The Massachusetts Eye and Ear Infirmary Illustrated Manual of Ophthalmology, 4th Ed.

12. Visual Acuity, Refractive Procedures, and Sudden Vision Loss

Refractive Error

Refractive Surgery Complications

Refractive Surgery Complications: Evaluation / Management

Vertebrobasilar Insufficiency

Migraine

Convergence Insufficiency

Accommodative Excess

Functional Visual Loss

Transient Visual Loss

Amblyopia

Cortical Blindness

Visual Pathway Lesions

Refractive Error

Definition

The state of an eye in which light rays are not properly focused on the retina, resulting in image blur.

Ametropia

A refractive error (e.g., myopia, hyperopia, or astigmatism).

Anisometropia

A difference in refractive error between the two eyes; usually 2D or more.

Astigmatism

Light rays are unequally focused producing two lines rather than a single point because the curvature of the cornea or, less commonly, the curvature of the lens varies in different meridians. If the cornea is steeper in the vertical meridian, it is referred to as “with-the-rule” astigmatism; if it is steeper in the horizontal meridian, it is called “against-the-rule” astigmatism. Astigmatism can also be designated regular (symmetric or asymmetric) or irregular. A cylindrical lens corrects regular astigmatism.

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FIGURE 12-1 Anisometropia with high myopia in the right eye (OD) (note minification from spectacle lens) and hyperopia in the left eye (OS) (note magnification from spectacle lens).

Emmetropia

No refractive error; light rays are focused on the retina, and thus no corrective lens is required for distance vision.

Hyperopia (Farsightedness)

Light rays are focused at a point behind the retina. A “plus” spherical lens is used to correct this refractive error.

Myopia (Nearsightedness)

Light rays from a distant object are focused at a point in front of the retina and those from a near object are focused on the retina. A “minus” spherical lens is used to correct this refractive error.

Presbyopia

Loss of accommodation of the crystalline lens with age; average age of the onset of symptoms is early 40s and this process continues through the early 60s. A “plus” spherical lens (i.e., bifocal “add”) is used to correct this problem.

Etiology

Astigmatism

The curvature of the cornea or, less commonly, the curvature of the lens varies in different meridians. Acquired forms may be caused by disorders of the eyelids (tumor, chalazion, ptosis), cornea (pterygium, limbal dermoid, degenerations, ectasias, surgery), lens (cataract), and ciliary body (tumor).

Hyperopia

The refractive power of the cornea is too weak or the axial length of the eye is too short. Acquired forms may be caused by disorders that decrease the eye’s refractive power (alteration in the lens [posterior lens dislocation, aphakia, diabetes], drugs [chloroquine, phenothiazines, antihistamines, benzodiazepines], poor accommodation [tonic pupil, drugs, trauma], corneal flattening [contact-lens-induced], intraocular silicone oil) or effective length (central serous retinopathy, retrobulbar masses, choroidal tumors).

Myopia

The refractive power of the eye is too strong or the axial length of the eye is too long. Acquired forms may be caused by disorders that increase the eye’s refractive power (alteration in the lens [diabetes, galactosemia, uremia, cataracts, anterior lenticonus, anterior lens dislocation], drugs [sulfonamides, miotic agents], excessive accommodation, corneal steepening [keratoconus, congenital glaucoma, contact-lens-induced]) or effective length (congenital glaucoma, posterior staphyloma, retinopathy of prematurity, scleral buckle surgery). Myopia also increases in the dark (night myopia).

Presbyopia

Loss of lens elasticity or possibly reduced ciliary muscle effectivity. Premature presbyopia may occur with debilitating illness, diphtheria, botulism, mercury toxicity, head injury, cranial nerve III palsy, Adie’s tonic pupil, and tranquilizers.

Epidemiology

Hyperopia is normally present during infancy and early childhood and then declines between ages 8 and 13 years, resulting in emmetropia in most adults. The incidence of refractive errors in the US population is approximately 25% for myopia and 25% for hyperopia; 50% have some degree of astigmatism. After the age of 40 years old, 50% of people have hyperopia. Hyperopia is associated with shallow anterior chambers and narrow angles; myopia is associated with lattice degeneration and retinal detachment.

Symptoms

Decreased vision when not wearing corrective lenses; distant objects are blurry and near objects are clear (myopia), distant and near objects are blurry (hyperopia), or near objects that are blurry become clearer when held further away (presbyopia). May have asthenopia (eye strain) due to sustained accommodative effort (overcorrected myopia, or undercorrected or uncorrected hyperopia; asthenopia may also be produced by convergence insufficiency or accommodative insufficiency [hypothyroidism, anemia, pregnancy, nutritional deficiencies, and chronic illness]). Hyperopia may be asymptomatic in children and young adults, who can compensate enough with accommodation.

Signs

Decreased uncorrected visual acuity that improves with pinhole testing, glasses, or contact lenses; hyperopes may have normal uncorrected visual acuity.

Differential Diagnosis

Normal eye exam except for decreased vision: amblyopia, retrobulbar optic neuropathy, other optic neuropathies (toxic, nutritional), nonorganic (functional) visual loss, rod monochromatism, cone degeneration, retinitis pigmentosa sine pigmento, cortical blindness.

Evaluation

• Complete ophthalmic history and eye exam with attention to pinhole visual acuity (corrects most low to moderate refractive errors to the 20 / 25 to 20 / 30 level), manifest (undilated) and cycloplegic (dilated) refraction, retinoscopy, pupils, keratometry, cornea, lens, and ophthalmoscopy.

• Consider potential acuity meter (PAM) testing, rigid contact lens overrefraction, and corneal topography (computerized videokeratography) if irregular astigmatism is suspected.

Management

• Glasses are the first line of treatment and can correct virtually all refractive errors, with the exception of irregular astigmatism.

• Contact lenses (soft or rigid); numerous styles of contact lenses are available to correct almost any refractive error; rigid lenses can correct irregular astigmatism.

• Consider refractive surgery (see below).

Prognosis

Good except for pathologic myopia (see Chapter 10).

Refractive Surgery Complications

Intraocular Refractive Procedures

Used to correct moderate to high degrees of myopia and hyperopia.

Refractive Lens Exchange

The noncataractous crystalline lens can be removed and replaced with an intraocular lens implant of appropriate power to correct the resulting aphakia. The main disadvantage of this method is loss of accommodation. This procedure is controversial for myopia because of the risk of retinal detachment in pseudophakic eyes; hyperopic eyes with nanophthalmos may develop choroidal effusions.

Phakic Intraocular Lens

A lens implant is placed in the anterior chamber, posterior chamber, or fixated to the iris with the optic centered over the pupil. Prophylactic peripheral iridotomies are performed prior to surgery to prevent postoperative pupillary block angle-closure glaucoma (see Chapter 6).

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FIGURE 12-2 Phakic intraocular lens demonstrating the Verisyse lens in the anterior chamber attached to the iris at the 3 o’clock and 9 o’clock positions.

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FIGURE 12-3 Phakic intraocular lens demonstrating the Visian ICL in the sulcus.

Symptoms

Postoperatively may have photophobia, pain, decreased vision, glare, and halos.

Signs and Complications

Corneal edema (endothelial cell loss), cataract, glaucoma, pupillary block, iridocyclitis, and endophthalmitis; may have residual refractive error. Additional complications of clear lens extraction include posterior capsular opacification, cystoid macular edema, retinal detachment, suprachoroidal hemorrhage, choroidal effusion, retained lens material, and iris damage.

Corneal Refractive Procedures

Incisional

Radial keratotomy (RK)

This procedure corrects low-to-moderate myopia. Deep, radial, corneal incisions are created with a diamond knife to flatten the central cornea. The surgical effect depends on various factors including depth and number of incisions, size of optical zone, patient age and gender, design of diamond blade, and surgeon experience. Radial keratotomy can be combined with astigmatic keratotomy for compound myopia (myopia with astigmatism). It is rarely performed anymore.

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FIGURE 12-4 Eight-incision radial keratotomy demonstrating near full-thickness corneal incisions at 90–95% depth.

Astigmatic keratotomy

This procedure corrects corneal astigmatism. Deep, midperipheral arcuate or straight incisions (parallel to the limbus) are made (traditionally with a diamond knife and more recently with femtosecond lasers) on the steep corneal meridian to flatten it. As with RK, the surgical effect depends on depth and number of incisions, size of optical zone (usually 7 mm), patient age, and surgeon experience. The incisions must not be > 90° or intersect with RK incisions. This technique is useful after penetrating keratoplasty for high-to-moderate astigmatism.

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FIGURE 12-5 Astigmatic keratotomy demonstrating a pair of 90% depth corneal incisions in the midperiphery of the vertical meridian.

Limbal relaxing incisions / peripheral corneal relaxing incisions

Similar to astigmatic keratotomy, this technique is used to correct low amounts of astigmatism, usually in association with cataract surgery. Arcuate incisions, 500–600 μm deep with a guarded blade, are placed at the 10–11 mm optical zone concentric to the limbus to correct 1–2D of astigmatism. Because ultrasound is not required, these relaxing incisions can be performed at the time of surgery or in the clinic. Femtosecond lasers allow these incisions to be created at greater depth, at smaller optical zones (8–10 mm), and also intrastromally, with more precise control of each parameter. Corneal topography is recommended prior to performing this procedure.

Symptoms

Postoperatively may have decreased vision (due to undercorrection, overcorrection, or irregular astigmatism), fluctuating vision, difficulty with night vision, halos, glare, starbursts, ghost images, double vision, and foreign body sensation.

Signs and Complications

Corneal scarring, infection, or perforation; may have residual refractive error, regression, or progression over time.

Excimer Laser

This ultraviolet laser (193 nm) ablates corneal tissue to correct myopia (central ablation), hyperopia (peripheral ablation), regular astigmatism (eliptical ablation), irregular astigmatism (topography-guided ablation), or reduce higher-order aberrations (wavefront ablation).

Photorefractive keratectomy (PRK)

This procedure uses excimer laser ablation to reshape the corneal stroma after epithelial removal (mechanical, alcohol, or laser). The visual recovery period is longer than with LASIK, but final visual outcomes are similar in low and moderate myopia. Patients may experience initial pain due to the epithelial defect, and decreased vision due to corneal haze.

Laser-assisted subepithelial keratectomy and epithelial-laser in-situ keratomileusis

These procedures combine PRK and laser in-situ keratomileusis (LASIK) techniques. A flap composed of only epithelium is created with topical alcohol (LASEK) or a mechanical epithelial separator (epi-LASIK), the epithelial flap is carefully retracted, laser energy is applied to the stromal bed, and the epithelial flap is replaced or excised. This procedure may combine the advantages of PRK and LASIK by decreasing the incidence of pain and haze associated with PRK and risk of flap complications associated with LASIK.

Laser in-situ keratomileusis

This procedure combines automated lamellar keratoplasty and PRK techniques. A mechanical microkeratome or femtosecond laser is first used to cut a partial-thickness hinged corneal flap, which is then folded back. The programmed excimer laser energy is applied to the underlying stromal bed, and the flap is replaced. LASIK allows for faster visual recovery and minimal pain after surgery, but there is a higher risk of complications due to flap-related problems than with PRK.

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FIGURE 12-6 Post-laser in-situ keratomileusis corneal topography map for a myopic excimer laser ablation: note the blue central flattening on the map created by the photoablation of corneal stroma.

Symptoms

Postoperatively may have decreased vision (due to undercorrection, overcorrection, irregular astigmatism, or haze), fluctuating vision, difficulty with night vision, halos, glare, starbursts, ghost images, double vision, and variable discomfort (ranging from foreign body sensation to moderate pain).

Signs and Complications

Corneal scarring, infection, keratectasia, central toxic keratopathy, decentration (apparent on corneal topography), or dry eyes; may have residual refractive error, regression over time. Additional LASIK complications include flap striae, epithelial ingrowth, flap trauma, and diffuse lamellar keratitis (DLK, “sands of the Sahara”). Haze from surface ablation may be early (due to delayed epithelial healing) or late (≥ 3 months, due to deeper ablations and UV exposure).

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FIGURE 12-7 Photorefractive keratectomy demonstrating moderate central corneal haze 6 months after a treatment for high myopia.

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FIGURE 12-8 Dense (4 +) central haze and scarring after photorefractive keratectomy in a corneal graft: the edge of the graft is visible as a fine white line at the right edge of the picture extending from the 1 o’clock to 5 o’clock positions.

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FIGURE 12-9 Atypical mycobacterial keratitis after laser in-situ keratomileusis demonstrating the infectious keratitis in the corneal flap interface.

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FIGURE 12-10 Laser in-situ keratomileusis flap striae demonstrating vertically curved wrinkles in the flap.

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FIGURE 12-11 Same patient as Figure 12-10 with laser in-situ keratomileusis flap striae demonstrating the curved striae that are enhanced with topical fluorescein and viewed with a blue light.

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FIGURE 12-12 Epithelial ingrowth after laser in-situ keratomileusis proliferating from the inferior corneal flap edge: the gray puddy-like pseudopods represent epithelium in the corneal flap interface. Inset shows transillumination of the epithelial ingrowth.

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FIGURE 12-13 Grade 2 diffuse lamellar keratitis or “sands of the Sahara” after laser in-situ keratomileusis demonstrating characteristic appearance of white granular interface material distributed in a wavelike pattern.

Implants

Intracorneal inlays

This procedure combines a partial-thickness corneal flap (similar to LASIK) with a thin, contact-lens-like, intrastromal implant that is placed in the central optical zone to correct refractive errors without removing corneal tissue. It may be most useful for treating presbyopia.

Intrastromal corneal ring segments (Intacs)

Polymethylmethacrylate (PMMA) ring segment implants are placed into peripheral corneal channels at two-thirds depth outside the visual axis to correct low-to-moderate myopia by flattening the cornea without cutting or removing tissue from the central optical zone. These channels can be made manually or with a femtosecond laser. Also used to treat mild-to-moderate keratoconus by shifting and stabilizing the cone, allowing for improved contact lens tolerance and best spectacle-corrected visual acuity.

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FIGURE 12-14 Intacs (intrastromal corneal ring segments) demonstrating two implants well positioned in the cornea.

Symptoms

Postoperatively may have decreased vision (due to undercorrection, overcorrection, or irregular astigmatism), fluctuating vision, difficulty with night vision, halos, glare, and foreign body sensation.

Signs and Complications

Implant extrusion, implant decentration, infection, stromal deposits (intrastromal corneal ring segments), flap striae (intracorneal inlays), epithelial ingrowth (intracorneal inlays); may have residual refractive error.

Thermokeratoplasty

Conductive keratoplasty

Radiofrequency energy is applied to the peripheral cornea to shrink collagen tissue and treat low-to-moderate hyperopia through central corneal steepening. A hand-held contact probe with a 450 μm needle directly delivers energy in a ring pattern outside the visual axis. The number of spots determines the amount of central steepening (8 to 32 spots).

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FIGURE 12-15 Thermokeratoplasty treatment demonstrating a double ring, staggered pattern of eight spots each, visible as opaque white corneal spots in the area overlying the pupillary border.

Symptoms

Postoperatively may have pain, foreign body sensation, decreased vision (irregular astigmatism, regression), glare, and halos.

Signs and Complications

Corneal scarring in area of application, regression over time; may have residual refractive error.

Refractive Surgery Complications: Evaluation / Management

Evaluation

• Complete ophthalmic history and eye exam with attention to visual acuity, manifest and cycloplegic refractions, pupil size, keratometry, cornea, lens, and ophthalmoscopy.

• Corneal topography (computerized videokeratography).

• Consider rigid contact lens overrefraction if irregular astigmatism is suspected.

Management

• No treatment recommended unless patient is symptomatic and vision is decreased. Choice of treatment depends on type of refractive surgery performed.

• Undercorrection or overcorrection: Modify topical medication regimen, glasses or contact lens; consider retreatment after corneal stabilization and failure of conservative management. Specific treatment must be tailored on an individual basis and is beyond the scope of this book, but should be performed by a cornea or refractive specialist.

• Infectious keratitis: Culture (lift corneal flap), topical anti-infective agents (see Chapter 5); may require flap amputation.

• Keratectasia: Glasses or RGP contact lens; consider corneal collagen cross-linking with riboflavin (CXL) or Intacs; may require penetrating keratoplasty.

• Central toxic keratopathy: Observe; may require hyperopic retreatment after opacity resolves.

• Decentration or irregular astigmatism: Rigid contact lens trial; retreatment with wavefront or topography-guided ablation.

• Halo, glare, and starbursts: Consider topical miotic agent (pilocarpine 0.5–1%) or brimonidine (Alphagan-P 0.15%) qd to bid, polarized sunglasses, or retreatment with enlarged treatment zone.

• Dry eye: Topical artificial tears (see Appendix) up to q1h; consider punctal plugs, topical cyclosporine 0.05% (Restasis) bid; may require a bandage contact lens for corneal surface irregularities.

• Pain (surface ablation): Bandage contact lens, topical nonsteroidal anti-inflammatory drug; consider topical dilute anesthetic drops, oral analgesic (Vicodin, Mepergan fortis, Toradol [20 mg then 10 mg every 4–6 hours], Neurontin [100 mg tid for 3 days] or Lyrica [75 mg tid for 5 days], Sumatriptan [100 mg once]), oral steroid (Prednisone taper [80, 60, 40, 20 mg qd for 4 days]); consider irrigating with chilled/frozen bismuth salicylate (BSS) solution for 30 seconds immediately after ablation.

• Haze (surface ablation): Prevent postoperatively with topical steroid for 1–3 months, oral vitamin C 500 mg po bid for 1 month, sunglasses to decrease UV exposure; consider topical mitomycin C (MMC) 0.02% for 12–30 seconds immediately after ablation. Treat existing haze with additional topical steroids; consider phototherapeutic keratectomy (PTK) with MMC.

• Epithelial ingrowth: Lift corneal flap and scrape undersurface of flap and stromal bed; consider suturing flap; consider Nd: YAG laser treatment.

• Diffuse lamellar keratitis: Frequent topical steroids (q1h initially) for grades 1 and 2 DLK; may require lifting flap and irrigating stromal bed to remove inflammatory debris (grades 3 and 4 DLK); consider short pulse of oral steroids.

• Flap striae: Lift flap, refloat, and stretch; may require removing epithelium and suturing flap; consider heating flap with warm spatula. On postoperative day 1, striae often can be removed with massage or stretching at the slit lamp.

Prognosis

Usually good; depends on specific surgical technique and any complications. Hyperopia treatments tend to regress with time.

Vertebrobasilar Insufficiency (Vertebrobasilar Atherothrombotic Disease)

Definition

Vertebrobasilar (posterior) circulation constitutes the arterial supply to the brain stem, cerebellum, and occipital cortex. Impaired blood flow to these areas may manifest in a myriad of symptoms. Transient ischemic attacks (TIAs) in this vascular territory are referred to as vertebrobasilar insufficiency (VBI).

Etiology

Thrombus, emboli, hypertension, arrhythmias, arterial dissection, hypercoagulable states, and subclavian steel syndrome. Approximately one-fourth of strokes and TIAs occur in the vertebrobasilar distribution. MRI studies suggest that 40% of patients with vertebrobasilar TIAs have evidence of brain-stem infarction.

Epidemiology

Male predilection (2 : 1); occurs in elderly, usually in seventh to eighth decades.

Symptoms

Vertigo is the hallmark of vertebrobasilar ischemia. Additionally, bilateral transient blurring or dimming of vision (seconds to minutes), photopsias (flashes of light), diplopia, unilateral weakness, sensory loss, ataxia, nystagmus, facial numbness, dysarthria, hoarseness, dysphagia, hearing loss, and vertigo; history of drop attacks (syncope) can occur.

Signs

Usually none; may have small, paracentral, congruous, homonymous visual field defects.

Differential Diagnosis

Amaurosis fugax, migraine, papilledema, temporal arteritis, labyrinthitis, vestibular neuronitis, benign paroxysmal positional vertigo.

Evaluation

• Complete ophthalmic history with attention to characteristics of attacks (monocular or bilateral, other symptoms, frequency, duration, etc.), neurologic exam, and eye exam with attention to motility, pupils, and ophthalmoscopy.

• Check visual fields.

• Lab tests: Complete blood count (CBC), erythrocyte sedimentation rate (ESR), and blood glucose (hypoglycemia).

• Check blood pressure.

• Head and orbital magnetic resonance imaging (MRI).

• Cervical spine radiographs (cervical spondylosis).

• Medical consultation for complete cardiovascular evaluation, including electrocardiogram, echocardiogram, duplex and Doppler scans of carotid and vertebral arteries.

• Neurology consultation.

Management

• Usually no effective treatment.

• Aspirin (325 mg po qd).

• May require long-term anticoagulation.

• Treat underlying etiology.

Prognosis

Usually poor.

Migraine

Definition

A neurologic syndrome characterized by recurrent attacks lasting 4–72 hours, often with unilateral throbbing moderate-to-severe headache, sensory changes, gastrointestinal symptoms, and mood disturbances. Five stages have been described: prodrome (premonitory symptoms 24–72 hours before other symptoms), aura (transient neurologic symptoms, usually visual), headache, resolution, and recovery. Often migraine is divided into the following categories: without aura, with aura, variant, and complicated. The formal migraine classification (according to the International Headache Society, second edition [IHS-2]) is:

Migraine without Aura (80%)

“Common” migraine; headache may or may not be preceded by a poorly defined prodrome of mood fluctuations (elation, hyperexcitability, food cravings, irritability, restlessness, depression, feeling of impending doom), excessive energy, fatigue, frequent yawning, and gastrointestinal disturbances (anorexia, nausea, and emesis).

Migraine with Aura

Aura (transient neurologic symptoms) develops over 5–20 minutes and lasts < 60 minutes; most commonly visual (bilateral) consisting of scintillations, zigzag lines (fortification phenomenon), spreading scotomas, tunnel vision, micropsia, blurred vision, and altitudinal field loss; can also be vertigo, sensory or motor disturbances, fainting, confusion, or possibly auditory hallucinations. Headache, nausea, photophobia, phonophobia, emesis, irritability, and malaise usually follow immediately after or within an hour; other symptoms include diarrhea, vertigo, tremors, sweating, and chills. Subtypes include:

Typical aura with migraine headache (15–20%)

“Classic” migraine; gradual aura lasting less than 1 hour.

Typical aura with nonmigraine headache

Headache does not satisfy criteria for migraine headache.

Typical aura without headache (5%)

“Acephalgic” migraine; aura (usually visual) without headache. Often occurs in older individuals with a history of classic migraine; 25% have a family history of migraine.

Hemiplegic migraine

Familial or sporadic; rare. Unilateral motor weakness or partial paralysis.

Basilar-type migraine (Bickerstaff syndrome)

Aura mimics vertebrobasilar artery insufficiency with brain-stem or bilateral occipital lobe symptoms (i.e., blindness, diplopia, vertigo, difficulty with speech or coordination). Rare; typically occurs in teenage girls and young women.

Childhood Periodic Syndromes

Recurrent disorders in children with migraine features that are usually precursors of migraine. These include: cyclical vomiting (recurrent episodes of nausea and emesis [at least 5 within 5 days]), abdominal migraine (recurrent attacks of midline abdominal pain for up to 72 hours with nausea, emesis, anorexia, and / or pallor), and benign paroxysmal vertigo of childhood (recurrent vertigo attacks, commonly with emesis or nystagmus).

Retinal Migraine

“Ocular” migraine; rare; monocular scotoma or visual loss for minutes to an hour due to retinal or optic nerve ischemia.

Complications of Migraine

This category includes: chronic migraine (headache for more than 15 days in a month), status migrainosus (headache lasting longer than 72 hours despite treatment, continuous or with brief interruptions [< 4 hours]), persistent aura without infarction (aura lasting longer than 72 hours), migrainous infarction (stroke during a migraine or neurologic deficit lasting longer than 1 week with corresponding lesion on neuroimaging), and migraine-triggered seizures (“migralepsy”; seizure during or immediately after a migraine).

Etiology

Although not completely elucidated, mounting evidence supports the role of neurogenic peptides in migraine formation, such as serotonin and dopamine, in the brain. These vasoactive neuropeptides stimulate an inflammatory cascade with the release of endothelial cells, mast cells, and platelets that produce vasodilation and a perivascular reaction. The susceptibility to headaches in migraineurs is due to a baseline state of hyperexcitability in the cerebral cortex, particularly the occipital area. The aura is caused by cortical spreading depression (a wave of neuronal excitation followed by suppression with blood vessel constriction and dilation); the headache is due to neurochemical release causing inflammation and blood vessel dilation. Dopamine stimulation may play a role, particularly in the prodrome. The serotonin receptor (5-HT) is believed to be the most important receptor in the headache pathway.

Epidemiology

Affects approximately 18% of women and 6% of men in the USA. Can occur at any age; family history of migraine in 70%, or a history of motion sickness is common. Commonly triggered by foods, alcohol, caffeine withdrawal, drugs (nitroglycerine, reserpine, hydralazine, ranitidine, estrogen), hormonal changes (menstruation, ovulation, oral contraceptives, hormone replacement), sleep alteration, exertion, stress, fatigue, and head trauma (also fasting, strong odors, flickering lights, sun glare, smoky or noisy environments, altitude, and weather changes). Associated with epilepsy, familial dyslipoproteinemias, Tourette syndrome, hereditary essential tremor, ischemic stroke, depression, asthma, patent foramen ovale. Migraine often demonstrates maternal inheritance and occurs more frequently in patients with mitochondrial disorders. Familial hemiplegic migraine has been mapped to chromosomes 19p13 and 1q.

Symptoms

May have prodrome, aura, headache, or other neurologic, gastrointestinal, or emotional symptoms (see above).

Signs

Usually none; may have visual field defect, cranial nerve palsy, or other neurologic deficits.

Differential Diagnosis

Serious: Meningitis, subarachnoid hemorrhage, temporal arteritis, malignant hypertension, intracranial tumor, arteriovenous malformation, vertebrobasilar artery insufficiency, aneurysm, subdural hematoma, transient ischemic attack, occipital or temporal lobe seizure, cerebrovascular accident.

Others: Tension or cluster headaches, trigeminal neuralgia, temporomandibular joint syndrome, cervical spondylosis, herpes zoster ophthalmicus, sinus or dental pathology, uveitis, angle-closure glaucoma, after lumbar puncture, nonorganic, caffeine withdrawal, carbon monoxide inhalation, and nitrite exposure.

Evaluation

• Complete ophthalmic history with attention to characteristics of attacks (precipitating factors, frequency, duration, associated symptoms, etc.), neurologic exam, and eye exam with attention to motility, pupils, tonometry, and ophthalmoscopy.

• Check visual fields.

• Check blood pressure and temperature.

• Consider lumbar puncture for suspected meningitis.

• Neuroimaging for complicated migraines or migraines with neurologic deficits.

• Medical or neurology consultation.

Management

• Rest in dark, quiet room.

• Pain relief: Nonsteroidal anti-inflammatory drugs (aspirin 325–500 mg po or ibuprofen 600 mg po qd), triptans (sumatriptan [Imitrex], rizatriptan [Maxalt], zolmitriptan [Zomig]), ergot alkaloids (ergotamine (1–3 mg po 1 tablet at onset of aura or headache, 1 more 15–20 min later) or dihydroergotamine [Migranal]); consider opioids (codeine, oxycodone). Triptans and ergots are vasoconstrictors and should not be used for complicated migraines.

• Consider antiemetics.

• Prevention: Avoid triggers and precipitating agents (foods, alcohol, stress), reduce stress, regulate sleep and meals, exercise; consider biofeedback and relaxation techniques; β-blockers (propranolol 20–40 mg po bid to tid initially), tricyclic antidepressants (amitriptyline 25–75 mg po qd to bid initially), calcium-channel blockers (nifedipine 10–40 mg po or verapamil 80 mg po tid); consider antiepileptics (valproic acid [Depakote 500–1000 mg po qd], topiramate [Topamax 30–100 mg po qd], gabapentin [Neurontin]) or botulinum toxin (Botox) injections to the scalp and temple.

• Treatment should be monitored by an internist or neurologist.

Prognosis

Good.

Convergence Insufficiency

Definition

Decreased fusional convergence with near fixation, a remote near point of convergence and a low accommodation convergence/accommodation (AC / A) ratio.

Etiology

Idiopathic but possibly innervational in origin; may be induced by drugs, trauma, or prismatic effect of glasses (base-out).

Epidemiology

Prevalence is estimated at 3–5%; typically occurs in teenagers and young adults, rare before 10 years of age; slight female predilection. Common cause of asthenopia (eye strain); aggravated by anxiety, illness, or lack of sleep. Often associated with an exophoria or intermittent exotropia at near.

Symptoms

Asthenopia, diplopia, blurred vision, headaches, difficulty reading.

Signs

Inability to maintain fusion at near (patient closes one eye while reading to relieve visual fatigue), distant near point of convergence, reduced fusional convergence amplitudes; possible exophoria at near without exotropia (especially after prolonged reading).

Differential Diagnosis

Presbyopia, refractive error (uncorrected hyperopia, overcorrected myopia), accommodative insufficiency.

Evaluation

• Complete ophthalmic history and eye exam with attention to manifest and cycloplegic refractions, motility (cover and alternate cover tests [exophoria at near]), near point of accommodation (normal is 5–10 cm, abnormal is 10–30 cm), fusional convergence amplitudes (normal is 30–35 prism diopters [PD] of base-out prism causes diplopia; abnormal is < 20PD), and 4PD base-in prism test (differentiates convergence insufficiency [near vision improves] from accommodative insufficiency [near vision worsens]).

Management

• Correct any refractive error (undercorrect hyperopes, fully correct myopes).

• Orthoptic exercises: Training of fusional convergence with pencil ‘push-ups’ bring pencil in from arm’s length toward nose while focusing on eraser, when diplopia [break point] develops, the exercise is repeated; each attempt is designed to bring the pencil closer without diplopia. Alternatively, use base-out prisms (increase amount of prism diopters until blur point is reached, usually 4–6PD, then increase further until break point is reached). Exercises are repeated 15 times, 5 times a day; can also use major amblyoscope (stereograms).

• When no improvement is noted with exercises, base-in prism reading glasses are helpful.

• Very rarely, muscle surgery with bimedial rectus muscle resection.

Prognosis

Usually good.

Accommodative Excess (Accommodative Spasm)

Definition

A clinical state of excessive accommodation (lens focusing); spasm of the near reflex is the triad of excess accommodation, excess convergence, and miosis.

Etiology

Often triggered by stress or prolonged reading.

Symptoms

Blurred distance vision, headache, brow ache, eye strain at near; may have diplopia.

Signs

Abnormally close near point, miosis, and normal amplitude of accommodation; relief of symptoms with cycloplegia and cycloplegic refraction uncovers more hyperopia than on manifest refraction.

Differential Diagnosis

Iridocyclitis, uncorrected refractive errors (usually hyperopes, but also astigmats and myopes), pseudomyopia (acquired myopia from systemic disorders, drugs, forward lens movement [see Myopia section]).

Evaluation

• Complete ophthalmic history and eye exam with attention to manifest and cycloplegic refractions, pupils, and motility.

Management

• Stop offending medication if applicable.

• Correct any refractive error, including prescribing a reading aid if esotropia exists at near.

• Consider cycloplegic (scopolamine 0.25% qd to qid) to break spasm (only occasionally needed).

• Instruct patient to focus intermittently at distance during periods of prolonged near work.

Prognosis

Good.

Functional Visual Loss

Definition

Visual abnormality not attributable to any organic disease process (nonphysiologic).

Malingering

Fabrication of the existence or extent of a disorder for secondary gain.

Hysteria

Subconscious (not willful) expression of symptoms.

Epidemiology

Twenty percent have coexistent organic disease. Malingering is usually associated with a financial incentive (i.e., legal action or compensation claim).

Symptoms

Decreased vision (monocular or binocular, usually very vague about quality of symptoms), diplopia, metamorphopsia, oscillopsia.

Signs

Decreased visual acuity (20 / 20 to no light perception), abnormal visual field (usually inconsistent or has characteristic pattern); may have voluntary nystagmus, gaze palsy, or blepharospasm. Malingerer is often uncooperative and combative, hysteric is often indifferent but cooperative; otherwise normal examination (especially pupils, optokinetic nystagmus response, fundus).

Differential Diagnosis

Functional visual loss is a diagnosis of exclusion; must rule out organic disease, especially amblyopia, early keratoconus, anterior basement membrane dystrophy, early cataracts, central serous retinopathy, early Stargardt’s disease, retinitis pigmentosa sine pigmento, rod monochromatism, cone degeneration, retrobulbar optic neuritis, optic neuropathy, and cortical blindness.

Evaluation

• Complete ophthalmic history and eye exam with attention to vision (distance and near, monocular and binocular, varying distance, fogging, red–green glasses with duochrome test or Worth 4-dot test, prism dissociation, stereopsis, startle reflex, proprioception, signing name, mirror tracking, optokinetic nystagmus response), retinoscopy, motility, pupils, and ophthalmoscopy.

• Check visual fields (monocular and binocular); beware tunnel vision, spiraling fields, crossing isopters.

• Consider corneal topography (computerized videokeratography).

• Consider electroretinogram, visual evoked response, fluorescein angiogram, or neuroimaging in difficult cases or if unable to prove normal vision and visual field.

Management

• Reassurance.

• Offer a way out by instilling a topical medication in the office and then retesting, especially for children.

• Consider repeat examination several weeks later.

• Psychiatry consultation usually not necessary.

Prognosis

No improvement in up to 30%.

Transient Visual Loss (Amaurosis Fugax)

Definition

Unilateral transient visual loss due to ischemia. This is a type of TIA also called temporary monocular blindness (TMB).

Etiology

Usually embolic from carotid artery or cardiac valvular disease; also due to arrhythmias, coagulation disorders, hyperviscosity syndromes, vasospasm, hypotension, and rarely an orbital mass.

Symptoms

Monocular, brief, reversible dimming or loss of vision (typically 2–5 minutes).

Signs

Usually none; may have visible emboli in retinal vessels.

Differential Diagnosis

Vertebrobasilar artery insufficiency, migraine, temporal arteritis, papilledema, pseudopapilledema (optic nerve drusen).

Evaluation

• Complete ophthalmic history with attention to characteristics of visual loss (monocular or bilateral, other symptoms, frequency, duration, etc.), neurologic exam, and eye exam with attention to pupils and ophthalmoscopy.

• Check visual fields.

• Medical consultation for complete cardiovascular evaluation including electrocardiogram, echocardiogram, and carotid Doppler studies.

Management

• Aspirin (325 mg po qd).

• Treat underlying etiology.

Prognosis

Depends on etiology; 1-year risk of cerebrovascular accident is 2%.

Amblyopia

Definition

Unilateral or bilateral loss of best corrected vision in an otherwise anatomically normal eye. Classified as mild (better than 20/40), moderate (20/40–20/80), and severe (20/ 100–20/400) based on visual acuity.

Etiology

Reduced visual input or abnormal binocularity during visual development (up to 6–8 years old). Various types:

Strabismic

Most common form of amblyopia; develops in a child when the visual input of a deviated eye is inhibited in order to prevent diplopia and visual confusion.

Refractive

Anisometropic

Due to unequal, uncorrected refractive errors between the two eyes, which causes a constant defocusing of the image; usually requires greater than 3D of myopic, greater than 1D of hyperopic, and greater than 1.5D of astigmatic anisometropia. May have associated strabismus (strabismic anisometropia).

Isoametropic

Bilateral amblyopia due to large, but equal, uncorrected refractive errors; usually requires greater than 8D of myopia, greater than 5D of hyperopia, and greater than 2.5D of astigmatism.

Deprivation

Uncommon; usually caused by congenital or acquired visual impairment such as cataract, corneal opacity, or ptosis; often results in significant loss of vision. Occlusion amblyopia (reverse amblyopia) is a rare form of deprivation amblyopia resulting from excessive treatment of amblyopia and is usually transient and reversible.

Epidemiology

Present in approximately 2% of general population. Increased risk with developmental delay, prematurity, ocular trauma, and positive family history. Strabismic and anisometropic account for more than 90% of amblyopia; isoametropic and deprivation are rare, each accounting for 1–2% of amblyopia.

Symptoms

Variable decreased vision.

Signs

Decreased visual acuity, which often improves with single-letter testing (due to crowding phenomenon: difficulty distinguishing optotypes that are close together) or is stable with neutral-density filters (strabismic amblyopia), decreased contrast sensitivity, reduced stereopsis; may have strabismus, nystagmus, ptosis, cataract, corneal opacity, small relative afferent pupillary defect.

Differential Diagnosis

Functional visual loss, retinal or optic nerve disorder.

Evaluation

• Complete ophthalmic history with attention to previous eye disease, trauma, surgery, and treatment (i.e., glasses, patching, drops).

• Complete eye exam with attention to vision with neutral-density filters and single letters, cycloplegic refraction, retinoscopy, contrast sensitivity, stereopsis, pupils, motility, lids, cornea, lens, and ophthalmoscopy. Accurate diagnosis is difficult in children < 3 years old.

• Consider imaging studies of the retina and optic nerve to rule out organic etiology.

Management

• The goal of treatment is to improve vision by removing any obstacle to visual input and forcing the use of the amblyopic eye.

• Treat the visual impairment in cases of deprivation (e.g., cataract extraction [by 2 months of age], ptosis repair, etc.).

• Correct any refractive error. Consider laser vision correction with surface ablation for severe anisometropic amblyopia.

• Occlusion therapy for children with full-time or part-time patching of preferred eye (full-time occlusion should not be used for more than 1 week per year of age before re-examination in order to prevent occlusion amblyopia). End point of therapy is spontaneous alternation of fixation or equal visual acuity in both eyes. Discontinue if no improvement after 3–6 months of compliant, full-time patching. May require maintenance or tapering therapy to maintain visual level. Other options for occlusion include opaque contact lens, spectacle filters/occluders, and tape or nail polish across one spectacle lens.

• Consider penalization therapy (usually pharmacologic with atropine 0.5% or 1%) to blur near vision in the healthy eye. Alternatively, optical penalization can be achieved with over-plused glass lens, contact lens, or elevated bifocal segment. Penalization therapy is used for mild to moderate amblyopia in conjunction with or instead of occlusion therapy to improve compliance.

• Protective eye wear with polycarbonate lenses to protect fellow eye if significant amblyopia exists because there is an increased lifetime risk of visual impairment in the healthy eye, usually due to trauma.

• Consider strabismus surgery after the amblyopia treatment.

Prognosis

Depends on severity and duration of amblyopia, age at which appropriate treatment is initiated (the younger the better), compliance with treatment, and type of amblyopia (poor for deprivation and high anisometropic, best for strabismic). Amblyopia responds to refractive correction alone in up to 77%. Occlusion therapy is successful in 73% after 1 year. The Amblyopia Treatment Studies (ATS) showed that, for children 3–7 years old, 6 hours of daily patching is as effective as full-time patching for severe amblyopia, and 2 hours is as effective as 6 hours of daily patching or twice-weekly atropine for moderate amblyopia. For children 7–12 years old, 2–6 hours of daily patching and atropine can improve amblyopia even if it has been previously treated. For children 13–17 years old, 2–6 hours of daily patching may improve amblyopia that has not been previously treated. The outcome of occlusion treatment is better in children < 6 years old than in those > 6 years old. After successful treatment, recurrence of amblyopia occurs in 25% within the first year (majority within 6 months) after discontinuation of occlusion therapy and is more common in children younger than 10 years old, with strabismic amblyopia, and when therapy is stopped abruptly and not tapered. Recurrence can be as high as 53% after 3 years.

Cortical Blindness (Cortical Visual Impairment)

Definition

Rare syndrome of bilateral blindness with intact pupillary light response due to widespread damage to the occipital lobes.

Etiology

Cerebrovascular accident (bilateral occipital lobe infarction), rarely neoplasia.

Symptoms

Complete visual loss; rarely, denies blindness (Anton’s syndrome), visual hallucinations.

Signs

Normal eye exam (including pupillary response) except for no light perception vision in both eyes; may demonstrate the Riddoch phenomenon (ability to perceive moving, but not static, objects) and “blind sight” (intact primitive mechanism that may allow navigation around objects).

Differential Diagnosis

Functional visual loss.

Evaluation

• Complete ophthalmic history, neurologic exam, and eye exam with attention to vision, pupils, and ophthalmoscopy.

• Head and orbital CT scan or MRI.

• Medical and neurology consultation.

Management

• No treatment recommended.

• Treat underlying etiology.

Prognosis

Poor.

Visual Pathway Lesions

Definition

Lesion of the visual pathway anywhere from the optic nerve to the occipital lobes (see Chapter 11 for Optic nerve lesions).

Etiology

Most commonly vascular or neoplastic; also due to trauma, infection, multiple sclerosis, sarcoidosis, and other rarer causes.

Symptoms

Asymptomatic or may notice decreased vision or visual field loss.

Signs

Normal or decreased visual acuity, visual field defect (usually a hemianopia or quadrantanopia [see Fig. 12-17]); may have relative afferent pupillary defect (if the lesion is anterior to the optic chiasm), may have associated endocrine abnormalities or other neurologic deficits.

u12-17a-9781455776443

u12-17b-9781455776443

FIGURE 12-17 Humphrey visual fields of a patient with a stroke demonstrating an incongruous right homonymous hemianopic field defect that is denser superiorly.

Differential Diagnosis

Amaurosis fugax, migraine, temporal arteritis, vertebrobasilar artery insufficiency, functional visual loss.

Evaluation

• Complete ophthalmic history, neurologic exam, and eye exam with attention to vision, pupils, and ophthalmoscopy.

• Check visual fields (defect helps localize the area of involvement).

• Head and orbital CT scan or MRI.

• Medical and neurology consultation.

Management

• Treat underlying etiology.

Prognosis

Usually poor, but depends on etiology.

u12-16-9781455776443

FIGURE 12-16 Visual pathway and corresponding visual field defects.