The epithelium consists of 3 layers: a) The basal columnar cells in a single layer attached to the basement membrane by hemidesmosomes.. b) The wing cells with wing-like extensions in 2-3 rows c) The surface cells with microplicae & microvilli in 2 layers joined by bridges..
Bowman's layer does not regenerate when damaged..
The stroma makes up 90% of corneal thickness, which is composed of keratocyes(collagen-producing fibroblasts), collagen fibrils & ground substance(composed of mucoprotein & glycoprotein).
Descemet's membrane consissts of an interior banded zone which develops in utero & a posterior non-banded zone which is laid down through out during life from the corneal endothelium..
The endothelium is a single layer of hexagonal cells with no capacity of regeneration..
Evaluation of the corneal disease
In SLB, three techniques are used to examine the cornea:
a) Direct illumination
b) Scleral scatter is useful for detection of subtle opacities & mild corneal oedema.
c) Retroillumination is useful for detection of fine epithelial & endothelial changes, KPs & small blood vessels.
Punctate epithelial erosions(Epitheliopathy) are slightly depressed grey-white spots that stain brilliantly with fluorescein but poorly with rose bengal..
superior- Subtarsal FB, Vernal keratoconjunctivitis & Superior limbic keratoconjunctivitis of Theodore
Inferior- Trichiasis, Entropion, Lagophthalmos, Staphylococcal blepharitis & Drug toxicity
Don't confuse this with Punctate epithelial keratitis, with lesions consisting of granular opalescent epithelial cells that stain brilliantly with rose bengal but poorly with fluorescein, the hallmark of viral infections of the cornea..
The common causes of corneal oedema are acute angle colsure glaucoma, surgical trauma, Fuch's dystrophy, disciform keratitis & keratoconus..
The common causes of corneal filaments(composed of mucous threads & hypertrophied epithelial cells attached to abnormal receptor sites) are keratoconjunctivitis sicca, superior limbic keratoconjunctivitis of Theodore, neurotrophic keratopathy, herpes zoster keratitis, recurrent corneal erosion syndrome & prolonged patching of the eye..
corneal neovascularization may be superficial or deep..
Pannus is usually b/w the epithelium & Bowman's layer
Superior pannus- trachoma & contact lens
Inferior pannus- exposure keratopathy, rosacea & long standing irritation of cornea from trichiasis
Generalized pannus- cicatricial pemphigoid, Stevens-Johnson syndrome, Mooren's ulcer & following chemical burns..
Fascicle is localized superficial vascularization..
Deep vascularization is derived from the anterior ciliary vessels..
Ghost vessels(non-perfused vessels) are best detected by retroillumination..
Lipid, calcium & proteinaceous material is deposited in long-standing inflammation..
In Band-shaped keratopathy, calcium is deposited in the sub-epithelial space & Bowman's layer..
Posterior embryotoxon is an unusual prominence of Schwalbe's line, which is present in about 15% of normal eyes.
Hassall-Henle warts are peripheral excrescences in Descemet's membrane, frequently seen in elderly individuals. (similar centrally located lesions are lesions are referred to as cornea guttata) also found in Fuch's dystrophy..
Haab's stria, breaks in Descemet's membrane, are seen in congenital glaucoma.
Iron is deposited in
stroma- hyphaema & siderosis
epithelium- Fleischer's ring in keratoconus, Hudson-Stahli line in old age, Stocker's line in pterygium & Ferry's line in filtering bleb..
Silver is deposited in stroma & Descemet's in Argyrosis.
Gold is deposited in stroma in chrysiasis.
Copper is deposited in Descemet's membrane in Wilson's disease- Kayser-Fleischer ring
Melanin is deposited on endothelium in pigment dispersion syndrome- Krukenberg's spindle
N. gonorrhoea, N. meningitidis & C. diphtheriae are able to invade the intact corneal epithelium..
As a symptom of corneal ulcer, photophobia is a misnomer. In fact, it is blepharospasm d/t corneal irritation which is greatly increased on attempt to separate eyelids..
Characterisitics of different corneal ulcers on SLE:
Staph. aureus- yelllow-white, densely opaque surrounded by relatively clear cornea..
Enterobacteriacae(E.coli, Proteus, Klebsiella)- shallow ulcer with greyish white pleomorphic suppuration & diffuse stromal opalescence, ring corneal infiltrates (corneal rings) d/t endotoxins..
Hypopyon corneal ulcer: commonest organism is pneumococcus. Others are pseudomonas pyocyanea, staphylococci, streptococci, gonococci & Moraxella...
The characteristic hypopyon corneal ulcer caused by pneumococcus is also called ulcus serpens. It is greyish-white or yellowish-white disc near the centre of cornea..
Descematocele is the sign of impending perforation..
2% freshly prepared aqueous solution of fluorescein is used for biomicroscopic examination of corneal ulcer..
Therapeutic keratoplasty is the best treatment for perforated corneal ulcer..
Marginal catarrhal ulcer:
They are superficial ylcers situated near the limbus, proposed cause being hypersensitivity reaction to staphylococcal toxins, Moraxella & Haemophilus aegypticus..
Steroids & antibiotic drops are treatment..
Mycotic corneal ulcer
Aspergillus is the most common fungus causing corneal ulcer.. Also Fusarium & Candida..
The characteristics of typical fungal ulcer are:
a) Feathery finger like extensions
b) Sterile immune ring of Wesseley(yellow line of demarcation)
c) satellite lesions
d) thick & immobile big hypopyon
The sites for latent state are trigeminal ganglion for HSV-1 & spinal ganglion for HSV-2.
Dendritic ulcers & geographic or amoeboid ulcers are the characteristics of recurrent ocular herpes..
Ohter causes of dendritic ulcers are Herpes zoster keratitis, A healing corneal abrasion, Thygeson's superficial punctate keratitis & Soft contact lenses..
Disciform keratitis is d/t Arthus reaction to HSV antigen.. Steroids are used in this viral keratitis only.. It is distingiushed from other causes of stromal corneal oedema by reduced corneal sensation & KPs..
In Herpes Zoster Ophthalmicus, frontal nerve is the most frequently involved nerve.. Ocular complcation are seen in about 50% of cases of HZ..
Hutchinson's rule: ocular involvement is freequent if the side or tip of nose presents vesicles..
Acanthamoeba keratitis
It is associated with soft contact lens use..
The typical feature is very severe pain out of proportion to the degree of inflammation d/t deep linear stromal infiltrates localized along corneal nerves..
Radial keratoneuritis is a feature of this infection..
Stains used are KOH mount, Calcoflour white stain, Lactophenol cotton blue stain, Gram, Giemsa, Gomeri's silver stain..
A diffuse or nodular scleritis is also a frequent finding associated..
They are d/t disturbance in metabolic activitry of the epithelial cells..
a) Neuroparalytic keratitis
It occurs d/t paralysis of the sensory nerve supply of the cornea..
5th nerve paralysis --> disturbances in antidromic corneal refelx --> disturbed metabolic activity of the corneal epithelium --> accumulation of metabolites --> oedema & exfoliation of epithelial cells --> corneal ulcer
Desquamation of corneal epithelium is the characteristic feature of this ulcer..
No pain or lacrimation, complete loss of corneal sensations & dull corneal sheen are the characteristic clinical features..
b) Exposure keratitis (Keratitis lagophthalmos)
It is d/t eyes being insufficiently covered by the lids or loss of protective mechanism of blinking..
Rosacea keratitis:
It is present in about 10% cases of acne rosacea..
Ocular features are chronic blepharoconjunctivitis, keratitis(with yellowish white marginal infiltrates, heavily vascularized ulcers) & in severe cases, iritis..
Treatment is topical steroids & systemic tetracycline..
Peripheral corneal ulceration is seen in CVDs such as RA, SLE, PAN & Wegener's granulomatosis..
RA is the most common CVD to affect the peripheral cornea..
4 types of peripheral corneal changes are seen:
a) sclerosing keratitis: c/b gradual peripheral thickening & opacification of the stroma adjacent to the site of scleritis..
c) peripeheral corneal guttering ('contact lens cornea): c/b circumferential thinning of entire corneal periphery --> central part remainds of normal thickness --> appearance resembles a contact lens placed on the eye..
d) keratolysis: c/b acute & severe melting of the clear cornea..
The most common ocular comlication of SLE is punctate epithelial keratopathy, others being keratoconjunctivitis sicca, scleritis, retinal vasculitis, anterior ischemic optic neuropathy & peripheral keratits..
The 2 types of peripheral corneal change are Asymptomatic non-infiltrative marginal thinning & Marginal ulceration with infiltration & vascularization..
The ocular manifestations of PAN are scleritis, choroidal vasculitis, retinal vasculitis, anterior ischaemic optic neuropathy & peripheral keratitis..
The ocular manifestations of Wegener's granulomatosis are orbital involvement, retinal vasculitis, uveitis, scleritis, conjunctivitis & peripheral keratitis..
Mooren's ulcer(chronic serpigenous or rodent ulcer)
It starts at corneal margin..
Probable etiologies are idiopathic degenerative condition, vasculitis of limbal vessels causing ischemic necrosis, collagenase & proteoglyconase from conjunctiva, autoimmune disease..
It has 2 forms- Benign form- slowly progressing, u/l, in elderly & virulent form- rapidly progressive, scleral involvement, b/l, in younger patients..
The presenting symptom is usually blurred vision d/t irregular astigmatism..
Whitish overhanging edge at the advancing border is the characteristic..
Non-ulcerative keratitis:
In non-ulcerative superficial keratitis, the inflammatory reaction is confined to epithelium, Bowman's membrane & superficial stromal lamellae..
Acute diffuse superficial keratitis is usually d/t staphylococcal or gonococcal infection..
Chronic diffuse superficial keratitis is usually seen in rosacea & phlyctenulosis..
Idoxuridine is the commonest drug associated with SPK.
Photo-ophthalmia
It is the occurrence of multiple epithelial erosions d/t effect of UV rays especially from 290-311 mmicron..
It occurs after a latent period of 4-5 hours..
Crooker's glass is used for prophylaxis..
Superior limbic keratoconjunctivitis of Theodore
It is idiopathic inflammation of superior limbic, bulbar & tarsal conjunctiva, punctate keratitis of the superior part of cornea, oedema of corneo-scleral limbal conjunctiva & corneal filaments..
It has association with hyperthyroidism..
Prognosis is excellent with eventual resolution..
Thygeson's SPK
It is idiopathic chronic, recurrent, b/l SPK with remissions & exacerbations..
Proposed etiologies are viral, allergic or dyskeratotic..
The characteristic is a superficial keratitis consisting of stellate round or oval conglomerates of distict grannular, greyish-white intraepithelial dots some of which may be associated with a mild subepithelial haze..
The systemic disorders associated with corneal filaments are diabetes mellitus, psoriasis & ectodermal dysplasia...
The causes of peripheral ulceration & thinning are Dellen, Marginal keratitis(catarrhal ulcer), Rosacea keratitis, Phlyctenulosis, Terrien' marginal degeneration, Mooren's ulcer & systemic CVDs..
Dellen
They are saucer-likr thinnings of the peripheral cornea occurring in the areas of tear film instability..
It presents as a band-shaped opacity in interpalpebral zone with a clear interval b/w the ends of the band & the limbus, the surface being stippled d/t holes in calcium plaques in the areas of nerve canals of Bowman's membrane..
0.01 M solution of EDTA or 0.01 M solution of sodium versenate is used for chemical removal..
Phototherapeutic keratectomy & Keratoplasty are also useful..
Salzman's nodular degeneration:
There is deposition of raised hyaline plaques b/w epithelium & Bowman's membrane..
It occurs in recurrent attacks of phlyctenular keratitis, trachoma & rosacea keratitis..
It is usually u/l, more in women..
It presents as 1-10 bluish white nodules in circular fashion..
Well First good luck
second follow the cross linking steps carefully(are you using ribofalvin with UV?)
watch the anterior chamber for the discoloration to avoid overdosage
good luck
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