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Chapter 6: Cornea
MISCELLANEOUS CORNEAL DISORDERS
THYGESON'S SUPERFICIAL PUNCTATE KERATITIS
Superficial punctate keratitis is an uncommon chronic and recurrent bilateral disorder more common in females. It is characterized by discrete and elevated oval epithelial opacities that show punctate staining with fluorescein, mainly in the pupillary area. The opacities are not visible grossly but can be easily seen with the slit lamp or loupe. Subepithelial opacities underlying the epithelial lesions (ghosts) are often observed as the epithelial disease resolves.
No causative organism has been identified, but a virus is suspected. A varicella-zoster virus has been isolated from the corneal scrapings of one case.
Mild irritation, slight blurring of vision, and photophobia are the only symptoms. The conjunctiva is not involved.
Epithelial keratitis secondary to staphylococcal blepharoconjunctivitis is differentiated from superficial punctate keratitis by its involvement of the lower third of the cornea and lack of subepithelial opacities. Epithelial keratitis in trachoma is ruled out by its location in the upper third of the cornea and the presence of pannus. Many other forms of keratitis involving the superficial cornea are unilateral or are eliminated by their histories.
Short-term instillation of corticosteroid drops will often cause disappearance of the opacities and subjective improvement, but recurrences are the rule. The ultimate prognosis is good since there is no scarring or vascularization of the cornea. Untreated, the disease runs a protracted course of 1-3 years. Long-term treatment with topical corticosteroids may prolong the course of the disease for many years and lead to steroid-induced cataract and glaucoma. Therapeutic soft contact lenses have been used to control symptoms in especially bothersome cases. Cyclosporine topical drops, 1% or 2%, have been effective as a substitute for steroids.
RECURRENT CORNEAL EROSION
This is a fairly common and serious mechanical corneal disorder that presents some classic signs and symptoms but may be easily missed if the physician does not look for it specifically. The patient is usually awakened during the early morning hours by a pain in the affected eye. The pain is continuous, and the eye becomes red, irritated, and photophobic. When the patient attempts to open the eyes in the morning, the lid pulls off the loose epithelium, resulting in pain and redness.
Three types of recurrent corneal erosions can be recognized:
Acquired recurrent erosion (traumatic): The patient usually gives a history of previous corneal injury. It is unilateral, occurs with equal frequency in males and females, and the family history is negative. The recurrent erosion occurs most frequently in the center below the pupil no matter where the site of the previous corneal injury was.
Recurrent erosion associated with corneal disease: After corneal ulceration heals, the epithelium may break down in a recurrent fashion (as in HSV "metaherpetic" ulcer).
Recurrent erosion associated with corneal dystrophies: Recurrent erosions of the cornea may be observed in patients with Cogan's microcystic corneal dystrophy, lattice dystrophy, fingerprint dystrophy, and Reis-Bücklers corneal dystrophy.
Recurrent corneal erosion is due to a defect in the basement membrane of the corneal epithelium. The hemidesmosomes of the basal layer of the corneal epithelium fail to adhere to the basement membrane, and the corneal epithelium remains loose over the basement membrane with very slight subepithelial edema. The loose epithelial layers are vulnerable to separation and erosion.
Instillation of a local anesthetic relieves the symptoms immediately, and fluorescein staining will show the eroded area. This is typically a small area in the lower central cornea.
Treatment consists of a pressure bandage on the eye to promote healing. Mechanical denuding of the loose corneal epithelium may be necessary. The other eye should be kept closed most of the time to minimize movement of the lid over the affected eye. Bed rest is desirable for 24 hours. The cornea usually heals in 2-3 days. To prevent recurrence and to promote continued healing, it is important for these patients to use a bland ointment (eg, boric acid or other ocular lubricant) at bedtime for several months. In more severe cases, artificial tears are instilled during the day. The use of hypertonic ointment (glucose 40%) or 5% saline drops (Adsorbonac 5%) is often of value. Therapeutic soft contact lenses and needle micropuncture of Bowman's layer as well as excimer laser shallow keratectomy have been useful in cases that do not respond to more conservative management.
INTERSTITIAL KERATITIS DUE TO CONGENITAL SYPHILIS
This self-limited inflammatory disease of the cornea is a late manifestation of congenital syphilis. There has been a sharp decrease in the incidence of the disease in recent years-almost to the point of extinction in some parts of the USA. It occasionally starts unilaterally but almost always becomes bilateral weeks to months later. It affects all races and is more common in females than males. Symptoms appear between the ages of 5 and 20. Pathologic findings include edema, lymphocytic infiltration, and vascularization of the corneal stroma.
Interstitial keratitis may be immune in nature since Treponema pallidum is not found in the cornea during the acute phase. It has been postulated that these organisms enter the cornea at birth and that later in life there is a violent hypersensitivity to intracorneal viral antigen.
Clinical Findings
A. Symptoms and Signs:
Other signs of congenital syphilis may be present, such as saddle nose and Hutchinson's triad (interstitial keratitis, deafness, and notched upper central incisors). The patient complains of pain, photophobia, and blurring of vision. Physical signs include conjunctival injection, corneal edema, vascularization of the deeper corneal layers, and miosis. There is an associated severe anterior granulomatous uveitis and blepharospasm due to photophobia. The grayish-pink appearance of the cornea (due to edema and vascularization) that occurs in the acute phase is sometimes referred to as a "salmon patch."
B. Laboratory Findings:
Serologic tests for syphilis are positive.
Complications & Sequelae
Corneal scarring and vascularization occur if the process has been particularly severe and prolonged. Secondary glaucoma may result from the uveitis.
Treatment
There are no specific measures. Treatment is aimed at preventing the development of posterior synechiae, which will occur if the pupil is not dilated.
Both eyes should be dilated with frequent instillation of 2% atropine solution. Corticosteroid drops often relieve the symptoms dramatically but must be continued for long periods to prevent recurrence of symptoms. Dark glasses and a darkened room may be necessary if photophobia is severe. Treatment should be given for systemic syphilis, even though this usually has little effect on the ocular condition.
Corneal scarring may necessitate corneal transplant, and glaucoma, if present, may be difficult to control.
Course & Prognosis
The corneal disease process itself is not affected by treatment, which is aimed at prevention of complications. The inflammatory phase lasts 3 or 4 weeks. The corneas then gradually clear, leaving ghost vessels and scars in the corneal stroma.
INTERSTITIAL KERATITIS DUE TO OTHER CAUSES
Although congenital syphilis is no longer a common cause of interstitial keratitis, the disease still occurs as a complication of other granulomatous diseases, eg, tuberculosis and leprosy. Certain viruses (eg, cytomegalovirus, measles virus, mumps virus) as well as the spirochete of Lyme disease have been described as causing a type of interstitial keratitis. Treatment is usually symptomatic, but it is important to establish the cause.
Cogan's syndrome is a rare disorder generally believed to be a vascular hypersensitivity reaction of unknown origin. It is a disease of young adults and is characterized by nonsyphilitic interstitial keratitis and a vestibuloauditory difficulty. Corticosteroids are reputed to be of value, but some degree of visual impairment and complete nerve deafness usually supervene.
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10.1036/1535-8860.ch6