Dr. Hemant Ramesh Sonawane, Dr. Madhu Shekhar,Dr. ZERVIN BAAM
Routine intraocular lens (IOL) power calculations in cataractous eyes that have had previous myopic refractive surgery underestimate the IOL power for emmetropia, resulting in a high incidence of postoperative unintentional hyperopia1-5
After laser in situ keratomileusis (LASIK), 1 or 2 errors are introduced into IOL power calculation formulas. The first error occurs in all formulas and involves the evaluation of the correct post-LASIK K-values needed for accurate IOL power calculations. The second error is in the calculation of the estimated lens position (ELP) by the commonly used third-generation IOL power formulas. When the refractive surgery parameters (pre-LASIK K-readings, amount of myopia corrected, or both) are known, many methods are available to correct the K-values and calculate a more accurate ELP.6–13 However, when the refractive surgery parameters are not known, these corrections are not possible.
There have been numerous formulas and calculation methods proposed for use in these eyes, and the process of employing them is typically time consuming and complex. As a result, surgeons and their staff are often uncomfortable when a patient presents for cataract surgery after refractive surgery. We retrospectively analysed the cases in which we implanted the IOL power calculated with ASCRS online calculator.
MATERIAL AND METHODS
Methods: Retrospective case series of 7 eyes of 7 cases with previous myopic LASIK surgery that underwent cataract surgery were analysed. All cases underwent phacoemulsification with foldable iol implantation under one surgeon .ASCRS average method was used and nearest higher available IOL power value was implanted.
| INCLUSION CRITERIA: | EXCLUSION CRITERIA: |
| Both eyes lasik | Hypermetropic correction |
| Uneventful myopic lasik surgery | Diagnosed amblyopia |
| Immature cataract | One eye lasik correction |
| Uneventful Phacoemulsification | Anisometropia |
| Myopic degeneration involving macula | |
| Other refractive surgeries: radial keratotomy |
RESULTS
TABLE 1: DEMOGRAPHY
| Case no | Age
(yrs) |
Sex | Duration between Lasik and cataract surgery (yrs) |
| 1. | 46 | M | 18 |
| 2. | 41 | F | 9 |
| 3. | 52 | F | 17 |
| 4. | 61 | M | 17 |
| 5. | 51 | F | 20 |
| 6. | 50 | F | 15 |
| 7. | 58 | M | 15 |
| MEAN | 51.28 | 51.86 |
TABLE 2: VISUAL ACUITY PRE OPERATIVELY
| Case no | UNVA
(LogMAR) |
Sphere (Dioptres) | Cylinder (Dioptres) | SE
(Dioptres) |
BCVA
(LogMAR) |
| 1. | 1.07 | -5.5 | – | -5.5 | 0.60 |
| 2. | 1.30 | -10 | -2.00 x 90 | -11.00 | 0.30 |
| 3. | 1.30 | -10 | – | -10.00 | 0.47 |
| 4. | 1.07 | -5.00 | -1.5 x 90 | -5.75 | 0.30 |
| 5. | 1.77 | -16.00 | – | -16.00 | 0.60 |
| 6. | 1.07 | -3.00 | – | -3.00 | 0.60 |
| 7. | 1.07 | -5.00 | – | -5.00 | 0.30 |
| MEAN | 1.24 | – | – | -8.03 | 0.45 |
Table 3: CATARACT GRADE AND IOL POWER CLACULATIONS:
| Case no | Cataract grade
(LOCS III) |
IOL POWER
(DIOPTRES) |
IOL DESIGN | |
| CALCULATED
(ASCRS METHOD) |
IMPLANTED | |||
| 1. | NC3NO3 | 17.37 | 17.50 | Aspheric |
| 2. | NC3NO3 | 10.31 | 11.00 | Aspheric |
| 3. | NC2NO2 | 14.01 | 14.00 | Acrylic |
| 4. | NC3NO3 | 21.19 | 21.00 | Acrylic |
| 5. | NC3NO3 | 6.96 | 6.50 | Acrylic |
| 6. | NC2NO2P2 | 14.07 | 14.00 | Acrylic |
| 7. | NC2NO2 | 14.75 | 15.00 | Aspheric |
| MEAN | – | 14.09 | 14.14 | – |
TABLE 4: VISUAL ACUITY POST-OPERATIVELY 1 MONTH
| Case no | UNVA
(LogMAR) |
Sphere (Dioptres) | Cylinder (Dioptres) | SE
(Dioptres) |
BCVA
(LogMAR) |
| 1. | 0 | – | – | – | 0 |
| 2. | 0.18 | – | – | – | 0.18 |
| 3. | 0.48 | – | – | – | – |
| 4. | 0.17 | +0.75 | – | – | 0 |
| 5. | 0.77 | +1.00 | -2.00 x 180 | +0.5 | 0.48 |
| 6. | 0.18 | – | – | – | 0.18 |
| 7. | 0.18 | – | – | – | 0.18 |
| MEAN | 1.24 | – | – | 0.07 | 0.45 |
DISCUSSION
Mean age was 51.28 yrs; 4 females 3 males. Mean duration between LASIK and age of presentation was 15.86 yrs. Preoperative Mean Uncorrected Visual Acuity (log MAR) was 1.24(<6/60); Mean Best Corrected Visual Acuity Was 0.45 (6/18) .Post operative Mean BCVA was 0.21(6/9.5); 2 cases had 0.48 (6/19) whose reasons could not be elicited and 5 cases had 0.18 (6/9) or better.
The ASCRS post refractive IOL calculator is a free online tool that enables surgeons to automatically generate a range of IOL power predictions by entering historical data (pre- and post-LASIK/PRK refraction), biometry measurements, and K measurements.
Patients who have previously undergone corneal refractive surgery to achieve spectacle independence understandably have high expectations with regard to the outcome of their cataract surgery. It should be made very clear that the limitations of available technology preclude precise IOL power calculations and that the calculations for their eyes remain problematic. Although our methods for IOL power selection are improving, refractive outcomes remain problematic.
CONCLUSION:
ASCRS average method of calculating IOL power after LASIK provided satisfactory results in post myopic LASIK cataract surgery.
REFRENCES
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