Genetic characterization of Stargardt clinical phenotype in South Indian patients using sanger and targeted sequencing

A Rare Occurrence of Stargardt Disease in a Quadragenarian Adult

The retina is the light-sensitive layer of the human eye. The macula forms the central part of the retina. The character of light responsiveness is attributed to the presence of photoreceptor cells here. Stargardt's disease is the most common cause of hereditary macular dystrophy. It is linked to disease-causing sequence variations/mutations in the ABCA4 gene on chromosome 1p21-p13, which destroys rod and cone cells within the retina. The disc membranes of rod and cone outer segments include an ATP-binding cassette transport protein encoded by the ABCA4 gene. All trans-retinal conjugates are transported across disc membranes by the ABCA4 protein. Abnormally high amounts of lipofuscin pigments build up in the retinal pigment epithelium (RPE) due to mutations in the ABCA4 gene, leading to RPE cell loss and secondary photoreceptor cell degeneration. As a result of this disease, the central or detailed vision becomes blurred, and the patient may find it challenging to discern colours. The retina presents with a distinctive "beaten-bronze" appearance due to the presence of prominent yellow dots. The phenotypic form of Stargardt disease, known as fundus flavimaculatus, is characterized by the widespread distribution of flecks throughout the fundus, including the periphery. In the given case report, we present a 46-year-old male patient who presented with complaints of persistence of a blind spot in central vision, difficulty in identifying faces, distortion of letters while reading, decreased visual acuity and difficulty in adapting from light to dark settings as symptoms. The stepwise assessment of the patient led to the diagnosis of Stargardt's disease. The case report reflects the disease history, pathogenesis, manifestations, prognosis, differential diagnosis and treatment options for this rare presentation.

Rare eye diseases in India: A concise review of genes and genetics

Rare eye diseases (REDs) are mostly progressive and are the leading cause of irreversible blindness. The disease onset can vary from early childhood to late adulthood. A high rate of consanguinity contributes to India’s predisposition to RED. Most gene variations causing REDs are monogenic and, in some cases, digenic. All three types of Mendelian inheritance have been reported in REDs. Some of the REDs are related to systemic illness with variable phenotypes in affected family members. Approximately, 50% of the children affected by REDs show associated phenotypes at the early stages of the disease. A precise clinical diagnosis becomes challenging due to high clinical and genetic heterogeneity. Technological advances, such as next-generation sequencing (NGS), have improved genetic and genomic testing for REDs, thereby aiding in determining the underlying causative gene variants. It is noteworthy that genetic testing together with genetic counseling facilitates a more personalized approach in the accurate diagnosis and management of the disease. In this review, we discuss REDs identified in the Indian population and their underlying genetic etiology.

Challenges to Gene Editing Approaches in the Retina

Retinal gene therapy has recently been at the cutting edge of clinical development in the diverse field of genetic therapies. The retina is an attractive target for genetic therapies such as gene editing due to the distinctive anatomical and immunological features of the eye, known as immune privilege, so that inherited retinal diseases (IRDs) have been studied in several clinical studies. Thus, rapid strides are being made toward developing targeted treatments for IRDs. Gene editing in the retina faces a group of heterogenous challenges, including editing efficiencies, off-target effects, the anatomy of the target organ, immune responses, inactivation, and identifying optimal application methods. As clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated nuclease (Cas) based technologies are at the forefront of current gene editing advances, their specific editing efficiency challenges and potential off-target effects were assessed. The immune privilege of the eye reduces the likelihood of systemic immune responses following retinal gene therapy, but possible immune responses must not be discounted. Immune responses to gene editing in the retina may be humoral or cell mediated, with immunologically active cells, including microglia, implicated in facilitating possible immune responses to gene editing. Immunogenicity of gene therapeutics may also lead to the inactivation of edited cells, reducing potential therapeutic benefits. This review outlines the broad spectrum of potential challenges currently facing retinal gene editing, with the goal of facilitating further advances in the safety and efficacy of gene editing therapies.

Intraocular lens power calculation in eyes with previous corneal refractive surgery

Intraocular lens (IOL) power calculation after corneal refractive surgery (CRS) becomes an expanding challenge for ophthalmologists as more and more cataract surgeries after CRS are required. These patients typically also have high expectations as to visual performance. Conventional IOL power calculation schemes frequently provide inaccurate results in these cases. This review aims to summarize and recommend currently available IOL power calculation methods for eyes with the most common CRS methods: radial keratotomy (RK), photorefractive keratectomy (PRK), laser in situ keratomileusis (LASIK), and small incision lenticule extraction (SMILE). To this end, biometry measuring methods and IOL formulas will be explained and combinations of both are proposed. In synopsis, it is evident that the latest generation of vergence formulas exhibit favorable IOL power prediction accuracy in post-CRS eyes, even though the predictive precision of methods in eyes without CRS is not attained. Ray tracing computation, intraoperative aberrometry, and machine learning–based formulas hold potential to further improve refractive outcomes in post-CRS eyes.