Good day everyone, Today we are going to discuss fully on disorders of the eye;
Learning outcomes
After studying this section, you should be able to:
- describe the pathological changes and effects of diseases of the eye.
Inflammatory conditions
Stye
Also known as hordeolum, this is an acute and painful bacterial infection of sebaceous or tarsal glands of the eyelid margin. The most common cause is Staphylococcus aureus. A ‘crop’ of styes may occur due to localised spread to adjacent glands. Infection of tarsal glands may block their ducts, leading to cyst formation (chalazion), which may damage the cornea.
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Blepharitis
This is chronic inflammation of the eyelid margins usually caused by bacterial infection or allergy, e.g. sta phylococcal infection or seborrhoea (excessive sebaceou gland secretion). If ulceration occurs, healing by fibrosi may distort the eyelid margins, preventing complete closure of the eye. This may lead to drying of the eye, conjunctivitis and possibly corneal ulceration.
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Conjunctivitis (eye disorder)
Inflammation of the conjunctiva may be caused by irritants, such as smoke, dust, wind, cold or dry air, microbes or antigens and may be acute or chronic. Corneal ulceration is a rare complication.
Infection. This is highly contagious and in adults is usually caused by strains of staphylococci, streptococci or haemophilus.
Neonatal conjunctivitis. Sexually transmitted disease in the mother, including gonorrhoea, chlamydia and genital herpes, can infect the newborn infant’s eyes as the baby passes through the birth canal.
Allergic conjunctivitis. This may be a complication of hay fever, or be caused by a wide variety of airborne antigens, eg, dust, pollen, fungus spores, animal dander, cosmetics, hair sprays, soaps. The condition sometimes becomes chronic
Trachoma
This chronic inflammatory condition is caused by Chlamy dia trachomatis and is a common cause of sight loss in developing countries. Deposition of fibrous tissue in the conjunctiva and cornea leads to eyelid deformity and corneal scarring as the eyelashes rub against the surface of the eye. The microbes are spread by poor hygiene, e.g. communal use of contaminated washing water, cross- infection between mother and child, or contaminated towels and clothing.
Corneal ulcer
This is local necrosis of corneal tissue, usually associated with corneal infection (keratitis) following trauma (e.g. abrasion), or infection spread from the conjunctiva or eyelids. Causative organisms include staphylococci, streptococci and herpes viruses. Acute pain, injection (redness of the cornea), photophobia and lacrimation interfere with sight during the acute phase. In severe cases extensive ulceration or perforation and healing by fibrosis can cause opacity of the cornea requiring corneal transplantation.
Glaucoma
This is a group of conditions in which intraocular pressure rises due to impaired drainage of aqueous fluid through the scleral venous sinus (canal of Schlemm) in the angle between the iris and cornea in the anterior chamber. Persistently raised intraocular pressure may damage the optic nerve by mechanical compression or compression of its blood supply causing ischaemia.
Damage to the optic nerve impairs vision; the extent of which varies from some visual impairment to complete loss of sight. In addition to the primary glaucomas below, it is occasionally congenital or secondary to other causes, e.g. anterior uveitis or a tumour.
Primary glaucomas
Primary open-angle glaucoma (POAG). There is a gradual painless rise in intraocular pressure with progressive loss of vision. Peripheral vision is lost first but may not be noticed until only central (tunnel) vision remains. As the condition progresses, atrophy of the
optic disc occurs leading to irreversible loss of vision. It is commonly bilateral and occurs mostly in people over 40 years of age. The cause is not known but there is a familial tendency.
Acute closed-angle glaucoma. This is most common in people over 40 years of age and usually affects one eye. During life the lens gradually increases in size, pushing the iris forward. In dim light when the pupil dilates, the lax iris bulges still further forward, and may come into contact with the cornea, blocking the scleral venous sinus (canal of Schlemm) suddenly raising the intraocular pressure. Sudden severe pain, photophobia, headache, nausea and blurred vision accompany an acute attack. It may resolve spontaneously if the iris responds to bright light, constricting the pupil and releasing the pressure on the scleral venous sinus. After repeated attacks spontaneous recovery may be incomplete and vision is progressively impaired.
Chronic closed-angle glaucoma. The intraocular pressure rises gradually without symptoms. Later, peripheral vision deteriorates followed by atrophy of the optic disc and loss of sight.
Strabismus (squint, cross-eye)
In normal binocular vision, the eyes are aligned so that each eye sees the same image, meaning that both eyes send the same image to the brain. In strabismus only one eye is directed at the observed object and the other diverges (is directed elsewhere). The result is that two different images are sent to the brain, one from each eye, instead of one. It is caused by one-sided extrinsic muscle weakness or impairment of the cranial nerve (III, IV or VI) supply to the extrinsic muscles. In most cases the image from the squinting eye is suppressed by the brain, otherwise is double vision (diplopia).
