External Layer Pathology Flashcards
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Corneal Edema
Contact lens wear may cause alterations in corneal physiology, which in turn can lead to epithelial, stromal and/or endothelial changes. Insufficient oxygen to the cornea may lead to endothelial and the stromal changes with consequent interference in metabolic activity and stromal swelling. A hypoxic cornea is edematous. Tight lenses, low Dk soft or RGPs, PMMA lenses, extended wear of regular hydrogel lenses, and overwear are causes of hypoxia, and consequently, edema of the cornea.
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Bacterial Corneal Ulcer
(also known as bacterial keratitis or microbial keratitis)
presents with dense grayish white opacity associated with epithelial loss and stromal involvement. A particular feature of bacterial keratitis is its rapid progression; corneal destruction may be complete in 24-48 hours with some of the more virulent bacteria. Corneal ulceration, stromal abscess formation, surrounding corneal edema, and anterior segment inflammation are characteristic of this disease.
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Recurrent Corneal Erosion
Recurrent corneal erosion, as its name suggests, is erosion of the cornea that continues to occur after the first episode. Recurrent attacks of acute pain associated with lacrimation, photophobia and a foreign body sensation usually occur on waking. There may be an associated blepharospasm and blurring of the vision. The problem may be unilateral or bilateral. Symptoms may gradually subside over the course of the day and then start all over again the next morning. The unpredictability of these episodes leads to anxiety on the part of the patient. Few patients will have their vision permanently affected.
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Dendritic Ulcer
A dendritic corneal ulcer is caused by the Herpes Simplex type 1 virus, the same virus that causes cold sores. These ulcers are easily identified by their branch or limb-like appearance.
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Microcysts
an accumulation of fluid in the intracellular space resulting from ruptured epithelial cell membranes. These are easily viewed using retroillumination on slit lamp examination. Symptoms include discomfort on lens insertion, photophobia, and epiphora, usually caused by adverse reaction to chemicals in some preserved contact lens solutions.
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Giant Papillary Conjunctivitis (GPC)
Giant papillary conjunctivitis is a common complication of contact lens wear. It has also been called contact lens induced papillary conjunctivitis. Allergic symptoms accompany papillary changes in the ocular tarsal palpebral conjunctiva as part of hypersensitivity reaction. Debris on the surface of contact lenses may be a cause, as well as a result. This leads to a spiral of inflammation that causes more lens deposits to form, leading to additional inflammation.
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Kayser-Fleischer Ring
an orange-brown coloration in the posterior cornea. It is seen at the level of Descemet’s membrane. Look carefully around the edges of the cornea. There is a subtle golden brown or greenish-brown discolouration. These are copper deposits and are typically a sign of Wilson’s disease.
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Acanthamoeba Keratitis
caused by a parasite, is a rare disease that can affect anyone, but is most common in individuals who wear contact lenses. If not treated properly and immediately, this disease can have devastating resulting complete loss of vision. Acanthamoeba keratitis affects primarily the cornea and sclera. It is caused by parasites that can be found in soil, fresh, brackish, and sea water, hot springs, sewage, swimming pools, contact lens equipment, and in poor storage and handling of contact lenses.
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Keratoconus
a non-inflammatory eye condition (best classified as a dystrophy but has some features of degeneration) in which the normally round dome-shaped cornea progressively thins, causing a cone-like bulge to develop. This results in significant visual impairment. The central to inferior cornea bulges forward and thinning is present. It is most often a bilateral condition, but one eye is usually more involved. The condition, in the early stages, causes slight blurring and distortion of vision and increased sensitivity to glare and light. These symptoms usually first appear in the late teens and early twenties. Keratoconus may progress for 10-20 years and then slow or stabilize. Each eye may be affected differently.
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Conjunctivitis
Types of conjunctivitis are: allergic, bacterial, and viral. With the exception of the allergic type, conjunctivitis is usually highly contagious and protective precautions should be taken when examining these patients.
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Bullous keratopathy
a degenerative condition in which the cornea becomes permanently swollen. This occurs because the corneal endothelium has been damaged and is not pumping fluid properly. Pockets of fluid, called ‘bullae’, form in corneal tissue and rise to the epithelial surface where they break and become painful. The cause of the endothelial damage may be from trauma, glaucoma, or inflammation after some types of ocular surgery. Patient with bullous keratopathy cannot wear contact lenses.
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Superficial Punctate Keratitis (SPK)
Symptoms are injection, lacrimation, photophobia, and slightly decreased vision. Diagnosis is made by slit-lamp examination. Treatment depends on the cause.
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Fleischer’s ring
is actually a type of pigmented dystrophy. It consists of partial or complete iron deposition in the deep epithelium encircling the base the cone in eyes with keratoconus. It appears as a yellowish to dark-brown coloured ring and can best be seen using a cobalt blue light with a slit lamp.
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Hudson-Stähli line
an orange-brown iron line at the level of the basement membrane of the epithelium in the band region of the normal cornea. It is a roughly horizontal line found in the middle third of the cornea. It is common in older corneas and injured corneas at any age.
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Corneal Folds and Striae
Folds appear as long, straight lines, and striae appear as fine white vertical lines in the posterior stroma. Both conditions may occur in the presence of corneal edema. Folds and striae are more commonly seen in patients who wear extended wear lenses or in high plus hydrogel lenses.
The patient may be asymptomatic or have issues with glare. Management requires refitting the patient in a higher Dk lens or changing to daily wear lenses.
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Pterygium
A pterygium is a triangle-shaped overgrowth of conjunctiva that crosses the limbal border. Patients with pterygium should be carefully evaluated prior to consideration of contact lens fitting, as pterygium may lead to dellen formation.
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Marginal Keratitis
an infiltrative immune response to staphylococcal exotoxins. Exotoxins produce a sterile response by forming intraepithelial infiltrates in the mid-peripheral cornea. Lesions are always islands, single or multiple on the peripheral margin, separated by clear cornea. Lesions range from 0.5 to 1.5 mm in diameter and may be flat or raised. Corneal edema is usually mild to moderate and can produce a haze around the infiltrates. Corneal involvement is most vulnerable at the 4 o’clock and 8 o’clock positions, but lesions may also be superior or circumlimbal. The bulbar conjunctiva is hyperemic.
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Superior Limbic Keratoconjunctivitis (SLK)
SLK is an inflammatory reaction induced by wearing soiled hydrogel lenses, which causes excessive movement. Signs include intense laxity and hyperemia of the superior bulbar conjunctiva, fine papillary hypertrophy of superior tarsal conjunctiva, epithelial and subepithelial infiltrates, and superior corneal and limbal punctate staining.
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Dellen
Dellen are focal, peripheral, saucer-shaped depressions, approximately one half of the corneal thickness, producing a “hole-like” appearance. Thinning occurs in the epithelium, Bowman’s layer, and superficial stroma
usually transient, lasting only 24 to 48 hours, but they may last for weeks and lead to scarring.
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Megalocornea
Megalocornea is a larger than normal cornea. It has a visible horizontal iris diameter of 13 mm or more. Ninety percent of megalocorneas occur in male patients and are usually bilateral. Often, there is a high refractive error, especially with astigmatism. A large, flat (16 mm) soft lens provides the best centration.
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Krukenberg’s spindle
consists of brownish, vertical, spindle-shaped pigment deposits on the posterior cornea. Look for old uveitis or pigment dispersion syndrome. All patients who have Krukenberg’s spindle should be closely monitored for glaucoma.
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Neovascularization
Neovascularization occurs when a small amount of peripheral superficial vascularization is caused by hypoxia, vascular compression from tight-fitting contact lenses, and trauma from damaged lenses, or sensitivity to a solution. The micro-trauma caused by a contact lens releases enzymes that cause inflammation. When the cells reach the area of epithelial damage, they stimulate growth of new vessels toward the site of injury.
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Keratic precipitates
white or pigmented deposits on the endothelial surface. They are suggestive of uveitis, trauma, or age.
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Microcornea
Microcornea is a smaller than normal cornea. It has a visible horizontal iris diameter of 10 mm or less. Microcornea is often associated with systemic or ocular syndromes. Microcorneas are often very steep and should be fit with an appropriately steep base curve.
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Pannus
Pannus is a condition in which fibrovascular connective tissue proliferates into the anterior layers of the peripheral cornea in inflammatory corneal disease. Patients with pannus should not be fit with contact lenses. If a patient is currently wearing lenses, lenses should be discontinued.
