Refractive error occurs when light does not focus perfectly onto the retina and a blurred image is formed.
The three types of refractive error are myopia, needing minus lens, hyperopia, needing plus lens and astigmatism requiring plus or minus power in any one meridian..
Refractive surgery is an eye care specialty for reducing without using glasses or contact lenses. The term, “refractive surgery” refers to several procedures, including Radial keratotomy ( RK ),
Photorefractive keraTIOtomy ( PRK ), Laser assisted in situ keratomileusis ( LASIK ), Laser assisted sub epithelial keratomileusis (LASEK ), and several emerging TIOhniques.
Today, LASIK is the most widely performed of all refractive surgery procedures.
Most patients who seek refractive surgery expect to see well without dependence on spectacles or contact lenses. Many patients do not need glasses or contacts after the procedure. But patients must understand that although refractive surgery is relatively precise, the outcome of surgery cannot be predicted exactly, because individuals vary in their wound-healing characteristic. . I,e, the effect of the surgery is different from patient to patient, Because of this variablility, some patients still need some form of correction to get the very best vision. Those patients with very high power of glasses are more likely to require glasses after the surgery. Furthermore, patients should understand that they will finally necessitate reading glasses when they reach 40 years or more.
So before deciding to undergo surgery, patients should understand the benefits and limitations of the procedure. They should also know about the possible complications during or after the surgery. To be more specific, there may be a rare possibility of losing the eye sight , should some major complication occur. The surgeon will be discussing about all these with the patient. The patient must have a stable power of his glasses for the last one year or so. He/she must be at least 18 years old. In addition the patient will be undergoing a list of investigations to find out whether he or she is really a good candidate for the surgery. Patient will not be considered fit for the surgery if he/she had other eye problems like cataract, glaucoma, corneal opacities, keratoconus , dry eyes, retinal or optic nerve problems. His general health should also be good.
In Tilganga, the type of refractive surgeries done are LASIK and PRK, which are the most popular TIOhniques all over the world as well. In both the procedures, laser light is used to cut the tissue. Both the procedures are carried out using eye drops as anesthesia.
PRK Photorefractive KeraTIOtomy (PRK) . PRK is useful for treating low to moderate levels of myopia or hyperopia with and without astigmatism. PRK involves first removing the outer layer of the cornea, called the epithelium. A laser beam is then applied to the cornea . The laser will burn out some portion of of the cornea ,hence decreasing its thickness .This would result in change of the central curvature of the cornea and the given refractive error will be corrected. A soft contact lens is placed over the eye as a bandage to help the outer layer to grow back. It usually takes 3-5 days for the outer layer to re-grow over the cornea. During that period, the patient may experience marked pain . Unlike with LASIK, it takes longer to achieve the final result in PRK since a greater amount of tissue healing takes place., This procedure is technically easier for the surgeon and technique related complications are less.
Laser in-situ keratomileusis (LASIK). In LASIK, a flap is created in the surface of cornea with the help of a special instrument called microkeratome. This hinged flap is reflected to one side. Then laser beam is applied to the exposed cornea like in PRK. This would result in thinning of the cornea and change in the curvature of the central cornea. The flap is repositioned and gets adhered in its original position. Visual recovery is rapid . Unlike in PRK, there is no pain in this procedure.
LASIK and PRK can treat both myopia and hyperopia with or without astigmatism.
After surgery, patients need to put topical antibiotics and steroids for several weeks and be followed, should any post operative complications occur.
PENETRATING KERATOPLASTY/ CORNEAL TRANSPLANT
In developing countries, corneal pathology is the second most common cause of blindness after cataract. Penetrating keratoplasty refers to the full-thickness replacement of diseased corneal tissue with a healthy donor from cadaver. Because of the advances in microsurgical techniques, corneal transplant has become the most frequently performed and successful transplant of human tissue Blindness due to corneal abnormalilty has considerably decreased in the developed countries in the last second half of the century.
Corneal transplant is indicated in the following conditions.
- Treatment of corneal thinning or perforation
- Treatment of non healing corneal ulcer ( caused by bacteria, fungus, virus etc )
- To improve vision in cases with corneal scarring.
- Correction of abnormal corneal contour
- Relief of pain secondary to corneal swelling
So corneal transplant is done only for the diseases of cornea. If the blindness is due to any other causes like cataract, retinal problem or optic nerve , or if the corneal pathology is associated with other blinding ocular conditions, then simply corneal transplant will not improve vision. So a thorough pre operative evaluation is needed to find out whether patient will benefit form the surgery or not. The surgeon should thoroughly disscuss with the parient about visual expectation and possible complications and in particular the long process of care needed after the surgery. Post operative care of the patient after corneal transplant is far more complex and challenging than pre operative evaluation and the surgical procedure.. Development of complications like wound leak, glaucoma, infection , non healing wound, can make a technical successful transplant fail. The success of corneal transplant surgery depends on the quality of the postoperative care. Furthermore there is always risk of graft rejection as long as the donor cornea is in patient’s eye.. Human body has ability to recognize and reject foreign tissue transplanted on it, whether be it cornea, kidney or bone marrow . If this happens , even a successful corneal transplant will fail. If the processs of rejection is diagnosed at early stage, the graft can be saved by aggressive medical treatment. To prevent such rejection, the patient should put steroid eye drops for several years or even life long. So the recipient of the cornea must be prepared for lifelong follow up. |
