Blue cone monochromacy (BCM) is a severe X-linked blinding disorder caused by mutations in the OPN1LW/OPN1MW locus, resulting in impaired cone function and structural degeneration. We conduct a comparative analysis of AAV gene therapy in Opn1mw-/-/Opn1sw-/- (double knockout, DKO) and Opn1mwC198R/Opn1sw-/- (C198R) BCM mouse models to contrast therapeutic outcomes at different stages. We demonstrate the AAV8Y733F capsid achieves superior rescue compared to AAV5. Both DKO and C198R models show comparable therapeutic outcomes, with efficacy consistently decreasing in older mice. Structural analysis reveals both models display rapid degenerative changes in cone outer and inner segments. We observe age-related reductions in transgene expression for both models, potentially resulting from decreased cone transducibility, transgene silencing/downregulation, or disease-related genome expression alterations. Notably, the Pde6c and Cngb3 promoters maintain robust activity in degenerating cones. These findings suggest use of an optimized cone promoter can ultimately extend the therapeutic window and treatment longevity in BCM cones.

Blue cone monochromatism (BCM) is a rare X-linked recessive disease characterized by an absent function of L and M cones and a normal function of S cones and rods. The estimated prevalence is 1 in 100,000 individuals, and males are predominantly affected. The patients usually present at birth or in early infancy. The clinical features include impaired color vision (patients only see colors in the blue range of light) and poor visual acuity (between 20/80 and 20/200), photophobia, pendular nystagmus (which may improve over time), and myopia. The condition is typically stationary, but progressive central retinal atrophy may be seen later in life. The presentation is similar to rod monochromatism (achromatopsia), an autosomal recessive disease that affects all three types of cones. However, BCM patients have better visual acuity, preserved tritan discrimination, and myopia (as opposed to hyperopia in achromatopsia). Electrophysiology, psychophysical testing (using Berson plates), and family history (x-linked recessive vs. autosomal recessive) help distinguish the two conditions.

L-cone opsin expression by gene therapy is a promising treatment for blue cone monochromacy (BCM) caused by congenital lack of long- and middle-wavelength-sensitive (L/M) cone function. Eight patients with BCM and confirmed pathogenic variants at the OPN1LW/OPN1MW gene cluster participated. Optical coherence tomography (OCT), chromatic perimetry, chromatic microperimetry, chromatic visual acuity (VA), and chromaticity thresholds were performed with unmodified commercial equipment and/or methods available in the public domain. Adaptive optics scanning laser ophthalmoscope (AOSLO) imaging was performed in a subset of patients. Outer retinal changes were detectable by OCT with an age-related effect on the foveal disease stage. Rod and short-wavelength-sensitive (S) cone functions were relatively retained by perimetry, although likely impacted by age-related increases in the pre-retinal absorption of short-wavelength lights. The central macula showed a large loss of red sensitivity on dark-adapted microperimetry. Chromatic VAs with high-contrast red gratings on a blue background were not detectable. Color vision was severely deficient. AOSLO imaging showed reduced total cone density with majority of the population being non-waveguiding. This study developed and evaluated specialized outcomes that will be needed for the determination of efficacy and safety in human clinical trials. Dark-adapted microperimetry with a red stimulus sampling the central macula would be a key endpoint to evaluate the light sensitivity improvements. VA changes specific to L-opsin can be measured with red gratings on a bright blue background and should also be considered as outcome measures in future interventional trials.

The aim of this exploratory study is to investigate the role of S-cones in oscillatory potentials (OPs) generation by individuals with blue-cone monochromacy (BCM), retaining S-cones, and achromatopsia (ACHM), lacking cone functions. This retrospective study analyzed data from 39 ACHM patients, 20 BCM patients, and 26 controls. Central foveal thickness was obtained using spectral-domain optical coherence tomography, while amplitude and implicit time (IT) of a- and b-waves were extracted from the ISCEV Standard dark-adapted 3 cd.s.m-2 full-field ERG (ffERG). Time-frequency analysis of the same measurement enabled the extraction of OPs, providing insights into the dynamic characteristics of the recorded signal. Both ACHM and BCM groups showed a significant reduction (p < .00001) of a- and b-wave amplitudes and ITs as well as the power of the OPs compared to the control groups. The comparison between ACHM and BCM didn't show any statistically significant differences in the electrophysiological parameters. The analysis of covariance revealed significantly reduced central foveal thickness in the BCM group compared to ACHM and controls (p < .00001), and in ACHM compared to controls (p < .00001), after age correction and Tukey post-hoc analysis. S-cones do not significantly influence OPs, and the decline in OPs' power is not solely due to a reduced a-wave. This suggests a complex non-linear network influenced by photoreceptor inputs. Morphological changes don't correlate directly with functional alterations, prompting further exploration of OPs' function and physiological role.

Inherited retinal diseases (IRD) are a leading cause of blindness in the working age population and in children. The scope of this review is to familiarise clinicians and scientists with the current landscape of molecular genetics, clinical phenotype, retinal imaging and therapeutic prospects/completed trials in IRD. Herein we present in a comprehensive and concise manner: (i) macular dystrophies (Stargardt disease (ABCA4), X-linked retinoschisis (RS1), Best disease (BEST1), PRPH2-associated pattern dystrophy, Sorsby fundus dystrophy (TIMP3), and autosomal dominant drusen (EFEMP1)), (ii) cone and cone-rod dystrophies (GUCA1A, PRPH2, ABCA4, KCNV2 and RPGR), (iii) predominant rod or rod-cone dystrophies (retinitis pigmentosa, enhanced S-Cone syndrome (NR2E3), Bietti crystalline corneoretinal dystrophy (CYP4V2)), (iv) Leber congenital amaurosis/early-onset severe retinal dystrophy (GUCY2D, CEP290, CRB1, RDH12, RPE65, TULP1, AIPL1 and NMNAT1), (v) cone dysfunction syndromes (achromatopsia (CNGA3, CNGB3, PDE6C, PDE6H, GNAT2, ATF6), X-linked cone dysfunction with myopia and dichromacy (Bornholm Eye disease; OPN1LW/OPN1MW array), oligocone trichromacy, and blue-cone monochromatism (OPN1LW/OPN1MW array)). Whilst we use the aforementioned classical phenotypic groupings, a key feature of IRD is that it is characterised by tremendous heterogeneity and variable expressivity, with several of the above genes associated with a range of phenotypes.