Ординатура / Офтальмология / Английские материалы / Ophthalmology A Short Textbook_Lang_2000

12.5 Retinal Dystrophies 343

12.5.2Retinitis Pigmentosa

Definition

This term is used to refer to a heterogeneous group of retinal disorders that lead to progressive loss of visual acuity, visual field defects, and night blindness. The name retinitis pigmentosa comes from the pigment deposits that characterize these disorders. In their classic form (see findings and diagnostic considerations) of such disorders, these deposits progress from the periphery to the center of the retina.

Epidemiology: The worldwide incidence of retinitis pigmentosa is estimated at between one per 35000 and one per 70000 persons. The estimated incidence of mutated alleles is one per 80 persons.

Forms of retinitis pigmentosa:

1.Rod-cone dystrophy (classic retinitis pigmentosa, by far the most frequent form).

2.Cone-rod dystrophy (inverse retinitis pigmentosa).

3.Sectoral retinitis pigmentosa.

4.Retinitis pigmentosa sine pigmento (form without pigment).

5.Unilateral retinitis pigmentosa.

6.Leber’s amaurosis (form occurring in early childhood).

7.Retinopathy punctata albescens (punctate retinitis).

8.In combination with other disorders in syndromes and metabolic disorders such as mucopolysaccharidoses, Fanconi’s syndrome, mucolipidosis IV, peroxisomal disorders, Cockayne’s syndrome, mitochondrial

myopathies, Usher’s syndrome, neuronal and ceroid lipofuscinoses, renal tubular defect syndromes, etc.

Retinitis pigmentosa occurs almost exclusively as rod-cone dystrophy. Therefore, the other extremely rare forms are not discussed here except for the inverse form of classic retinitis pigmentosa, which is presented for purposes of comparison.

Inheritance: Individual genetic forms may be identified from among the heterogeneous group of disorders comprising retinitis pigmentosa. This group of disorders can involve various genotypes as well as variable phenotypic expression or different stages of a disorder with one specific genotype. There are over 15 purely ocular forms of retinitis pigmentosa. The most common form of inheritance is autosomal recessive (60%), followed by autosomal dominant (up to 25%), and X-linked (15%). Rhodopsin gene mutations (chromosome 3) and “retinal degeneration slow” (RTS) gene mutations (chromosome 6) have also been described.

344 12 Retina

Symptoms: Initial symptoms of retinitis pigmentosa include glare, night blindness, progressive visual field defects, loss of visual acuity, and color vision defects. The age of manifestation depends on the type of inheritance.

Findings and diagnostic considerations: The diagnosis is made by ophthalmoscopy on the basis of a classic picture.

Rod-cone dystrophy (primarily the rods are affected first). “Bone-spicule” proliferation of retinal pigment epithelium is observed in the middle periphery of the retina. This will gradually spread toward the center and farther peripherally (Fig. 12.31). Early deficits include color vision defects and disturbed contrast perception. Atrophy of the optic nerve, discernible as a waxy yellow appearance of the optic disk, will occur in the advanced stages. The arteries will appear narrowed, and the fundus reflex will be extremely muted. The patient will typically have a “gun-barrel” visual field with good visual acuity for a surprisingly long time but with progressive loss of the peripheral visual field.

Cone-rod dystrophy (primarily the cones are affected first). Here, there is early loss of visual acuity with gradual progressive loss of visual field. In both forms of retinitis pigmentosa, the diagnosis is confirmed by electroretinography. Light response in the electroretinogram will be sharply reduced or absent early in the clinical course of the disease.

Differential diagnosis: Differential diagnosis should consider changes collectively referred to as pseudoretinitis pigmentosa because they simulate the clinical picture of retinitis pigmentosa. The most common causes that should be excluded in this context are:

Advanced retinitis pigmentosa.

Fig. 12.31 Typical signs include narrowed retinal vessels, waxy yellow appearance of the optic disk due to atrophy of the optic nerve, and “bone-spicule” proliferation of retinal pigment epithelium.

12.6 Toxic Retinopathy 345

Posttraumatic changes.

Postinflammatory or postinfectious changes. These may include degenerative retinal pigment epithelial disease secondary to rubella with “salt and pepper” fundus of punctate areas of atrophy and proliferation of retinal pigment epithelium. Other causes include syphilis, which may present with placoid lesions of pigment epithelial atrophy and proliferations.

Tumors.

Medications, such as chloroquine, Myambutol (ethambutol), and thioridazine.

Treatment: The causes of the disorder cannot be treated. Edge-filtered eyeglasses (eyeglasses with orange or blue colored lenses that filter out certain wavelengths) and magnifying near vision aids can help make better use of the patient’s remaining vision.

Prophylaxis: No prophylaxis is possible.

Clinical course and prognosis: Retinitis pigmentosa is chronically progressive. The clinical course depends on the specific form of the disorder; severe forms lead to blindness.

12.6Toxic Retinopathy

Definition

Retinal changes resulting from use of medications.

Epidemiology: Toxic retinopathy is rare.

Pathogenesis: Toxic retinopathy can remain asymptomatic for a long time. Loss of visual acuity occurs if the macula is affected.

Chloroquine in doses exceeding 250 g causes retinal damage. Macular edema can occur initially. Later, punctate pigment epithelial changes develop, which may progress to bull’s eye maculopathy with concentric rings of hypopigmentation and hyperpigmentation in the macular region (Fig. 12.32). These findings are usually bilateral and symmetrical. Other toxic retinal changes are listed in the appendix.

Diagnostic considerations: The diagnosis is made by binocular ophthalmoscopy with the pupil dilated and confirmed by electrophysiologic studies that include an electroretinogram, electro-oculogram, and visual evoked potentials (see Fig. 12.2a).

Differential diagnosis: Retinal pigment epithelium or retinal bleeding can result from many other retinal disorders, and may also be associated with the underlying disease for which the medication was prescribed.

346 12 Retina

Chloroquine toxicity (bull’s eye maculopathy).

Fig. 12.32 Chronic use of this medication causes concentric rings of atrophy and proliferation of retinal pigment epithelium (arrows).

Treatment: The medication should be discontinued if possible.

Prophylaxis: Regular ophthalmologic follow-up examinations are indicated before and during treatment that involves medications with known ocular side effects.

Clinical course and prognosis: The clinical course depends on the specific medication and dose. Findings may improve after the medication is discontinued. However, with chloroquine in particular, findings may continue to worsen even years later.

12.7Retinal Inflammatory Disease

12.7.1Retinal Vasculitis

Definition

Retinal vasculitis is an inflammation of the retinal vasculature. Typical findings include cells in the vitreous body.

Epidemiology: Retinal vasculitis is one of the more frequent clinical syndromes.

Etiology: The cause of retinal vasculitis often remains obscure. It can be caused by a pathogen or occur in association with immunologic processes (Table 12.8).

Symptoms: Patients report loss of visual acuity or black dots in their visual field. These are due to the presence of cells in the vitreous body.

Diagnostic considerations: The ophthalmologic diagnostic work-up includes clinical examination, ophthalmoscopy, and slit-lamp examination. The slit-lamp examination will reveal cells in the vitreous body. Ophthalmoscopic findings will include whitish preretinal infiltrates (Fig. 12.33), vascular constriction (usually involving the veins), vascular occlusion, intraretinal bleeding, and retinal edema. Fluorescein angiography may be used to evaluate the presence and activity of neovascularization. Underlying systemic disease, immunologic processes, and infections (see Table 12.8) must be excluded.

Differential diagnosis: Other vascular diseases of the retina such as vein occlusion should be excluded. These vascular diseases may be distinguished from vascular retinitis by the absence of cells in the vitreous body.

Retinal vasculitis.

Fig. 12.33 Ophthalmoscopy reveals whitish preretinal vitreous infiltrates (arrow).

348 12 Retina

Treatment: The causes of known underlying disorders should be treated. Symptoms are treated with topical steroids and systemic steroids in the absence of contraindications. Neovascularization is treated with laser therapy.

Prophylaxis: No prophylaxis is possible except for possible treatment of an underlying disorder.

Clinical course and prognosis: Vascular occlusion can result in neovascularization that may lead to vitreous hemorrhage. Tractional retinal detachment is another possible complication.

12.7.2Posterior Uveitis Due to Toxoplasmosis

Definition

Focal chorioretinal inflammation caused by infection.

Epidemiology: This clinical syndrome is encountered frequently.

Pathogenesis: The pathogen, Toxoplasma gondii, is transmitted by ingestion of tissue cysts in raw or undercooked meat or by oocysts from cat feces. In congenital toxoplasmosis, the child acquires the pathogen through transplacental transmission.

Symptoms and diagnostic considerations: As a general rule, a negative complement-fixation test does not exclude Toxoplasma infection where classic clinical symptoms are present. Both forms of the disorder present with characteristic grayish white chorioretinal focal lesions surrounded by vitreous infiltration and associated vasculitis (Fig. 12.34). In congenital toxoplasmosis, the affected children have a macular scar that significantly impairs visual acuity. This often leads to secondary strabismus. Intracerebral involvement can also result in hydrocephalus and intracranial calcifications. In the acquired form, visual acuity is impaired only where the macula is involved. This is rarely the case.

Congenital toxoplasmosis results in a macular scar that significantly impairs visual acuity.

Differential diagnosis: Chorioretinitis with tuberculosis, sarcoidosis, borreliosis (Lyme disease), or syphilis should be excluded by serologic studies.

Treatment: The treatment of choice consists of a combination of pyrimethamine, sulfonamide, folinic acid, and steroids in their respective standard doses.

Prophylaxis: Avoid raw meat and cat feces.

Recurrent toxoplasmosis.

Fig. 12.34 Acute grayish white chorioretinal focal lesion (arrow) and brownish white chorioretinal scars (arrowhead). Lesions usually recur at

the margin of the original scar, the ”mother spot”.

Clinical course and prognosis: Posterior uveitis due to toxoplasmosis usually heals without severe loss of visual acuity where the macula is not involved. However, it can recur at any time. There is no cure for the congenital form.

12.7.3AIDS-Related Retinal Disorders

Definition

Retinal disorders in AIDS involve either AIDS-associated microangiopathy or infection.

Epidemiology: Up to 80% of all AIDS patients have retinal disorders as a result of the disease. Other ocular involvement is rare.

Pathogenesis: The pathogenesis of microangiopathy is still unclear. Opportunistic infections are frequently caused by viruses.

Symptoms: Microangiopathy is usually asymptomatic. Patients with infectious retinal disorders report loss of visual acuity and visual field defects.

Diagnostic considerations: Ophthalmoscopic findings in AIDS-associated microangiopathy include hemorrhages, microaneurysms, telangiectasia, and cotton-wool spots. Direct involvement of vascular endothelial cells in HIV infection or immune-complex-mediated damage to endothelial cells and vascular structures is thought to play a role.

350 12 Retina

Cytomegalovirus retinitis.

Fig. 12.35 Typical signs include extensive white areas of retinal necrosis and hemorrhages.

Cytomegalovirus retinitis occurs in 20–40% of older patients. Peripheral retinal necrosis and intraretinal bleeding (Fig. 12.35) are frequently observed. Vascular occlusion is rare. Secondary rhegmatogenous retinal detachment may develop. These lesions heal to produce fine granular pigment epithelial scars.

Less frequently, AIDS may involve retinal infection caused by herpes simplex and varicella-zoster viruses, Toxoplasma gondii, or Pneumocystis carinii. The diagnosis of a viral retinal infection in AIDS is confirmed by attempting to obtain positive serum cultures and by resistance testing.

Differential diagnosis: Inflammatory retinal changes due to other causes should be excluded by serologic studies.

Treatment: Microangiopathy does not require treatment. Viral retinitis is treated with ganciclovir or foscarnet. Herpes simplex and varicella-zoster viruses are treated with acyclovir.

Prophylaxis: Ophthalmologic screening examinations are indicated in the presence of known viral infection.

Clinical course and prognosis: The prognosis for microangiopathy is very good. Infectious retinitis will lead to blindness if left untreated. Visual acuity can often be preserved if a prompt diagnosis is made.

12.7.4Viral Retinitis

Definition

Retinal disorder caused by viral infection.

Epidemiology: Viral retinitis is a rare disorder

Pathogenesis: Infection of the retina and retinal vasculature caused by cytomegalovirus, herpes simplex, varicella-zoster, or rubella viruses. Viral retinitis frequently occurs in immunocompromised patients.

Symptoms: Patients report loss of visual acuity and visual field defects.

Diagnostic considerations: Slit-lamp examination will reveal cells in the vitreous body. Ophthalmoscopic findings will include retinal necrosis with intraretinal bleeding (see Fig. 12.35). Necrosis can occur as acute lesions and spread over the entire retina like a grassfire within a few days. When the retinitis heals, it leaves behind wide-area scarring.

During pregnancy, rubella virus can cause embryopathy in the child. Ophthalmic examination will reveal typical fine granular pigment epithelial scars on the fundus that are often associated with a congenital cataract. The diagnosis is confirmed by measuring the serum virus titer. The possibility of compromised immunocompetence should be verified or excluded.

Differential diagnosis: Posterior uveitis and vasculitis should be excluded. These disorders may be distinguished from viral retinitis by the absence of necrosis.

Treatment: The disorder is treated with high doses of an antiviral agent (acyclovir, ganciclovir, or foscarnet) according to the specific pathogen.

Prophylaxis: Ophthalmologic screening examinations are indicated in immunocompromised persons with suspected viral infection.

Clinical course and prognosis: Viral retinitis can be arrested if diagnosed early. However, recurrences are frequent in immunocompromised patients. Blindness usually cannot be prevented in retinal necrosis syndrome.

12.7.5Retinitis in Lyme Disease

Definition

Inflammation of the retina usually caused by Borrelia burgdorferi.

Epidemiology: The incidence of this retinal disorder has increased in recent years.

352 12 Retina

Etiology: The inflammation is caused by spirochetes usually transmitted by bites from infected ticks.

Findings and symptoms: Lyme disease can lead to many inflammatory ocular changes with their respective symptoms. These include conjunctivitis, keratitis, and iridocyclitis. Retinal vasculitis, retinal artery occlusion, neuroretinitis, optic neuritis, and choroiditis have also been described.

Lyme disease should be excluded as a possible cause of posterior uveitis of uncertain etiology.

Diagnostic considerations: The diagnosis is made by ophthalmoscopy and serologic studies to identify the pathogen.

Differential diagnosis: Inflammatory ocular changes due to other causes (such as toxoplasmosis or tuberculosis) should be excluded.

Treatment: Antibiotic treatment with tetracycline, penicillin G, or thirdgeneration cephalosporins is indicated.

Clinical course and prognosis: Retinal changes due to Lyme disease tend to recur.

12.7.6Parasitic Retinal Disorders

Definition

Inflammation of the retina caused by infection with parasites such as Onchocerca volvulus (the pathogen that causes onchocerciasis), Toxocara canis or Toxocara cati (nematode larvae that are normally intestinal parasites of dogs and cats), Taenia solium, (pork tapeworm), and other parasites.

Epidemiology: Onchocerciasis, like trachoma and leprosy, is one of the most frequent causes of blindness worldwide. However, like the other parasitic diseases discussed here, it is rare in Europe and North America.

Etiology: Onchocerca volvulus is transmitted by the bite of black flies. This allows the larvae (microfilaria) to penetrate the skin, where they form fibrous subcutaneous nodules. There they reach maturity and produce other microfilaria, which migrate into surrounding tissue. The danger of ocular infiltration is particularly great where there are fibrous nodules close to the eye.

Toxocara canis or Toxocara cati (eggs of nematodes infesting dogs and cats) are transmitted to humans by ingestion of substances contaminated with the feces of these animals. The eggs hatch in the gastrointestinal tract, where they gain access to the circulatory system and may be spread throughout the entire body. The choroid can become infested in this manner.