Ординатура / Офтальмология / Английские материалы / Clinical Ophthalmology A Systematic Approach 7th Edition_Kanski, Bowling_2011

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Corneal degenerations

Age-related degenerations

Arcus senilis

1Systemic implications. Arcus senilis is the most common peripheral corneal opacity; it frequently occurs without predisposing systemic conditions in elderly individuals. Occasionally arcus may be associated with familial and non-familial dyslipoproteinaemias. Arcus has also been noted in patients with Schnyder crystalline corneal dystrophy.

2Signs (Fig. 6.61A)

•Stromal lipid deposition which starts in the superior and inferior perilimbal cornea and then progresses circumferentially to form a band about 1 mm wide.

•The band is usually wider in the vertical than horizontal meridian.

•The central border is diffuse and the peripheral edge is sharp and separated from the limbus by a clear zone.

•This lucid interval may occasionally undergo mild thinning (senile furrow).

Fig. 6.61 Age-related degenerations. (A) Arcus senilis; (B) Vogt limbal girdle; (C) cornea farinata; (D) crocodile shagreen

Vogt limbal girdle

Vogt limbal girdle is a common innocuous condition which is more common in women and is present in up to 60% of individuals over 40 years of age.

1Signs

•Bilateral, arc-like, whitish crescentic lines composed of chalk-like flecks located at the limbus at 9 and/or 3 o’clock, more common nasally (Fig. 6.61B).

•There may be irregular central extensions.

2Classification

aType I may be closely related to band keratopathy, featuring a ‘Swiss cheese’ hole pattern and a clear area separating the lesion from the scleral margin.

bType II is distinguished from type I by the absence of holes and sometimes also absence of a juxtalimbal clear zone.

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Cornea farinata

Cornea farinata is a visually insignificant condition characterized by bilateral, minute, flour-like deposits in the deep stroma, most prominent centrally (Fig. 6.61C).

Crocodile shagreen

Crocodile shagreen is characterized by asymptomatic, greyish-white, polygonal stromal opacities separated by relatively clear spaces (Fig. 6.61D). The opacities most frequently involve the anterior two-thirds of the stroma (anterior crocodile shagreen), although on occasion they may be found more posteriorly (posterior crocodile shagreen). It resembles the central cloudy dystrophy of François (see Fig. 6.57).

Lipid keratopathy

1Primary lipid keratopathy is rare and occurs spontaneously. It is characterized by white or yellowish stromal deposits consisting of cholesterol, fats and phospholipids and is not associated with vascularization (Fig. 6.62A).

2Secondary lipid keratopathy is much more common and is associated with previous ocular injury or disease which has resulted in corneal vascularization (Fig. 6.62B). The most common causes are herpes simplex and herpes zoster disciform keratitis.

3Treatment is primarily aimed at medical control of the underlying inflammatory disease. Other treatment options include:

aArgon laser photocoagulation to the arterial ‘feeder’ vessels may induce resorption of the lipid infiltrate provided the vessels can be identified by fluorescein angiography.

bNeedle point cautery is performed by grasping a 6 mm or similar suture needle in thermal cautery forceps and applying the hot needle tip to the feeder vessels at the limbus under microscopic control.

cPenetrating keratoplasty may be required in advanced but quiescent disease, although vascularization, thinning and hypoaesthesia may prejudice the outcome.

Fig. 6.62 Lipid keratopathy. (A) Primary; (B) secondary to vascularization

(Courtesy of S Tuft – fig. B)

Band keratopathy

1Histology shows deposition of calcium salts in Bowman layer, epithelial basement membrane and anterior stroma (Fig. 6.63A).

2Causes

aOcular. Chronic anterior uveitis (particularly in children), phthisis bulbi, silicone oil in the anterior chamber, chronic corneal

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oedema and severe chronic keratitis.

bAge-related affects otherwise healthy individuals.

cMetabolic (metastatic calcification). This is rare and includes increased serum calcium and phosphorus, hyperuricaemia and chronic renal failure.

dHereditary causes include familial cases and ichthyosis.

3Signs

•Peripheral interpalpebral calcification with clear cornea separating the sharp peripheral margins of the band from the limbus (Fig. 6.63B).

•Gradual central spread to form a band-like chalky plaque containing transparent small holes and occasionally clefts (Fig. 6.63C).

•Advanced lesions may become nodular and elevated with considerable discomfort due to epithelial breakdown.

4Treatment is indicated if vision is threatened or if the eye is uncomfortable. It is important to recognize and treat any underlying condition.

aChelation is simple and effective for relatively mild cases and is performed under the microscope.

•Large chips of calcium can be scraped off the cornea with forceps.

•The corneal epithelium overlying the opacity and any solid layer of calcification is scraped off with a number 15 blade.

•The cornea is rubbed with a cotton-tipped bud (Fig. 6.63D) dipped in a solution of ethylenediaminetetraacetic acid (EDTA) 1.5–3.0% until all calcium has been removed (Fig. 9.60D); allow adequate time (15–20 minutes) for chelation to occur.

•Re-epithelialization can take many days.

•Recurrence is not uncommon, particularly in patients with an underlying systemic condition or persistent uveitis.

bOther modalities include the use of a diamond burr, excimer laser keratectomy and lamellar keratoplasty.

Fig. 6.63 Band keratopathy. (A) Histology shows black calciumdeposits – von Kossa stain; (B) early involvement; (C) advanced; (D) chelation

(Courtesy of J Harry and G Misson, from Clinical Ophthalmic Pathology, Butterworth-Heinemann 2001 – fig. A)

Spheroidal degeneration

1Pathogenesis. Spheroidal degeneration (corneal elastosis, Labrador keratopathy, climatic droplet keratopathy and Bietti nodular dystrophy) is a bilateral, degenerative condition of unknown cause which typically occurs in men whose working lives are spent outdoors. The main postulated predisposing factor is ultraviolet exposure, since severity correlates closely with the length of time spent outdoors. The condition is relatively innocuous although visual impairment may occur rarely.

2 Histology shows irregular protein deposits in the anterior stroma that replace Bowman layer (Fig. 6.64A).

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3Signs

•Amber-coloured granules in the superficial stroma of the peripheral interpalpebral cornea.

•Increasing opacification, coalescence and central spread.

•Advanced lesions are nodular and the surrounding stroma often hazy (Fig. 6.64B).

4Treatment options include protection against ultraviolet damage with sunglasses, and superficial keratectomy or lamellar keratoplasty to improve vision.

Fig. 6.64 Spheroidal degeneration. (A) Histology shows dark red proteinaceous deposits in the anterior stroma that replace Bowman layer; (B) advanced involvement

(Courtesy of J Harry and G Misson, from Clinical Ophthalmic Pathology, Butterworth-Heinemann 2001 – fig. A; R Fogla – fig. B)

Salzmann nodular degeneration

1Pathogenesis. Salzmann nodular degeneration can occur in any form of chronic corneal irritation or inflammation, especially trachoma.

2Signs

•Discrete, elevated grey or blue-grey, nodular, superficial stromal opacities (Fig. 6.65).

•The lesions are located in scarred cornea or at the edges of transparent cornea.

•The base of a nodule may be surrounded by epithelial iron deposits.

•Recurrent epithelial erosions may occur.

3 Treatment is similar to that of spheroidal degeneration.

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Fig. 6.65 Salzmann nodular degeneration

(Courtesy of R Bates)

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Metabolic keratopathies

Cystinosis

1Pathogenesis. Cystinosis is a rare AR disorder characterized by widespread tissue deposition of non-protein cystine crystals as a result of a defect in lysosomal transport.

2Systemic features include severe growth retardation, early-onset renal failure, hepatosplenomegaly and hypothyroidism. Patients with the most severe nephropathic form usually succumb before the 2nd decade. Treatment with systemic cysteamine may forestall renal disease. Non-nephropathic (‘ocular’) cystinosis is characterized by absence of renal disease.

3Keratopathy may present by 1 year of age and is characterized by progressive deposition of cystine crystals in the conjunctiva and cornea which cause intense photophobia, blepharospasm, epithelial erosions and visual disability by the end of the 1st decade. Peripherally, crystals involve the entire stromal thickness, whereas centrally only the anterior two-thirds are affected (Fig. 6.64A). Later, involvement of the iris, lens capsule and retina further affects vision.

4Treatment with topical cysteamine 0.2% for several weeks can reverse corneal crystal deposition.

Mucopolysaccharidoses

1Pathogenesis. The mucopolysaccharidoses (MPS) comprise a group of inherited deficiencies of catabolic glycosidase necessary for hydrolysis of mucopolysaccharides. The altered metabolite accumulates in intracellular vacuoles in various tissues and organs and may also be detected in the urine.

2Inheritance is mainly AR, although the two subtypes of Hunter syndrome are X-linked recessive.

3Systemic features, which vary with the type of MPS, include facial coarseness, skeletal anomalies, mental retardation and heart disease.

4Keratopathy is characterized by punctate corneal opacification and diffuse stromal haze (Fig. 6.66B). It occurs in all MPS except Hunter and Sanfilippo. In Hurler and Scheie syndromes corneal deposits are most severe and are present at birth. Corneal clouding in this setting should be differentiated from that secondary to congenital glaucoma, rubella keratopathy, congenital hereditary endothelial dystrophy and birth trauma.

5Other ocular features

a Pigmentary retinopathy occurs in all except Morquio and Maroteaux–Lamy. b Optic atrophy occurs in all six MPS and is most severe in Hurler.

c Glaucoma is uncommon.

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Fig. 6.66 Metabolic keratopathies. (A) Cystinosis; (B) mucopolysaccharidoses; (C) Wilson disease; (D) Norumdisease; (E) immunoprotein deposits

(Courtesy of L Merin – fig. A; W Lisch – fig. D)

Wilson disease

1Pathogenesis. Wilson disease (hepatolenticular degeneration) is a rare condition caused by deficiency of caeruloplasmin resulting in widespread deposition of copper in the tissues.

2Presentation is with liver disease, basal ganglia dysfunction or psychiatric disturbances.

3Keratopathy is present in nearly all patients and is characterized by a zone of copper granules in the peripheral part of Descemet membrane (Kayser–Fleischer ring, best detected on gonioscopy when subtle) which change colour under different types of illumination (Fig. 6.66C). The deposits are preferentially distributed in the vertical meridian and may disappear with penicillamine therapy.

4Anterior capsular ‘sunflower’ cataract is seen in some patients.

Lecithin-cholesterol-acyltransferase deficiency (Norum disease)

This is an AR disease characterized by hyperlipidaemia, early atheroma, anaemia and renal disease. Keratopathy is characterized by numerous minute greyish dots throughout the stroma, often concentrated in the periphery in an arcus-like configuration (Fig. 6.66D).

Immunoprotein deposits

1Pathogenesis. Diffuse or focal immunoprotein deposition is a relatively uncommon manifestation of several systemic diseases, including multiple myeloma, Waldenström's macroglobulinaemia, monoclonal gammopathy of unknown cause, certain lymphoproliferative disorders and leukaemia. Corneal involvement may be the earliest manifestation.

2Signs. Gradual development of bilateral bands of multiple punctate flake-like opacities, mostly at the level of the posterior stroma (Fig. 6.66E).

3Treatment should address the underlying systemic disease with cytotoxic chemotherapy or steroids. Severe corneal involvement may require penetrating keratoplasty.

Fabry disease (angiokeratoma corporis diffusum)

1Pathogenesis. Fabry disease is an X-linked lysosomal storage disorder caused by deficiency of alpha-galactosidase A.

2Systemic features include periodic burning pain in the extremities, purple cutaneous telangiectasis (angiokeratoma corporis diffusum; Fig. 6.67A), hypertrophic cardiomyopathy and renal disease.

3Keratopathy is characterized by faint but extensive vortex changes (Fig. 6.67B) similar to those seen with chloroquine.

4Other ocular manifestations include wedge-shaped cataract, conjunctival vascular tortuosity and aneurysm formation (Fig. 6.67C),

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retinal vascular tortuosity (especially venous), 3rd nerve palsy and nystagmus.

Fig. 6.67 Fabry disease. (A) Angiokeratoma corporis diffusum; (B) vortex keratopathy; (C) conjunctival tortuosity and aneurysms

Tyrosinaemia type 2 (Richner–Hanhart syndrome)

1Pathogenesis. Tyrosinaemia type 2 is a rare AR disease in which there is deficiency of hepatic cytosolic tyrosine aminotransferase with resultant increase in plasma tyrosine levels. Ocular involvement may occasionally be the presenting feature.

2Systemic features include painful, palmar and plantar hyperkeratotic lesions (Fig. 6.68), and variable central nervous system involvement which may cause mental retardation, nystagmus, tremor, ataxia and convulsions.

3Keratopathy is characterized by recalcitrant pseudodendritic keratitis with crystalline edges. In contrast to true herpetic ulcers the lesions are usually bilateral and inferotemporal, corneal sensation is normal, there is lack of response to antiviral therapy, typical terminal bulbs are absent and staining with fluorescein is limited.

Fig. 6.68 Plantar hyperkeratotic lesions in tyrosinaemia type 2

(Courtesy of D Taylor and C Hoyt, from Pediatric Ophthalmology and Strabismus, Elsevier 2005)

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Contact lenses

Therapeutic uses

The risks of fitting a contact lens to an already compromised eye are greater than with lens wear for cosmetic reasons. The balance between benefit and risk should therefore be carefully considered, and close monitoring is vital to ensure early diagnosis and treatment of complications. The choice of lens type is dictated by the nature of ocular pathology.

Optical

Optical indications are aimed at improving visual acuity when this cannot be achieved by spectacles in the following conditions:

1Irregular astigmatism associated with keratoconus can be corrected with rigid contact lenses after spectacles have failed and long before corneal grafting becomes necessary. Patients with astigmatism following corneal grafting may also benefit.

2Superficial corneal irregularities can be neutralized by rigid contact lenses providing a smoother and optically more regular surface. Visual acuity can thus be improved, if irregularities are not too severe.

3Anisometropia in which binocular vision cannot be achieved by spectacles due to aniseikonia and prismatic effects, as may occur following cataract surgery.

Promotion of epithelial healing

1Persistent epithelial defects often heal if the regenerating corneal epithelium is protected from constant rubbing action of the lids. This allows the development of hemidesmosomal attachments to the basement membrane.

2Recurrent corneal erosions, if associated with basement membrane dystrophy, may require long-term contact lens wear. In posttraumatic cases, lens wear can usually be discontinued after a few weeks. Lens wear also improves comfort.

Pain relief

1Bullous keratopathy can be managed with soft bandage lenses which relieve pain by protecting the exposed corneal nerve endings from the shearing forces of the lids during blinking. The lens may also flatten bullae into diffuse fine epithelial cysts.

2Filamentary keratitis associated with profuse lacrimation, as seen in patients with brainstem strokes and essential blepharospasm, can be treated with soft contact lenses.

3Other indications include Thygeson superficial punctate keratitis and protection of the corneal epithelium from aberrant lashes.

Preservation of corneal integrity

1A descemetocele can be temporarily capped with a tight-fitting, large-diameter soft or scleral lens to prevent perforation and allow natural healing to occur.

2Splinting and apposition of the edges of a small corneal wound can be achieved by means of a contact lens which supports the cornea during healing (see Fig. 4.6A). Slightly larger perforations may be sealed with glue followed by insertion of a bandage contact lens to both protect the glue and prevent irritation of the lids from the glue's irregular surface.

Miscellaneous indications

1Ptosis props to support the upper lids in patients with ocular myopathies.

2 Maintenance of the fornices to prevent symblepharon formation in cicatrizing conjunctivitis.

3Drug delivery can be enhanced by a hydrogel lens imbued with topical medication.

Complications

Mechanical and hypoxic keratitis

1Pathogenesis. Insufficient oxygen transmission through the lens. A tightly fitting contact lens which does not move with blinking will impair tear circulation under the lens. This is exacerbated by lid closure if the lens is worn during sleep. Hypoxia leads to anaerobic metabolism and lactic acidosis that inhibits the normal barrier and pump mechanisms of the cornea.

2Superficial punctate keratitis is the most common complication. The pattern may give a clue as to the aetiology. For example, staining at 3 and 9 o’clock is associated with incomplete blinking and drying in rigid lens wearers.

3 The tight lens syndrome is characterized by indentation and staining of the conjunctival epithelium in a ring around the cornea.

4Acute hypoxia is characterized by epithelial microcysts (Fig. 6.69A) and necrosis, and endothelial blebs. Very painful macroerosions may develop several hours after lenses are removed following a period of overwear.

5Chronic hypoxia may result in vascularization and lipid deposition (Fig. 6.69B); superficial peripheral neovascularization of <1.5 mm is common in myopic contact lens wearers and can be monitored.

6Treatment depends on the cause and may involve the following:

•Increasing oxygen permeability by refitting with a thinner lens, a gas permeable rigid lens or a silicone hydrogel soft lens.

•Modifying lens fit to increase movement.

•Reducing lens wearing time.

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