The observed results suggest that naturalistic images are more likely to trigger top-down processes that regulate activation in early visual cortex in patients with central vision loss.

Fixation Stability Recording: How Long for Eyes with Central Vision Loss?

Fixation examination with the MP-1 microperimeter (Nidek Technologies Srl., Vigonza, PD, Italy) determines the preferred retinal loci and fixation stability in patients with central vision loss. It is typically done for periods of 15 to 30 s as per the manual's recommendations, which are arbitrary. In this study, we examined (1) whether fixation stability depends on the duration of recording and (2) whether fixation stability changes over time. Raw eye-position data from 76 patients with bilateral central vision loss (mean age = 80 ± 9.6 yrs) who had fixation examination recordings with the MP-1of at least 15 s were used. Bivariate contour ellipse areas (BCEAs) were calculated and compared for intervals of 0 to 5 s, 0 to 10 s, and 0 to 15 s and for three consecutive 5-s intervals (0-5 s, 5-10 s, and 10-15 s). Ellipse's centroid location, axes extent, and tilt angle were also evaluated for each of these intervals. BCEA worsened significantly with increasing the time of fixation recording (P < .001). Compared to the BCEA during the first 5 s of examination recording, median BCEA increased by a factor of 1.4 for the first 10 s and of 1.6 for the first 15 s of recording. However, the bivariate ellipses for the three consecutive 5-s intervals were the same in terms of area, centroid location, and axes extent, but differed significantly in tilt angle (P = .005). Fixation stability (BCEAs) results were also confirmed with an additional analysis performed on shorter sampling intervals. Fixation stability deteriorates with increasing duration of the fixation recording, but when fixation is evaluated in shorter consecutive 5-s intervals, only a difference in ellipse's tilt angle is found. These results suggest that the current recommendations for fixation stability recording with the MP-1 can be shortened to a less demanding duration.

A preferred retinal location of fixation can be induced when systematic stimulus relocations are applied.

Patients with central vision loss obtain visual information by fixating on an object eccentrically with a preferred retinal locus of fixation (PRL). Patients do not always choose the most efficient PRL position, and as a consequence, visual performance is not always fully exploited. This study investigates whether PRLs can be induced by applying systematic stimulus relocations. The PRL was trained using a central scotoma simulation in 15 healthy subjects. They performed different visual tasks during four sessions, after which their reading performance was evaluated. In five subjects the stimulus was relocated to the left hemifield whenever a saccade would place the stimulus on the opposite hemifield. In five different subjects the relocation was inversed: The stimulus was located in the right hemifield. The relocation was 7.5° of visual angle and it was applied horizontally. Five additional subjects naturally chose the PRL location. They were used as the control group to evaluate the development of a PRL. After training, subjects performed visual search tasks on static stimuli. Evaluation after training showed that systematic stimulus relocations can be used to influence the development of the PRL. These results might be significant for the development of training strategies for the visually impaired.

Peripheral oculomotor training in individuals with healthy visual systems: Effects of training and training transfer

Individuals with pathological or simulated central visual field loss can be trained to use a preferred retinal locus (PRL) as a substitute for their non-functioning fovea. The functional benefits of a stable PRL are well documented, but little is known about oculomotor adaptations during PRL acquisition or transfer of training to another location in response to real or simulated disease progression. In this study, eight normally-sighted observers were trained to use a pseudo-PRL (pPRL) at one of two locations by guiding an eccentrically placed, gaze-contingent ring over a fixation target. The pPRL location was 6.4 degrees in either inferior or right visual field, balanced across observers. Training was completed in two sessions of 200 hundred trials separated by a week. Between sessions, the pPRL position was switched. Task performance was quantified both in terms of gaze stability around the fixation target and gaze accuracy in terms of distance between the target and ring centers. The latter was used to provide feedback by covarying the diameter of the ring to make the task easier or harder on the basis of subject performance. Accuracy and stability significantly increased with training and was comparable at each trained location. Performance gains were retained over a week and transferred from the first to the second pPRL location. Thus, pPRL training with feedback can provide sustained, generalizable improvements in oculomotor control following simulated foveal vision loss. These results suggest that low vision rehabilitation specialists may prioritize PRL training locations based on sensory function alone, since oculomotor gains are relatively uniform; and that training early in the disease process may benefit later adaptations should eye disease progress.

Fixation Stability and Viewing Distance in Patients with AMD.

People with normal vision perform activities of daily living binocularly, while changing viewing distance frequently and effortlessly. Typically, in patients with age-related macular degeneration (AMD), fixation stability is recorded with monocular instruments at a fixed viewing distance (i.e. optical infinity) to determine the location and precision of the preferred retinal loci (PRLs)-the part of the functional retina that fulfills the role of a pseudo-fovea. Fixation stability recorded with these instruments has been related to performance on visual tasks at shorter viewing distances, although it is not known how viewing distance affects the precision of ocular motor control in these patients. This study examined whether viewing distance affects fixation stability during binocular and monocular viewing. Thirty patients with bilateral AMD, 10 older controls, and 10 younger controls participated. Each patient's better eye (BE) and worse eye (WE) were identified based on their visual acuity. Fixation stability was recorded with a binocular eye-tracker at three viewing distances (40 cm, 1 m, 6 m) in binocular and monocular (with BE and with WE) viewing conditions. Fixation stability was evaluated with a bivariate contour ellipse area. For the AMD group, there was no effect of viewing distance on fixation stability, regardless of viewing condition (i.e. binocular, monocular with the BE or with the WE). The same pattern of results was found for the two control groups. Viewing distance does not affect fixation stability in patients with AMD. Fixation stability data recorded with an instrument at a fixed viewing distance can be related to performance on visual tasks at other viewing distances.

Morpho-functional analysis of Stargardt Disease for reading

ObjectiveTo analyze Stargardt disease (STGD) by morpho-functional examination and investigate the relationship between morpho-functional measures and reading performance. DesignObservational case series study. ParticipantsFifteen patients with STGD. MethodsTwenty-six eyes of 15 patients underwent complete ophthalmic evaluation. Spectral domain optical coherence tomography, fundus autofluorescence (FAF), best corrected visual acuity (BCVA), and microperimetric examinations were performed. FAF and optical coherence tomography (OCT) overlap on microperimetric images was obtained in order to evaluate both tomographic and FAF features passing through the eccentric fixation area. Both morphologic features and functional data were correlated with magnification of prescribed device and reading rate. ResultsUnivariable analysis showed a significant correlation between magnification power and greatest linear dimension of both OCT and FAF (r = 0.69 and r = 0.67; p < 0.05). Magnification power was related to best corrected visual acuity (r = 0.56; p < 0.05). Retinal sensitivity map (r = 0.57; p < 0.05) was considered an indicator of reading rate. Magnification levels showed a positive correlation with eccentric preferred retinal location (p = 0.03) and the degree of FAF alteration (normal, dishomogeneous, ipoautofluorescence; p < 0.0001). ConclusionsAs a result of the overlapping of OCT/FAF imaging on microperimetric exam, residual activity of outer retinal layers passing through the eccentric fixation area seems to be related with required magnification and reading rate. Identification of morpho-functional parameters is helpful for designing a customized rehabilitative program.