Ординатура / Офтальмология / Английские материалы / Pediatric Ophthalmology for Primary Care 3rd edition_Wright, Farzavandi_2008

inhibitors (acetazolamide or methazolamide). Weight loss is important in obese patients, as well as elimination of any precipitating agents and medica tion. Some practitioners have recommended urgent therapy with intrave nous corticosteroids followed by a slow taper over several months; however, corticosteroids may contribute to the elevation of intracranial pressure. If medical therapy does not improve the condition, serial lumbar punctures or optic nerve sheath decompression can be performed. A unilateral optic nerve sheath decompression on the more involved side can prevent further visual loss, can provide relief from headaches, and may allow resolution

of the disc edema bilaterally. These more invasive procedures are usually recommended only after progressive visual field loss occurs despite conser vative medical therapy. The natural history of pseudotumor cerebri is spon taneous resolution over approximately 3 months to 1 year. Close ophthalmic follow up is important to document visual status because visual loss can occur in a small subset of patients.

Optic Disc Drusen

Optic disc drusen are calcific bodies within the optic disc. Fundus appear ance shows blurred optic disc margins and a swelling of the optic disc substance with globular calcific structures on the surface of the optic disc (Figure 9 6). They are a result of axonal degeneration and secondary cal cification. They first become visible during the teenage years and enlarge over time. Approximately 75% are bilateral and some are inherited as an autosomal dominant trait. Drusen do not produce true disc edema but do cause optic disc swelling. Visual acuity is usually excellent. Rarely, however, peripheral visual field loss and anterior ischemic optic neuropathy can occur secondary to compression of nerve fibers caused by deep drusen. Optic disc drusen can be identified by B scan ultrasonography or on com puted tomography scan by demonstrating calcium. In young children, the amount of calcium may be small and the scans may be negative. Most optic nerve drusen are idiopathic and not associated with systemic disease; how ever, they have been reported to occur with hypertensive retinopathy and chronic papilledema.

Figure 9 6.

Optic nerve drusen. A, Pseudopapilledema appearance with blurred disc margins. Note the globular calcific structures within the disc substance and the absence of a central cup. The retinal vessels tend to be distorted as they leave the optic nerve. B, Autofluorescence obtained using an exciter filter and barrier filter, showing the location of the calcific deposits.

Optic Disc Atrophy

Optic disc atrophy is the end stage of optic nerve disease. It can be caused by diffuse retinal disease or disease of the optic nerve and chiasm, orbital trauma, or compression from craniosynostosis. The optic nerve appears pale with decreased capillaries, and there are diminished nerve fiber layer stria tions in the peripapillary area (Figure 9 7). The presence of optic atrophy of unknown etiology should prompt a full investigation, including neuroimag ing to rule out an orbital lesion compressing the optic nerve or chiasm. See Chapter 7 for discussion of hereditary optic atrophy.

Figure 9 7.

Optic disc atrophy. Optic disc is pale and there is an absence of nerve fibers. This is a traumatic optic disc atrophy from blunt eye trauma.

Glaucoma

Glaucoma is increased intraocular pressure that causes optic nerve damage and atrophy. See Chapter 12 for a discussion of glaucoma.

3 components: face turn (horizontal head posturing), chin elevation or depression, and head tilt (tilting to the left or right). Patients with ptosis adopt a chin elevation, whereas patients with incomitant strabismus or nys tagmus can adopt any or all 3 components. When examining a patient for ocular torticollis, passively move the head opposite to the face turn and look for evidence of nystagmus or strabismus.

Ptosis and Ocular Torticollis

Ptosis may cause a chin elevation. The chin elevation compensates for the droopy eyelid, allowing the eye to lower and clear the droopy lid. Both uni lateral and bilateral ptosis will induce a chin elevation. Children with ptosis can have amblyopia even with a chin elevation, so they need prompt referral to an ophthalmologist. See Chapter 17 for more information on ptosis.

Strabismus and Ocular Torticollis

Patients with incomitant strabismus who have good alignment in an eccen tric gaze adopt a compensatory face turn to put the eyes where they are aligned, thereby establishing binocular vision and stereo acuity. Several types of incomitant strabismus can cause ocular torticollis. These include Duane syndrome, Brown syndrome, double elevator palsy, cranial nerve palsies, and restrictive strabismus. Congenital fourth nerve palsy is the most common cause for a head tilt (Figure 4 8), and Duane syndrome is the most common cause for a face turn (Figure 4 12). Eye muscle surgery is often effective in correcting strabismus related ocular torticollis.

Nystagmus and Ocular Torticollis

Patients with congenital nystagmus may show less nystagmus in an eccentric position of gaze. This position of gaze where the nystagmus is least is called the null point. Patients with an eccentric null point will adopt a compensa tory face posturing to place the eyes at the null point to damp the nystagmus and improve vision (Figure 10 1). The compensatory face posturing may be a face turn, head tilt, chin elevation or depression, or any combination

of these. A patient with a null point to right gaze, for example, adopts a left

face turn to move the eyes to the right, placing the eye at the null point. The treatment of nystagmus related head posturing is based on using eye muscle surgery to move the null point from an eccentric position to primary posi tion. This is called the Kestenbaum procedure.

Chapter 11

Pupil and Iris

Abnormalities

Abnormal Pupillary Reaction

Normally, the pupils are round and symmetrical, approximately 3 to 4 mm in diameter. The condition of having pupils of unequal size is called aniso coria. Anisocoria of 0.5 mm is generally accepted as normal, as it occurs in approximately 20% of the normal population. One millimeter or more of anisocoria is abnormal and should prompt further investigation.

When the eyes focus on objects that move from distance to near, a near reflex is invoked and the pupil reacts accordingly. This reflex consists of convergence (eyes move in together), miosis (pupillary constriction), and accommodation (increasing lens focus power). These 3 components keep the eyes aligned on an object as it approaches (convergence), increase depth of focus (miosis), and keep the image in focus (accommodation). Monitoring pupillary reaction during the near reflex may reveal an anisocoria and pos sibly indicate an abnormality.

Afferent Pupillary Abnormalities

The afferent visual pathway transmits information from the retina through the optic nerves to the lateral geniculate nucleus and on to the occipital cor tex. Afferent axons from the retina undergo hemidecussation at the chiasm, with nasal retinal axons coursing to the opposite optic tract and temporal retinal axons coursing to the ipsilateral optic tract (Figure 11 1). These afferent fibers synapse with the pretectal nucleus, sending efferent fibers to the ipsilateral and contralateral Edinger Westphal nucleus. This crossover of the right and left pathways is the reason that both pupils constrict when light is directed into one of the eyes. Ipsilateral pupillary constriction is called the direct pupillary response, and contralateral pupillary constriction is called the consensual pupillary response. A significant abnormality involving the retina or the optic nerve of one eye can diminish both direct and consensual pupillary responses and produces an afferent pupillary defect, also called a Marcus Gunn pupil. Patients with an afferent pathway defect of one eye will

Figure 11 1.

Anatomy of a light reflex pathway with parasympathetic outflow to the iris sphincter. Note that light directed into one eye results in bilateral pupillary constriction. Grey line denotes afferent pathway, red line denotes efferent pathway.

have symmetrically sized pupils because of the intact consensual pupillary response (Figure 11 2).

The swinging flashlight test is a method of detecting an afferent pupil lary defect and is based on comparing pupillary responses of fellow eyes. An afferent pathway defect of one eye (right eye) results in minimal constriction of both pupils when light is shined into the abnormal right eye (Figure 11 2, top left). Light directed into the normal left eye produces strong constric tion of both pupils (Figure 11 2, top right). This difference in pupillary light reaction can be appreciated by alternating a light source from one eye to the other eye. When the light stimulation moves from the normal eye to the eye with the afferent defect, both pupils will dilate (look at Figure 11 2, right

Figure 11 2.

A patient with a right afferent pupillary defect. Light shone on the involved right eye results in minimal constriction of both pupils (top left). When redirected to the uninvolved left eye, both pupils constrict (top right). The same test can be performed with ordinary room light by measuring the pupillary diameter with the uninvolved eye covered (bottom left) and then with the involved eye covered (bottom right). Note that the pupil is larger on the involved right side.

photo first, then compare to the left photo). On a practical note, it is best to perform the swinging flashlight test under dim ambient illumination with a bright, focused light source. Be sure to focus the light only on the eye being tested, as light scatter to the contralateral normal eye will confound the test. An afferent pupillary defect indicates afferent pathway disease anterior to the decussation of the chiasm such as a large retinal lesion, a lesion of the optic nerve, or a lesion of the anterior chiasm. Small retinal lesions do not cause

a clinically significant afferent pupillary defect even though small macular lesions may severely affect vision. Media opacities such as cataracts or cor neal opacities will not cause an afferent pupillary defect.

If a pupil of one eye is damaged and not functioning, one can test for light perception in that eye by testing for a consensual pupillary response. Shine light into the eye with the damaged pupil and observe the sound eye for a consensual pupillary response. Lack of a consensual pupillary response indicates no light perception.