The association between cone density and visual function in the macula of patients with retinitis pigmentosa

Retinal Imaging Findings in Inherited Retinal Diseases

Inherited retinal diseases (IRDs) represent one of the major causes of progressive and irreversible vision loss in the working-age population. Over the last few decades, advances in retinal imaging have allowed for an improvement in the phenotypic characterization of this group of diseases and have facilitated phenotype-to-genotype correlation studies. As a result, the number of clinical trials targeting IRDs has steadily increased, and commensurate to this, the need for novel reproducible outcome measures and endpoints has grown. This review aims to summarize and describe the clinical presentation, characteristic imaging findings, and imaging endpoint measures that are being used in clinical research on IRDs. For the purpose of this review, IRDs have been divided into four categories: (1) panretinal pigmentary retinopathies affecting rods or cones; (2) macular dystrophies; (3) stationary conditions; (4) hereditary vitreoretinopathies.

Spatially-dependent model for rods and cones in the retina

We develop a mathematical model for photoreceptors in the retina. We focus on rod and cone outer segment dynamics and interactions with a nutrient source associated with the retinal pigment epithelium cells. Rod and cone densities (number per unit area of retinal surface) are known to have significant spatial dependence in the retina with cones located primarily near the fovea and the rods located primarily away from the fovea. Our model accounts for this spatial dependence of the rod and cone photoreceptor density as well as for the possibility of nutrient diffusion. We present equilibrium and dynamic solutions, discuss their relation to existing models, and estimate model parameters through comparisons with available experimental measurements of both spatial and temporal photoreceptor characteristics. Our model compares well with existing data on spatially-dependent regrowth of photoreceptor outer segments in the macular region of Rhesus Monkeys. Our predictions are also consistent with existing data on the spatial dependence of photoreceptor outer segment length near the fovea in healthy human subjects. We focus primarily on the healthy eye but our model could be the basis for future efforts designed to explore various retinal pathologies, eye-related injuries, and treatments of these conditions.

Adaptive optics imaging in inherited retinal diseases: A scoping review of the clinical literature

Adaptive optics (AO) imaging enables direct, objective assessments of retinal cells. Applications of AO show great promise in advancing our understanding of the etiology of inherited retinal disease (IRDs) and discovering new imaging biomarkers. This scoping review systematically identifies and summarizes clinical studies evaluating AO imaging in IRDs. Ovid MEDLINE and EMBASE were searched on February 6, 2023. Studies describing AO imaging in monogenic IRDs were included. Study screening and data extraction were performed by 2 reviewers independently. This review presents (1) a broad overview of the dominant areas of research; (2) a summary of IRD characteristics revealed by AO imaging; and (3) a discussion of methodological considerations relating to AO imaging in IRDs. From 140 studies with AO outcomes, including 2 following subretinal gene therapy treatments, 75% included fewer than 10 participants with AO imaging data. Of 100 studies that included participants' genetic diagnoses, the most common IRD genes with AO outcomes are CNGA3, CNGB3, CHM, USH2A, and ABCA4. Confocal reflectance AO scanning laser ophthalmoscopy was the most reported imaging modality, followed by flood-illuminated AO and split-detector AO. The most common outcome was cone density, reported quantitatively in 56% of studies. Future research areas include guidelines to reduce variability in the reporting of AO methodology and a focus on functional AO techniques to guide the development of therapeutic interventions.

Cone Density Is Correlated to Outer Segment Length and Retinal Thickness in the Human Foveola

Purpose

Assessment of the relationship between in vivo foveolar cone density, cone outer segment length (OSL), and foveal retinal thickness (RT).

Methods

Foveolar cone density maps covering the central ±300 µm of the retina were derived from adaptive optics scanning laser ophthalmoscopy images. The corresponding maps of foveal cone OSL and RT were derived from high-resolution optical coherence tomography volume scans. Alignment of the two-dimensional maps containing OSL and RT with the cone density map was achieved by placing the location of maximum OSL on the cone density centroid (CDC).

Results

Across 10 participants (27 ± 9 years; 6 female), cone density at the CDC was found to be between 147,038 and 215,681 cones/mm². The maximum OSL and minimum RT were found to lie between 31 and 40, and 193 and 226 µm, respectively. A significant correlation was observed between cone density at the CDC and maximum OSL (P = 0.001), as well as the minimal RT (P < 0.05). Across all participants, the best fit for the relationship between normalized cone density and normalized OSL within the central 300 µm was given by a quadratic function.

Conclusions

Using optical coherence tomography-derived measurements of OSL enables to estimate CDC cone density and two-dimensional foveal cone density maps for example in patient eyes unsuitable for adaptive optics imaging. Furthermore, the observation of a fixed relationship between the normalized OSL and cone density points to a conserved mechanism shaping the foveal pit.

Progression of Rare Inherited Retinal Dystrophies May Be Monitored by Adaptive Optics Imaging

Inherited retinal dystrophies (IRDs) are bilateral genetic conditions of the retina, leading to irreversible vision loss. This study included 55 eyes afflicted with IRDs affecting the macula. The diseases examined encompassed Stargardt disease (STGD), cone dystrophy (CD), and cone-rod dystrophy (CRD) using adaptive optics (Rtx1™; Imagine Eyes, Orsay, France). Adaptive optics facilitate high-quality visualisation of retinal microstructures, including cones. Cone parameters, such as cone density (DM), cone spacing (SM), and regularity (REG), were analysed. The best corrected visual acuity (BCVA) was assessed as well. Examinations were performed twice over a 6-year observation period. A significant change was observed in DM (1282.73/mm2 vs. 10,073.42/mm2, p< 0.001) and SM (9.83 μm vs. 12.16 μm, p< 0.001) during the follow-up. BCVA deterioration was also significant (0.16 vs. 0.12, p = 0.001), albeit uncorrelated with the change in cone parameters. No significant difference in REG was detected between the initial examination and the follow-up (p = 0.089).

Modeling rod and cone photoreceptor cell survival in vivo using optical coherence tomography

Many retinal diseases involve the loss of light-sensing photoreceptor cells (rods and cones) over time. The severity and distribution of photoreceptor loss varies widely across diseases and affected individuals, so characterizing the degree and pattern of photoreceptor loss can clarify pathophysiology and prognosis. Currently, in vivo visualization of individual photoreceptors requires technology such as adaptive optics, which has numerous limitations and is not widely used. By contrast, optical coherence tomography (OCT) is nearly ubiquitous in daily clinical practice given its ease of image acquisition and detailed visualization of retinal structure. However, OCT cannot resolve individual photoreceptors, and no OCT-based method exists to distinguish between the loss of rods versus cones. Here, we present a computational model that quantitatively estimates rod versus cone photoreceptor loss from OCT. Using histologic data of human photoreceptor topography, we constructed an OCT-based reference model to simulate outer nuclear layer thinning caused by differential loss of rods and cones. The model was able to estimate rod and cone loss using in vivo OCT data from patients with Stargardt disease and healthy controls. Our model provides a powerful new tool to quantify photoreceptor loss using OCT data alone, with potentially broad applications for research and clinical care.

Application of Adaptive Optics in Ophthalmology

The eye, the photoreceptive organ used to perceive the external environment, is of great importance to humans. It has been proven that some diseases in humans are accompanied by fundus changes; therefore, the health status of people may be interpreted from retinal images. However, the human eye is not a perfect refractive system for the existence of ocular aberrations. These aberrations not only affect the ability of human visual discrimination and recognition, but restrict the observation of the fine structures of human eye and reduce the possibility of exploring the mechanisms of eye disease. Adaptive optics (AO) is a technique that corrects optical wavefront aberrations. Once integrated into ophthalmoscopes, AO enables retinal imaging at the cellular level. This paper illustrates the principle of AO in correcting wavefront aberrations in human eyes, and then reviews the applications and advances of AO in ophthalmology, including the adaptive optics fundus camera (AO-FC), the adaptive optics scanning laser ophthalmoscope (AO-SLO), the adaptive optics optical coherence tomography (AO-OCT), and their combined multimodal imaging technologies. The future development trend of AO in ophthalmology is also prospected.

Structural evaluation in inherited retinal diseases

Ophthalmic genetics is a field that has been rapidly evolving over the last decade, mainly due to the flourishing of translational medicine for inherited retinal diseases (IRD). In this review, we will address the different methods by which retinal structure can be objectively and accurately assessed in IRD. We review standard-of-care imaging for these patients: colour fundus photography, fundus autofluorescence imaging and optical coherence tomography (OCT), as well as higher-resolution and/or newer technologies including OCT angiography, adaptive optics imaging, fundus imaging using a range of wavelengths, magnetic resonance imaging, laser speckle flowgraphy and retinal oximetry, illustrating their utility using paradigm genotypes with on-going therapeutic efforts/trials.

Effect of Applying Binocular Visual Training after Slanted Lateral Rectus Recession on Orthophoric Rate and Binocular Visual Function Recovery on Patients with Convergence Insufficiency-Type Intermittent Exotropia

OBJECTIVE

To explore the effect of applying binocular visual training after slanted lateral rectus recession on orthophoric rate and binocular visual function recovery on patients with convergence insufficiency-type intermittent exotropia (CI-IXT).

METHODS

A total of 76 CI-IXT child patients treated at the Strabismus and Pediatric Ophthalmology Department of our hospital from June 2019 to June 2020 were selected as the research objects, and those who met the inclusion criteria were equally divided into group A (63 eyes) and group B (61 eyes) according to the sealed envelope randomization. All child patients accepted the slanted lateral rectus recession, and after that, those in group A accepted the binocular visual training and those in group B accepted the conventional visual function rehabilitation training, so as to compare their position of eye, the best corrected visual acuity, etc., after training for statistical analysis.

RESULTS

Compared with group B after one month of surgery, group A had significantly less patients with grade I binocular vision function (P < 0.001) and more patients with grade II and III vision function (P < 0.05); between group A and group B, after 3 months and 6 months of treatment, the number of eyes with normal stereoscopic vision was significantly higher in group A (P < 0.05); at 15 days, 1 month, 3 months, and 6 months of treatment, the visual strain scores of group A were significantly lower (P < 0.001); after treatment, the number of orthophoria eyes was significantly higher in group A (P < 0.001), while the numbers of overcorrected eyes and undercorrected eyes were significantly higher in group B (P < 0.001); and the total incidence rate of adverse reactions was significantly lower in group A (P < 0.05).

CONCLUSION

Applying binocular visual training to child patients with CI-IXT after slanted lateral rectus recession can promote the recovery of binocular vision and ensure higher safety, and further study will help to establish a better solution for the affected children.