الفهرس 
• Correction of pre-existing astigmatism during lens surgeryOnly 14 pages are availabe for public view
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Abstract
Refractive cataract surgery is defined as the uncomplicated removal of cataract while minimizing postoperative spectacle dependence as cataract surgery has gone beyond just being a means to get the lens out of the eye. Postoperative astigmatism plays an important role in the evaluation of final outcome of surgery. Achieving the desired postoperative spherical correction and reducing or eliminating preoperative astigmatism in each patient accomplishes this goal. Recent emphasis has been on the reduction or elimination of astigmatism rather than on minimizing postoperative spherical error. There are several approaches to correcting astigmatism at the time of cataract surgery.
Manual small incision cataract was developed mainly as a cost-effective alternative to phacoemulsification cataract surgery. The basis of manual small incision cataract surgery is the tunnel construction for entry to the anterior chamber. The parameters important for the structural integrity of the tunnel are the self-sealing property of the tunnel, the location of the wound on the sclera with respect to the limbus, and the shape of the steep wound and to achieve emmetropia the incision must be centered along the steep meridian, the cataract surgeon must know that Longer incisions produce more flattening, Posterior incisions decrease against-the-rule wound drift, Straight or frown incisions decrease against-the-rule drift, Scleral tunnel incisions minimize suture-induced astigmatism and provide greater wound-healing surface and it is more stable from the refractive standpoint.
Site and size of the incision is one of the important items for reduction of surgically induced astigmatism in modern cataract surgery. For preoperative mild to moderate corneal astigmatism, on-axis incision induced slightly more flattening of the steeper corneal meridian than temporal incision. A 3.2-mm clear corneal phacoemulsification incision results in surgically induced astigmatism of 0.5 D.
Paired opposite clear corneal incisions on the steep axis is a useful way to correct mild to moderate astigmatism in cataract patients. The technique requires no additional skill or instrumentation when 3.2 mm phacoemulsification incisions are used.
Limbal relaxing incision is a simple, safe and effective method not only for reducing pre-existing astigmatism during cataract surgery but in providing good unaided visual acuity. Astigmatism between 1 and 4 diopters can be managed by LRIs according to Gills nomogram
For astigmatism greater than 4 diopters it can be managed by combined toric IOL and LRIs.
Toric IOL opened the doors for correction of higher levels of astigmatism to compliment or replace corneal astigmatic incisions. Higher magnitudes of astigmatism may be treated optically by toric IOL compared to the tissue- limited treatment. Implanting a toric intraocular lens (IOL) is successfully used for cases of up to 30 diopters of astigmatism. But it is still limited in use due to IOL rotation.
Laser in situe keratomileusis (LASIK) is now one of the most popular corneal refractive surgeries because of lower postoperative discomfort, early visual rehabilitation and decrease postoperative haze. LASIK are relatively effective and predictable surgical procedures for the correction of residual myopia or mixed astigmatism ranging from 3 to 6 diopters after cataract surgery, but there are many factors affecting postoperative quality of vision as corneal thickness and size of the pupil. LASIK may result for complications related to the flap; interface and underlying stromal bed; it could be avoided by careful selection of the patient.