Age-related changes of color visual acuity in normal eyes

Purpose To evaluate the age-related change in color visual acuity (CVA) in normal eyes. Methods In total, 162 normal eyes (162 subjects, women: 52, men: 110, age range: 15–68 years) with best-corrected visual acuity (BCVA) ≥20/13 were enrolled. Fifteen colors from the New Color Test (chroma 6) were applied to Landolt “C” rings, white point D65 was applied as background, and a luminance of 30 cd/m2 was set for both the rings and the background. These rings were used to measure the chromatic spatial discrimination acuity as the CVA value, while changing the stimulus size. Correlations of the CVA value of each color and age were evaluated. Mean CVA values of all 15 colors (logarithm of the minimum angle of resolution) were compared between age groups in 10-year increments. Results Nine CVA values (red, yellow-red, red-yellow, green, blue-green, green-blue, purple, red-purple, and purple-red) were negatively correlated with age (all p<0.05); the remaining six (yellow, green-yellow, yellow-green, blue, purple-blue, and blue-purple), as well as BCVA were not. The age groups with the best to worst mean CVA values of 15 colors were as follows: 20–29 (mean ± standard deviation, 0.303 ± 0.113), 30–39 (0.324 ± 0.096), 10–19 (0.333 ± 0.022), 50–59 (0.335 ± 0.078), 40–49 (0.339 ± 0.096), and 60–69 (0.379 ± 0.125) years. There were statistically significant differences between mean CVA values of the following groups: 20–29 and 40–49 years; 20–29 and 60–69 years; 30–39 and 60–69 years (all p<0.01). Conclusions The CVA values related to the medium/long-wavelength-sensitive cones were more susceptible to aging than those related to the short-wavelength-sensitive cones. This differed from previous reports, and may be related to the difference in the range of foveal cone function evaluated with each examination.

Weeklong improved colour contrasts sensitivity after single 670 nm exposures associated with enhanced mitochondrial function

Mitochondrial decline in ageing robs cells of ATP. However, animal studies show that long wavelength exposure (650–900 nm) over weeks partially restores ATP and improves function. The likely mechanism is via long wavelengths reducing nanoscopic interfacial water viscosity around ATP rota pumps, improving their efficiency. Recently, repeated 670 nm exposures have been used on the aged human retina, which has high-energy demands and significant mitochondrial and functional decline, to improve vision. We show here that single 3 min 670 nm exposures, at much lower energies than previously used, are sufficient to significantly improve for 1 week cone mediated colour contrast thresholds (detection) in ageing populations (37–70 years) to levels associated with younger subjects. But light needs to be delivered at specific times. In environments with artificial lighting humans are rarely dark-adapted, hence cone function becomes critical. This intervention, demonstrated to improve aged mitochondrial function can be applied to enhance colour vision in old age.

Mouse Models of Achromatopsia in Addressing Temporal “Point of No Return” in Gene-Therapy

Achromatopsia is characterized by amblyopia, photophobia, nystagmus, and color blindness. Previous animal models of achromatopsia have shown promising results using gene augmentation to restore cone function. However, the optimal therapeutic window to elicit recovery remains unknown. Here, we attempted two rounds of gene augmentation to generate recoverable mouse models of achromatopsia including a Cnga3 model with a knock-in stop cassette in intron 5 using Easi-CRISPR (Efficient additions with ssDNA inserts-CRISPR) and targeted embryonic stem (ES) cells. This model demonstrated that only 20% of CNGA3 levels in homozygotes derived from target ES cells remained, as compared to normal CNGA3 levels. Despite the low percentage of remaining protein, the knock-in mouse model continued to generate normal cone phototransduction. Our results showed that a small amount of normal CNGA3 protein is sufficient to form “functional” CNG channels and achieve physiological demand for proper cone phototransduction. Thus, it can be concluded that mutating the Cnga3 locus to disrupt the functional tetrameric CNG channels may ultimately require more potent STOP cassettes to generate a reversible achromatopsia mouse model. Our data also possess implications for future CNGA3-associated achromatopsia clinical trials, whereby restoration of only 20% functional CNGA3 protein may be sufficient to form functional CNG channels and thus rescue cone response.

Spatial and temporal resolution of the photoreceptors rescue dynamics after treatment with voretigene neparvovec

BackgroundVoretigene neparvovec is a gene therapeutic agent for treatment of retinal dystrophies caused by bi-allelic RPE65 mutations. In this study, we report on a novel and objective evaluation of a retinotopic photoreceptor rescue.MethodsSeven eyes of five patients (14, 21, 23, 24, 36 years, 1 male, 4 females) with bi-allelic RPE65 mutations have been treated with voretigene neparvovec. The clinical examinations included visual acuity testing, dark-adapted full-field stimulus threshold (FST), dark-adapted chromatic perimeter (DAC) with a 30-degree grid, and a 30 degrees grid scotopic and photopic chromatic pupil campimetry (CPC). All evaluations and spectral domain optical coherence tomography were performed at baseline, 1 month and 3 months.ResultsAll except the oldest patient had a measurable improvement of the rod function assessed via FST, DAC or scotopic CPC at 1 month. The visual acuity improved slightly or remained stable in all eyes. A cone function improvement as measured by photopic CPC was observed in three eyes. The gain of the dark-adapted threshold with blue FST and the DAC stimuli (cyan) average correlated strongly with age (R2>0.7). The pupil response improvement in the scotopic CPC correlated with the baseline local retinal volume (R2=0.5).ConclusionsThe presented protocols allow evaluating the individual spatial and temporal effects of gene therapy effects. Additionally, we explored parameters that correlated with the success of the therapy. CPC and DAC present new and fast ways to assess functional changes in retinotopic maps of rod and cone function, measuring complementary aspects of retinal function.

A demonstration of cone function plasticity after gene therapy in achromatopsia

Achromatopsia (ACHM) is an inherited retinal disease characterised by complete loss of cone photoreceptor function from birth. In recent years, gene therapies have successfully been used to induce signal processing in dormant cones in animal models of ACHM, with greater functional benefits for younger animals. With several completed or on-going clinical trials of gene therapy for ACHM, preliminary evidence suggests that effects on visual function in adults with ACHM may be subtle. Given the known constraints of age on neural plasticity, it is possible that gene therapy earlier in life will have a greater impact. Sensitive, child-friendly tests of cone function are therefore needed to facilitate the optimisation of these treatment strategies. Here, we present a new method that leverages a multimodal approach, linking psychophysical estimates of cone function to cone-mediated signals in visual cortex, measured using fMRI. In a case study of two children with ACHM undergoing gene therapy, we find individual differences in recovery of cone function over time, with one child demonstrating strong concurrent evidence of improved cone function, and retinotopically organised responses in visual cortex to cone-selective stimuli. Integrated fMRI and psychophysical measures may provide insight into the utility of new sight-rescuing therapies at different stages of human development.

Rod photoreceptor clearance due to misfolded rhodopsin is linked to a DAMP-immune checkpoint switch

Chronic ER stress resulting from misfolding of the visual pigment rhodopsin (RHO) can lead to loss of rod photoreceptors, which initiates Retinitis Pigmentosa, characterized initially by diminished nighttime and peripheral vision. Cone photoreceptors depend on rods for glucose transport, which the neurons use for assembly of visual pigment-rich structures; as such, loss of rods also leads to a secondary loss of cone function, diminishing high resolution color vision utilized for tasks including reading, driving and facial recognition. If dysfunctional rods could be maintained to continue to serve this secondary cone preservation function, it might benefit to patients with Retinitis Pigmentosa, but the mechanisms by which rods are removed are not fully established. Using pigs expressing mutant RHO , we find that induction of a Danger-Associated Molecular Pattern (DAMP) “eat me” signal on the surface of mutant rods is correlated with targeting the live cells for programmed cell removal (PrCR) by retinal myeloid cells. Glucocorticoid therapy leads to replacement of this DAMP with a “don’t eat me” immune checkpoint on the rod surface and inhibition of PrCR. Surviving rods then continue to promote glucose transport to cones, maintaining their viability.