Diseases of the Cornea

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[edit] Diseases of the Cornea

Thomas J. Byrd

Although only 12 mm across and less than 1 mm thick, the cornea is optically transparent and has no blood supply, but it is far more complex than a simple “watch crystal” crowning the globe.

[edit] ANATOMY

The cornea is composed of five layers: epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium. The epithelium is five or six cell layers thick and richly supplied with free nerve endings only, since specialized receptors would compromise corneal clarity. Bowman's layer is a collagenous layer 8 to 10 μg thick to which the basal epithelial cells adhere via hemidesmosomes. The stroma constitutes about 90% of the total corneal thickness. It consists almost entirely of an extracellular matrix of collagen (and other glycoproteins), interspersed with fibroblasts and keratocytes. The regularity and organization of the collagen fibril orientation are responsible for corneal clarity. The cornea becomes cloudy when edema or new collagen synthesis alters the spacing of these fibrils. The endothelium is a monolayer of hexagonal cells rich in cytoplasmic organelles, especially mitochondria. These cells actively pump fluid across an osmotic gradient from the corneal stroma to the aqueous cavity and thus are responsible primarily for maintenance of corneal clarity. These cells do not replicate and therefore steadily decrease in number with advancing age or disease.

Cellular mediators of infection must migrate in from adjacent limbal vessels unless the cornea has been vascularized by an earlier process. Corneal physiology is best summarized by the renowned corneal specialist Dr. Herbert E. Kaufman: “The cornea breathes air and eats aqueous.”

[edit] DIAGNOSTIC APPROACH

As with all ocular disease, a thorough history and eye examination are the keys to accurate diagnosis of corneal disease (see Chapter 172 ). The physician should document the presence of protective eyewear, contact lens type and wearing schedule, photophobia, decreased vision, or type of foreign body. Unilaterality, bilaterality, and time course may be important. Lids matted shut in the morning suggests conjunctivitis. Autoimmune disease can cause lacrimal insufficiency. Severe pain on opening the eyes in the morning is diagnostic of recurrent erosion.

Visual acuity with optical correction must be measured, noting any improvement from looking through a pinhole. A pinhole compensates for uncorrected refractive errors and can limit visual degradation due to diffraction from corneal (or lens) opacities or irregularities. Improved acuity through a pinhole therefore suggests the cornea or lens as the etiology for visual disturbance. Intraocular, inflammatory, hemorrhagic, retinal, optic nerve, or cortical causes of decreased acuity are not correctable with a pinhole.

Conjunctival injection helps to define the process as either inflammatory or noninflammatory. The lids should be evaluated for signs of inflammation and the lash bases examined for dried scales, which may indicate staphylococcal infection. Fingertip pressure at the lid margin should elicit clear, oily, meibomian gland secretions, not white strands that resemble toothpaste.

Although gross corneal foreign bodies or opacities may be visible with a penlight, a slit lamp is essential for any detailed examination of the cornea. The optical cross section combined with high magnification allows comprehensive assessment of the multiple layers of the cornea. Contour irregularities, stromal thinning, and epithelial hypertrophy are readily detected. Fluorescein dye highlights areas where the epithelium is disrupted or missing. Useful information can be difficult to obtain, however, if too much dye is applied. Decreased corneal sensation can be measured using a wisp of cotton if herpes simplex virus is suspected. Corneal disorders can be categorized first based on whether they generally cause a red eye (Fig. 175-1).

Figure 175-1 Approach to the patient with corneal disorders. Y, Yes; N, no.

[edit] THE RED EYE

[edit] Anterior Blepharitis

Bacteria (overwhelmingly Staphylococcus) colonize the lash bases, form a crusty scale where lash meets skin, secrete toxins into the tear film, and can cause a red eye and possible corneal infiltrates. Blepharitis is usually bilateral, with the chief complaint of itching of lid margins, which may be injected. Lash whitening (poliosis) or loss (madarosis) can occur. Foam often forms on the lid margins as the toxins saponify the tear lipids, and conjunctival injection is common. When a sebaceous gland at the base of a lash becomes acutely infected and forms a painful localized purulent abscess, it is known as a hordeolum or stye.

Initial treatment is simple hygiene twice daily. A 5-minute hot washcloth soak softens the scales. The area is then cleansed by scrubbing the lash bases with a cotton ball soaked in a 50:50 mixture of baby shampoo and water, followed by rinsing and patting dry. For initial treatment, local or systemic antibiotics usually are not warranted, although severe styes may require incision and drainage. If significant debris persists for 2 months, erythromycin ointment is applied to the lash bases at the end of treatment. This chronic problem usually requires chronic treatment.

[edit] Allergic Blepharitis

The predominant symptom of ocular allergy is itching, often accompanied by lid edema, mucoid discharge, conjunctival hyperemia, burning, lacrimation, and conjunctival edema (chemosis). Eosinophils are seen on Giemsa staining of conjunctival scrapings, except in mild cases. Brief episodes of these symptoms with nasal involvement are often seen in hay fever conjunctivitis after exposure to airborne allergens. Acute treatment consists of cool compresses, topical vasoconstrictor-antihistamine combinations, or topical nonsteroidal antiinflammatory drugs (NSAIDs). Prophylactic treatment may include topical mast-cell stabilizing agents such as cromolyn sodium or lodoxamide tromethamine. Topical steroids may be indicated in severe cases.

Vernal conjunctivitis causes severe itching, photophobia, and a heavy, ropy mucous discharge. Symptoms begin in the first two decades of life, are bilateral, and typically recur in the spring months in nontropical climates. About 90% of patients have a history of atopy. Giant cobblestone papillae are characteristically found on the superior tarsal conjunctiva and cause corneal complications in severe cases. Environmental control of allergens is the best initial treatment, followed by therapy for hay fever conjunctivitis. Treatment seldom eradicates symptoms altogether, and the physician must be cautious to avoid steroid-induced ocular complications in this generally self-limited disease.

The incidence of ocular involvement in atopic dermatitis is approximately 25%. Atopic keratoconjunctivitis causes a moist, erythematous skin eruption that becomes vesicular and then crusts. The lid skin ultimately becomes scaly and excessively wrinkled. Although sometimes difficult to differentiate from vernal conjunctivitis, atopic symptoms are perennial, the tarsal conjunctival papillae are smaller, and corneal involvement tends to be more severe. Treatment is similar to that of vernal conjunctivitis, with the same caution to avoid chronic steroid use.

The delicate and distensible lid tissues are particularly susceptible to irritants, including environmental allergens, cosmetics, topical medications, and some chemicals. Eczematoid inflammation of the lids is characteristic of contact dermatitis. Topical steroid ointment is used to treat the acute inflammation, while elimination of the offending agent is the definitive treatment.

[edit] Posterior Blepharitis

Meibomian glands are responsible for secreting the oily layer of the tear film. When they become inspissated and plugged, an acute chalazion may develop if the lipid is extruded into the surrounding tissues. In most cases the secretions are merely thick and of poor quality, causing tear film instability and ocular irritation symptoms.

Initial treatment is simple hygiene twice daily. A 10-minute hot soak is needed to heat the meibomian glands sufficiently to thin the secretions. Vigorous fingertip compression of the eyelid against the globe then forces the fluids to flow and avoid stagnation. If symptoms are not relieved after 2 months of this hygiene regimen, oral tetracycline is added for its effect on lipid metabolism, not for its antibiotic effect; 250 mg is given four times daily for a month, then once daily. The thinner secretions then cause fewer symptoms.

[edit] Conjunctivitis

Conjunctival injection is a nonspecific indicator of inflammation. Follicles are small white bumps in the conjunctiva that represent collections of lymphocytes that have displaced adjacent blood vessels. They suggest a viral or chlamydial cause of conjunctivitis. Papillae are velvety red conjunctival bumps with a central vessel that are nonspecific indicators of conjunctival inflammation. Papillary conjunctivitis is more likely bacterial in origin. Examination also should note the presence of preauricular adenopathy. Because the lower conjunctiva drains there, the presence of tender preauricular nodes suggests adenoviral conjunctivitis.

Conjunctivitis is approximately 50% bacterial and 50% adenoviral in children. The bacterial cases tend to have a more mucopurulent discharge, less adenopathy, and no other viral symptoms. The three most common agents are Staphylococcus aureus, Streptococcus pneumoniae, and Haemophilus influenzae, with the latter most often affecting young children. Because adenoviral conjunctivitis is self-limiting and topical antibiotics are safe, virtually all cases of pediatric conjunctivitis are treated as bacterial. Either sulfacetamide 10% or trimethoprim–polymyxin B (better H. influenzae coverage) is given four times a day for a week to 10 days. Patients may worsen for 1 or 2 days before they improve. The infection may spread to the other eye. Family members should use separate washcloths to avoid transmission, and frequent handwashing is advised. Infected children should not attend school, and adults who deal with the public should not attend work. Hot or cool compresses may provide symptomatic relief. Conjunctivitis in adults is approximately 85% adenoviral and 15% bacterial, so routine antibiotic treatment of all patients is unnecessary. Antibiotics are used for patients with a more purulent discharge, no nodes, and no follicles, since the latter two suggest a viral etiology. Any conjunctivitis that does not improve in 7 to 10 days merits ophthalmologic evaluation.

[edit] Episcleritis

Ocular redness without irritation is characteristic of episcleritis. Transient and self-limited, it affects adults and lasts approximately 1 to 3 weeks, with spontaneous resolution. Episcleritis is generally not related to systemic immunologic disease. The redness is often in the interpalpebral zone, with inflammation of the straight episcleral vessels perpendicular to the limbus. Unlike the vascular injection of scleritis, these vessels are salmon pink in sunlight, can be moved over the underlying sclera with a cotton-tipped applicator, and blanch with topical phenylephrine 10% solution.

Simple episcleritis usually requires no treatment, although the nodular form is more severe, lasts longer, and requires topical steroids. The redness of simple episcleritis may be treated with topical vasoconstrictors. When present, pain may be relieved with topical NSAIDs or mild topical steroids.

[edit] Scleritis

Scleritis is much more serious than episcleritis and is usually associated with a systemic immunologic disease (see Chapter 172 ). Patients complain of severe, deep pain, and the eye is often tender to palpation. Examination in sunlight reveals a blue or violet hue to the affected sclera. The vessels are not straight and radial, cannot be moved with a cotton-tipped applicator, and do not blanch with topical phenylephrine 10% solution. The patient may have significant visual morbidity.

Scleritis is divided anatomically into anterior and posterior forms. Anterior scleritis is further divided into three clinical subtypes: diffuse, nodular, and necrotizing. Diffuse anterior scleritis is the most benign form of the disease. The vascular injection is nonfocal without nodularity or avascularity. It is associated with connective tissue disease in approximately 30% of cases. Heavy topical steroids are often sufficient to control the inflammation. As in all scleritis, subconjunctival steroid injection is contraindicated because of the propensity for the sclera to melt at the injection site. Nodular anterior scleritis consists of single or multiple, deep-red or purple nodules of immobile scleral tissue with overlaying edematous episclera. Half the patients have an autoimmune disorder. Necrotizing anterior scleritis can result in vision and life-threatening complications. The lesion is usually inflammatory with a pale center, but scleral necrosis without inflammation (scleromalacia perforans) can also occur, usually in patients with longstanding rheumatoid arthritis. In most cases, symptoms of severe, boring pain are out of proportion to inflammatory signs. The sclera thins, and the dark underlying uveal tissue becomes visible as the disease progresses. About 60% of necrotizing scleritis patients develop bilateral disease, and approximately 30% die within 5 years of diagnosis, usually from complications of vasculitis.

Only 10% of patients with posterior scleritis have had an associated systemic disease. The diagnosis can be easily missed in the absence of anterior inflammation, especially if the pain is referred elsewhere in the head. Pain, proptosis, and visual loss are common complaints. Visual consequences may ensue from exudative retinal detachment and optic disc edema.

Topical steroids are seldom sufficient to control more severe scleritis. Systemic NSAIDs often can control the inflammation in diffuse or nodular scleritis. Control of the pain is a useful guide to therapy. Oral corticosteroids are used in severe or necrotizing cases, with the addition of systemic cytotoxic immunosuppressive therapy as needed (e.g., cyclophosphamide, azathioprine, methotrexate). Patients with systemic autoimmune disease often receive prednisone for its rapid effect while waiting a week or more for immunosuppressant therapy to become effective.

[edit] Chemical Injury

Chemical injury is one of only two true ophthalmic emergencies, the other being central retinal artery occlusion. Minutes or even seconds of delay in treatment can result in irreparable tissue damage and loss of vision. Chemical injury is the only condition when treatment may be initiated before assessing visual acuity.

The first priority is immediate and copious irrigation with any noncaustic liquid. Although sterile irrigating solution or saline is preferable once the patient arrives at the office, tap water is usually most practical at the time of injury. Fifteen minutes of continuous irrigation at home or a liter of fluid irrigation in a medical setting is recommended, with the emphasis on rapid dilution of the offending agent. Topical anesthetic drops and a lid speculum make irrigation more comfortable and effective. Tears should be tested with pH paper a few minutes later. If not within the 7.2 to 7.8 range, another liter of irrigation should be administered after inspection of the everted lids to detect retained particulate matter.

A good history with an exact description of the agent should be obtained after irrigation. The container that identifies the chemical is helpful. Documentation of protective eyewear is important, particularly for work-related accidents. Alkali burns are generally worse than acid, although either can be blinding. Acid is precipitated and inactivated by the tissue proteins it destroys, whereas alkali saponifies collagen and damages underlying tissue. Hydrocarbons can be quite irritating but usually cause much less tissue damage. The epithelium should be assessed with fluorescein stain, realizing that “all off” is easily confused with “all on” when no clear demarcation line is present. Prophylactic topical antibiotics are used three or four times a day, and some physicians omit a patch for the first 24 hours to permit additional clearing of any retained chemical.

Steroid-antibiotic combinations are often used to help decrease inflammation. “Clean” chemical injuries and bilateral ocular allergies are two of the very few indications for topical ocular steroid use by the nonophthalmologist. Aminoglycoside antibiotics impair epithelial healing and should be avoided. Oral analgesia and sedatives enhance patient comfort, whereas topical nonsteroidals such as ketorolac provide effective pain control in an unpatched eye when used four times a day for up to 4 days. When present, epithelial defects must be healed, and daily examinations to rule out infection and monitor progress are mandatory. Healing is slower than with a comparable abrasion for the first 1 or 2 days because the remaining epithelium has also been chemically damaged. The physician should apply ointment and patch an epithelial defect daily. Having the patient remove and reapply the patch at home is not effective, so patients should not apply topical medications when patching. Steroid-antibiotic drops to reduce inflammation are continued for approximately a week after epithelialization is complete.

Severe chemical burns, large epithelial defects, any suspicion of infection or tissue thinning, slow healing, and the development of conjunctival adhesions are indications for immediate referral to an ophthalmologist. Ultimate prognosis is related to the degree of limbal ischemia as well as symblepharon (conjunctival adhesion) formation.

[edit] Foreign Body

After a thorough history, including use of protective eyewear, visual acuity is assessed in the patient with a foreign body before other examination or placement of eyedrops. Proparacaine drops are then used to facilitate further examination. Both upper lids should always be everted to look for additional foreign bodies, and their absence should be documented to prevent patching over a retained foreign body. Multiple vertical, linear, superficial abrasions indicate a foreign body trapped under the upper lid. Eversion is simple and painless when performed properly with consideration of the tarsal plate, which makes the inferior 10 mm of the upper lid rigid and unfoldable. The patient is asked to look down, and the upper lashes are grasped with the fingers. A cotton-tipped applicator (or any small, blunt instrument) is then placed 10 to 12 mm superior to the lash margin, and the lid is everted using the applicator as a fulcrum. When the examination is completed, the lid will right itself if the patient is asked to look up and blink.

Although using a slit lamp is preferable, a hand light may be used to look for a corneal foreign body. If not readily visible, a small particle can sometimes be detected by observing its shadow cast on the iris. Vigorous irrigation or a moistened cotton-tipped applicator are the only methods that should be used to remove a superficial foreign body without the assistance of a slit lamp. Many ophthalmologists routinely dilate such patients with a mid-acting mydriatic such as homatropine 5% or scopolamine 0.25% to prevent pain from iritis. The presence of “consensual photophobia” (pain in the injured eye when a light is shone only in the opposite eye) is a good indication for dilation.

With daily follow-up and patching, healing should be steady and rapid over 1 or 2 days. No steroids are used. Inability to remove the particle, the presence of a rust ring or infiltrate, worsening vision, and failure to heal are indications for immediate ophthalmologic evaluation.

[edit] Corneal Abrasion

The examination of a corneal abrasion begins with a thorough history, including protective eyewear. Visual acuity measurement is followed by proparacaine drops to ease the examination. The lid is everted to detect a foreign body. A small quantity of fluorescein outlines the defect, and charting a diagram with a size estimate simplifies follow-up. The general principles of monitoring and facilitating epithelial healing are identical to those used for chemical injuries, with daily patching and follow-up with or without cycloplegia. Antibiotic ointment without steroid use is appropriate for these presumably contaminated wounds. The presence of an infiltrate, worsening vision, and failure to heal are indications for immediate ophthalmologic referral. Nonhealing epithelial defects are one of the most frustrating ophthalmologic maladies. Treatment options restricted to ophthalmologists and corneal subspecialists include bandage soft contact lenses, placement of collagen shields, mechanical or excimer laser debridement, anterior stromal micropuncture, tarsorrhaphy, and placement of a conjunctival flap.

[edit] Recurrent Corneal Erosion

A good history is the key to diagnosis and treatment of recurrent corneal erosions. Patients present with symptoms (and often signs) of a corneal abrasion but without acute trauma. Patients almost always report being asymptomatic when going to bed and awakening with severe pain as the eye is first opened. Symptoms subside gradually over several hours, but recur another morning several days or weeks later. The pathophysiology is based on a defect of epithelial adhesion. Patients often have a history of prior traumatic abrasion, classically a paper cut or fingernail injury. The injury causes defects in Bowman's layer. During the 6 to 8 weeks required for re-formation of hemidesmosomal complexes, the epithelium is often separated from the underlying Bowman's layer by a thin fluid layer. This separation occurs at night, when evaporative loss is diminished by closed lids. The epithelium then sticks to the inside of the upper lid and is torn off when the eyes open in the morning. Treatment therefore must focus on eliminating the fluid layer, so that hemidesmosomes may form, and preventing adhesion between the epithelium and lid.

Clinically, this corneal erosion often appears identical to a corneal abrasion on hand light examination. The edges often are more loose and ragged. Initial treatment is for an abrasion, with patching, pain control, and optional cycloplegia. Once epithelialized, hyperosmotics become the mainstay of treatment. Five percent sodium chloride ointment is used at bedtime for a full 8 weeks after the most recent erosive episode. This agent both dehydrates the subepithelial space and lubricates the epithelial surface. Simple lubricating ointment often works but is less effective because it does not have a dehydrating effect. Concomitant use of 5% NaCl drops four times a day for 2 weeks after an acute episode is also helpful. Patients must know why ointment is necessary for 8 weeks so they will not stop treatment and precipitate another erosion.

Patients with recurrent erosion but without a prior history of trauma usually have Cogan's anterior basement membrane dystrophy, an abnormality of Bowman's layer that includes reduplication of the layer and the presence of epithelial inclusion cysts. Fortunately, their initial treatment is identical to that of those with traumatic erosion because the dystrophy cannot be detected without a slit lamp.

Referral indications include recurrence during hyperosmotic treatment, as well as those for corneal abrasion. Ophthalmologic treatment options are those used for corneal abrasions.

[edit] Corneal Ulcer

Corneal ulcer is a keratitis accompanied by an overlying epithelial defect. Most are bacterial, with Staphylococcus, Streptococcus, and Pseudomonas the most common agents. This medical urgency requires ophthalmologic evaluation and initiation of treatment within hours of diagnosis to prevent permanent visual loss. Because the cornea has no blood supply and is less than 1 mm thick, certain virulent collagenolytic organisms can penetrate the full thickness and perforate in less than 24 hours. The primary care physician's role is early diagnosis, differentiation from nonurgencies, and immediate referral once the diagnosis is suspected.

A good history includes questions about trauma and contact lens wear. Patients who sleep wearing lenses have an eightfold increased risk of ulceration compared with those who do not sleep wearing lenses; the latter are at increased risk over nonlens wearers. Patients complain of pain, tearing, and photophobia similar to abrasion patients. A bacterial ulcer causes a red eye and a localized corneal opacity containing bacteria, inflammatory cells, and edema. Other, noninfectious causes of a corneal opacity in a red eye cannot be differentiated without a slit lamp, experience, and often diagnostic testing. Any such lesion is a bacterial ulcer until proved otherwise. Patients should be instructed to bring their contact lenses and the case (for culture) on referral. Antibiotic treatment should not be started without prior approval of the consultant. The antibiotics used by nonophthalmologists are seldom adequate for treatment and usually only prevent obtaining good cultures. If consultation must be delayed, treatment should consist of ciprofloxacin 0.3% every half hour around the clock until the patient can be evaluated.

Ophthalmologic treatment of corneal ulceration consists of thorough culturing directly onto culture plates, followed by frequent doses of specially formulated topical cephalosporin and aminoglycoside antibiotics. Recent reports of effective monotherapy with commercially available fluoroquinolones are the rationale for the ciprofloxacin recommendation, and many ophthalmologists still treat small ulcers with such monotherapy. Emerging concern about the effectiveness of these agents against Streptococcus species (common causes of ulceration) have prompted most ophthalmologists to retain the cephalosporin-aminoglycoside combination in severe cases.

[edit] Herpes Simplex Virus

The possibility of herpetic keratitis is the reason no practitioner should treat a red eye with steroids without first performing a slit-lamp examination. Such unwitting treatment can hasten the demise of an eye with an already severe and recurrent problem. The medicolegal consequences can be severe as well.

More than 95% of cases of clinical herpetic disease are recurrences that develop long after the primary infection. Although primary infection usually occurs by 5 years of age, most adults do not have a history of clinical herpetic disease. The cervical and trigeminal ganglia become host to the latent herpes simplex virus (HSV), which is reactivated intermittently and travels via the neuronal network to the end organ. Corneal nerves are thought to shed reactivated HSV into the tears, which may cause corneal disease. Herpetic blepharitis is most likely to occur with a primary infection, exhibiting classic vesicles on the eyelids and surrounding skin. Although most patients will not develop ocular disease, many ophthalmologists recommend prophylactic treatment with an ocular antiviral agent. Recurrent follicular conjunctivitis can be caused by HSV, even without corneal disease, and should be considered before initiating steroid treatment of a chronic conjunctivitis of undetermined etiology.

Herpetic epithelial and stromal keratitis (HSV keratitis) are potentially blinding disorders that require care by an ophthalmologist. Dendritic staining patterns with fluorescein or rose bengal and decreased corneal sensation are classic signs of HSV keratitis but are not always present. As with syphilis, HSV is “the great mimic” in the eye and must be included in many differential diagnoses. Epithelial, endothelial, and stromal forms of herpetic keratitis are described. Treatment with assorted combinations of topical and systemic antivirals and corticosteroids is complicated and often chronic.

[edit] Varicella-Zoster Virus

Ocular involvement during primary varicella infection occurs infrequently. Lid lesions begin as papules, become vesicular and pustular, and then crust. Conjunctivitis is the most common ocular involvement. Recurrent varicella-zoster virus (VZV) infection in the trigeminal distribution is more likely to cause corneal disease. The ophthalmic division is most often involved (herpes zoster ophthalmicus). Because the nasociliary branch of the trigeminal nerve innervates both the tip of the nose and the cornea, the presence of herpetic vesicles on the nose tip (Hutchinson's sign) often suggests corneal disease. Lid edema impairs proper closure (lagophthalmos) and leads to the most common cause of permanent ocular damage from zoster. Liberal use of lubricating ointments can prevent this complication. Epithelial dendrites are the next most common type of VZV ocular involvement. These eyes lose sensation much more often than those with HSV and frequently have chronic surface problems that are challenging to manage.

Antivirals are of little use in treating active VZV corneal infections, although oral acyclovir decreases the incidence and severity of dendritiform keratopathy, stromal keratitis, and uveitis when taken within 72 hours of onset of the skin lesions. Acyclovir therefore should be given to any patient with herpes zoster ophthalmicus as early as possible.

[edit] Acute Glaucoma

Acute glaucoma can overwhelm the endothelial ability to maintain corneal stromal deturgescence in the presence of an elevated intraocular pressure (IOP). A hot, red eye and cloudy cornea (with or without epithelial defects) may ensue. Palpation of the globe through the closed lid will reveal a unilateral increase in IOP, which establishes the underlying diagnosis of acute glaucoma. Treatment focuses on the glaucoma (see Chapter 173 ). The corneal problems usually resolve spontaneously, with restoration of normal IOP.

[edit] Acute Hydrops in Keratoconus

Keratoconus is a degenerative corneal ectasia characterized by noninflammatory stromal thinning that is most pronounced at the apex of the cone. Patients have progressive myopia and increasing astigmatism that becomes irregular and uncorrectable with glasses. Hard or gas-permeable contact lenses are required to correct vision adequately, and corneal transplantation is required when lenses can no longer be worn or when central scarring prevents useful vision.

Acute corneal hydrops can cause a red painful eye, with corneal clouding in a patient with keratoconus. Tears in Descemet's membrane can violate the endothelial barrier and lead to acute stromal edema (hydrops) in the region of the cone. The clinical scenario is a patient wearing contact lenses who has a unilateral red, painful, photophobic eye with decreased acuity and a corneal opacity. This presentation is similar to that of an infectious corneal ulcer. Because keratoconus patients are at increased risk of ulceration from epithelial instability at the cone apex, they presumably have an infectious ulcer and should be referred immediately to an ophthalmologist. Once ulceration has been ruled out, watchful waiting will allow the edema to resolve in about 4 months.

[edit] THE WHITE EYE

[edit] Keratitis Sicca

Keratoconjunctivitis sicca (dry eye) is seen frequently in patients with connective tissue disease. Keratoconjunctivitis sicca plus xerostomia is classified as a primary Sjögren's syndrome; the addition of a connective tissue disease is secondary Sjögren's syndrome. A wide variety of drugs (e.g., antihistamines, nasal decongestants, analgesics, sedatives, tricyclic antidepressants) decrease lacrimation. Patients complain mainly of chronic “dryness” and foreign body sensation. A dry cornea can cause blurring of vision. Many patients report increased mucus in the cul-de-sacs. Examination reveals decreased tear strips along the lower lid margins, as well as punctate staining of the ocular surface with fluorescein. Tear film deficiency can cause severe problems (e.g., ulceration, perforation) for an ocular surface designed to function as a wet system. Artificial tear substitutes (drops by day and ointments at night) are the mainstay of treatment. Referral to an ophthalmologist is indicated if symptoms persist with artificial tears used four times daily. Plugging of the lower lacrimal punctae (tear drains) with silicone plugs or hot cautery can provide dramatic relief. Heavier ointments or partial lid closure (tarsorrhaphy) can be used in severe cases.

[edit] Corneal Dystrophies

As corneal anatomy suggests, a variety of dystrophies affect the epithelium, basement membrane, Bowman's layer, stroma, Descemet's membrane, and endothelium. These inherited, bilateral abnormalities of the cornea are not associated with systemic disease or prior inflammation. Most dystrophies present in the first few decades of life and demonstrate autosomal dominant inheritance. Basement membrane and Bowman's layer dystrophies manifest through the faulty epithelial adhesion of recurrent erosion. Stromal dystrophies generally cause blurriness and glare trouble, although some anterior stromal dystrophies cause epithelial adhesion problems. Endothelial dystrophies lead to corneal decompensation through failure of the pump function. The history may reveal a family member with similar complaints. Penlight examination may reveal (at most) a vague loss of corneal luster or clarity. The diagnosis requires an experienced observer using a slit lamp, so any patient suspected of having a dystrophy should be referred for complete ophthalmologic evaluation.

[edit] Corneal Degenerations

Several corneal stromal degenerations lead to corneal thinning (e.g., keratoconus, keratoglobus, pellucid marginal degeneration). The resulting ectasia causes a visual disturbance from irregular astigmatism. Degenerations tend to have a later onset, more rapid progression, and unilateral occurrence, distinguishing them from the dystrophies. Because physical findings are unremarkable on penlight examination, all patients must be referred to an ophthalmologist for slit-lamp evaluation. In some early cases, changes are not visible on slit-lamp examination. New computerized topographic mapping systems can diagnose many more subtle disorders of corneal contour in these patients.

[edit] Pterygium

Pterygium is a triangular wedge of fibrovascular tissue that begins on the epibulbar conjunctiva and grows slowly onto the cornea. Its unsightly appearance and occasional inflammation often bring it to a physician's attention. Prevalence of pterygium is directly related to the proximity to the equator; the incidence is negligible beyond the 40th parallel. Ultraviolet exposure seems to be the primary factor; with such exposure, only surgery can arrest growth. The variety of available surgical techniques and reported recurrence rates, ranging from 3% to 40%, illustrate the propensity for pterygium to recur. Because growth often stops spontaneously and surgery may stimulate a fast-paced regrowth, excision is delayed until necessary. Clear indications for excision are lesions that encroach on the visual axis, induce significant irregular astigmatism causing loss of acuity, and restriction of eye movement enough to cause double vision. A “soft” but valid indication is cosmesis. Any lesion causing concern to the patient should be referred to an ophthalmologist for a detailed discussion of prognosis and treatment options.

[edit] ADDITIONAL READINGS

• FS Brightbill: Corneal surgery: theory, technique, and tissue ed 2. St Louis: Mosby; 1993:
• TA Casey, KW Sharif: A colour atlas of corneal dystrophies & degenerations Aylesbury, England: Wolfe; 1991:
• M Grayson: Diseases of the cornea St Louis: Mosby; 1979:
• HE Kaufman, BA Barron, MB McDonald, SR Waltman: The cornea New York: Churchill Livingstone; 1988:
• FH Roy: Ocular differential diagnosis ed 5. Philadelphia: Lea & Febiger; 1993:
• W Tasman, EA Jaeger: Clinical ophthalmology, vol 4, rev ed Philadelphia: Lippincott; 1993: