Inflammation of the conjunctiva can often be secondary to other more important primary pathology. The following are some of the possible underlying causes of this type of conjunctivitis:
• Lacrimal obstruction
• Corneal disease
• Lid deformities
• Systemic disease.
Lacrimal obstruction can cause recurrent unilateral purulent conjunctivitis and it is important to consider this possibility in recalcitrant cases because early resolution can be achieved simply by syringing the tear ducts. Corneal ulceration from a variety of causes is often associated with conjunctivitis and here the treatment is aimed primarily at the cornea. Occasionally, the presence of one of the two common acquired lid deformities, entropion and ectropion, can be the underlying cause. Sometimes the diagnosis may be missed, especially in the case of entropion, when the deformity is not present all the time. Other lid deformities can also have the same effect. A special type of degenerative change is seen in the conjunctiva, which is more marked in hot, dry, dusty climates. It appears that the combination of lid movement in blinking, dryness and dustiness of the atmosphere and perhaps some abnormal factor in the patient's tears or tear production can lead to the heaping up of subconjunctival yellow elastic tissue, which is often infiltrated with lymphocytes. The lesion is seen as a yellow plaque on the conjunctiva in the exposed area of the bulbar conjunctiva and usually on the nasal side. Such early degenerative changes are extremely common in all climates as a natural ageing phenomenon, but under suitable conditions the heaped-up tissue spreads into the cornea, drawing a triangular band of conjunctiva with it. The eye becomes irritable because of associated conjunctivitis and in worst cases the degenerative plaque extends across the cornea and affects the vision. The early stage of the condition, which is common and limited to a small area of the conjunctiva, is termed a pingueculum and the more advanced lesion spreading onto the cornea is known as a pterygium (Figure 6.6). Pterygium is more common in Africa, India, Australia, China and the Middle East than in Europe. It is rarely seen in white races living in temperate climates. Treatment is by surgical excision if the cornea is significantly affected with progression towards the visual axis; antibiotic drops might be required if the conjunctiva is infected. Non-infective inflammation of pterygium is treated with topical steroids.
Finally, when considering secondary causes of conjunctivitis, one must be aware that redness and congestion of the conjunctiva with secondary infection can be an indicator of systemic disease. Examples of this are the red eye of renal failure and gout, and also polycythemia rubra. The association of conjunctivitis, arthritis and nonspecific urethritis makes up the triad of Reiter's syndrome. Some diseases cause abnormality of the tears and these have already been discussed with dry eye syndromes, the most common being rheumatoid arthritis. However, there are other rarer diseases that upset the quality or production of tears, such as sarcoidosis, pemphigus and Stevens-Johnson syndrome. Thyrotoxicosis is a more common
systemic disease, which is associated with conjunctivitis, but the other eye signs, such as lid retraction, conjunctival oedema and proptosis, are usually more evident. A rather persistent type of conjunctivitis is seen in patients with acne rosacea. Here, the diagnosis is usually, but not always, made evident by the appearance of the skin of the nose, cheeks and forehead, but the corneal lesions of rosacea are also quite characteristic (Figure 6.7). The cornea becomes invaded from the periphery by wedge-shaped tongues of blood vessels associated with recurrent corneal ulceration. Severe rosacea kerato-conjunctivitis is seen less commonly now, perhaps because it responds well to treatment with the combination of systemic doxycycline, lubricants for associated dry eye and the judicious use of weak topical steroids. Usually, it is also necessary to instruct the patient to clean the lids and perform "lid hygiene", as such patients are often also affected by blepharitis.
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