The Logistical Backbone of Photoreceptor Cell Function: Complementary Mechanisms of Dietary Vitamin A Receptors and Rhodopsin Transporters

In this review, we outline our current understanding of the mechanisms involved in the absorption, storage, and transport of dietary vitamin A to the eye, and the trafficking of rhodopsin protein to the photoreceptor outer segments, which encompasses the logistical backbone required for photoreceptor cell function. Two key mechanisms of this process are emphasized in this manuscript: ocular and systemic vitamin A membrane transporters, and rhodopsin transporters. Understanding the complementary mechanisms responsible for the generation and proper transport of the retinylidene protein to the photoreceptor outer segment will eventually shed light on the importance of genes encoded by these proteins, and their relationship on normal visual function and in the pathophysiology of retinal degenerative diseases.

Adverse COVID-19 outcomes in American Veterans with age-related macular degeneration: a case-control study

OBJECTIVES

Prior studies suggest that patients with age-related macular degeneration (AMD) have poorer COVID-19 outcomes. This study aims to evaluate whether AMD is associated with adverse COVID-19 outcomes in a large clinical database.

DESIGN

Case-control study.

SETTING

We obtained demographic and clinical data from a national US Veterans Affairs (VA) database for all Veterans aged 50 years or older with positive COVID-19 testing prior to 2 May 2021.

PRIMARY AND SECONDARY OUTCOME MEASURES

The primary outcome measure was hospitalisation. Secondary outcome measures were intensive care unit admission, mechanical ventilation and death. Potential associations between AMD and outcome measures occurring within 60 days of COVID-19 diagnosis were evaluated using multiple logistic regression analyses.

RESULTS

Of the 171 325 patients in the study cohort, 7913 (5%) had AMD and 2152 (1%) had severe AMD, defined as advanced atrophic or exudative AMD disease coding. Multiple logistic regression adjusting for age, Charlson Comorbidity Index, sex, race, ethnicity and COVID-19 timing showed that an AMD diagnosis did not significantly increase the odds of hospitalisation (p=0.11). Using a Bonferroni-adjusted significance level of 0.006, AMD and severe AMD also were not significant predictors for the secondary outcomes, except for AMD being modestly protective for death (p=0.002).

CONCLUSIONS

After adjusting for other variables, neither AMD nor severe AMD was a risk factor for adverse COVID-19 outcomes in the VA healthcare system. These findings indicate that an AMD diagnosis alone should not alter recommended ophthalmic management based on COVID-19 adverse outcome risk.

In Silico Prediction of MYO1C-Rhodopsin Interactions and Its Significance in Protein Localization and Visual Function

Rods and cones are photoreceptor neurons in the retina that are required for visual sensation in vertebrates, where proper protein localization and compartmentalization are critical for phototransduction and visual function. In human retinal diseases, improper protein transport to the outer segment (OS) or mislocalization of proteins to the inner segment (IS) could lead to impaired visual responses and photoreceptor cell degeneration, causing a loss of visual function. We showed involvement of an unconventional motor protein, MYO1C, in the proper localization of rhodopsin to the OS, where loss of MYO1C in a mammalian model caused mislocalization of rhodopsin to IS and cell bodies, leading to progressively severe retinal phenotypes. In this study, using modeling and docking analysis, we aimed to identify the protein-protein interaction sites between MYO1C and Rhodopsin to establish a hypothesis that a physical interaction between these proteins is necessary for the proper trafficking of rhodopsin and visual function.

The role of motor proteins in photoreceptor protein transport and visual function

BACKGROUND

Rods and cones are photoreceptor neurons in the retina that are required for visual sensation in vertebrates, wherein the perception of vision is initiated when these neurons respond to photons in the light stimuli. The photoreceptor cell is structurally studied as outer segments (OS) and inner segments (IS) where proper protein sorting, localization, and compartmentalization are critical for phototransduction, visual function, and survival. In human retinal diseases, improper protein transport to the OS or mislocalization of proteins to the IS and other cellular compartments could lead to impaired visual responses and photoreceptor cell degeneration that ultimately cause loss of visual function.

RESULTS

Therefore, studying and identifying mechanisms involved in facilitating and maintaining proper protein transport in photoreceptor cells would help our understanding of pathologies involving retinal cell degeneration in inherited retinal dystrophies, age-related macular degeneration, and Usher Syndrome.

CONCLUSIONS

Our mini-review will discuss mechanisms of protein transport within photoreceptors and introduce a novel role for an unconventional motor protein, MYO1C, in actin-based motor transport of the visual chromophore Rhodopsin to the OS, in support of phototransduction and visual function.

Beneficial Effects of Spatial Remapping for Reading With Simulated Central Field Loss

Purpose

People with central field loss (CFL) lose information in the scotomatous region. Remapping is a method to modify images to present the missing information outside the scotoma. This study tested the hypothesis that remapping improves reading performance for subjects with simulated CFL.

Methods

Circular central scotomas, with diameters ranging from 4° to 16°, were simulated in normally sighted subjects using an eye tracker on either a head-mounted display (HMD) (experiments 1, 2) or a traditional monitor (experiment 3). In the three experiments, reading speed was measured for groups of 7, 11, and 13 subjects with and without remapping of text.

Results

Remapping increased reading speed in all three experiments. On the traditional monitor, it increased reading speed by 34% (8°), 38% (12°), and 35% (16°). In the two HMD experiments, remapping increased reading speed only for the largest scotoma size, possibly due to latency of updating of the simulated scotoma.

Conclusions

Remapping significantly increased reading speed in simulated CFL subjects. Additional testing should examine the efficacy of remapping for reading and other visual tasks for patients with advanced CFL.

Association of Disorganization of Retinal Inner Layers With Vision After Resolution of Center-Involved Diabetic Macular Edema

IMPORTANCE

Macular edema (ME) prognosis and treatment response vary according to the underlying abnormalities. Biomarkers of visual acuity (VA) improvement could influence management decisions in different types of ME.

OBJECTIVE

To investigate whether disorganization of retinal inner layers (DRIL) and other spectral-domain optical coherence tomography (SD-OCT)-derived variables are associated with subsequent VA after ME resolution in both nondiabetic and diabetic ME.

DESIGN, SETTING, AND PARTICIPANTS

A retrospective, longitudinal cohort study in which Snellen VA testing and SD-OCT macular imaging were performed, was conducted at a tertiary referral eye center for retinal diseases. The medical records of all patients with ME from December 1, 2010, to December 31, 2012, were reviewed. The date of the last follow-up was June 1, 2013. Participants included 55 patients (70 eyes) with center-involved ME that had resolved during an 8-month period. Patients were grouped based on the source of ME (diabetic vs nondiabetic). Exclusion criteria included significant media opacity interfering with good-quality SD-OCT image acquisition. Masked graders analyzed the central 1500-μm macular region for changes, including cysts, DRIL length and extent, and outer retinal layers disruption. Intragrader and intergrader agreement Spearman rank correlation coefficients ranged from 0.70 to 0.93 for quantitative measurement, and κ values ranged from 0.88 to 1.00 for qualitative grading.

MAIN OUTCOMES AND MEASURES

Visual acuity and morphologic changes measured on SD-OCT.

RESULTS

In both groups, VA after ME resolution correlated with baseline VA. In diabetic ME involving a multivariable model including baseline VA and DRIL, total length was associated with subsequent VA as determined by a parameter estimate (PE) of 0.0003 (95% CI, 0-0.0006) (P = .03). The VA change during the 8-month period, after adjusting for baseline VA, was best associated with DRIL change (PE, 0.0002 [95% CI, 0-0.0003]; P = .04). Participants whose DRIL resolved, both early and late, showed improvement in their VA deficit at 8 months (least squares mean [SE], 41.3 [28.5] and 40.9 [37.5], respectively) compared with nonresolvers, whether inconsistent or persistent, whose VA worsened. After adjustment for baseline VA, eyes with persistent DRIL showed the largest difference in VA deficit compared with those with no baseline DRIL (-89.6 [27.2] vs 49.7 [19.6], respectively; P = .006).

CONCLUSIONS AND RELEVANCE

The presence of DRIL at baseline and its resolution pattern may be associated with subsequent VA after resolution of center-involved diabetic ME.

Retinal optical coherence tomography image enhancement via shrinkage denoising using double-density dual-tree complex wavelet transform

ABSTRACT. Image enhancement of retinal structures, in optical coherence tomography (OCT) scans through denoising, has the potential to aid in the diagnosis of several eye diseases. In this paper, a locally adaptive denoising algorithm using double-density dual-tree complex wavelet transform, a combination of the double-density wavelet transform and the dual-tree complex wavelet transform, is applied to reduce speckle noise in OCT images of the retina. The algorithm overcomes the limitations of commonly used multiple frame averaging technique, namely the limited number of frames that can be recorded due to eye movements, by providing a comparable image quality in significantly less acquisition time equal to an order of magnitude less time compared to the averaging method. In addition, improvements of image quality metrics and 5 dB increase in the signal-to-noise ratio are attained.