Diseases of the Cornea

Diseases of the Cornea

KERATITIS

Corneal ulcer

Bacterial corneal ulcer

• Commonest causative organism is pneumococcus, others are staphylococcus, pseudomonas and gonococcus.
• Pathogens which can invade the normal intact corneal epithelium are: neisseria gonorrhoea, neisseria meningitis, corynebacterium diphtheriae, listeria and haemophillus.
• Commonest organism/etiological agent responsible for different corneal ulcers are:

– Hypopyon comeal ulcer : Pneumococcus
– Mycotic comeal ulcer : Aspergillus fumigatus
– Marginal corneal ulcer(Catarrhal corneal ulcer) : Koch-Weeks bacillus (Haemophilus aegyptius)
– Typical dendritic comeal ulcer : Herpes simplex virus
– Very rapidly progressive sloughing corneal ulcer : Pseudomonas
– Ulcus serpens : Pneumococcus
– Fascicular ulcer : Phlyctenulosis
– Atheromatous ulcer : Degenerative change in old leucoma

Hypopyon corneal ulcer

• Staphylococci, streptococci, gonococci and moraxella may produce hypopyon; but by far the most dangerous are pseudomonas pyocyanea and the pneumococcus.
• Characteristic hypopyon ulcer caused by pneumococcus is called ulcus serpens which has a tendency to creep over the comea.
• Commonest cause of failure in treatment is secondary glaucoma.

Diseases of the CorneaMycotic corneal ulcer

• Common causative fungi are aspergillus (most common), Candida and fusarium.
• Common mode of infection is injury by vegetative material e.g., thorn, branch of a tree etc.
• Injudicious use of antibiotic and steroids increase the incidence of fungal infections.
• Typical fungal ulcer is dry looking, greyish white with finger like extensions into the surrounding stroma under the intact epithelium. A sterile immune ring and multiple satellite lesions are characteristic. Usually a big hypopyon is present even if the ulcer is very small. Corneal vascularization is conspicuously absent.

Herpes simplex corneal ulcer

• Herpes simplex virus (HSV) is a DNA virus. Ocular infection is more common with HSV-1 and rare with HSV type II.
• Primary ocular herpes occurs in non-immune children. Lesions are vesicles of skin of the lids, acute follicular conjunctivitis. Fine or coarse punctate epithelial keratitis occurs in 50 percent cases.
• Recurrent ocular herpes is caused by periodic reactivation of virus (which lies dormant in the trigeminal ganglion) by following precipitating stimuli: fever such as malaria or flu, general ill health, exposure to ultraviolet rays (sunlight), immunocompromised patients e.g., in AIDS, and excessive use of topical or systemic steroids
• Lesions of recurrent ocular herpes are:
– Punctate epithelial keratitis is initial lesion
– Dendritic ulcer is pathognomonic lesion
– Geographical (amoeboid) ulcer is formed when branches of dendritic ulcer enlarge and coalesce
– Disciform keratitis is a delayed hypersensitivity reaction to HSV antigen, characterised by a focal disc-shaped patch of stromal oedema without necrosis
– Metaherpetic ulcer is a sterile trophic ulceration which occurs due to healing defect at the site of previous herpetic ulcer
• Antiviral drugs effective against HSV are:
– 5-iodo-2 deoxy uridine (IDU) – 1 percent drops 1 hourly during day and 2 hourly at night
– Trifluorothymidine (TFT) – 1 percent drops 2 hourly
– Acyclovir – 3 percent ointment 5 times a day. It is the only drug effective in stromal keratitis.

Herpes zoster ophthalmicus

• Varicella-zoster virus is a neurotropic DNA virus which produces acidophilic intranuclear inclusion bodies.
• Herpes zoster virus is the most common virus causing the corneal ulcer.
• Lesions are strictly limited to one side of the midline of the head.
• Frontal nerve is more frequently affected than the lacrimal and nasociliary.
• Cutaneous lesions in the area of distribution of the involved nerve appear after 3-4 days of onset of disease.
• Ocular lesions occur in 50 percent cases.
• Hutchinson’s rule which implies that ocular involvement is frequent if the side or tip of the nose presents vesicles is useful but not infallible.
• Superficial punctate epithelial keratitis is the most common feature
• Nummular keratitis may occur as multiple tiny granular deposits surrounded by a halo of stromal haze
• Iridocyclitis occurs in 50 percent cases of Zoster keratitis
• Neuroparalytic keratitis occurs as a complication of Gasserian ganglion destruction
• Episcleritis and scleritis occur in 50 percent cases
• Palsy of 3rd, 6th and 7th cranial nerve may occur in severe infection
• Optic neuritis occurs in 1 percent cases
• Post-herpetic neuralgia may persist for months or years
• Oral acyclovir 800 mg 5 times a day x 10 days is effective .
• Systemic steroids are indicated in cranial nerve palsies and optic neuritis.

Acanthamoeba keratitis

• Acanthamoeba is found in soil, freshwater, well water, sea water, sewage and air.
• Keratitis is more common in contact lens wearers using home-made saline.
• Severe pain, out of proportion to the degree of inflammation is typical feature.
• Typical lesions are central or paracentral ring shaped stromal infiltrates with overlying epithelial defects with associated radial keratoneuritis.
• KOH and lactophenol cotton blue stained film may demonstrate cysts.
• Culture medium: non-nutrient agar with E.coli.
• Treatment consists of 0.1 percent propamidine isethionate (Brolene) drops and neomycin eye drops. Keratoplasty is required in resistant cases.

Neuroparalytic keratitis

• Occurs due to paralysis of sensory nerve supply of the cornea. Most typically as a result of 5th nerve paralysis and as a result of radical treatment of trigeminal neuralgia.

• Typical features are absence of pain, and lacrimation and complete loss of corneal sensations.

Exposure keratitis

• It occurs in conditions producing lagophthalmos such as extreme proptosis, facial nerve palsy, coma, overcorrection of ptosis etc.

• Initial dessication due to exposure occurs in the interpalpebral area leading to fine punctate epithelial keratitis followed by frank ulceration and vascularization:

Rosacea keratitis

• Rosacea, a disease of sebaceous glands of the skin, occurs in elderly women as facial eruptions.
• Ocular lesions include blepharoconjunctivitis, keratitis, comeal vascularization and iritis in severe cases.
• Treatment consists of topical steroids and systemic tetracycline.

Mooren’s ulcer (Chronic serpiginous or Rodent ulcer)

• Exact etiology is not known, probably it is an autoimmune disease.
• Typical ulcer is a shallow furrow with whitish over-hanging edge, vascularized base accompanied by severe pain.
• Immunosuppression with cyclosporin is useful.

Non-healing corneal ulcer

Local causes

• Raised intraocular pressure
• Misdirected cilia
• Large concretions
• Chronic dacryocystitis
• Impacted foreign body
• Lagophthalmos
• Inadequate therapy
• Wrong therapy

General causes

• Diabetes mellitus
• Severe anaemia
• Malnutrition
• Vitamin-A deficiency
• Immuno-compromised patients

Superficial punctate keratitis

Characterised by multiple spotty lesions in superficial layers of cornea associated with acute pain, photophobia and lacrimatoin.

Etiology ofSPK includes: viral infections, chlamydial infections, toxic due to staphylococcal toxins, exposure keratitis and neuroparalytic keratitis, allergic lesions, keratoconjunctivitis sicca, Thygeson’s SPK, and photophthalmia.

Treatment. Topical weak steroids have suppressive effect.

Photophthalmia

• Superficial punctate keratitis which occurs due to effect of ultraviolet rays (especially 290-31 lnm) associated with exposure to:

– Naked arc light, as in industrial welding and cinema operators
– Bright light of short circuiting
– Reflected ultraviolet rays from snow surface (snow blindness)
• Typically, it is characterised by severe burning pain, lacrimation, marked photophobia and blepharospasm occurring 4-5 hours after exposure to the ultraviolet rays.

Superior limbic keratoconjunctivitis

• Occurs with greater frequency in female patients with hyperthyroidism.

• Conjunctiva in the region of superior limbus and adjoining parts of bulbar and tarsal conjunctiva are congested. Cornea shows superficial punctate keratitis which stains both with fluorescein and rose bengal.

Thygeson’s superficial punctate keratitis

• It is a chronic, recurrent, bilateral, superficial keratitis characterised by coarse punctate epithelial lesions .
• Each lesion is a cluster of heterogenous granular grey dots.

Filamentary keratitis

• Superficial punctate keratitis associated with formation of epithelial filaments which are freely movable over the cornea, firmly attached at the base and stain both with fluorescein and rose bengal.

• Common causes are: Keratoconjunctivitis sicca, superior limbic keratoconjunctivitis, prolonged patching, following epithelial erosions as in herpes simplex, Thygeson’s keratitis, recurrent corneal erosion syndrome and trachoma.

Interstitial keratitis

An inflammation of the comeal stroma without primary involvement of the epithelium or endothelium.

Common causes are syphilis, tuberculosis, Cogan’s syndrome, trypanosomiasis, malaria, leprosy, and sarcoidosis.

Syphilitic (leutic) interstitial keratitis

• Ninety percent cases are associated with congenital syphilis.
• In congenital syphilis, manifestations are usually bilateral and develop between 5 and 15 years of age.
• In acquired syphilis, manifestations are usually unilateral.
• Interstitial keratitis may occur alone or as a part of Hutchinson’s triad which also includes: Hutchinson’s teeth and vestibular deafness.
• Disease is a result of antigen-antibody reaction.
• Ground glass appearance of cornea and ‘Salmon patches’ are typical features.
• After healing, corneal opacities and ghost vessels are left behind.

Tubercular interstitial keratitis

• It is more frequently unilateral and sectorial.

Cogan’s syndrome

It comprises interstitial keratitis of unknown etiology, acute tinnitus, vertigo and deafness typically occurring in middle-aged adults. It is often bilateral.

CORNEAL DEGENERATIONS

Arcus senilis

• Annular lipid infiltration of corneal periphery seen in elderly people. The ring of opacity is separated from the limbus by a clear zone (lucid interval of Vogt).

• Most commonly encountered peripheral corneal opacity.

Arcus juvenilis

• Condition similar to arcus senilis occurring in young persons (below 40 years of age).

Calcific degeneration (Band keratopathy)

• Characterised by deposition of calcium salts in Bowman’s membrane and most superficial part of stroma.
• It is associated with chronic uveitis in adults, children with Still’s disease, phthisis bulbi, chronic glaucoma, chronic keratitis, and ocular trauma.
• Presents as band-shaped opacity in the interpalpebral area.
• Surface of the opaque band is stippled due to holes in the calcium plaques in the area of nerve canals of Bowman’s membrane.
• Treatment consists of chemical removal of calcium salts with 0.01 molar solution of EDTA. Phototherapeutic keratectomy (PTK) with excimer laser is very effective in clearing the cornea.

Salzmann’s nodular degeneration

• Occurs in eyes with recurrent attacks of phlyctenular keratitis, rosacea keratitis or trachoma.
• Cornea shows one to ten bluish white nodules arranged in a circular fashion, due to deposition of hyaline plaques between epithelium and Bowman’s membrane.

Spheroidal degeneration (climatic droplet keratopathy)

• Occurs in men who work outdoors, especially in hostile climates. Its occurrence has been related to exposure to ultraviolet rays and/or ageing.

• Cornea shows amber-coloured spheroidal granules accumulated at the level of Bowman’s membrane and anterior stroma in the interpalpebral area.

CORNEAL DYSTROPHIES

Classification

1. Anterior dystrophies (superficial dystrophies), primarily affecting epithelium and Bowman’s layer:
• Epithelial basement membrane dystrophy
• Reis Buckler’s dystrophy
• Meesman’s dystrophy
• Recurrent comeal erosion syndrome
• Stocker-Halt dystrophy

2. Stromal dystrophies
• Granular (Groenouw’s type I) dystrophy
• Lattice dystrophy
• Macular (Groenouw’s type II) dystrophy
• Crystalline (Schnyder’s dystrophy).

3. Posterior dystrophies, affecting primarily the comeal endothelium and Descemet’s membrane:
• Cornea guttata
• Fuch’s epithelial endothelial dystrophy (late hereditary endothelial dystrophy)
• Posterior polymorphous dystrophy of Schlichting
• Congenital hereditary endothelial dystrophy (CHED).

4. Ectatic dystrophies
• Keratoconus (anterior)
• Posterior keratoconus
• Keratoglobus

Salient points

• Cogan’s microcystic dystrophy is the most common of all corneal dystrophies seen in working-age adults.
• Rcis-Buckler’s dystrophy primarily involves Bowman’s membrane.
• In macular dystrophy acid mucopolysaccharides are deposited in the cornea.
• Cornea guttata may occur independently or as a part of early stage of Fuch’s dystrophy.
• Primary open-angle glaucoma is a common association of Fuch’s dystrophy.

Keratoconus

Non-inflammatory ectatic condition of cornea giving it a conical shape with resultant irregular myopic astigmatism. It is usually bilateral (85%). It is more common in girls after puberty. Its important signs are:

• Irregularity of circles on placido disc examination
• Fleischer’s ring seen at the base of cone is perhaps due to hemosiderin deposition in epithelium
• An annular dark shadow is seen on distant direct ophthalmoscopy
• Munson’s sign i.e., localised bulging of lower lid when patient looks down, is positive in late stages.

Keratoglobus

• It is a familial and hereditary (autosomal recessive) bilateral congenital disorder characterised by thinning and hemispherical protrusion of the entire cornea.

• It should be differentiated from buphthalmos where increased corneal size is associated with raised intraocular pressure, angle anomaly and cupping of the disc.

MISCELLANEOUS KERATOPATHIES

Vortex keratopathy

• Also called cornea verticillata
• Characterized by bilateral, symmetrical, grayish or golden corneal epithelial deposits.
• Occurs in patients taking chloroquine, amiod- arone, amodiaquine, meperidine, indomethacin, chlorpromazine and tamoxifen. Also seen in patients with Fabry’s disease (glycolipidosis).

Crystalline keratopathy

Chrysiasis refers to deposition of gold in corneal stroma following prolonged administration in patients with rheumatoid arthritis.

Cystinosis refers to widespread deposition of cysteine crystals in conjunctiva, cornea, iris, lens and retina. A hereditary disorder (autosomal recessive) leading to defect in its lysosomal transport. Monoclonal gammopathy refer to deposition of crystal in comeal epithelium and stroma seen in patients with:
• Multiple myeloma,
• Waldenstrom’s macroglobulinemia, and
• Lymphoma.

SYMPTOMATIC CONDITIONS OF CORNEA

Vascularization of cornea

Superficial comeal vascularization

• The vessels are arranged in an arborizing pattern, present below the epithelial layer and their continuity can be traced with the conjunctival vessels.

• Causes: Trachoma, phlyctenular keratoconjunctivitis, superficial comeal ulcers and rosacea keratitis.

Deep corneal vascularization

• The vessels are derived from the anterior ciliary arteries and lie in the comeal stroma. These vessels are usually straight, not anastomosing and their continuity cannot be traced beyond the limbus.

• Causes: Interstitial keratitis, disciform keratitis, deep corneal ulcer, chemical burns, sclerosing keratitis and comeal graft.

Corneal Opacity

• Nebular comeal opacity is a faint opacity resulting from superficial scars involving Bowman’s layer and superficial stroma. A nebular opacity covering the pupil produces more discomfort and blurring of vision (owing to irregular astigmatism) than a leucoma which completely cuts off the light rays.

• Adherent leucoma is a leucomatous opacity in which iris tissue is incarcerated. It results following corneal perforation.

• Kerectasia refers to bulged-out thin corneal scar.

• Anterior staphyloma is bulging out of ectatic opaque cornea (pseudocomea) with iris tissue plastered behind it. Pseudocomea is a scar formed from organized exudates and fibrous tissue covered with epithelium. It results following total sloughing of the cornea.

CONGENITAL ANOMALIES

Megalocornea

• The horizontal diameter of cornea at birth is 10 mm. The adult size of 11.7 is attained by the age of 2 years.
• Megalocornea is labelled when the horizontal diameter of cornea is of adult size at birth or 13 mm or greater after the age of 2 years. Cornea is clear with normal thickness and normal vision. Megalocornea is often associated with Marfan’s syndrome.

Microcornea

• In microcornea, the horizontal diameter is less than 10 mm since birth.

• The condition may occur as an isolated anomaly (rarely) or in association with nanophthalmos (normal small eyeball) or microphthalmos (abnormal small eyeball). Eye is usually hypermetropic.

Congenital cloudy cornea

The conditions responsible can be denoted by the eponym STUMPED as follows:
• Sclerocomea
• Tears in Descemet’s membrane
• Ulcer
• Metabolic conditions
• Posterior corneal defect
• Endothelial dystrophy
• Dermoid

SOME SALIENT POINTS

• Rheumatoid arthritis is the most common collagen vascular disorder to affect the peripheral cornea.
• The most common ocular complication of SLE is punctate epithelial keratopathy.
• Pneumococcus is the commonest organism responsible for corneal ulceration.
• Macular dystrophy is the least common corneal dystrophy in clinical practice.
• Pseudocornea has only two layers—the connective tissue lined with epithelium.
• Poor antigenicity of corneal stroma is due to avascularity, sparse cell count and separation of cells by ground substance.
• Lamellar keratoplasly is the treatment of choice for Mooren’s ulcer.
• Therapeutic keratoplasty is the treatment of choice for impending corneal perforation.
• In Keratoconus, the cone is situated just below the centre of the cornea.
• Pachymetry refers to measurement of corneal thickness.
• Specular microscopy is useful for study of endothelial cells.
• Keratometry is measurement of corneal curvature.
• Corneal topography is the study of corneal shape.