Basic Anatomy of the Eye and Corneal Abrasion - Essay Example

- Basic anatomy of the eye "The human eye is the organ which gives us the sense of sight, allowing us to learn more about the surrounding world morethan with any of the other four senses. The eye allows us to see and interpret the shapes, colors, and dimensions of objects in the world by processing the light they reflect or emit. The eye is able to see in bright light or in dim light, but it cannot see objects when light is absent"1. When we look at an object, light rays are reflected from the object to the cornea. The light rays are bent, refracted and focused by the cornea, lens, and vitreous. 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. - Introduction: Corneal abrasion 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 size of other symbols, such as Landolt Cs or Tumbling E. A visual acuity of 20/20 is frequently described as meaning that a person can see detail from 20 feet away the same as a person with normal eyesight would see from 20 feet. In, Europe where measurements are in meteres, the usuall measurement for VA is 6/6.4 If, in a patient with corneal abrasion, blepharospasm is detected and it is sufficiently intense to preclude an acuity measurment, one drop of topical anesthetic (eg, proparacaine 0.5% or tetracaine 0.5%) can be administered. After the anesthetic has been administered, the VA testing should proceed imidietly. Although there is little damage to the VA in patients with corneal abrasions, nevertheless, VA can be reduced from 6/6 to 6/9 depending on the seriuousness of the defect. In light injury there is always "restitutio ad integrum" when the treatment is completely finished.5 Another important diagnostic tool is the slit lamp. The slip lamp focuses the height and width of a beam of light for a precise stereoscopic view of the eyelids, conjunctivae, cornea, anterior chamber, iris, lens, and anterior vitreous. It is widely and very often used to detect corneal foreign bodies and abrasions as well as measuring the depth of and identifying inflammation or cells in the anterior chamber. It can also identify ciliary flush, inflammation localized to the limbal region over the ciliary body seen with uveitis; and scleral edema, seen as a bowing forward of the slit beam when it is focused beneath the conjunctiva and usually a sign of scleritis.6 The eye examination should continue with evertation of the eyelids and scrutinization of the fornices to eliminate the presence of foreign material. Fluorescent dye is usually applied to identify foreign bodies, in the situation where anesthetic was not previously applied. The Seidel test, which represents painting of the wound with dye and observing for aqueous leakage, is used to uncover full thickness injuries. The abrasion also should be documented for size, shape, location and depth with a detailed drawing or photograph with the purpose to aid in the follow-up visits and to confirm that epithelial healing is indeed taking place. Special attention should be directed to the endothelium of the cornea and the pupil of the iris, which might be the indicator of a more serious case. If the endothelium is clearly damaged, and the iris has any defects or the pupil is misshapen (peaked), a penetrating wound should be suspected. Intraocular foreign bodies should also be seriously considered and in order for them to be ruled out, plain film X-rays or computed axial tomography (CT scan) are the imaging procedures of choice. Metallic foreign bodies are especially dangerous, and if there is a suspicion of their intraocular presence, such techniques like magnetic resonance imaging (MRI) are contra-indicated. When particulate matter is involved, aggressive lavage with sterile saline and double lid eversion using a tool called Desmarre eyelid retractor is imperative. If there are superficial foreign bodies , they are gently removed using a "cotton-tipped applicator, spud, 27 1/2 gauge needle on a tuberculin syringe, loop or algar brush. "Extraction should always begin by focusing on the foreign body in the cornea. The instrument to be used for the extraction should be placed into the light beam in front of the patient's cornea. The tool can be brought into focus by carefully moving it back towards the spot of the cornea where the microscope was already focused. Removal is accomplished with a tangential probing action. This is designed to unsettle the object. Once the body is loosened, final removal is accomplished with cotton - tipped applicator".7 Other important factor that we must include in the examination and treatment of ocular injures, as well as corneal abrasions is the visual field. The visual field represents spatial array of visual sensations available to observation in introspectionist psychological experiments.8 Visual fields can be assessed by direct confrontation testing or more formal methods. In direct confrontation, the patient maintains a fixed gaze at the examiner's eye or nose. The examiner brings a small target (eg, a match or a finger) from the patient's visual periphery into each of the 4 visual quadrants and asks the patient to indicate when he first sees the object. Each eye is tested separately. Abnormalities in target detection should prompt formal testing with more precise instruments. More formal methods include use of a "tangent screen," Goldmann perimeter, or computerized automated perimetry (in which the visual field is constructed quickly by a computer based on the patient's response to flashing lights). Patients with corneal abrasions may have problems with their visual field, mostly localized in the region where the defect of the corneal epithelium exists. Nevertheless, most patients with corneal abrasions do not have problems with the visual field, but if complications that arise from corneal abrasions such as corneal ulcers that reach the Bowman membrane or other layer of the eye are detected, a visual field test is usually required.9 - Treatment There are several approaches to treating corneal abrasions. Such are bandage soft contact lenses, dissolvable collagen lenses, pressure patching, antibiotic ointments and drops, topical non-steroidal and steroidal anti-inflammatory preparations, cycloplegic drops and hypertonic solutions and ointments. If standard medical therapy is not successful, then surgical procedures are recommended. The treatment that is most used to deal with corneal abrasions is the treatment with topical antibiotics. The greatest side effect of such an injury as corneal abrasion represents the invasion of infectious organisms. . Amino glycoside drops or ointments which include gentamicin, neomycin, tobramycin, macrolide preparations such as erythromycin ointment, combination ophthalmic ointments like polymyxin B-bacitracin - neomycin and polymyxin B-trimethoprim and the fluorinated quinolones, which offer a broad spectrum of antibiosis, are all appropriate for providing prophylacsis.10 References: 1. St. Luke's Cataract & Laser Institute, http://www.stlukeseye.com/Anatomy.asp 2. WebMD Health; January 18, 2006; http://www.emedicine.com/oph/topic247.htm 3. Ted M. Montgomery, O.D.; http://www.tedmontgomery.com/the_eye/acuity.html 4. http://en.wikipedia.org/wiki/Visual_acuity 5. http://press.psprings.co.uk/emj/september/756_em35501.pdf 6. Merck & Co. Inc; http://www.merck.com/mmpe/sec09/ch098/ch098a.html 7. Andrew S. Gurwood, OD; December 1, 2000, OT; page 27 http://www.optometry.co.uk/files/8175563d35931c733a9165c8651b4bcf_gurwood20001201.pdf 8. http://en.wikipedia.org/wiki/Visual_field 9. Merck & Co. Inc; http://www.merck.com/mmpe/sec09/ch098/ch098a.html 10. Andrew S. Gurwood, OD; December 1, 2000, OT; page 28 http://www.optometry.co.uk/files/8175563d35931c733a9165c8651b4bcf_gurwood20001201.pdf Read More