Contrast sensitivity and aging

Preservation of Intrinsically Photosensitive Retinal Ganglion Cells (ipRGCs) in Late Adult Mice: Implications as a Potential Biomarker for Early Onset Ocular Degenerative Diseases

Purpose

Intrinsically photosensitive retinal ganglion cells (ipRGCs) play a crucial role in non-image-forming visual functions. Given their significant loss observed in various ocular degenerative diseases at early stages, this study aimed to assess changes in both the morphology and associated behavioral functions of ipRGCs in mice between 6 (mature) and 12 (late adult) months old. The findings contribute to understanding the preservation of ipRGCs in late adults and their potential as a biomarker for early ocular degenerative diseases.

Methods

Female and male C57BL/6J mice were used to assess the behavioral consequences of aging to mature and old adults, including pupillary light reflex, light aversion, visual acuity, and contrast sensitivity. Immunohistochemistry on retinal wholemounts from these mice was then conducted to evaluate ipRGC dendritic morphology in the ganglion cell layer (GCL) and inner nuclear layer (INL).

Results

Morphological analysis showed that ipRGC dendritic field complexity was remarkably stable through 12 months old of age. Similarly, the pupillary light reflex, visual acuity, and contrast sensitivity were stable in mature and old adults. Although alterations were observed in ipRGC-independent light aversion distinct from the pupillary light reflex, aged wild-type mice continuously showed enhanced light aversion with dilation. No effect of sex was observed in any tests.

Conclusions

The preservation of both ipRGC morphology and function highlights the potential of ipRGC-mediated function as a valuable biomarker for ocular diseases characterized by early ipRGC loss. The consistent stability of ipRGCs in mature and old adult mice suggests that detected changes in ipRGC-mediated functions could serve as early indicators or diagnostic tools for early-onset conditions such as Alzheimer's disease, Parkinson's disease, and diabetes, where ipRGC loss has been documented.

Factors Affecting Contrast Sensitivity in Healthy Individuals: A Pilot Study

Objectives:

To determine the demographic and ocular features affecting contrast sensitivity levels in healthy individuals.

Materials and Methods:

Seventy-four eyes of 37 subjects (7-65 years old) with refractive errors less than 1.0 diopter, no history of ocular surgery, and 20/20 visual acuity were included in the study. The participants were divided by age into three groups: group 1, 7-19 years, n=11; group 2, 20-49 years, n=15; and group 3, 50-65 years, n=11. All subjects underwent anterior and posterior segment evaluation, intraocular pressure measurements, refraction measurements, and clinical evaluation for strabismus. Contrast static test was performed using Metrovision MonPack 3 vision monitor system after measuring pupil diameter. Photopic and mesopic measurements were taken sequentially from right eyes, left eyes, and both eyes together.

Results:

Contrast sensitivity at intermediate and high spatial frequencies was lower with increasing age. Binocular measurements were better than monocular, and mesopic measurements were better than photopic measurements at all spatial frequencies. Contrast sensitivity at higher spatial frequency was lower with hyperopic refraction values.

Conclusion:

Increasing age, small pupil diameter, hyperopia, and photopic conditions were associated with lower contrast sensitivity in healthy individuals. Binocular contrast sensitivity measurements were better than monocular contrast sensitivity measurements in all conditions and spatial frequencies.