Cornea/LASIK

Corneal Diseases, Corneal Surgery and LASIK

The cornea is the clear front lens of the eye bending light and protecting the sensitive internal tissues.  It requires adequate moisture from the tears and protection from the environment by lids that can blink completely.  The front surface is called the epithelium, the back surface is the endothelium and the stroma comprising 90% of the cornea is made from collagen.  There are numerous nerves that make the cornea sensitive to pain but there are normally no blood vessels so that it does not heal quickly.

The following is an abbreviated list of corneal disorders and their most frequent causes:

• Foreign body:  lashes that turn in, abnormal lid configurations, and paint, metal and other foreign materials

• Punctate keratitis:  the most common cause of these small dot-like defects in the corneal epithelium is dry eye syndrome.  Preservatives, most commonly, BAK in standard eye drops and wetting solutions can be very irritating to the cornea and are often overlooked.  Chemicals in the air, water, and rarely food, can cause this condition.  Always take artificial tears with you in airplanes and dry environments

• Chemical burns can be caused by acid or base chemicals, which are delivered from occupational accidents or intentionally as a weapon.  Biological elements such as mustard gas can cause the same corneal ulceration and scarring.

Infections

• Pink eye is the most frequent and most infectious cause of conjunctivitis with occasionally long lasting corneal inflammation.  It is often seasonal, bilateral and highly contagious requiring frequent hand washing and prescription eye drops.

• Herpes simplex lives in our tears and our saliva, which can be triggered by sunlight, decreased immunity,  injury, and even too much nuts and chocolate.

• Herpes zoster, better known as shingles, should involve multiple layers of the eye and requires rapid  treatment

• Trachoma is a type of conjunctivitis that can cause corneal scarring and is common in much of the developing world

• Soft contact lenses may harbor bacteria ,which is the most frequent cause of serious corneal ulcers in the United States

• Parasites, such as acanthamoeba, cause devastating corneal diseases.  River blindness is caused by a different organism in Western Africa. There are specific therapies for each of these diseases.

• Trauma:  people really do “watch out” and therefore get hit in the eye whether at work, at play, or accidentally trimming a bush, or playing sports.  Children need to be advised about eye protection as do workers, military personnel, and in fact, all of us.

Degenerations and Dystrophies

Corneal degenerations can occur in one or both eyes and are often superficial, not involving vision.  Corneal dystrophies on the other hand usually are bilateral, can occur at an early age and may be present in any three layers of the cornea.  For convenience I have clumped them together.

• They may consist of bilateral surface opacities called fingerprint or anterior membrane dystrophies

• There is a large variety of corneal stromal dystrophies some of which have specific genetic causes

• Fuch’s endothelial dystrophy is a common one and has two distinct classes, only one of which continues to progress requiring corneal transplantation

• Keratoconus:  is a condition with thinning of the cornea so that it takes a cone shape instead of a hemispherical contour.  90% of people will have a mild case of keratoconus and only small amounts of aberration of vision; these people may find that they cannot be corrected to 20/20 vision.  However 10% will progress such that contact lenses will be required; ultimately the cornea may thin so much that cornea transplantation is the only resort.

Many conditions cause permanent opacity and scarring.  Occasionally a rigid contact lens will significantly improve vision; otherwise surgery is required.

Complimentary Therapies For Corneal Disease

• Vitamin A is the treatment for night blindness and corneal thinning from vitamin A deficiency due to starvation or alcoholism

• Vitamin C strengthens the cornea after any injury including cornea or cataract surgery.  1000 – 2000 mg is important for maintaining corneal strength after injury

• Omega-3 Fatty Acids produce non-inflammatory components that maintain the tear film, which lubricates the cornea.  They remain the standard of therapy for contact lens wearers, dry eyes, and after cornea or lid surgery

• Lysine 500 mg,  Zinc 15 mg, Vitamin C 1000 mg, will help prevent recurrences of the herpes simplex virus

Traditional Corneal Therapies

• Antibiotic therapy remains the basic treatment for infections, dry eyes, burns, and foreign bodies.

• Keratocunus:   there is a new technique for cross-linking collagen using riboflavin and ultraviolet light.  This shrinks the cornea so the contact lenses can then be worn comfortably once again.

• Penetrating Corneal Transplantation is the standard for removing vision-impairing corneal scars.  This remains the standard for disease that involves all the layers of the cornea, herpes ulcers and scars with irregular thinning.  However there are new procedures being used such as the partial fitness cornea transplant (DALK) and DSEK.  DSEK consists of removing the back layers of the cornea and replacing them with a clear button through a very small incision.  This has become the procedure of choice for Fuch’s dystrophy and corneal disturbances that may arise as a complication of cataract surgery.

• Synthetic corneas are being used experimentally for anterior corneal diseases in some cases.  Lastly, there are three artificial corneal models, which can be employed when corneal tissue transplantation is not advisable.  The most popular model is the Boston KPro.

LASIK Surgery

LASIK surgery and its variations have become common methods of altering the shape of the cornea to treat near-sightedness, far-sightedness, and astigmatism of moderate amounts.  The surgery is performed under a topical anesthetic (eye drops).  A thin layer of corneal surface tissue is folded back and then light from an Excimer laser removes a thin layer of corneal tissue.  The flap is replaced, a contact lens is then placed over the eye and patient’s vision is almost perfect right away.

An older laser procedure was called PRK.  This has been replaced by EPI-LASIK surgery.  In this case the laser is applied without the need to create a corneal flap.  This is useful for smaller amounts of correction and for those who do not want any potential complication due to making a corneal flap.

There are customized procedures using modern WaveFront technology so that microscopic irregularities in the cornea are smoothed over much as a cruise missile flies over irregular terrain.  If considering LASIK you should have a screening examination and ask your ophthalmologist which would be the most appropriate procedure for you.

LASIK and its derivatives have become so standard that the military is encouraging its soldiers who will be entering potential conflict zones to have the procedure done.  This way they can return to action sooner and not risk any difficulties wearing spectacles or contact lenses.

Unlike the older Radial Keratotomy, people will not get fluctuations of vision at high altitude.  UV blocking sunglasses are highly recommended for all people but especially for anyone who has had corneal disease or corneal surgery of any kind.