Ординатура / Офтальмология / Английские материалы / Ophthalmology A Short Textbook_Lang_2000

12.8 Retinal Tumors and Hamartomas 353

Taenia solium: The pork tapeworm infestation can occur from eating pork contaminated with larvae or other substances contaminated with tapeworm eggs. Mature tapeworms can also release eggs into the intestine. The larvae travel through the bloodstream to various organs and can also infest the eye.

Diagnostic considerations and findings: Ophthalmoscopy will reveal intraocular inflammation. Onchocerciasis has been known to be associated with posterior uveitis as well as keratitis and iritis. Histologic examination will demonstrate microfilaria in the retina. Visceral larva migrans, Toxocara canis, or Toxocara cati can cause complications involving endophthalmitis and retinal detachment. Subretinal granulomas and larval inflammation of the retina have been known to occur. The larvae of different species of worms can produce diffuse unilateral subacute neuroretinitis with the typical clinical picture of grayish white intraretinal and subretinal focal lesions. Fly larvae can also invade the subretinal space in ophthalmomyiasis.

Differential diagnosis: Other causes of retinal inflammation and subretinal granulomas should be excluded.

Treatment: Laser photocoagulation or surgical removal of the worm larvae may be indicated.

Clinical course and prognosis: It is not uncommon for these disorders to lead to blindness.

12.8Retinal Tumors and Hamartomas

12.8.1Retinoblastoma

Definition

A retinoblastoma is a malignant tumor of early childhood that develops from immature retinal cells.

Epidemiology: Retinoblastoma is the most common malignant ocular tumor in children, occurring in approximately one of 20000 births. In 30% of all cases, it is bilateral.

Pathogenesis: A somatic mutation is detected in about 95% of all patients. In the other patients, it is inherited as an autosomal dominant trait. Changes on chromosome 13q have been observed in germ-cell mutations. Retinoblastomas may then occur at several locations in the retina or bilaterally.

Where retinoblastoma is inherited as an autosomal dominant trait, the siblings of the affected child should be regularly examined by an ophthalmologist.

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Symptoms: Retinoblastoma manifests itself before the age of three in 90% of affected children. Parents observe leukocoria (a whitish yellow pupil; Fig. 12.36) in 60% of these children, strabismus in 20%, and a reddened eye in 10%.

Every child presenting with strabismus should undergo examination of the fundus with the pupil dilated to exclude a retinoblastoma.

Findings and diagnostic considerations: A grayish white, vascularized retinal tumor will be observed on ophthalmoscopy. In its advanced stages, this tumor was formerly referred to as an amaurotic cat's eye. Infiltration of the vitreous body, anterior chamber (pseudohypopyon), and orbit may occur. A retinoblastoma that also involves the fellow eye and pineal body is referred to as a trilateral retinoblastoma.

A trilateral retinoblastoma is defined as additional manifestation of the tumor in the pineal body.

Calcifications frequently occur in these tumors. Radiographs or CT images that show calcifications can therefore help to confirm the diagnosis in uncertain cases.

Differential diagnosis: Several other disorders should be excluded by ophthalmoscopy. These include:

Cataract (with leukocoria).

Primary strabismus (with strabismus).

Infection (with a reddened eye).

Leukocoria in the left eye due to a retinoblastoma.

Fig. 12.36 The whitish gleam of the

pupil of the left eye is a typical finding in retinoblastoma.

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Retinal detachment, persistent hyperplastic primary vitreous (PHPV), and Coats’ disease should also be excluded.

Treatment: Tumors less than four pupil diameters may be managed with radiation therapy delivered by plaques of radioactive ruthenium or iodine (brachytherapy) and cryotherapy. Larger tumors require enucleation of the eye.

Prophylaxis: Following the diagnosis, the fellow eye should be examined with the pupil dilated every three months for five years. After that, follow-up examinations may be performed at greater intervals.

Clinical course and prognosis: Left untreated, a retinoblastoma will eventually metastasize to the brain and cause death. Patients frequently develop a second malignant tumor such as an osteosarcoma.

12.8.2Astrocytoma

Definition

An astrocytoma or astrocytic hamartoma is a benign tumor that develops from the astrocytes of the neuroglial tissue.

Epidemiology: Astrocytomas are rare.

Etiology: Astrocytomas belong to the phakomatoses and are presumably congenital disorders that develop from the layer of optic nerve fibers. They may manifest themselves as purely ocular disorders or in association with tuberous sclerosis (Bourneville’s disease).

Symptoms: Patients usually have no ocular symptoms. Calcifying astrocytic hamartomas in the region of the basal ganglia or ventricles can cause epilepsy and mental deficiency. An astrocytoma in Bourneville’s disease will be associated typically with an adenoma sebaceum in the facial skin.

Findings and diagnostic considerations: Astrocytomas are either incidental findings in ophthalmic examinations performed for other reasons, or they are diagnosed in patients presenting with reduced visual acuity. Ophthalmoscopy will reveal single or multiple “mulberry” tumors one to two pupil diameters in size. These will appear white and are often calcified. The tumors are inherently fluorescent when observed in blue light in fluorescein angiography with a blue filter.

Differential diagnosis: A retinoblastoma should be excluded in children. That is usually larger than an astrocytoma on ophthalmoscopy. A possible Toxocara canis granuloma should be confirmed or excluded by serologic studies.

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Treatment: No ophthalmologic treatment is required. The patient should be referred to a neurologist to exclude cerebral involvement.

Clinical course and prognosis: These tumors rarely increase in size.

12.8.3Hemangiomas

Definition

Capillary hemangiomas or hemangioblastomas occur in angiomatosis retinae (von Hippel-Lindau disease).

Von Hippel-Lindau disease.

Fig. 12.37

a A hemangioblastoma (arrow) in von Hippel-Lin- dau disease with enlarged retinal arteries and veins and retinal detachment with hard exudate (arrowhead).

b Corresponding fluorescein angiogram.

12.8 Retinal Tumors and Hamartomas 357

Epidemiology: Hemangiomas are rare.

Etiology: These are benign congenital changes. There may be an autosomal dominant inheritance.

Symptoms: Loss of visual acuity will result where exudative retinal detachment develops.

Findings and diagnostic considerations: Retinal hemangiomas are characterized by thickened tortuous arteries and veins (Figs. 12.37a and b). Bilateral changes are present in 50% of all patients.

Differential diagnosis: Coats’ disease, branching retinal hemangiomas in Wyburn-Mason syndrome, and cavernous hemangiomas should be considered. Cerebral hemangiomas, renal cysts, hypernephromas, and pheochromocytomas should also be excluded.

Treatment: Retinal hemangiomas may be treated by laser or cryocautery therapy. However, exudative retinal detachment will develop as the treatment increases this risk.

Clinical course and prognosis: The disorder is gradually progressive. The prognosis for visual acuity is poor in the disorder where retinal detachment develops.

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13 Optic Nerve

Oskar Gareis and Gerhard K. Lang

13.1Basic Knowledge

The optic nerve extends from the posterior pole of the eye to the optic chiasm (Fig. 13.1). After this characteristic crossing, the fibers of the optic nerve travel as the optic tract to the lateral geniculate body. Depending on the shape of the skull, the optic nerve has a total length of 35–55 mm. The nerve consists of:

An intraocular portion.

An intraorbital portion.

An intracranial portion.

Path of the optic nerve.

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13.1.1Intraocular Portion of the Optic Nerve

The intraocular portion of the optic nerve is visible on ophthalmoscopy as the optic disk. All the retinal nerve fibers merge into the optic nerve here, and the central retinal vessels enter and leave the eye here. The complete absence of photoreceptors at this site creates a gap in the visual field known as the blind spot.

Shape and size: The optic disk (Fig. 13.2) is normally slightly vertically oval with an average area of approximately 2.7 mm2 and a horizontal diameter of approximately 1.8 mm. There is a wide range of physiologic variability in the size of the optic disk; its area may vary by a factor of seven, and its horizontal diameter by a factor of two and one-half.

Color: The normal physiologic color is yellowish orange. The temporal half of the optic disk is usually slightly paler.

Margin: The margin of the optic disk is sharply defined and readily distinguished from the surrounding retinal tissue. On the nasal side, the greater density of the nerve fibers makes the margin slightly less distinct than on the temporal side. A common clinical observation is a crescent of pigment or irregular pigmentation close to the optic disk on the temporal side; sometimes the sclera will be visible through this crescent.

Prominence of the optic disk: The normal optic disk is not prominent. The nerve fibers are practically flush with the retina.

Normal optic disk.

Fig. 13.2 Typical signs of a normal pupil include a yellowish orange neuroretinal rim sharply set off from the retina.

13.1 Basic Knowledge 361

Neuroretinal rim (Fig. 13.2): This consists of the bundles of all the optic nerve fibers as they exit through the scleral canal. The rim has a characteristic configuration: The narrowest portion is in the temporal horizontal region followed by the nasal horizontal area; the widest areas are the vertical inferior and superior areas.

Optic cup: This is the slightly eccentric cavitation of the optic nerve that has a slightly flattened oval shape corresponding to that of the neuroretinal rim. It is the brightest part of the optic disk. No nerve fibers exit from it (Fig. 13.2). The size of the optic cup correlates with the size of the optic disk; the larger the optic disk, the larger the optic cup. Because enlargement of the optic cup means a loss of nerve fibers in the rim, it is particularly important to document the size of the optic cup. This is specified as the horizontal and vertical ratios of cup to disk diameter (cup/disk ratio). Due to the wide range of variability in optic disk size, it is not possible to specify absolute cup/disk ratios that indicate the presence of abnormal processes.

Central retinal artery and vein: These structures usually enter the eye slightly nasal to the center of the optic disk. Visible pulsation in the vein is normal. However, arterial pulsation is always abnormal and occurs with disorders such as increased intraocular pressure and aortic stenosis.

Cilioretinal vessels are aberrant vessels originating directly from the choroid (short posterior ciliary arteries). Resembling a cane, they usually course along the temporal margin of the optic disk and supply the inner layers of the retina (Fig. 13.2).

Blood supply to the optic disk (Fig. 13.3): The optic disk receives its blood supply from the ring of Zinn, an anastomotic ring of small branches of the short posterior ciliary arteries and the central retinal artery. Both groups of vessels originate from the ophthalmic artery, which branches off of the internal carotid artery and enters the eye through the optic canal. The central retinal artery and vein branch into the optic nerve approximately 8 mm before the point at which the optic nerve exits the globe. Approximately 10 short posterior ciliary arteries penetrate the sclera around the optic nerve.

13.1.2The Intraorbital and Intracranial Portion of the Optic Nerve

The intraorbital portion begins after the nerve passes through a sieve-like plateofscleralconnectivetissue,thelaminacribrosa. Insidetheorbit,theoptic nerve describes an S-shaped course that allows extreme eye movements.

After the optic nerve passes through the optic canal, the short intracranial portion begins and extends as far as the optic chiasm. Like the brain, the intraorbital and intracranial portions of the optic nerve are surrounded by sheaths of dura mater, pia, and arachnoid (see Fig. 13.3). The nerve receives its blood supply through the vascular pia sheath.

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Vascular structures supplying the head of the optic nerve.

Retina Pigment epithelium Choroid Sclera

Dura mater sheath

Arachnoid sheath

Pia mater sheath

Vascular plexus of the pia sheath

Lamina cribrosa

Central retinal vein

Central retinal artery

Ring of Zinn

Posterior ciliary artery

Short posterior ciliary arteries

Fig. 13.3 The optic nerve is supplied with blood from both the short posterior ciliary arteries and the central retinal artery.

13.2Examination Methods

These include:

Ophthalmoscopy (see Chapter 1).

Visual acuity testing (see Chapter 1).

Perimetry test (see Chapter 14).

Pupillary light reflex (see Chapter 9).

Testing color vision (for example with the panel D 15 test).

Visual evoked potential (VEP).

Panel D 15 test of color vision: This is a color marker sorting test. The patient is presented with 15 small color markers that he or she must select and sort according to a fixed blue color marker. Patients with color vision defects will typically confuse certain markers within the color series. The specific color vision defect can be diagnosed from these mistakes.