Terrien's Marginal Degeneration : Introduction, Symptoms, Causes, Diagnosis, Management and Prevention - www.genericdrugscan.com

Terrien's Marginal Degeneration : Information

Terriens Marginal Degeneration (TMD) is a slowly progressive, bilateral, peripheral corneal thinning disorder associated with corneal neovascularisation, opacification and lipid deposition. The disease is usually bilateral but may initially present in one eye. The cause of Terriens marginal degeneration is not known and patients may have high degrees of astigmatism. Up to about one third of patients may have associated episcleral or scleral inflammation. Patients are typically between 20-40 years of age, although it may present in childhood or in older people (age ranges from 10 to 70 years). It is more common in men than in women.

Terrien (1900) first described this disorder. The condition is usually bilateral and starts in the superonasal quadrant as a fine, yellow- white punctate stromal opacity that may progress along the circumference of the cornea.

Two types of Terriens marginal degeneration have been documented. One type occurs primarily in the older population. It is usually asymptomatic and slowly progressive. The other, more inflammatory type characteristically occurs in younger patients and may be associated with episcleritis or scleritis. It has also been reported in patients with posterior polymorphous dystrophy, anterior basement membrane dystrophy, and erythema elevatum diutinum (rare chronic dermatosis).

Marked astigmatism may be corrected initially with spectacle or contact lenses. Surgical intervention may be required to correct visually disabling astigmatism, prevent impending perforation, and to treat corneal perforation.

References:

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http://eyewiki.aao.org/Terrien's_Marginal_Degeneration

http://www.djo.harvard.edu/print.phpurl=/physicians/gr/336&print=1

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Terrien F. Dystrophie marginale symtrique des deux cornes avec astigmatisme rgulier consquetif et gurison par la cautrisation igne. Arch Ophthalmol (Paris) 1900; 20: 12- 21.

Austin P, Brown SI. Inflammatory Terriens marginal corneal disease. Am J Ophthalmol 1981; 92: 189- 192.

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Patients are asymptomatic with initial mild disease.

Patient with advanced disease may have symptoms such as:

• Painless progressive blurred vision.
• Progressive change of glasses.

Less common symptoms may be:

• Recurrent attacks of ocular irritation.
• Pseudo-pterygium.]

The cause of Terrien s marginal degeneration remains unknown. There are two types:

• Classic form: The classic form most commonly affects patients older than 40 years of age without rheumatoid arthritis and progression is extremely slow.
• Inflammatory type: Inflammatory variant of Terrien s marginal degeneration affects younger subjects and it is characterised by recurrent and disabling attacks of acute pain and inflammation.

Pathogenesis:

Terrien s bilaterality, extremely slow progression, lack of significant clinical and histological inflammation, and lipid deposition suggests a degenerative process in most cases.

The inflammatory form showed perivascular lymphocytic and neutrophilic infiltration, vascular occlusion, and fibrinoid necrosis. Austin and Brown (1981) described an inflammatory type in younger subjects. However, later they stated that the description of central progression with epithelial breakdown were more consistent with Mooren s ulcer rather than with Terrien s marginal degeneration.

Terrien s marginal degeneration may be associated with:

• Episcleritis.
• Scleritis.
• Posterior polymorphous dystrophy.
• Keratoconus.
• Anterior basement membrane dystrophy.
• Erythema elevatum diutinum (rare chronic dermatosis characterised by red- brown papules and nodules on extensor surfaces).]

The diagnosis of Terrien s marginal degeneration is clinical, based on history, slit lamp (bio-microscopy) examination of the eye, and corneal topography.

The disease process is extremely slow, often taking 30 years. Patients give history of progressive change of glasses with slowly deteriorating vision from severe against-the-rule astigmatism (caused by progressive flattening of the vertical meridian).

Clinical signs:

Terrien s marginal degeneration usually begins superonasally with peripheral, fine, yellow-white punctate stromal opacities. A lucid zone of clear cornea separates the opacities from the limbus. In due course, the opacities coalesce into a line similar to arcus senilis, superficial vessels advances from the limbus, with thinning of the intervening stroma. The thinning slowly spreads circumferentially and rarely towards the center as well. In advanced stages, localised areas of ectasia develop along the course of corneal thinning. Circumferential ectasia is rare. Epithelium is intact throughout the course of the disease.

Spontaneous breaks in Descemet s membrane resulting in corneal hydrops have been reported. Corneal hydrops presents as a clear intracorneal pocket of aqueous rather than stromal clouding. Since Bowman s membrane remains intact, there is corneal intra-lamellar dissection and formation of corneal cysts. Occasionally, intracorneal aqueous pockets become continuous with subconjunctival space with formation of filtering blebs and resultant hypotony. Perforation either spontaneous or following minor trauma may occur, but is rare.

Pseudo-pterygium may develop rarely in some patients with Terrien s marginal degeneration. The pseudo-pterygium characteristically occurs in positions other than interpalpebral 3 o clock and 9 o clock position and grows onto the cornea at an oblique angle. This variant may be the same as Fuch s superficial marginal keratitis.

Occasionally, Terrien s may present with recurrent painful episodes of inflammation. Collagen vascular disease should be ruled out.

Salient features are:

• High against-the-rule or oblique astigmatism.
• Leading edge of lipid.
• Steep central edge.
• Sloping peripheral edge.
• Superficial vascularisation.
• Intact epithelium.

Terrien s marginal degeneration is distinguished from other peripheral corneal thinning disorders by:

• Lack of inflammation.
• Presence of superficial vascularisation.
• Advancing linear deposition of lipid.
• Lack of epithelial defect.
• Slow progressive course.

Corneal topography/ Videokeratography: Corneal topography/ Videokeratography measures corneal curvature, elevation and the amount of corneal astigmatism. This also helps in fitting rigid gas permeable contact lenses. Corneal topography reveals flattening over the peripheral areas of corneal thinning. It shows steepening opposite to the mid-point of corneal thinning.

Scanning slit topography: Scanning slit topography utilises optical slits that scan along multiple points of the cornea. This allows for measurements of the anterior and posterior cornea including pachymetry (measures corneal thickness).

Ultrasound biomicroscopy: Ultrasound biomicroscopy quantifies the thickness of the cornea and help to detect progression of disease. Due to its high magnification and ability to depict the size and shape of structures, it can reveal subtle changes in the cornea.

Histopathology:

The epithelium may be normal, thickened, or thinned. Basal epithelial cells show degeneration. Bowman s membrane and anterior stromal lamella are lost and replaced by vascularised loose connective tissue. Limbal vessels advance centrally within the superficial connective tissue, loop at the central margin of furrow, and revert back to the limbus passing just anterior to Descemet s layer.

The remaining stromal lamella is compressed and shows lipid deposition. Lipid deposition is most prominent anterior to the vascular arcades. Histiocytes line the blood vessels and contain phagocytosed lipid, corneal collagen, and ground substance. Tear fluid contains higher levels of lysosomal enzymes.

Descemet s membrane is usually intact and may be thickened or thinned. However, reports also describe presence of healed ruptures of Descemet s membrane. The endothelium is intact and is either normal or attenuated.

Differential diagnosis:

• Mooren s Ulcer:

- Active Mooren s ulcer: Active Mooren s ulcer is usually associated with pain and conjunctival inflammation, whereas Terrien s marginal degeneration is usually painless and uninflamed. Mooren s ulcer may have inflammatory infiltrate and an overhanging central edge, usually with an epithelial defect. There is no lipid deposition. Ulceration involves anterior one- third of the cornea and usually spreads rapidly, both circumferentially and centrally with infiltration and vascularisation at the leading edge. An autoimmune trigger or a history of insult or trauma to the cornea may be the causative factor for Mooren s ulcer. Terrien s marginal degeneration shows a gradually sloping central edge with intact epithelium and it shows lipid deposition. Terrien s, probably a degenerative process, progresses slowly and circumferentially. Peripheral cornea may be vascularised in both conditions.

- Healed Mooren s ulcer: Healed Mooren s ulcer is a common disease mimicking Terrien s marginal degeneration. Both diseases lack systemic findings. Mooren s ulcer may be bilateral or unilateral, whereas Terrien s is usually bilateral.

• Pellucid marginal degeneration: Peripheral corneal thinning associated with pellucid marginal degeneration is inferior and lacks lipid deposition and vascularisation. It is usually bilateral but may be asymmetric. Onset occurs during fourth and fifth decades of life. There is a slowly progressive 1- 2mm band of inferior thinning leaving 1- 2mm margin from the limbus. It presents with an area of steepening superior to the area of corneal thinning.
• Keratoconus: Keratoconus is a progressive stromal thinning occurring centrally or paracentrally. It is bilateral, but may be asymmetric, and begins around puberty. Retinoscopy shows scissoring reflex. Slit lamp (bio- microscopy) may reveal Vogt striae (vertical stress lines in deep stroma) or epithelial Fleischer ring (iron deposit at the base of the cone). Keratoconus patients have progressive myopia, irregular astigmatism with steep keratometry readings. Munson s sign, which is bulging of lower lid on down- gaze, may also be present. Rizutti s sign is an arrowhead pattern at the nasal limbus being produced by focusing of a light beam shown from temporal side across the cornea in keratoconus. Severe cases may develop acute hydrops (stromal oedema due to leakage of aqueous humour through breaks in Descemet s membrane).
• Furrow or gutter degeneration: Furrow or gutter degeneration lacks vascularisation.
• Collagen vascular diseases: Corneal thinning in collagen vascular diseases such as rheumatoid arthritis, Wegener s granulomatosis and polyarteritis nodosa is usually associated with systemic findings.
• Arcus senilis: Arcus senilis may mimic peripheral opacification associated with early stages of Terrien s marginal degeneration. Arcus senilis is characterised by both superior and inferior peripheral corneal opacification, absence of vascularisation, and lack of corneal thinning. It progresses circumferentially to form a band about 1mm wide in perilimbal cornea. The peripheral edge is sharp and separated from the limbus by a clear zone.
• Vernal keratoconjunctivitis: Vernal keratoconjunctivitis is a recurrent bilateral condition presenting with itching, photophobia, foreign body sensation and mucous discharge. It affects palpebral conjunctiva, limbal area of the cornea or both. It produces giant papillae in superior palpebral conjunctiva and/or limbal papillae with a white apex called Horner-Trantas dots. Corneal changes such as punctate epithelial erosions, macro-erosions and shield ulcers may also occur.
• Ocular rosacea: Rosacea is an idiopathic skin condition affecting sun- exposed areas. Clinical features include facial flushing, papulopustular rash and thickening of skin that may evolve into rhinophyma (swollen enlarged nose). Ocular symptoms include irritation, watering and burning. The lids may show superficial telangiectasias and blepharitis. There may be conjunctival hyperaemia. Cornea may develop punctate epithelial erosions, marginal keratitis, corneal vascularisation or scarring.
• Staphylococcal marginal keratitis: Staphylococcal marginal keratitis lesions usually have a lucid interval (separated from the limbus by a clear zone) between the limbus and the infiltrate and only rarely cause thinning.]

Management should be carried out under medical supervision.

Usually no treatment is required, unless perforation or impending perforation occurs. However, spectacles and rigid gas permeable lenses are prescribed for refractive errors.

Medical therapy:

• Spectacle correction: To begin with in the early mild cases of the disease, spectacle correction is prescribed. Patients with high astigmatism may be prescribed with high refractive index sphero-cylindrical glasses. Due to the risk of corneal perforation in the area of TMD, polycarbonate lenses are recommended. Polycarbonate lenses are light weight and impact resistant.
• Rigid gas permeable (RGP) contact lenses: Rigid gas permeable (RGP) contact lenses may be required for cases of TMD. Piggyback rigid gas permeable contact lenses may be used. In piggyback, a soft contact lens is worn under the gas permeable lens, acting as a cushion to reduce or eliminate any discomfort caused by the gas- permeable lens. It is recommended that patients wear plano polycarbonate glasses over their contact lens prescription to avoid any risk of corneal perforation due to thinning.

Surgical therapy:

• Keratoplasty: Keratoplasty is considered for patients with TMD whose vision is inadequate with contact lenses or for patients who are intolerant to lens. Reconstructive keratoplasty is performed when thinning becomes so severe that corneal perforation is threatened or it occurs.

Penetrating keratoplasty: In general, patients with TMD are usually poor candidates for penetrating keratoplasty as the corneal thinning occurs close to the limbus. As a result, large eccentric grafts are required and must be positioned very close to the limbus thus increasing the chances of graft rejection or suture-induced complications.

Lamellar crescentic keratoplasty: In lamellar crescentic keratoplasty, crescent-shaped donor lamellar (partial thickness) cornea is used.

Full- thickness crescentic keratoplasty: In Full- thickness crescentic keratoplasty, thinned cornea is removed entirely and the Descemet s membrane of the donor is retained.

Annular lamellar keratoplasty: Annular lamellar keratoplasty grafts may be required in severe cases of Terrien s marginal degeneration, involving complete 360 .

Lamellar keratoplasties are often preferred over penetrating keratoplasty because of the decreased risk of graft rejection, corneal opacification and development of irregular astigmatism.

Prognosis:

Most patients with no impending perforation may be managed successfully with glasses or rigid gas- permeable contact lenses. Because there is typically no epithelial defect, the risk of infectious keratitis and acute corneal thinning is low. However, these patients require regular monitoring.