Posterior Segment Eye Diseases

The vitreous body is a transparent, gelatinous substance that is present in the space between the lens and the retina, providing structural stability and maintaining the shape of the eye. Some conditions that can affect the vitreous body are posterior vitreous detachment, vitreous hemorrhage, synchysis scintillans, asteroid hyalosis, and persistent fetal vasculature. The conditions can be asymptomatic or present with floaters in the field of vision, photopsia, and decreased visual acuity. Funduscopy and slit-lamp microscopy are commonly used in the diagnosis of these diseases. Treatment methods depend on the condition and severity, but may include observation, vision correction, and surgery.

A cataract is a condition defined as painless clouding or opacity of the lens. It causes visual impairment, as the lens provides part of the eye’s refractive power. Although all age groups can be affected, the age-related or senile type of cataract is the most common. Aside from age, there are multiple risk factors, including systemic diseases, medications, or trauma. Patients present with blurry vision, glare sensitivity, and color vision change. Ophthalmologic inspection often shows darkening of or opacities in the red reflex. Slit-lamp examination will show the extent and location of the cataract. The treatment is surgery, which is indicated when loss of vision function interferes with daily function.

Age-related macular degeneration (AMD) is visual impairment due to changes in the macula, the area responsible for high-acuity vision. It is marked by central vision loss with peripheral vision relatively spared. Risk factors include advanced age, smoking, family history, and cardiovascular disease. The 2 types of AMD are exudative (wet) or non-exudative (dry). The difference between these 2 types is the presence of choroidal neovascularization in wet AMD, which manifests as visual distortion or loss. The more frequently occurring dry AMD is usually asymptomatic but in a minority of cases leads to vision loss. There is no treatment for early dry AMD but Age-Related Eye Disease Study 2 (AREDS 2) supplements are recommended for advanced disease. Inhibitors of vascular endothelial growth factor are used for wet AMD.

A cataract is a condition defined as painless clouding or opacity of the lens. Cataracts cause visual impairment, as the lens provides part of the eye’s refractive power. The condition is one of the most common causes of pediatric blindness. Cataracts can be present from birth (congenital) or can develop after infancy (acquired). Genetic mutations, systemic diseases, trauma, and medications can lead to cataract development. Children present with an abnormal red reflex, leukocoria, or decreased visual acuity. An ophthalmologic examination reveals the morphology and location of the cataract. Management depends on age of presentation and visual defects. When opacity is of a certain size or is causing visual impairment, strabismus, and nystagmus, cataract surgery is recommended.

Retinal detachment is the separation of the neurosensory retina from the retinal pigmented epithelium and choroid. Rhegmatogenous retinal detachment, the most common type, stems from a break in the retina, allowing fluid to accumulate in the subretinal space. In the setting of an intact retina, detachment occurs when the vitreous pulls on the retina (traction) or when an underlying condition leads to increased leakage of fluid (exudative). Symptoms of photopsia, floaters, and visual defects can present over hours or gradually over weeks. Retinal detachment with visual loss is an emergency. Once macular detachment occurs, visual prognosis is poor. Symptomatic rhegmatogenous retinal detachment with intact central acuity warrants urgent surgery. For non-rhegmatogenous retinal detachments, treatment is directed toward the primary process.

A retinal vessel occlusion is a blockage in a major artery or vein of the retina. Depending on the location, the occlusion can be classified as central retinal artery occlusion (CRAO), branch retinal artery occlusion (BRAO), central retinal vein occlusion (CRVO), or branch retinal vein occlusion (BRVO). Typically, a retinal vessel occlusion is a thromboembolic event. Risk factors include hypertension, diabetes mellitus, and cardiac valvular disease. Central retinal artery occlusion is characterized by sudden, unilateral, painless loss of vision and/or transient vision loss (amaurosis fugax). Treatment options are limited in all cases and usually ineffective. When the macula is involved, prognosis is especially poor, leading to permanent vision loss.

Hypertension has many adverse effects on the eye, of which retinopathy is the most common presentation. Hypertensive retinopathy consists of retinal vascular changes that develop as a direct effect of elevated blood pressure. In acute increases of blood pressure, autoregulation results in retinal arteriolar narrowing. In chronic hypertension, structural changes consistent with arteriosclerosis affect the retinal vasculature. Endothelial wall damage ensues and various signs appear including hemorrhages, cotton-wool spots, and exudates. In severe cases of uncontrolled hypertension, papilledema is seen. Management is focused on controlling hypertension. Patients with severe hypertensive retinopathy have an increased risk for coronary artery disease and stroke; therefore, detection and treatment of underlying hypertension are important.

The primary visual pathway consists of a relay system, beginning at the retina, whose ganglion cell axons form the optic nerve. The optic nerve fibers from each eye hemidecussate in the optic chiasm (OC), with nasal fibers joining the temporal fibers of the contralateral nerve. The nasal fibers continue as the optic tract on each side, synapsing with the lateral geniculate nucleus (LGN) of the thalamus. Signals are then transmitted to the primary visual cortex of the occipital lobe. The right and left visual fields are processed by opposite hemispheres. Lesions along the pathway result in vision loss or visual field deficits. Based on the type of presentation, the location of the lesion in the pathway can be ascertained.

Endophthalmitis is an inflammatory process of the inner layers of the eye, which may be either infectious or sterile. Infectious endophthalmitis can lead to irreversible vision loss if not treated quickly. Based on the entry mode of the infectious source, endophthalmitis is divided into endogenous and exogenous types. Exogenous endophthalmitis occurs via direct inoculation of infectious organisms during cataract surgery, ocular trauma, or intravitreal injection. Endogenous endophthalmitis results from hematogenous seeding. Sterile endophthalmitis may result from toxins or retained lens material after an ocular operation. Clinical features vary depending on the type and course of the disease. Features may include decreased vision, conjunctival injection, ocular pain, hypopyon, and corneal edema. The diagnosis primarily depends on history and ophthalmological examination, and treatment is based upon the underlying cause. Sterile endophthalmitis generally resolves spontaneously while infectious endophthalmitis is treated with antimicrobials (antibiotics or antifungals). Vitrectomy may be needed in severe disease.

Retinopathy of prematurity (ROP) is a condition seen in premature infants of low birth weight that is characterized by progressive and excessive neovascularization. The condition is caused by the formation of blood vessels and fibrovascular tissue behind the lens (hence the former use of the term “retrolental fibroplasia”). Infants affected by ROP develop severe visual impairment or can become blind. Treatment with laser photocoagulation prevents vision loss in 95% of cases.