Porth's Essentials of Pathophysiology, 4e

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Disorders of Special Sensory Function: Vision, Hearing, and Vestibular Function

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Retinal Detachment Retinal detachment involves the separation of the neurosensory retina from the pigment epithelium. The disorder, which is one of most time-critical events seen in an emergency department, occurs when traction on the inner sensory layer or a tear in this layer allows fluid, usually vitreous, to accumulate between the two layers of the retina. 6,23,30 There are three types of retinal detachments: exudative, traction, and rhegmatogenous. Exudative Detachment. Exudative (or serous) retinal detachment results from the accumulation of serous or hemorrhagic fluid in the subretinal space due to severe hypertension, inflammation, or neoplastic effusions. It usually resolves with successful treatment of the underlying disease and without visual impairment. Traction Retinal Detachment. Traction retinal deat- tachment occurs with mechanical forces on the retina, usually mediated by fibrotic tissue, resulting from previ- ous hemorrhage (e.g., from diabetic retinopathy), injury, infection, or inflammation. Intraocular surgery such as cataract extraction may produce traction on the periph- eral retina that causes eventual detachment months or even years after surgery. Correction of traction retinal detachment requires disengaging scar tissue from the retinal surface, and vision outcomes are often poor. Rhegmatogenous Detachment. Rhegmatogenous detachment, themost common type of retinal detachment, is a full thickness break (“rhegma”) in the sensory retina, with the passage of liquefied vitreous through the break into the subretinal space. Although typically an acute event, detachment is a consequence of lifelong liquefaction of the vitreous humor, and is highly age-dependent with 27% of patients in their seventies and 63% in their eighties. 30 As the collagenous and mucopolysaccharide matrix of the vitreous humor begins to liquefy and shrink, it pulls away from the retinal surface. Rhegmatogenous detachment occurs when the liquid vitreous enters the subretinal space through a retinal tear (Fig. 38-9). Detachment of the neural retina from the retinal pigment layer separates the visual receptors from their major blood supply, the choroid. If retinal detachment continues for some time, permanent destruction and blindness of that part of the retina occur. Persons with high grades of myopia or nearsightedness may have abnormalities in the peripheral retina that predispose to sudden detachment. In moderate to severe myopia, the anteroposterior length of the eye is increased, and the retina tends to be thinner and more prone to formation of a hole or tear. 30 As a result, there is greater vitreoretinal traction, and posterior vitreous detachment may occur at a younger age than in persons without myopia. Clinical Manifestations. The primary symptom of retinal detachment is painless changes in vision. Commonly, flashing lights or sparks, followed by small floaters or spots in the field of vision, are early symptoms. As detachment progresses, the person

first detectable sign of diabetic retinopathy. These vessels grow in front of the retina along the posterior surface of the vitreous or into the vitreous. They threaten vision in two ways. First, they often leak blood into the vitreous cavity and decrease visual acuity. Second, they attach firmly to the retinal surface and the posterior surface of the vitreous chamber, such that normal movement of the vitreous humor may exert a pull on the retina, causing retinal detachment and progressive blindness. Current guidelines recommend that persons with diabetes have yearly eye examinations. 27 Personswith any level of macular edema, severe nonproliferative diabetic retinopathy, or any proliferative retinopathy require the prompt care of an ophthalmologist experienced in the management and treatment of diabetic retinopathy. Women with preexisting diabetes who plan to become pregnant or are pregnant should have a comprehensive eye examination and be counseled about the risk for initiation or progression of diabetic retinopathy. Preventing diabetic retinopathy from developing or progressing is considered the best approach to pre- serving vision. Growing evidence suggests that careful control of blood glucose levels in persons with diabetes mellitus may retard the onset and progression of reti- nopathy. There also is a need for intensive management of hypertension and hyperlipidemia, both of which have been shown to increase the risk of diabetic retinopathy in persons with diabetes. 28 Treatment strategies for diabetic retinopathy include laser photocoagulation applied directly to leaking microaneurysms and grid photocoagulation with a checkerboardpatternof laserburnsappliedtodiffuseareas of leakage and thickening. Because laser photocoagulation destroys the proliferating vessels and the ischemic retina, it reduces the stimulus for further neovascularization. Intravitreal injections of anti-VEGF agents are also being used to reduce active neovascularization and vitreous hemorrhage. 28 Vitrectomy may be used for removing vitreous hemorrhage and severing vitreoretinal membranes that develop. Hypertensive Retinopathy. As with other blood vessels in the body, the retinal vessels undergo changes in response to chronically elevated blood pressure. In the initial, vasoconstrictor stage, there is vasospasm and an increase in retinal arterial tone because of local autoregulatory mechanisms. On ophthalmoscopy, this stage is represented by a general narrowing of the retinal arterioles. Persistently elevated blood pressure results in the compensatory thickening of arteriolar walls, which effectively reduces capillary perfusion pressure. 29 With severe uncontrolled hypertension, there is disruption of the blood-retina barrier, necrosis of smooth muscle and endothelial cells, exudation of blood and lipids, and retinal ischemia. These changes are manifested in the retina by microaneurysms, intraretinal hemorrhages, hard exudates, and cotton-wool patches. Swelling of the optic disk may occur at this stage and usually indicates severely elevated blood pressure (malignant hypertension). Elderly persons often have more rigid vessels that are unable to respond to the same degree as those in younger individuals.