Ординатура / Офтальмология / Английские материалы / Oxford American Handbook of Ophthalmology_Tsai, Denniston, Murray_2011

536 CHAPTER 16 Neuro-ophthalmology

Optic disc coloboma

This rare condition arises from incomplete closure of the embryonic fissure (inferonasal), with variable involvement of the adjacent retina and choroid. It may be sporadic or autosomal dominant and may be isolated, part of a syndrome, or occasionally associated with transsphenoidal encephalocele (Table 16.12).

Clinical features

•dVA (according to severity of coloboma), superior visual field defect.

•Glistening white bowl-shaped excavation within the disc (inferior part predominantly affected) ± chorioretinal/ciliary body or iris colobomata.

Morning glory anomaly

This very rare condition describes a usually unilateral excavation of the posterior globe that includes the optic disc and may even include the macula (“macula capture”).

Clinical features

•Severe dVA.

•Enlarged pink disc located within the excavation and surrounded by an elevated and irregularly pigmented annular zone. Vessels are

abnormally straight, with arteries and veins being of similar appearance.

•Complications: serous retinal detachments may occur in 30%.

•Associations: syndrome of transsphenoidal encephalocele with hyertelorism, flat nasal bridge, midline cleft lip/palate, and often panhypo-pituitarism.

Megalopapilla

Megalopapilla describes an unusually large but essentially normal disc. The patients have a high cup–disc ratio that may be confused with glaucomatous change.

Table 16.12 Associations of optic disc hypoplasia

CHIASMAL DISORDERS 537

Chiasmal disorders

The chiasm enables the hemidecussation of visual information from the temporal fields so that information from the right visual field of both eyes is processed in the left visual cortex and vice versa. It lies in an anatomically crowded region, so chiasmal syndromes may be accompanied by other neurological or endocrine abnormalities.

The most common and best-described disorder of the chiasm is a pituitary adenoma causing bitemporal hemianopia; however, a wide range of other lesions and clinical presentations may be seen (Table 16.13).

Clinical features

•Often asymptomatic unless central (decrease VA) or advanced peripheral field loss; in advanced cases, a pre-existing phoria may lead to hemifield slide due to loss of overlap between the two eyes (can also cause diplopia). During close work, an object placed just beyond fixation may disappear (postfixation blindness).

•Field loss: classically bitemporal but often asymmetric and dependent on exact site of lesion (Table 16.14).

•Headache (usually frontal).

Associated features

•Involvement of CN III, IV, V1, V2, and VI and sympathetic nerve fibers may result in abnormalities of pupils (including Horner’s syndrome), ocular motility, and facial sensation. Rarely, seesaw nystagmus may occur.

•iICP may cause nausea, vomiting, pulsatile tinnitus, and papilledema. Hydrocephalus (blockage of foramen of Munro from posterior chiasmal lesions) may cause abnormal gait, urinary incontinence, drowsiness, and Parinaud’s syndrome.

•Functioning pituitary tumors may cause acromegaly or gigantism (iGH; large hands and feet and coarsening of features or abnormal height), Cushing’s syndrome (iACTH; moon face, truncal obesity, hypertension), and hyperprolactinemia (impotence and galactorrhea).

•Pituitary destruction causes hypopituitarism with loss of LH/FSH (dlibido, amenorrhea; may present as primary infertility), GH (silent unless pubertal), TSH (hypothyroidism), and ACTH (secondary hypoadrenalism with collapse). Hypothalamic involvement may cause diabetes insipidus (dADH; polydipsia, polyuria).

Investigations

•Accurate visual field testing and interpretation is vital.

•Urgent neuroimaging: MRI (gadolinium enhanced) is preferred, although CT is better at detecting bony involvement.

•Consider endocrinological consultation and LP for CSF analysis.

Treatment

The ophthalmologist’s role is to diagnose, refer for appropriate treatment (e.g., to endocrinology, neurosurgery, or often to a multispecialty pituitary team; see Table 16.15), and monitor the patient’s vision long term (VA, color vision, visual fields). Late loss of vision may represent tumor recurrence or be the result of treatment (radiotherapy).

RETROCHIASMAL DISORDERS 539

Retrochiasmal disorders

Most retrochiasmal disorders are associated with significant additional neurological morbidity. Hence such patients tend to have already been assessed, investigated, and started on treatment and rehabilitation before seeing an ophthalmologist. However, lesions that are otherwise clinically silent (e.g., some occipital pathology) may present first to the ophthalmologist.

The patient will usually be vague about the problem with his/her vision, and even a dense hemianopia may be missed unless visual fields are routinely assessed (e.g., by confrontational testing).

Clinical features

Optic tracts

•Incongruous homonymous hemianopia, optic atrophy, contralateral RAPD, larger pupil on the side of the hemianopia (Behr pupil), pupillary hemiakinesia (Wernicke’s pupil).

Lateral geniculate nucleus

•Incongruous homonymous hemianopia, normal pupils; often associated with thalamic and corticospinal signs (mild hemiparesis).

Optic radiations

Parietal lesions

•Inferior incongruous homonymous defect, usually sparing fixation (macula fibers pass between parietal and temporal lobes); may be associated with damage to the posterior limb of the internal capsule (contralateral hemiparesis + hemianesthesia), injury to the pursuit pathways (patient fails to pursue to the side of the lesion; cannot follow an optokinetic nystagmus (OKN) drum rotated to the side of the lesion), and Gerstmann’s syndrome (dominant parietal lobe only).

Temporal lesions

•Superior incongruous homonymous defect (“pie in sky”), usually sparing central vision. They may be associated with memory loss, hallucinations (olfactory, gustatory, auditory), and receptive dysphasia.

Calcarine cortex (occipital) lesions

•Congruous homonymous defect; variants include sparing of the temporal crescent (represented anteriorly), sparing of the macula (represented posteriorly), or a congruous homonymous macular lesion (selective injury to the occipital tip). These may be associated with visual hallucinations (usually in the hemianopic field) and denial of blindness (Anton’s syndrome).

Investigations

•Urgent neuroimaging: MRI (gadolinium enhanced) is preferable, although CT may be adequate for many lesions and may be advantageous in the presence of extensive hemorrhage.

•Further investigations will be directed by the nature of the lesion found.

540 CHAPTER 16 Neuro-ophthalmology

Treatment

After diagnosis, the main role of the ophthalmologist is to refer for appropriate treatment of the underlying cause (e.g., to stroke unit, neurosurgery, oncology). A secondary role is coordination of visual rehabilitation and support (which may include visual impairment registration).

MIGRAINE 541

Migraine

Migraine is a very common condition that may be severely disabling. Its prevalence is estimated at up to 20% for men and 40% for women. Around 25% of cases present before the age of 10 years, and 90% present before age 40. Overall, it is more common in women, but under 12 years of age it is slightly more common in boys.

It is classified as migraine without aura (“common migraine”) or migraine with aura (“classic migraine”); migraine without aura is three times as common as migraine with aura. A first-degree relative confers a relative risk of 3.8 for classic migraine and 1.9 for common migraine.

The mechanism is uncertain: patients with migraines appear to have an inherited susceptibility to environmental factors that trigger noradrenaline and serotonin release. These cause constriction of cortical vessels (spreading neuronal depression aura) and dilation of extracranial vasculature (perivascular pain receptors lheadache).

Clinical features

Migraine without aura

•Prodrome: mood and autonomic system disturbance (e.g., fatigue, hunger, irritability).

•Headache: unilateral (may generalize), throbbing, moderate to severe intensity, worsens over 1–2 hours, usually subsides over 4–8 hours but may last 1–3 days. It may be associated with nausea, photophobia, and sensitivity to noise (phonophobia).

•Termination and postdrome phase: recovery stages marked by fatigue.

Migraine with aura

This variant is characterized by an aura that usually precedes the headache phase, but may coincide with or follow it. The aura is most often visual but may be somatosensory, motor, or speech.

•Visual (99% of patients): typically starts paracentrally and expands temporally; the advancing edge forms a positive scotoma (flickering, shimmering, zigzag, multicolored lights), whereas the trailing edge is negatively scotomatous. Other visual phenomena include foggy vision, heat waves, tunnel vision, and complete loss of vision (see Box 16.4).

•Somatosensory (40%): hemisensory paresthesia/anesthesia.

•Motor (18%): hemiparesis.

•Speech (20%): dysphasia.

Other migraine variants (see Table 16.16)

Investigation

Migraine (with or without aura) may be diagnosed on the basis of a typical history in the presence of a normal neurological examination. Atypical features in the history (e.g., age >55 years, occipitobasal headache) or persistent neurological deficits require further assessment by a neurologist (which may include neuroimaging, carotid Doppler scan, ECG, echocardiography, and vasculitis screen).

542 CHAPTER 16 Neuro-ophthalmology

Treatment

•Prophylactic: avoid trigger factors (e.g., cheese, chocolate, coffee, citrus, cola, Chinese food/MSG, contraceptive pill); medical treatment is considered if there are 2 disabling attacks per month (e.g., propranolol, amitriptyline, sodium valproate).

•Therapeutic: relax in a dark quiet room; aspirin, NSAIDs, or combination analgesics. Consider 5HT1 agonist (e.g., sumatriptan 50 mg PO or 10 mg nasally stat) for more severe attacks.

Box 16.4 Ophthalmic complications of migraine

•Visual aura

•Retinal migraine

•Ophthalmoplegic migraine

•Retinal arterial occlusion

•Anterior ischemic optic neuropathy

•Posterior ischemic optic neuropathy

•Benign unilateral episodic mydriasis

•Adies pupil

•Increased risk of normal tension glaucoma

Table 16.16 Migraine classification

SUPRANUCLEAR EYE MOVEMENT DISORDERS (1) 543

Supranuclear eye movement disorders (1)

Eye movements serve to either bring an object of interest on to the fovea (saccades, quick phase of nystagmus) or maintain it there (vestibular, optokinetic, pursuit, vergences). Movement of the globe requires sufficient contraction of the extraocular muscles to first overcome orbital viscosity and then to sustain the new position against the elastic restoring force. The ocular motor neurons (originating from III, IV, VI nuclei; see Table 16.17) achieve this by pulse-step innervation whereby they generate first a phasic and then a tonic stimulus. For example, in saccades, a highfrequency signal from excitatory burst neurons excites the ocular motor nucleus directly (resulting in a pulse) but also indirectly via neural integrators (which mathematically integrate the signal to give a step).

Pause cells act as dampers to prevent unwanted saccadic activity. Supranuclear pathways control this activity.

Horizontal conjugate gaze requires the CN VI nucleus to simultaneously drive ipsilateral LR, drive contralateral MR (via the MLF to contralateral CN III nucleus), and inhibit the contralateral LR (via inhibitory burst cells to contralateral CN VI nucleus).

Saccades originate in the contralateral frontal eye field (FEF). Pursuit eye movements originate in the ipsilateral parieto-occipito-temporal (POT) junction. Vestibular input (e.g., for vestibulo-ocular reflex [VOR]) is from the contralateral vestibular nuclei. Convergence input is directly to both CN III nucleus complexes, avoiding the MLF (Fig. 16.2).

Control of vertical eye movements is more complex, since the system is effectively a torsional one that has been subverted to allow vertical movements.

Table 16.17 Location of ocular premotor and motor neurons

544 CHAPTER 16 Neuro-ophthalmology

Figure 16.2 Supranuclear inputs for horizontal eye movements. Connections are shown for eye movements to the left (including saccades from FEF, smooth pursuit from POT, and vestibulo-ocular reflex from vestibular nucleus). For convergence movements, the CN III nuclei are innervated directly to drive both MR. For further explanation, see text.

Disorders of horizontal gaze

Horizontal gaze palsy

Lesions of the paramedian pontine reticular formation (PPRF) or CN VI nucleus result in failure to move the eyes beyond the midline to the side of the lesion. The VOR is preserved in a PPRF lesion but is lost in a CN VI nucleus lesion.

Internuclear ophthalmoplegia (INO)

Lesions of the MLF result in failure of ipsilateral adduction and overshoot of the contralateral eye (ataxic nystagmus), which are best demonstrated on saccadic movements. It may be associated with upbeat and torsional nystagmus, loss of vertical smooth pursuit, abnormal VOR, and skew deviation. Convergence is preserved.

One-and-a-half syndrome

Lesions of the MLF and the PPRF (or CN VI nuc) on the same side result in an ipsilateral gaze palsy and a contralateral INO. There is loss of horizontal movements other than abduction of the contralateral eye.