The lens provides a sharp focus on the retina, where the resulting image is upside down. From here, the light rays are turned into electrical impulses and, through the optic nerve, are sent to the brain center for optical activity.
Corneal abrasion represents a defect of the epithelial layers of the cornea. It is specifically localized in that region and does not penetrate the inner layers of the eye, such as the Bowman membrane. In some cases though, bulbar conjunctiva is also involved. It is probably one of the most common eye defects and because of its nature, in perspective with other eye defects, it is probably the most neglected. The fact that corneal abrasions heal very rapidly contributes to the fact that they are frequently missed and are considered of no consequence.
Corneal abrasions occur in every situation where there is epithelial compromise of the cornea. Such situations include certain corneal or epithelial diseases like dry eyes, superficial corneal injury or ocular injuries such as those caused by foreign objects (dust, fingernails ect.) and the use of contact lenses.
Corneal abrasions are often viewed by the patients as minor, but extremely unpleasant injuries. Nevertheless, in certain cases, corneal abrasions can cause serious ocular and visual morbidity. When the patients are asked for their symptoms, they present the following: photophobia, watering, foreign body sensation, gritty feeling, pain and circumcorneal injection. In certain advanced cases, corneal edema, bacterial corneal ulcers, fungal, amebic, or viral corneal ulcers and uveitis can also be detected. Serious ocular morbidity caused by corneal abrasion can include recurrent corneal erosion (RCE), filamentary keratitis, corneal abscess and corneal perforation (ulcers).2
- Clinical examination
Clinical examination of patients with corneal abrasion begins with the appropriate recording of the time, place and activity surrounding the injury. This information should be recorded for medical as well as legal purposes. In order to administer the appropriate treatment, standard medical practice demands the measurement of visual acuity (AC). In the next section we will present the nature and basis of measurement of VA and how it correlates to corneal abrasion.
Visual acuity, in essence, represents the clarity of a persons' vision. It is often referred as the the "Snellen" acuity, named after the Dutch ophthalmologist Hermann Snellen, who created the letters used in the procedure to measure it. VA is a quantitative measure of the ability to identify black symbols on a white background at a standardized distance as the size of the symbols is varied. VA represents the most common clinical measurement of visual function.3
Visual acuity is typically measured monocularly rather than binocularly with the aid of an optotype chart for distant vision, an optotype chart for near vision, and an occluder to cover the eye not being tested. Occludion of the eye which is not beeing testet can be performed by placing a tissue behind the glasses, if the patient has one, or simply ask the patient to cover the eye with his or her hand. This latter method is usually avoided, because the patient might peak through his or her fingers, or press the eye, and therefore alter the measurments when that eye is evaluated.
Visual acuity is often measured according to the size of letters viewed on a Snellen chart or the