Contrast Sensitivity and Equivalent Intrinsic Noise in X-Linked Retinoschisis

Additional measures of macular function beyond visual acuity

PURPOSE

Visual function is a complex process in which external visual stimuli are interpreted. Patients with retinal diseases and prolonged follow-up times may experience changes in their visual function that are not detected by the standard visual acuity measure, as they are a result of other alterations in visual function. With the advancement of different methods to evaluate visual function, additional measurements have become available, and further standardization suggests that some methods may be promising for use in clinical trials or routine clinical practice. The objectives of this article are to review these additional measurements and to provide guidance on their application.

METHODS

The Vision Academy's membership of international retinal disease experts reviewed the literature and developed consensus recommendations for the application of additional measures of visual function in routine clinical practice or clinical trials.

RESULTS

Measures such as low-luminance visual acuity, contrast sensitivity, retinal fixation and microperimetry, and reading performance are measures which can complement visual acuity measurements to provide an assessment of overall visual function, including impact on patients' quality of life. Measures such as dark adaptation, color vision testing, binocular vision testing, visual recognition testing, and shape discrimination require further optimization and validation before they can be implemented in everyday clinical practice.

CONCLUSION

Additional measurements of visual function may help identify patients who could benefit from earlier diagnosis, detection of disease progression, and therapeutic intervention. New and additional functional clinical trial endpoints are required to fully understand the early stages of macular disease, its progression, and the response to treatment.

Retinoschisin Deficiency Induces Persistent Aberrant Waves of Activity Affecting Neuroglial Signaling in the Retina

Genetic disorders that present during development make treatment strategies particularly challenging because there is a need to disentangle primary pathophysiology from downstream dysfunction caused at key developmental stages. To provide a deeper insight into this question, we studied a mouse model of X-linked juvenile retinoschisis, an early-onset inherited condition caused by mutations in the Rs1 gene encoding retinoschisin (RS1) and characterized by cystic retinal lesions and early visual deficits. Using an unbiased approach in expressing the fast intracellular calcium indicator GCaMP6f in neuronal, glial, and vascular cells of the retina of RS1-deficient male mice, we found that initial cyst formation is paralleled by the appearance of aberrant spontaneous neuroglial signals as early as postnatal day 15, when eyes normally open. These presented as glutamate-driven wavelets of neuronal activity and sporadic radial bursts of activity by Müller glia, spanning all retinal layers and disrupting light-induced signaling. This study confers a role to RS1 beyond its function as an adhesion molecule, identifies an early onset for dysfunction in the course of disease, establishing a potential window for disease diagnosis and therapeutic intervention.SIGNIFICANCE STATEMENT Developmental disorders make it difficult to distinguish pathophysiology due to ongoing disease from pathophysiology due to disrupted development. Here, we investigated a mouse model for X-linked retinoschisis, a well defined monogenic degenerative disease caused by mutations in the Rs1 gene, which codes for the protein retinoschisin. We evaluated the spontaneous activity of explanted retinas lacking retinoschisin at key stages of development using the unbiased approach of ubiquitously expressing GCaMP6f in all retinal neurons, vasculature, and glia. In mice lacking RS1, we found that an array of novel phenotypes, which present around eye opening, are linked to glutamatergic neurotransmission and affect visual processing. These data identify a novel pathophysiology linked to RS1, and define a window where treatments might be best targeted.

Noise Generation Methods Preserving Image Color Intensity Distributions

In many visual perception studies, external visual noise is used as a methodology to broaden the understanding of information processing of visual stimuli. The underlying assumption is that two sources of noise limit sensory processing: the external noise inherent in the environmental signals and the internal noise or internal variability at different levels of the neural system. Usually, when external noise is added to an image, it is evenly distributed. However, the color intensity and image contrast are modified in this way, and it is unclear whether the visual system responds to their change or the noise presence. We aimed to develop several methods of noise generation with different distributions that keep the global image characteristics. These methods are appropriate in various applications for evaluating the internal noise in the visual system and its ability to filter the added noise. As these methods destroy the correlation in image intensity of neighboring pixels, they could be used to evaluate the role of local spatial structure in image processing.

Spatial and Temporal Integration Abnormalities in X-Linked Retinoschisis

Purpose

To evaluate spatial and temporal integration across the visual field in individuals with juvenile X-linked retinoschisis (XLRS).

Methods

Nine subjects with XLRS and 10 visually normal individuals participated. Luminance thresholds were measured at 15 locations along the horizontal visual field meridian. Locations were grouped into four regions for analysis: foveal, parafoveal (2°), perifoveal (5°-10°), and peripheral (10°-60°). For spatial integration measurements, stimulus duration was 100 ms, and size ranged from 0.01 to 2.32 deg2 (Goldmann I-V). For temporal integration measurements, stimulus size was 0.15 deg2 (Goldmann III), and duration ranged from 12 to 800 ms. The effect of stimulus size and duration on the subjects' threshold was described using integration models.

Results

Luminance thresholds for the XLRS group were more elevated for small targets (2.0×-12.6×) than for large targets (1.25×-3.2×) compared to controls for all locations. Likewise, thresholds for the XLRS group were more elevated for short durations (6.3×) than for long durations (4.0×) in the fovea and parafovea but were similarly elevated at all durations (2.0×-2.5×) in the perifovea and periphery. For both the size and duration experiments, thresholds measured in the fovea, parafovea, and perifovea of XLRS subjects were highly similar to those measured from the peripheral field of the controls.

Conclusions

Spatial and temporal integration characteristics of the XLRS fovea, parafovea, and perifovea are similar to those of the normal periphery. The results also indicate that scaling stimulus size equates thresholds for the XLRS and control subjects throughout the visual field, but scaling duration does not.