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The Eyelids and
Cornea |
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The eyelids are the site of several tumours
and cysts. The main tumours of the eyelid are derived from skin and skin
appendages, and are histologically similar to those arising elsewhere in the
skin. Cysts may develop from blockage and dilatation of skin appendages and
minor glands in the eyelid.
• Xanthelasmas, plaque-like, yellow lesions seen in the skin around the eyelids,
are collections of lipid-filled histiocytes in the dermis. They may be
associated with hyperlipidaemic states.
• Conjunctival melanocytic naevi are the most common tumour of the conjunctiva.
They are classified in a similar way to those seen in the skin
• Conjunctival papillomas are benign, red polypoid lesions that arise from the
palpebral or bulbar conjunctiva; some have a viral aetiology.
• Basal-cell carcinomas are common tumours that involve the skin of the eyelid
up to the lid margin. They are locally invasive and identical to those arising
in other sites.
• Squamous-cell carcinomas arise from the skin of the eyelid or, less commonly,
from the conjunctiva, where they may be preceded by intraepithelial carcinoma.
• Malignant melanomas can arise in the conjunctiva or from the skin of the
eyelid. Both intraepithelial and invasive lesions are seen, which are like those
described in the skin.
• Sebaceous gland carcinomas are uncommon but highly malignant tumours arising
from the meibomian glands.
Chalzion
Blockage and infection of a meibomian gland causes swelling and acute
inflammation of the affected gland. A chalazion is a firm swelling in the
eyelid, which bulges under the palpebral conjunctiva. Caused by rupture of a
meibomian gland, it histologically consists of a foreign-body histiocytic
chronic inflammatory response to lipid-rich material derived from the destroyed
gland
A chalazion represents a histiocytic inflammatory response to lipid material
released from damaged meibomian glands.
A chalazion (meibomian cyst) develops from blockage and inflammation of a
meibomian gland. At first, lesions are red and tender, but later form firm
nodules in the lid. Most resolve with local antibiotic ointment but some require
curettage.
Lesions which do not resolve should be regarded with suspicion, as uncommon
malignant tumours of the lid may present in this manner.
Proliferation of sub-epithelial support tissues gives rise to pingueculae, which
are small areas of yellow thickening of the bulbar conjunctiva. Caused by
cumulative exposure to damaging environmental stimuli such as sun, wind and
dust, they increase in incidence with age. Similar areas that encroach over the
limbus onto the cornea are termed pterygia.
Corneal diseases
The important diseases of the cornea result in structural changes leading to
opacification and impairment of visual acuity.
Minor trauma to the cornea can cause painful loss of surface epithelium, termed
corneal abrasion. This may be complicated by secondary infection, but in most
cases heals with regeneration.
Infective or inflammatory disorders of the cornea, which are collectively termed
keratitis, can result in scarring leading to opacification. Infection is most
commonly due to viruses (herpes simplex), Chlamydia trachomatis (causing
trachoma) and bacteria.
Corneal oedema is caused by loss of, or damage to, corneal endothelium. As the
cornea becomes opaque with accumulation of interstitial fluid from failure of
endothelial function, blurring of vision occurs. In severe cases, extremely
painful bullae form beneath corneal surface epithelium, with secondary
superficial scarring.
Corneal diseases commonly cause scarring and loss of visual acuity
The cornea is covered by a non-keratinized squamous epithelium and is composed
of a stroma with a lining endothelium. The endothelium is vital to normal
corneal function because it actively pumps fluid out of the corneal stroma. The
stroma is composed of highly organized parallel layers of collagen. Deposition
of abnormal collagen leads to an opaque scar termed a leukoma.
Arcus senilis,} seen as a yellow-white line at the corneal margin, is due to
accumulation of lipid in between the corneal stromal lamellae. It is normal with
ageing, but is associated with hyperlipidaemia when it arises in young patients.
Squamous metaplasia of the surface corneal epithelium may occur, causing corneal
opacification. This is usually secondary to lack of normal lubrication by tears,
e.g. in dry-eye syndromes or when diseases prevent eyelids covering the cornea.
It can also be caused by vitamin A deficiency. |
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