7.1 Background

Corneal and external eye disease includes a diverse range of conditions affecting both the ocular surface (lids, conjunctiva and associated organs such as the lacrimal gland) together with the layers of the cornea deep to its epithelial surface. The biological role of these tissues is to ensure that the cornea, the "window of the eye" remains clear. A range of infective, inflammatory, degenerative and dystrophic disorders may interfere with the normal function of these tissues resulting in a spectrum of disease. This spectrum extends from minor short term conditions causing irritation, discharge, foreign body sensation, dryness, itching and discomfort in bright light (photophobia), through diseases resulting in identical but chronic symptoms lasting many years, and resulting in demoralisation and fear of blindness, to the most severe problems of corneal perforation and corneal blindness. Unlike many other eye diseases pain and discomfort, as well as blindness, are common.

Classification of disease: Ocular surface disease is a new term that has been coined in the last 10 years to describe the diverse conditions that affect the surface of the eye. Ocular surface disease can be defined as "a group of disorders, of diverse pathogenesis, in which disease results from failure of the mechanisms responsible for maintaining a healthy ocular surface". The group of disorders causing ocular surface disease not only comprise the bulk of referrals to the primary eye care services, due to minor conditions that result in discomfort and absence from work, but also result in ocular surface failure in which blindness results from failure to maintain a normal corneal epithelium leading to ulceration, infection, scarring and loss of sight.

Examples of minor conditions include: lid margin inflammation, dry eye disease, hay fever conjunctivitis, and bacterial or viral infections of the conjunctiva. Sight threatening ocular surface disease includes Sjogrens syndrome, atopic eye diseases other than hay fever conjunctivitis (particularly common in Asian British), ocular cicatricial pemphigoid and Stevens-Johnson syndrome. Although these disorders are uncommon individually they lead to blindness through the common pathway of ocular surface failure requiring common treatment strategies.

Corneal and external diseases also comprise a further group of conditions in which the corneal tissues deep to the epithelium are the site of primary involvement causing loss of sight. These include inherited and degenerative diseases of the cornea, which result in corneal distortion (keratoconus) or corneal opacity (dystrophies such as macular and granular dystrophy), leading to blindness

Lastly, corneal & external eye disease is a subspecialty in ophthalmology notable for the impact of socio-cultural and lifestyle factors on health. The widespread use of contact lenses for correction of refractive errors (in most cases, short- or long-sightedness) in the past two decades has resulted in striking increases in incidence of both bacterial and protozoal corneal infections whilst freeing millions of individuals from dependence on spectacles. More recently surgical or laser 'treatment' (refractive surgery) of the normal cornea in individuals with refractive errors has provided an alternative to contact lenses. These refractive surgery techniques may lead to new and sight-threatening abnormalities of corneal structure and function and complicate management of individuals later developing cataract or who become potential corneal donors.

   7.2 Research Potential