Retinal diseases
The retina is the innermost light-sensitive layer of the eye. It is called the “fundus” when viewed with an instrument called an ophthalmoscope, showing blood vessels and the optic nerve head. The retina has a higher metabolic rate and oxygen consumption than other body cells. The retina is divided into the neurosensory retina and the retinal pigment epithelium (RPE), separated by a potential space (the subretinal space). The central part of the retina is called the macula. It has a part called the fovea centralis which is a depression on the macula responsible for sharp spatial and color vision.
Retinal disease conditions vary based on age, genetic factors, and pre-existing health issues.
Diabetic retinopathy is the most common retinal vascular disorder, followed by retinal vein occlusion. Proliferative diabetic retinopathy involves neovascularization (abnormal new vessel formation) caused by diabetes-induced ischaemia (inadequate blood supply), while the non-proliferative type results from diabetes-related retinal vascular changes. Diabetic macular edema occurs when fluid leaks into the macula from abnormal new retinal vessels.
Sickle cell retinopathy is caused by recurrent occlusion of retinal vessels by sickled cells and can present with both proliferative and non-proliferative features.
Retinal detachment occurs when the neurosensory retina separates from the supporting retinal pigment epithelium (RPE). It can be caused by trauma, vitreous detachment, and myopia, which lead to thinning of the retina, degeneration, and retinal tears with fluid accumulation. It is also observed in retinopathy of prematurity due to incomplete or abnormal retinal vascularization resulting from premature birth. Early screening and treatment of abnormal retinal vessel signs, such as demarcation lines indicating possible detachment, are essential to prevent progression and vision loss. Abnormal retinal vessels (telangiectasia) also occur in Coats disease, leading to fluid buildup that can cause retinal detachment if detected early.
Normal aging of the macula can cause deposits around the base of the RPE, leading to changes in pigmentation or macular atrophy in age-related macular degeneration. Hypertension can cause narrowing of retinal arteries with infarction in the nerve fiber layer causing a hypertensive retinopathy.
Inherited dystrophies of the photoreceptors include retinitis pigmentosa, characterized by abnormal disc color, thin vessels, and deposition of specific pigments, as well as associated complications such as glaucoma.
Inflammation of the retina occurs in various infectious and inflammatory conditions, including congenital cytomegalovirus infection transmitted from the mother, varicella zoster, herpes, syphilis, tuberculosis, cat-scratch disease (Bartonella), Toxoplasmosis, Toxocariasis, and Zika virus.
Medications such as Tamoxifen and Hydroxychloroquine are toxic to the retina, so patients require evaluation before starting therapy, and fundus changes and vision should be monitored throughout treatment.
Retinoblastoma is the most common malignant tumour of the eye in children and occurs when the tumour suppressor RB1 gene is mutated, leading to tumours that can spread through the retina or vitreous if not detected and managed early.
Regular fundoscopy is essential in all cases of unexplained visual impairment following visual screening across all age groups and is recommended every 6 months for early detection and prompt management of subtle retinal changes, especially in patients with pre-existing conditions like diabetes, hypertension, sickle cell disease, atherosclerosis, cancers, and those using therapeutic agents toxic to the retina.