Corneal Ulcers

Alternative Names :
Bacterial keratitis; Fungal keratitis; Acanthamoeba keratitis; Herpes simplex keratitis
Definition :An erosion in the cornea, the transparent outer part of the front of the eye, is called a corneal ulcer. These ulcers can be very painful and, if they are left untreated, may cause scarring and lead to permanently impaired vision, blindness, or even loss of the eye. People who wear contact lenses are at increased of corneal ulcers.

It is associated with infection by a bacterium, virus, fungus, or parasite.

A corneal ulcer, or ulcerative keratitis, is an inflammatory or more seriously, infective condition of the cornea involving disruption of its epithelial layer with involvement of the corneal stroma. It is a common condition in humans particularly in the tropics and the agrarian societies. In developing countries, corneal ulcer is frequently the cause of great morbidity as well as economic loss to the person and family. Children afflicted by Vitamin A deficiency are at high risk for corneal ulcer and may become blind in both eyes, which may persist lifelong, causing tremendous & avoidable loss to the person and the society.

Corneal anatomy of the human
The cornea is a transparent structure that is part of the outer layer of the eye. It refracts light and protects the contents of the eye. The corneal thickness ranges from 450 to 610 micrometres and on an average 550 µm. thick in caucasian eyes. In Indian eyes, the average thickness is slightly less at 510 µm. The trigeminal nerve supplies the cornea via the long ciliary nerves. There are pain receptors in the outer layers and pressure receptors are deeper.

Transparency is achieved through a lack of blood vessels, pigmentation, and keratin, and through tight layered organization of the collagen fibers. The collagen fibers cross the full diameter of the cornea in a strictly parallel fashion and allow 99 percent of the light to pass through without scattering.

There are five layers in the human cornea, from outer to inner:

1.Epithelium


2.Bowman’s layer


3.Stroma

4.Descemet’s membrane

5.Endothelium

CLICK & SEE THE PICTURES

The outer layer is the epithelium, which is 25 to 40 µm micrometers and five to seven cell layers thick. The epithelium holds the tear film in place and also prevents water from invading the cornea and disrupting the collagen fibers. This prevents corneal edema, which gives it a cloudy appearance. It is also a barrier to infectious agents. The epithelium sticks to the basement membrane, which also separates the epithelium from the stroma. The corneal stroma comprises 90 percent of the thickness of the cornea. It contains the collagen fibers organized into lamellae. The lamellae are in sheets which separate easily. Posterior to the stroma is Descemet’s membrane, which is a basement membrane for the corneal endothelium. The endothelium is a single cell layer that separates the cornea from the aqueous humor.

Causes :
Corneal ulcers are most commonly caused by an infection with bacteria, viruses, fungi or amoebae. Other causes are abrasions (scratches) or foreign bodies, inadequate eyelid closure, severely dry eyes, severe allergic eye disease, and various inflammatory disorders and also corneal injury.

Corneal ulcers may be caused by an eye injury, an infection, or a combination of both. A relatively small injury such as a corneal abrasion, can develop into a corneal ulcer if the damaged area becomes infected. A more severe injury, such as that caused by a caustic chemical, can produce an ulcer in the absence of infection. However, an ulcer that becomes infected may enlarge and penetrate more deeply into the cornea. Only rarely do infections cause corneal ulcers without prior injury. The most common of these infections are herpes zoster, known as shingles, and herpes simplex infections.

Contact lens wear, especially soft contact lenses worn overnight, may cause a corneal ulcer. Herpes simplex keratitis is a serious viral infection. It may cause repeated attacks that are triggered by stress, exposure to sunlight, or any condition that impairs the immune system.

Fungal keratitis can occur after a corneal injury involving plant material, or in immunosuppressed people. Acanthamoeba keratitis occurs in contact lens users, especially those who attempt to make their own homemade cleaning solutions.

Your ads will be inserted here by

Easy Plugin for AdSense.

Please go to the plugin admin page to
Paste your ad code OR
Suppress this ad slot.

Risk factors are dry eyes, severe allergies, history of inflammatory disorders, contact lens wear, immunosuppression, trauma, and generalized infection.

Symptoms:
If you have a corneal ulcer, you may experience the following symptoms:

·Intense pain in the eye.
·Redness and discharge from the eye.
·Blurry vision.
·Increased sensitivity to light.
.Impaired vision
.White patch on the cornea
.Sensitivity to light (photophobia)
.Watery eyes
.Eye burning, itching and discharge

with an untreated infected ulcer, the infection may spread and permanently damage the vision in that eye and the eye itself. consult your doctor immediately if you develop a painful, red eye along with blurry vision.

Corneal ulcers are extremely painful due to nerve exposure, and can cause tearing, squinting, and vision loss of the eye. There may also be signs of anterior uveitis, such as miosis (small pupil), aqueous flare (protein in the aqueous humour), and redness of the eye. An axon reflex may be responsible for uveitis formation — stimulation of pain receptors in the cornea results in release inflammatory mediators such as prostaglandins, histamine, and acetylcholine.
Diagnosis:
Diagnosis is done by direct observation under magnified view of slit lamp revealing the ulcer on the cornea. The use of fluorescein stain, which is taken up by exposed corneal stroma and appears green, helps in defining the margins of the corneal ulcer, and can reveal additional details of the surrounding epithelium. Herpes simplex ulcers show a typical dendritic pattern of staining. Rose-Bengal dye is also used for supra-vital staining purposes, but it may be very irritating to the eyes. In descemetoceles, the Descemet’s membrane will bulge forward and after staining will appear as a dark circle with a green boundary, because it does not absorb the stain. Doing a corneal scraping and examining under the microscope with stains like Gram’s and KOH preparation may reveal the bacteria and fungi respectively. Microbiological culture tests may be necessary to isolate the causative organisms for some cases. Other tests that may be necessary include a Schirmer’s test for keratoconjunctivitis sicca and an analysis of facial nerve function for facial nerve paralysis.
Exams and Tests :

.Visual acuity
.Refraction test
.Tear test
.Slit-lamp examination
.Pupillary reflex response
.Keratometry (measurement of the cornea)
.Scraping the ulcer for analysis or culture
.Fluorescein stain of the cornea

Blood tests to check for inflammatory disorders may also be needed.
Treatment :
Treating corneal ulcers and infections depends on the cause. They should be treated as soon as possible to prevent further injury to the cornea. Patients usually start treatment with antibiotic that is effective against many bacteria. More specific antibiotic, antiviral, or antifungal eye drops are prescribed as soon as the cause of the ulcer has been identified.

Corticosteroid eye drops may be used to reduce inflammation in certain conditions. Severe ulcers may need to be treated with corneal transplantation.

Your doctor may place fluorescein eye-drops in the affected eye and examine it under blue light, using a slit lamp. He or she may also take a swab to identify the cause. If the eye reveals an ulcer, you may be given antibiotic or antiviral eye-drops to treat the infection. even severe ulcers usually clears up within 1-2 weeks of treatment, but they can leave scars that permanently affect vision.

Proper diagnosis is essential for optimal treatment. Bacterial corneal ulcer require intensive fortified antibiotic therapy to treat the infection. Fungal corneal ulcers require intensive application of topical anti-fungal agents. Viral corneal ulceration caused by herpes virus may antivirals like topical acyclovir oint instilled at least five times a day. Alongside, supportive therapy like pain medications are given, including topical cycloplegics like atropine or homatropine to dilate the pupil and thereby stop spasms of the ciliary muscle. Superficial ulcers may heal in less than a week. Deep ulcers and descemetoceles may require conjunctival grafts or conjunctival flaps, soft contact lenses, or corneal transplant. Proper nutrition, including protein intake and Vitamin C are usually advised. In cases of Keratomalacia, where the corneal ulceration is due to a deficiency of Vitamin A, supplementation of the Vitamin A by oral or intramuscular route is given. Drugs that are usually contraindicated in corneal ulcer are topical corticosteroids and anesthetics – these should not be used on any type of corneal ulcer because they prevent healing, may lead to superinfection with fungi and other bacteria and will often make the condition much worse.

Prognosis:
Untreated, a corneal ulcer or infection can permanently damage the cornea. Untreated corneal ulcers may also perforate the eye (cause holes), resulting in spread of the infection inside, increasing the risk of permanent visual problems.
Possible Complications :
.Corneal scarring
.Severe vision loss
.Loss of the eye

Melting ulcers:
Melting ulcers are a type of corneal ulcer involving progressive loss of stroma in a dissolving fashion. This is most commonly seen in Pseudomonas infection, but it can be caused by other types of bacteria or fungi. These infectious agents produce proteases and collagenases which break down the corneal stroma. Complete loss of the stroma can occur within 24 hours. Treatment includes antibiotics and collagenase inhibitors such as acetylcysteine. Surgery in the form of corneal transplantation (penetrating keratoplasty) is usually necessary to save the eye.

Prevention :
Prompt, early attention by an ophthalmologist for an eye infection may prevent the condition from worsening to the point of ulceration. Wash hands and pay rigorous attention to cleanliness while handling contact lenses, and avoid wearing contact lenses overnight.

Disclaimer: This information is not meant to be a substitute for professional medical advise or help. It is always best to consult with a Physician about serious health concerns. This information is in no way intended to diagnose or prescribe remedies.This is purely for educational purpose.

Resources:
http://www.nlm.nih.gov/medlineplus/ency/article/001032.htm
http://www.charak.com/DiseasePage.asp?thx=1&id=43
http://en.wikipedia.org/wiki/Corneal_ulcer

Leave a Reply

Your email address will not be published. Required fields are marked *