|LETTER TO EDITOR
|Year : 2004 | Volume
| Issue : 1 | Page : 81
Essential parameters for accurate intraocular lens (IOL) power estimation in post refractive surgery cataract patients.
R Fogla, Srinivas K Rao, P Padmanabhan
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Fogla R, Rao SK, Padmanabhan P. Essential parameters for accurate intraocular lens (IOL) power estimation in post refractive surgery cataract patients. Indian J Ophthalmol 2004;52:81
Corneal refractive surgery, photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) have revolutionised the correction of refractive errors since the early 1990s. It is estimated that approximately 1.3 million refractive procedures were performed in the United States alone in 2001. Although a majority of the patients treated are in their second or third decade of life, a significant number of patients over the age of 40 also undergo refractive procedures. With time some of these patients tend to develop visually significant lens changes requiring cataract extraction. Current methods of IOL power estimation perform well with great accuracy when used for eyes with physiologic prolate corneas. But, when these formulae are applied for eyes which have undergone refractive surgical procedures, they do not seem to function well and result in postoperative refractive surprises. Eyes that have had myopic refractive procedures tend to develop hyperopia and vice versa. This is quite disturbing to patients, who have high expectations and expect good unaided visual acuity, similar to one following refractive procedures.
There have been several publications regarding methods of estimating the effective keratometry value of the post refractive surgery cornea for accurate IOL power calculation in these patients., The preferred method is the clinical history method of deriving the post refractive surgery keratometric values, suggested by Holladay in 1989. This method requires three variables, i) preoperative manifest refraction, ii) preoperative keratometry values, and iii) stable postoperative manifest refraction. The change in spherical equivalent refraction induced by the refractive procedure is subtracted from the preoperative keratometry power to derive the actual keratometry power post refractive surgery. This keratometry value when used for IOL power calculation, reduces the risk of postoperative ametropia following cataract surgery.
The number of centres providing facilities for refractive surgery is on the rise in India. Although we do not have exact figures on how many patients undergo laser refractive surgery every year, a rough estimate would be approximately 50,000 to 80,000 considering that each centre treats 1,000 to 1,500 patients per year. Managing cataracts in these patients can be challenging with regards to postoperative refractive outcome. Hence it is essential that certain information should be provided to every patient undergoing a refractive surgical procedure. The refractive surgeon should provide a report containing the three variables mentioned earlier, i.e., the preoperative refractive error, keratometry values and stable postoperative refractive error.
| References|| |
United States Census 2000. Available online at : http://www.census.gov/prod/2001pubs/c2kbr01-12.pdf.
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Hamilton RD, Hardten DR. Cataract surgery in patients with prior refractive surgery. Curr Opin Ophthalmol
Holladay JT. IOL calculations following RK. Refract Corneal Surg