Outer Segment Thickness Predicts Visual Field Response to QLT091001 in Patients with RPE65 or LRAT Mutations

Quantitative and qualitative characterization of retinal dystrophies in canine models of inherited retinal diseases using spectral domain optical coherence tomography (SD-OCT)

The purpose of this study was to establish spectral domain optical coherence tomography (SD-OCT) assessment data in well-established canine models of inherited retinal dystrophies: PDE6B-rod-cone dysplasia 1 (RCD1: early onset retinitis pigmentosa), PRCD-progressive rod-cone degeneration (PRCD: late onset retinitis pigmentosa), CNGB3-achromatopsia, and RPE65-Leber congenital amaurosis (LCA). High resolution SD-OCT images of the retina were acquired from both eyes in 5 planes: temporal; superotemporal; superior; nasal; and inferior in adult dogs with: RCD1 (n = 4 dogs, median age: 1.5 yrs); PRCD (n = 2, 4.3 yrs); LCA (n = 3, 5.2 yrs); achromatopsia (n = 3, 4.2 yrs); and wild types (wt, n = 6, 5.5 yrs). Total, inner and outer retinal thicknesses and ellipsoid zone were analyzed. In selected animals, histomorphometric evaluations were performed. In dogs with RCD1, PRCD, and LCA, the thickness of the outer retina was, compared to wt, significantly decreased (p ≤ 0.02) in all OCT imaging planes, and in superotemporal and inferior imaging planes in dogs with achromatopsia. No significant thinning was observed in inner retina thickness in any disease model except in the inferior imaging plane in dogs with RCD1. Dogs with RCD1, PRCD, and LCA had significantly more areas with disrupted ellipsoid zone in the presumed area centralis than wt (p ≤ 0.001). OCT findings provide baseline information for research of retinal dystrophies using these canine models.

Inherited Retinal Dystrophies: Role of Oxidative Stress and Inflammation in Their Physiopathology and Therapeutic Implications

Inherited retinal dystrophies (IRDs) are a large group of genetically and clinically heterogeneous diseases characterized by the progressive degeneration of the retina, ultimately leading to loss of visual function. Oxidative stress and inflammation play fundamental roles in the physiopathology of these diseases. Photoreceptor cell death induces an inflammatory state in the retina. The activation of several molecular pathways triggers different cellular responses to injury, including the activation of microglia to eliminate debris and recruit inflammatory cells from circulation. Therapeutical options for IRDs are currently limited, although a small number of patients have been successfully treated by gene therapy. Many other therapeutic strategies are being pursued to mitigate the deleterious effects of IRDs associated with oxidative metabolism and/or inflammation, including inhibiting reactive oxygen species’ accumulation and inflammatory responses, and blocking autophagy. Several compounds are being tested in clinical trials, generating great expectations for their implementation. The present review discusses the main death mechanisms that occur in IRDs and the latest therapies that are under investigation.

Leber congenital amaurosis/early-onset severe retinal dystrophy: current management and clinical trials

Leber congenital amaurosis (LCA) is a severe congenital/early-onset retinal dystrophy. Given its monogenic nature and the immunological and anatomical privileges of the eye, LCA has been particularly targeted by cutting-edge research. In this review, we describe the current management of LCA, and highlight the clinical trials that are on-going and planned. RPE65-related LCA pivotal trials, which culminated in the first Food and Drug Administration-approved and European Medicines Agency-approved ocular gene therapy, have paved the way for a new era of genetic treatments in ophthalmology. At present, multiple clinical trials are available worldwide applying different techniques, aiming to achieve better outcomes and include more genes and variants. Genetic therapy is not only implementing gene supplementation by the use of adeno-associated viral vectors, but also clustered regularly interspaced short palindromic repeats (CRISPR)-mediated gene editing and post-transcriptional regulation through antisense oligonucleotides. Pharmacological approaches intending to decrease photoreceptor degeneration by supplementing 11-cis-retinal and cell therapy's aim to replace the retinal pigment epithelium, providing a trophic and metabolic retinal structure, are also under investigation. Furthermore, optoelectric devices and optogenetics are also an option for patients with residual visual pathway. After more than 10 years since the first patient with LCA received gene therapy, we also discuss future challenges, such as the overlap between different techniques and the long-term durability of efficacy. The next 5 years are likely to be key to whether genetic therapies will achieve their full promise, and whether stem cell/cellular therapies will break through into clinical trial evaluation.

Long-Term Follow-Up of Retinal Degenerations Associated With LRAT Mutations and Their Comparability to Phenotypes Associated With RPE65 Mutations

Purpose

To investigate the natural history in patients with LRAT-associated retinal degenerations (RDs), in the advent of clinical trials testing treatment options.

Methods

A retrospective cohort of 13 patients with LRAT-RDs.

Results

Twelve patients from a genetic isolate carried a homozygous c.12del mutation. One unrelated patient carried a homozygous c.326G>T mutation. The mean follow-up time was 25.3 years (SD 15.2; range 4.8–53.5). The first symptom was nyctalopia (n = 11), central vision loss (n = 1), or light-gazing (n = 1), and was noticed in the first decade of life. Seven patients (54%) reached low vision (visual acuity < 20/67), four of whom reaching blindness (visual acuity < 20/400), respectively, at mean ages of 49.9 (SE 5.4) and 59.9 (SE 3.1) years. The fundus appearance was variable. Retinal white dots were seen in six patients (46%). Full-field electroretinograms (n = 11) were nondetectable (n = 2; ages 31–60), reduced in a nonspecified pattern (n = 2; ages 11–54), or showed rod–cone (n = 6; ages 38–48) or cone–rod (n = 1; age 29) dysfunction. Optical coherence tomography (n = 4) showed retinal thinning but relative preservation of the (para-)foveal outer retinal layers in the second (n = 1) and sixth decade of life (n = 2), and profound chorioretinal degeneration from the eighth decade of life (n = 1).

Conclusions

LRAT-associated phenotypes in this cohort were variable and unusual, but generally milder than those seen in RPE65-associated disease, and may be particularly amenable to treatment. The window of therapeutic opportunity can be extended in patients with a mild phenotype.

Translational Relevance

Knowledge of the natural history of LRAT-RDs is essential in determining the window of opportunity in ongoing and future clinical trials for novel therapeutic options.

[Thickness of the retinal photoreceptor layers and the choroid, and bioelectrical activity of the macula in retinitis pigmentosa]

PURPOSE

To assess the changes in photoreceptor retinal layers and the choroid in comparison with bioelectrical activity of the macula in patients with retinitis pigmentosa (RP).

MATERIAL AND METHODS

The study included 10 patients (20 phakic eyes) with RP. Mean age was 27±18.5 years; mean best corrected visual acuity was 0.38±0.22. In addition to standard ophthalmological examination and fundus photography, each patient underwent an electrophysiological study on an electroretinograph MBN (Russia) recording general electroretinogram (ERG), maximal ERG (cone-rod response), 30 Hz flicker ERG and macular ERG (mERG). Choroidal thickness (CT) measurement and segmentation of the retina with following calculation of the thickness of different retinal layers was performed on SD-OCT RS-3000 Advance 'Nidek', Japan), it included obtainment of the 6-mm-diameter map in accordance with the Early Treatment Diabetic Retinopathy Study (ETDRS).

RESULTS

The study revealed a decrease in thickness of the choroid, retina, and the photoreceptor layers: 1) the layer with photoreceptor outer segment (OS) and retinal pigment epithelium (RPE) and 2) the layer with photoreceptor inner segment (IS) and outer nuclear layer. Decreased thickness of these layers is associated with the reduction of bioelectric activity of the macula as seen with mERG.

CONCLUSION

Decreased thickness of the retina, choroid and photoreceptor layers in all segments of the macula according to EDTRS standards is associated with reduced bioelectric activity of the macula recorded with mERG.

Morphologic characteristics and clinical significance of the macular-sparing area in patients with retinitis pigmentosa as revealed by multicolor imaging

Retinitis pigmentosa (RP) is an inherited retinal disease caused by the degeneration of photoreceptors and retinal pigment epithelium cells within the eye. The present study aimed to evaluate the effectiveness of multicolor imaging as a novel technique for the depiction of morphological features in the macular area of patients with RP. Additionally, the correlation between the size of the macular-sparing area and the best corrected visual acuity (BCVA), central visual field function and subfoveal choroidal thickness (SFCT) was analyzed. A total of 25 individuals with RP (n=50 eyes) and 35 healthy individuals (n=70 eyes) were enrolled in the current study. Images of the macular area were captured using multicolor imaging and traditional fundus photography, and their ability to depict retinal features was compared. The size of the macular-sparing area in patients with RP was measured using built-in measurement software programs. The correlations between the macular-sparing area and the BCVA, visual field and SFCT were analyzed using a Spearman's rank correlation test. The results demonstrated that multicolor imaging revealed clinical features of the macular area in greater detail than traditional fundus photography irrespective of whether the patient also had complications, including cataracts and epiretinal membranes. Multicolor imaging clearly defined the borders of the macular-sparing area corresponding to the relatively intact outer retinal structures on optical coherence tomography images, particularly the status of the ellipsoid zone and external limiting membrane. There was a significant positive correlation between the macular-sparing area and BCVA (r=−0.631; P<0.001), and the visual field in terms of MD (r=0.402; P<0.05) and PSD (r=0.595; P<0.001), however, there was not a statistically significant correlation between the macular-sparing area and SFCT. The present study demonstrated that multicolor imaging is capable of detecting macular changes and complications in patients with RP. Multicolor imaging may be particularly useful in assessing the detailed characteristics of the macular-sparing area, as this appears to be associated with visual function.

Safety and Proof-of-Concept Study of Oral QLT091001 in Retinitis Pigmentosa Due to Inherited Deficiencies of Retinal Pigment Epithelial 65 Protein (RPE65) or Lecithin:Retinol Acyltransferase (LRAT)

Restoring vision in inherited retinal degenerations remains an unmet medical need. In mice exhibiting a genetically engineered block of the visual cycle, vision was recently successfully restored by oral administration of 9-cis-retinyl acetate (QLT091001). Safety and visual outcomes of a once-daily oral dose of 40 mg/m²/day QLT091001 for 7 consecutive days was investigated in an international, multi-center, open-label, proof-of-concept study in 18 patients with RPE65- or LRAT-related retinitis pigmentosa. Eight of 18 patients (44%) showed a ≥20% increase and 4 of 18 (22%) showed a ≥40% increase in functional retinal area determined from Goldmann visual fields; 12 (67%) and 5 (28%) of 18 patients showed a ≥5 and ≥10 ETDRS letter score increase of visual acuity, respectively, in one or both eyes at two or more visits within 2 months of treatment. In two patients who underwent fMRI, a significant positive response was measured to stimuli of medium contrast, moving, pattern targets in both left and right hemispheres of the occipital cortex. There were no serious adverse events. Treatment-related adverse events were transient and the most common included headache, photophobia, nausea, vomiting, and minor biochemical abnormalities. Measuring the outer segment length of the photoreceptor layer with high-definition optical coherence tomography was highly predictive of treatment responses with responders having a significantly larger baseline outer segment thickness (11.7 ± 4.8 μm, mean ± 95% CI) than non-responders (3.5 ± 1.2 μm). This structure-function relationship suggests that treatment with QLT091001 is more likely to be efficacious if there is sufficient photoreceptor integrity.