Ординатура / Офтальмология / Английские материалы / Clinical Ocular Pharmacology 5th edition_Bartlett, Jaanus_2008

480 CHAPTER 25 Diseases of the Conjunctiva

conjunctival abrasions include superficial epithelial cell loss, chemosis, and subconjunctival hemorrhage. Most conjunctival contusions result in subconjunctival hemorrhages. Lacerations are usually associated with hemorrhaging and frequently result in loose conjunctival tissue flaps if they are full-thickness tears.The white sclera may be visible, flanked by clumping of conjunctival tissue, chemosis, and subconjunctival hemorrhages. The sclera must be carefully evaluated to rule out perforation of the globe.A Seidel test should be performed.

Management

Conjunctival abrasions and lacerations should be irrigated with sterile normal saline or extraocular irrigating solution to remove any foreign material. Abrasions may be treated with topical trimethoprim-polymyxin B (Polytrim) or aminoglycoside solution applied four times daily for several days or until the abrasion is healed. In pediatric cases, bacitracin-polymyxin B ointment may be substituted, if necessary, to improve patient comfort. Many conjunctival abrasions do not require patching. Conjunctival lacerations may be managed with bacitracin-polymyxin B or aminoglycoside ointment applied four times daily for 5 to 7 days or until the wound is sufficiently healed. Conjunctival lacerations frequently require semipressure patching with cycloplegia and topical antibiotic ointment to achieve adequate resolution. Sutures are not needed for small uncomplicated conjunctival lacerations.

Once healing has begun, frequent use of nonpreserved artificial tears or lubricating gels often improves patient comfort. No specific therapy is required for conjunctival contusions, because most involve only subconjunctival hemorrhages that are self-limiting. Warm compresses used for 15 to 20 minutes several times daily may hasten resorption of blood.

FACTITIOUS CONJUNCTIVITIS (OCULAR MUNCHAUSEN SYNDROME)

Although not often reported in the literature, self-abuse— either accidental or intentional—is an important differential diagnosis in otherwise inexplicable cases of conjunctivitis.

Etiology

A variety of underlying factors can lead to self-abuse. Munchausen syndrome describes the situation wherein patients actively but surreptitiously harm themselves. These patients sometimes go to great extremes to hide this behavior and may shift methods when detection is eminent. Although the specific reasons vary for each patient, such behavior is often an attention-seeking device.

Diagnosis

Factitious conjunctivitis should be considered whenever an examiner is confronted with a clinical picture that

seemingly makes little sense. Young female patients and those who have such motivations as seeking workers’ compensation or sick leave should be examined with suspicion. Because of purposeful deception, a specific diagnosis often remains elusive, and prior consultations with physicians are not uncommon. A confusing clinical picture is the first sign. Inserting foreign objects is a common method, with chalk being among the objects used most frequently. Chalk is readily available to young students and can be broken into pieces small enough to be placed in the eye furtively.The mild alkali causes irritation and eventually dissolves, rendering detection difficult. Solutions and medications are also common tools for these patients.Topical anesthetic, secretly removed from a prior doctor’s office, is another frequent source of factitious conjunctivitis, producing confusing corneal and conjunctival findings. Chronic, long-standing, unilateral membranous conjunctivitis may be a sign of factitious causes. Instruments may also be used to create focal conjunctival damage. Because damage to the cornea produces so much pain, the conjunctiva is the area most likely to be involved.

Mucus fishing syndrome is an example of inadvertent damage caused by patient-induced irritation to the ocular surface. Patients use their fingernails to fish out strings of mucus. They often report foreign body sensation, irritation, and excessive mucous production. The behavior exacerbates the problems, causing a worsening spiral. A careful history examination will reveal the actual cause.

Management

Treatment of self-abusive behavior typically requires medical counseling and psychological or psychiatric intervention. Identification of the inciting events and subsequent confrontation may not be productive, because the actual cause of the problem might not be addressed.When children are involved, parents should be counseled to approach the issue with caution and sensitivity. Because detecting these cases may be difficult, patients often are seen by several clinicians, and parents may be angry and frustrated when they discover that their child is causing the problem.

Mucus fishing syndrome requires treatment of the underlying condition and education about the patient’s role in creating the disorder. When present, allergy must be addressed. The newer antihistamine–mast cell stabilizer combination products, such as olopatadine, have been particularly helpful in managing the disorder in these patients.

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The cornea is the avascular, transparent, richly innervated anterior-most surface of the globe, which is the eye’s primary refracting surface. As a result of these characteristics, diseases and disorders of the cornea can result in symptomatology, such as loss of vision, pain, and photophobia, that generally prompts the patient to seek care. Both the prevalence and potential severity of corneal conditions obligates the eye care provider to be fully versed in the diagnosis, treatment, and management of corneal diseases and disorders.

This chapter provides practical information regarding common corneal conditions that may require treatment. By nature of its anatomic proximity to and integration with other ocular and adnexal structures, corneal abnormalities may result from diseases primary to the eyelids, conjunctiva, lacrimal system, episclera, and other tissues. The details of these conditions are not emphasized in this chapter; thus the reader should refer to other appropriate chapters for this information.

CLINICAL ANATOMY AND

PHYSIOLOGY

The Normal Cornea

Histologic cross-section of the cornea reveals five identifiable layers: epithelium, Bowman’s layer, stroma, Descemet’s membrane, and endothelium. Fluid surrounds the cornea in the forms of the tear film in front and the aqueous behind. The various corneal layers combine to form a structure that is approximately 633 mcm thick at the inferior periphery, 673 mcm at the superior periphery, and 515 mcm thick centrally. The adult corneal diameter measures 11 to 12 mm horizontally and 9 to 11 mm vertically, creating a horizontally oriented ellipse. The radius of curvature of the central 3-mm optical zone ranges between 7.5 and 8.0 mm.

The epithelium is stratified and composed of five to seven layers of interconnected squamous cells of various types,sizes,and shapes.The deepest layer of epithelial cells,

known as the basal cell layer, adheres to a basement membrane and is the source for new cells that gradually move toward the surface. The outcome of this process is replacement of the entire epithelium every 7 days. An intact corneal epithelium helps to protect the cornea from most potential pathogenic organisms.

Bowman’s layer is a thin homogeneous sheet of acellular randomly arranged collagen fibers lying between the epithelial basement membrane and the stroma. Bowman’s layer is relatively tough and provides substantial resistance to corneal injury or infection. Because it cannot regenerate, scarring results when it is disrupted.

The stroma constitutes approximately 90% of the total corneal thickness and is primarily composed of collagen fibers, keratocytes, and glycosaminoglycans. The uniform arrangement of the collagen fibers is the major determinant of corneal transparency, in contrast to the opaque and less regularly arranged fibers of the sclera. Disruption of the stromal layer regularity results in loss of corneal transparency and potential scar formation.

Descemet’s membrane (posterior limiting lamina) is a strong, homogeneous, and resistant membrane consisting of very fine collagen fibers in a regular array, which thickens throughout life. Descemet’s membrane does not regenerate if damaged; however, endothelial cells migrate over the disrupted site and resurface the defect.

The endothelium consists of a single layer of interdigitating cells, which provides a slightly leaky barrier to the aqueous humor. The abundance of cellular organelles within the endothelial cells is consistent with the high level of metabolic activity provided by these cells as they actively transport aqueous out of the cornea. Maintenance of relative corneal dehydration also is achieved by the barrier functions of the epithelium and endothelium against the influx of tears and aqueous, respectively. Endothelial cells do not replicate in vivo. Loss of endothelial cells due to injury may disrupt corneal transparency and results in enlargement of the remaining adjacent cells to cover the affected area.

484 CHAPTER 26 Diseases of the Cornea

DEGENERATIONS AND DYSTROPHIES

Corneal Dystrophies

The corneal dystrophies are a group of corneal disorders genetically determined and traditionally classified with respect to the layer of the cornea they involve. Classification was based on slit-lamp examination and clinical appearance in an attempt to determine an apparent inheritance pattern and to monitor the natural progression. Histopathologic examination was typically performed postmortem or after corneal removal in transplant surgery.With the advent and increased understanding of molecular science, a new picture is emerging with respect to the genetic defects causing corneal disorders. Molecular science not only allows a basic understanding of the disease etiology and manifestation, but also offers potential for therapeutic intervention.

In addition to the explosion in molecular science, there has been a dramatic improvement in the ability to view the intact cornea and other ocular structures. In particular, the use of confocal microscopy has allowed for detailed corneal imaging in vivo and throughout the disease course. Table 26-1 outlines the contemporary inherited corneal disorder classification system, using information gathered from both molecular science and improved structural analysis.Table 26-1 lists the “old” name, the new name if applicable, the defective gene, inheritance pattern, phenotype, and typical complications. Each corneal dystrophy and gene has a unique OMIM (Online Mendelian Inheritance in Man) reference number, which is part of the national database. In addition, each gene has been assigned a symbol by the Human Genome Organization, also known as HUGO, which was established to standardize the gene names according to the family to which they belong.

Central visual axis progressively opacifies and scarring results

in decreased vision. Central cornea is

progressively opacified by stromal haze, with scarring and deterioration of vision. RCE are

also present.

RCE and visual loss less common than other lattice dystrophies.There is relative corneal anesthesia, with increased risk of neurotropic ulcer. Glaucoma may be present secondary to amyloid deposition in trabecular meshwork.

Vision typically mildly affected. May be associated systemic complications.

Generally asymptomatic, though mild photophobia may be present.

Resulting functional loss results in corneal edema and corneal decompensation.

Visual loss is generally not significant though glaucoma and keratoconus have been associated.

486 CHAPTER 26 Diseases of the Cornea

Treatment of the corneal dystrophies has been limited, for the most part, to the treatment of the associated complications. For example, most dystrophies result in the patient experiencing recurrent corneal erosions (RCEs). Patients are treated for the erosions without treating the underlying disease. Excimer laser phototherapeutic keratectomy (PTK) has been performed on patients with a variety of pathologies in the anterior one-third of the cornea with varying success. Excimer PTK is useful in the treatment of superficial stromal opacification and surface irregularity. PTK can restore and preserve useful function for a significant period of time.Although corneal dystrophies are likely to recur, successful retreatment with PTK is possible.

Traditionally, when a patient’s vision had become significantly impaired, penetrating keratoplasty was performed to improve vision and function. However, with genetically determined disorders, the graft tissue has the potential to undergo the same disease process. Because the underlying etiology of these disorders is genetic, the latest therapeutic approach is evolving from the area of gene therapy. Gene therapy is being explored in corneal graft survival, corneal haze treatment, modulation of corneal wound healing, and the treatment of corneal dystrophies.

The following discussion focuses on the specific corneal dystrophies and degenerations that are most commonly encountered clinically.

Anterior Basement Membrane Dystrophy

Etiology

Abnormal corneal epithelial regeneration and maturation, along with an abnormal basement membrane, are the primary features in anterior basement membrane dystrophy (ABMD).The prevalence of ABMD has been reported to be as low as 2% and as high as 42% of all patients. In patients over the age of 70 the estimates are as high as 76%. Although ABMD often is considered the most common corneal dystrophy, it may be an age-related degeneration. The large number of patients with the condition, its increasing prevalence with age, and its late onset support classifying ABMD as a degeneration instead of a dystrophy.

Diagnosis

Not all patients with this condition are symptomatic.The estimates of symptomatic ABMD patients range from lows of 10% to 20% to highs of 69%.The most common symptom is a mild foreign body sensation that usually is worse in dry weather, wind, and air conditioning. Blurred vision from irregular astigmatism or a rapid tear breakup may occur, especially in patients over the age of 45. Pain, when reported, usually is caused by RCE, which is estimated to occur in 10% of patients with ABMD.

It is easy to overlook ABMD during a clinical examination. This lack of detection may be the reason for such

wide variations in reported prevalence. The condition typically is bilateral but is often asymmetric. Females are affected more often than males. It often is first diagnosed between the ages of 40 and 70 years, but it has been reported in patients as young as 5 years.

With careful biomicroscopy examination, the most common findings in ABMD are gray chalky patches, intraepithelial microcysts, and fine lines, or a combination of these seen in the central two-thirds of the cornea. These findings are known as maps, dots, and fingerprints. These corneal changes may vary in appearance at each examination.

Maps appear as diffuse gray patches with sharp margins and thick irregular lines that may be surrounded by a haze. Maps often are separated by clear zones and may contain lacunae or white microcysts within their borders (Figures 26-1 and 26-2).They are seen most easily with tangential illumination. The tears over map areas break up rapidly and NaFl helps outline areas of mapping due to negative staining (Figure 26-3). Maps are caused by thickening of the basement membrane due to a proliferation of collagen material.

Dots contain degenerated epithelial cells that are trapped in intraepithelial extensions of the basement membrane. This prevents the normal migration of these cells toward the epithelial surface. Dots develop two different appearances. Some appear gray-white and have distinct edges. They often form clusters and vary in size from barely visible to 1 mm.These dots are seen easily on direct illumination and exhibit positive staining with NaFl only when they break through to the corneal surface. If the dots are very prominent, the condition is known as Cogan’s microcystic dystrophy. Blebs, the second type of dots, are fine, clear, closely clustered refractile lesions that are seen only on retroillumination.They have no effect on tear breakup time and do not enhance the likelihood of RCEs. Blebs are formed by the accumulation of fibrogranular material between the basement membrane and Bowman’s layer.

Fingerprint lines are thin, translucent, hair-like lines often arranged parallel to each other, resembling fingerprints (Figure 26-4).They are caused by a thickened and reduplicated basement membrane that extends into the epithelial layers. Retroillumination or indirect illumination are the best methods for seeing these lines, but a rapid tear breakup time over the areas also helps distinguish them. Findings similar to fingerprint lines also can develop in association with herpes simplex keratitis and bullous keratopathy.

Management

Treatment is directed toward preventing RCEs and most commonly consists of the use of 5% sodium chloride ointment instilled into the conjunctival sac at bedtime. This agent is especially indicated for patients who notice blurring of their vision upon awakening due to associated edema. If epithelial edema consistently contributes to a

Figure 26-2 ABMD mapping is seen in retroillumination. The irregular corneal surface caused by this condition may result in reduced visual acuity. (Courtesy of Pat Caroline.)

Figure 26-4 Subtle fingerprint lines are noted in this diffuse illumination photo. (Courtesy of Pat Caroline.)

488 CHAPTER 26 Diseases of the Cornea

Patients with ABMD who have undergone laser in situ keratomileusis (LASIK) may present with visual complaints and/or RCEs. Patients who have signs or symptoms of ABMD may not be ideal candidates for LASIK and should be carefully screened for this condition before pursuing surgery.

Guttata and Fuchs’ Dystrophy

Etiology

The endothelium functions as both a barrier and “pump” and is responsible for maintaining corneal transparency by regulating stromal hydration. The endothelium undergoes an age-related decrease in cell density due to a reduced proliferation rate that does not keep pace with cell loss. As a result, the endothelium becomes “fragile” and its function can potentially be compromised as a result of trauma or disease.

The development of corneal guttata is a common form of endothelial anomaly.The endothelium produces excessive amounts of an abnormal basement membrane material resulting in the formation of a posterior collagenous layer. Guttata are wart-like prominences on Descemet’s membrane and result from excessive accumulations of the abnormal corneal endothelial secretions. Histologic studies indicate that guttata are accompanied by thinning of the overlying endothelial cells along with thickening of Descemet’s membrane.

Guttata generally are located in the central cornea, except in the case of Fuchs’ endothelial dystrophy, when the peripheral endothelium also becomes involved.When these lesions are noted in the peripheral corneal endothelium only, they are termed Hassall-Henle bodies. Guttata usually are first noticed in patients in their thirties and forties or older, although the density of the guttata may vary significantly from patient to patient. Mild guttata commonly appear as occasional scattered lesions in the central cornea. Moderate guttata appear as a relatively dense collection of lesions in the central cornea. Pigment is commonly associated with guttata and may be entrapped in the irregular endothelial surface. Moderate guttata may exhibit a plaque-like appearance in the central cornea, which somewhat obscures the typical guttata detail due to clinically significant thickening of Descemet’s membrane. In the presence of mild to moderate guttata, the overlying stroma and epithelium remain clear, and these conditions tend to remain stationary for years. Guttata have also been reported in association with keratoconus.

Fuchs’ (endothelial) dystrophy has a component of guttata, but the involvement is such that corneal physiology is affected adversely. Fuchs’ dystrophy occurs bilaterally, has been reported to be transmitted dominantly (with incomplete penetrance), and females are three times more likely to develop the condition. Prominent guttata initially occur centrally and then become extensive enough to involve the peripheral cornea. In Fuchs’ dystrophy the

endothelial cells become sufficiently compromised to interfere with their metabolic “pump” ability, thus permitting aqueous to enter the cornea. As a result, and over a course lasting several decades, stromal edema, epithelial edema, and bullous keratopathy ensue. Histologic studies suggest an initial increase in the pump site activity in early Fuchs’, followed by a gradual deterioration toward end-stage Fuchs’. Secondary abnormalities in the basement membrane and Bowman’s layer also develop and may result in conditions such as RCE.

Transient secondary guttata may develop in association with degenerative corneal disease, trauma, or inflammation. Transient guttata associated with corneal edema have been termed pseudoguttata.

Diagnosis

The diagnosis of corneal guttata is made using the biomicroscope. In direct illumination, particularly with a parallelepiped, guttata appear as small refractile “drops’’ on the corneal endothelium. Closer inspection using specular reflection microscopy reveals orange peel– like “dimpling’’ of the endothelium caused by the guttata, appearing as dark spots in the reflected light (Figure 26-5).This clinical presentation may be accentuated by evaluating the cornea after pupillary dilation. The pigmentation and plaque-like haze of moderate guttata are quite apparent.

Established Fuchs’ dystrophy consists of dense guttata, most pronounced centrally but involving the entire corneal endothelium. The endothelium may acquire a bronzed, beaten, metal-like appearance. Accompanying stromal edema appears as a central whitish haze (Figure 26-6). Epithelial edema may appear as corneal bedewing, best seen in indirect illumination, and frank bullae may be present. Long-standing corneal edema may result in corneal scarring, and advanced cases may exhibit subepithelial fibrosis and vascularization.

Patient symptomatology varies with the extent of the guttata. Mild corneal guttata have no effect on visual function. Moderate corneal guttata, with its central and rather dense distribution, may affect visual function, including light scatter and reduced visual acuity to approximately 20/25 to 20/30. Decreased visual acuity due to corneal edema may be noticed upon awakening, which may improve during the course of the day as the corneal fluid evaporates. The visual impact of moderate guttata will be most noticeable under conditions of pupillary constriction. Overlying corneal edema in association with moderate guttata is not generally visible using a biomicroscope; however, anecdotal evidence suggests that patients with this condition may report blurring of vision upon awakening in the morning, which may represent an exacerbation of corneal edema resulting from closure of the lids overnight. Rupture of associated bullae produces symptoms of foreign body sensation, pain, and redness.

Management

Treatment options are primarily palliative, with the goal of improving patient comfort and function. The use of topical ophthalmic hypertonic agents may reduce epithelial edema related to Fuchs’ dystrophy; however, these agents do not reduce stromal edema. The use of topical 5% sodium chloride drops six to eight times daily, along with 5% sodium chloride ointment instilled into the conjunctival sac at bedtime,may be instituted to determine

the effect on symptoms and visual acuity. Although epithelial edema is not an obvious factor in moderate corneal guttata, 5% sodium chloride ointment instilled into the conjunctival sac at bedtime may relieve the symptoms of those patients who experience accentuated blurring of vision upon awakening.

To help relieve patient discomfort due to the rupture of epithelial bullae, a therapeutic soft contact lens may be tried. Effective restoration of patient comfort and visual function for well-established Fuchs’ dystrophy, however, may be best achieved through penetrating keratoplasty (Figure 26-7). Fuchs’ dystrophy is the primary condition