Calculation of Intraocular Lens Power with the Srk Ii Formula for Axial High Myopia

Improving the accuracy of the SRK/T formula in Chinese with implanting less than 10 D IOL calculated by the SRK/T formula: the SRK/T-Li formula

PURPOSE

To explore the accuracy of the improved SRK/T-Li formula in eyes following implantation of intraocular lens (IOL) of less than 10 D as calculated by using the SRK/T formula in Chinese.

METHODS

A total of 489 eyes from 489 patients with cataracts were included in this study. These patients were divided into a training set (271 patients) and a testing set (218 patients). The IOL power calculated by using SRK/T was less than 10 D. We evaluated the accuracy of the modified SRK/T-Li formula (P = PSRK/T × 0.8 + 2 (P = implanted IOL power; PSRK/T = IOL power calculated by SRK/T)). We evaluated the mean absolute error (MAE), percentage of prediction error (PE) within ± 0.25, ± 0.50, and ± 1.00 D, and the percentage of postoperative hyperopia.

RESULTS

The MAE values in order of lowest to highest were as follows: 0.412 D (SRK/T-Li), 0.414 D (Barrett Universal II, (BUII)), 0.814 D (SRK/T), and 1.039 D (Holladay 1). The percentage of PE within ± 0.25 D, ± 0.50 D, and ± 1.00 D was 38.99%, 69.27% and 92.66% (BUII), 40.83%, 69.27% and 94.04% (SRK/T-Li), 20.64%, 41.28% and 71.56% (SRK/T), and 7.34%, 16.51% and 53.21% (Holladay 1), respectively. SRK/T-Li had the smallest postoperative hyperopic shift.

CONCLUSIONS

For Chinese patients with an IOL power of less than 10 D as calculated by using the SRK/T, the SRK/T-Li has good accuracy and is the best choice to reduce postoperative hyperopic shift.

Update on Intraocular Lens Formulas and Calculations

Investigators, scientists, and physicians continue to develop new methods of intraocular lens (IOL) calculation to improve the refractive accuracy after cataract surgery. To gain more accurate prediction of IOL power, vergence lens formulas have incorporated additional biometric variables, such as anterior chamber depth, lens thickness, white-to-white measurement, and even age in some algorithms. Newer formulas diverge from their classic regression and vergence-based predecessors and increasingly utilize techniques such as exact ray-tracing data, more modern regression models, and artificial intelligence. This review provides an update on recent literature comparing the commonly used third- and fourth-generation IOL formulas with newer generation formulas. Refractive outcomes with newer formulas are increasingly more and more accurate, so it is important for ophthalmologists to be aware of the various options for choosing IOL power. Historically, refractive outcomes have been especially unpredictable in patients with unusual biometry, corneal ectasia, a history of refractive surgery, and in pediatric patients. Refractive outcomes in these patient populations are improving. Improved biometry technology is also allowing for improved refractive outcomes and surgery planning convenience with the availability of newer formulas on various biometry platforms. It is crucial for surgeons to understand and utilize the most accurate formulas for their patients to provide the highest quality of care.

Accuracy of intraocular lens power calculation using partial coherence interferometry in patients with high myopia

PURPOSE

Ultrasound-A-scan-biometry intraocular lens power calculation for cataract surgery sometimes shows lack of accuracy in patients with high myopia. The purpose of this retrospective study was to assess the accuracy of lens power calculation with optical biometry using the Zeiss IOLMaster across a large range of myopia levels.

METHODS

We included 37 consecutive, myopic eyes with an axial length >26.5mm (31 patients, 62±13years old, average preoperative refraction of -14.46±6.61D, range -3.5 to -32.0D which underwent phacoemulsification and implantation of an intraocular lens following biometry using the IOLMaster. For lens power calculation, the Haigis formula was used in all cases. For comparison, refraction was back-calculated using the SRK/T and Holladay I formulae.

RESULTS

  The preoperative mean axial length was 29.37±2.44 mm with a range of 26.50-35.52mm. Thirty eyes (81.1%) showed a postoperative spherical equivalent which differed 1.00D or less from the predicted value, in 20 cases (54.1%) the postoperative refractive error was within±0.50D. The mean absolute error (MAE) was 0.70±0.59D (Holladay I, 0.85±0.68; SRK/T, 1.01±0.61D).

CONCLUSIONS

  Optical biometry for intraocular lens power calculation seems to deliver reliable results for cataract surgery in patients with high myopia, although our data describe an increasing lack of accuracy beyond an axial length of 30mm. The Haigis formula provided the best predictability of postoperative refractive outcome for myopic eyes in general.

Small incision clear lens extraction for correction of high myopia

PURPOSE

To evaluate the effectiveness, predictability, and safety of clear lens extraction in the correction of high myopia.

SETTING

Kartal Education and Research Hospital, Istanbul, Turkey.

METHODS

This retrospective study comprised 56 eyes of 30 patients who had clear lens extraction to correct myopia of 12.00 diopters (D) or more. Small incision clear lens extraction using an anterior chamber maintainer was performed and low-power posterior chamber intraocular lens (IOL) was implanted. The mean postoperative follow-up was 40.2 +/- 11.9 months.

RESULTS

Uncorrected visual acuity improved in 94.6% of eyes. Best-corrected visual acuity (BCVA) improved in 37 eyes (66%); 27 (48.2%) gained two or more lines. The percentage of eyes achieving a BCVA of 20/40 or better increased from 26.7% preoperatively to 58.9% postoperatively. Of the eyes, 38 (67.8%) were within +/- 1.00 D of targeted refractive error and 52 (92.8%) were within +/- 2.00 D. Posterior capsule tear with vitreous loss occurred in one eye (1.7%). During the follow-up, retinal detachment (RD) occurred in 2 eyes (3.5%).

CONCLUSIONS

Clear lens extraction and IOL implantation was effective and had an acceptable predictability and a low morbidity in correcting high myopia. Regular retinal examination is necessary to prevent postoperative RD.

Refractive Lens Exchange With an Array Multifocal Intraocular Lens

PURPOSE

To prospectively evaluate safety, efficacy, predictability, stability, complications, and patient satisfaction after refractive lens exchange (clear lens extraction) followed by posterior chamber implantation of a multifocal intraocular lens (IOL).

METHODS

Fifty eyes of 25 patients (mean age 51 years, range 44 to 62 years) with preoperative spherical equivalent refraction between -15.50 and +5.75 D and cylinder between 0 and 1.50 D underwent bilateral implantation of a zonal progressive multifocal IOL (Array, AMO).

RESULTS

Eyes were divided into group A (n=24; myopia, average preoperative spherical equivalent refraction -7.11 +/- 3.25 D (-1.75 to -15.50 D), and group B (n=26; hyperopia, average preoperative spherical equivalent refraction +3.04 +/- 1.04 D). Follow-up was 6 months in all eyes. Postoperatively, all eyes of both groups were within +/-1.00 D of target refraction. No eye in group A and three eyes in group B sustained a loss of one line of BSCVA. Forty-seven eyes (94%) remained unchanged or gained one or more lines of their preoperative BSCVA. In all eyes, postoperative UCVA was 20/40 or better. When compared to preoperative, uncorrected near visual acuity improved (statistically significant). All patients achieved uncorrected binocular visual acuity of 20/30 and J4 or better. Patient satisfaction was extremely high; no intra- or postoperative complications were reported.

CONCLUSION

Six-month results of implantation of the AMO Array multifocal IOL for refractive lens exchange demonstrated safety, efficacy, and predictability in correcting high ametropia and significant improvement of uncorrected near and distance visual acuity.

Clear lens phacoemulsification for correction of high myopia

PURPOSE

To assess phacoemulsification and posterior chamber intraocular lens (IOL) implantation as an effective, safe, and predictable technique for the correction of high myopia.

SETTING

University Eye Clinic of Verona, Verona, Italy.

METHODS

A series of 25 eyes with myopia higher than -12.0 diopters (D) had clear lens extraction by phacoemulsification and IOL implantation in the capsular bag. The mean postoperative follow-up was 42.92 months +/- 3.76 (SD).

RESULTS

No serious intraoperative complications occurred. Uncorrected visual acuity improved in all cases. The mean postoperative best corrected visual acuity improved by an average of 1 line. One case (4.0%) of postoperative retinal detachment (RD) occurred at 12 months. One case (4.0%) of biometric error (3.0 D) occurred.

CONCLUSION

Clear lens extraction by phacoemulsification and IOL implantation in a series of highly myopic eyes was effective and had an acceptable predictability and a low rate of complications. Careful evaluation of the retinal periphery by indirect ophthalmoscopy is recommended to avoid postoperative RD.

Clear lens extraction and implantation of negative-power posterior chamber intraocular lenses to correct extreme myopia

PURPOSE

To evaluate the effectiveness, predictability, and safety of clear lens extraction to correct extreme myopia.

SETTING

Clinica de Nuestra Señora de la Concepción, Fundación Jiménez Díaz, Madrid, Spain.

METHODS

This retrospective study comprised 26 eyes of 17 highly myopic patients who had clear lens extraction and implantation of a negative-power posterior chamber intraocular lens (IOL). The IOL power was calculated using the SRK/T formula. Analyzed were visual and refractive results and intraoperative and postoperative complications. Follow-up was at least 12 months in all cases.

RESULTS

Uncorrected visual acuity improved in all cases, with 80.77% of eyes achieving 20/100 or better and 42.30%, 20/40 or better. Best spectacle-corrected visual acuity (BSCVA) improved in 23 eyes (88.46%). The percentage of eyes achieving a BSCVA of 20/100 or better increased from 73.07% preoperatively to 92.30% postoperatively and the percentage achieving 20/40 or better, from 23.07 to 73.07%. Of the 26 eyes, 76.91% were within 1.00 diopter (D) of refractive error and 96.16% were within 2.00 D. No intraoperative complications occurred. Although postoperatively 3 eyes (11.53%) developed choroidal detachment and 5 (19.23%) had an intraocular pressure greater than 25 mm Hg, all had a favorable outcome. Four eyes (15.38%) developed posterior capsule opacification and had a neodymium:YAG laser posterior capsulotomy 6 months postoperatively. No retinal detachments were observed.

CONCLUSION

Clear lens extraction with negative-power IOL implantation using the SRK/T formula had good effectiveness, acceptable predictability, and a low morbidity in eyes with extreme myopia over a short follow-up. A longer follow-up with more cases is needed to assess the safety of the procedure.