Intraocular lens power calculation after laser in situ keratomileusis: Aphakic refraction technique

A No-History Multi-Formula Approach to Improve the IOL Power Calculation after Laser Refractive Surgery: Preliminary Results

This retrospective comparative study proposes a multi-formula approach by comparing no-history IOL power calculation methods after myopic laser-refractive-surgery (LRS). One-hundred-thirty-two eyes of 132 patients who had myopic-LRS and cataract surgery were examined. ALMA, Barrett True-K (TK), Ferrara, Jin, Kim, Latkany and Shammas methods were evaluated in order to back-calculate refractive prediction error (PE). To eliminate any systematic error, constant optimization through zeroing-out the mean error (ME) was performed for each formula. Median absolute error (MedAE) and percentage of eyes within ±0.50 and ±1.00 diopters (D) of PE were analyzed. PEs were plotted with corresponding mean keratometry (K), axial length (AL), and AL/K ratio; then, different ranges were evaluated. With optimized constants through zeroing-out ME (90 eyes), ALMA was better when K ≤ 38.00 D-AL > 28.00 mm and when 38.00 D < K ≤ 40.00 D-26.50 mm < AL ≤ 29.50 mm; Barrett-TK was better when K ≤ 38.00 D-AL ≤ 26.50 mm and when K > 40.00 D-AL ≤ 28.00 mm or AL > 29.50 mm; and both ALMA and Barrett-TK were better in other ranges. (p < 0.05) Without modified constants (132 eyes), ALMA was better when K > 38.00 D-AL ≤ 29.50 mm and when 36.00 < K ≤ 38.00 D-AL ≤ 26.50 mm; Barrett-TK was better when K ≤ 36.00 D and when K ≤ 38.00 D with AL > 29.50 mm; and both ALMA and Barrett-TK were better in other ranges (p < 0.05). A multi-formula approach, according to different ranges of K and AL, could improve refractive outcomes in post-myopic-LRS eyes.

IOL Power Calculations and Cataract Surgery in Eyes with Previous Small Incision Lenticule Extraction

Small incision lenticule extraction (SMILE), with over 5 million procedures globally performed, will challenge ophthalmologists in the foreseeable future with accurate intraocular lens power calculations in an ageing population. After more than one decade since the introduction of SMILE, only one case report of cataract surgery with IOL implantation after SMILE is present in the peer-reviewed literature. Hence, the scope of the present multicenter study was to compare the IOL power calculation accuracy in post-SMILE eyes between ray tracing and a range of empirically optimized formulae available in the ASCRS post-keratorefractive surgery IOL power online calculator. In our study of 11 post-SMILE eyes undergoing cataract surgery, ray tracing showed the smallest mean absolute error (0.40 D) and yielded the largest percentage of eyes within ±0.50/±1.00 D (82/91%). The next best conventional formula was the Potvin–Hill formula with a mean absolute error of 0.66 D and an ±0.50/±1.00 D accuracy of 45 and 73%, respectively. Analyzing this first cohort of post-SMILE eyes undergoing cataract surgery and IOL implantation, ray tracing showed superior predictability in IOL power calculation over empirically optimized IOL power calculation formulae that were originally intended for use after Excimer-based keratorefractive procedures.

The Use of Intraoperative Aberrometry in Normal Eyes: An Analysis of Intraocular Lens Selection in Scenarios of Disagreement

PURPOSE

To compare prediction error outcomes between the Optiwave Refractive Analysis System (ORA) (Alcon Laboratories, Inc) and two modern intraocular lens (IOL) formulas (Hill-RBF2.0 [HRBF] and Barrett Universal II [BUII]), and further analyze IOL selection in scenarios of disagreement between methods.

METHODS

Patients with no previous history of corneal refractive surgery who underwent cataract extraction and had intraoperative aberrometry measurements between October 2016 and December 2019 were analyzed. The prediction error for the ORA, HRBF, and BUII were calculated based on the postoperative manifest refraction. Further analysis was performed evaluating prediction error for scenarios of disagreement between the three methods.

RESULTS

After exclusions, 281 eyes were included. The mean absolute prediction errors were 0.28 diopters (D) (ORA), 0.31 D (HRBF), and 0.33 D (BUII) (P < .05). In instances when the IOL recommended by the ORA was in disagreement with what was selected preoperatively, there was no benefit when the lens recommended by the ORA was selected based on anecdotal experience. When further analyzing these instances of disagreement, selecting the ORA-recommended lens when it is higher in power results in improved refractive outcomes: the ORA resulted in more eyes within ±0.25 diopters (D) of predicted spherical error (65% ORA, 37% HRBF, 32% BUII; P = .004) and fewer hyperopic surprises (5% ORA, 15% HRBF, 24% BUII; P = .009).

CONCLUSIONS

In normal eyes without previous corneal refractive surgery, intraoperative aberrometry is not different from to two modern preoperative IOL formulas. Placing the ORA-recommended lens when it is higher in power than that selected preoperatively results in better refractive outcomes. [J Refract Surg. 2022;38(5):304-309.].

Predictability of intraocular lens power calculation after small-incision lenticule extraction for myopia

PURPOSE

To evaluate and compare the predictability of intraocular lens (IOL) power calculation after small-incision lenticule extraction (SMILE) for myopia and myopic astigmatism.

SETTING

Department of Ophthalmology, Philipps University of Marburg, Marburg, Germany.

DESIGN

Retrospective comparative case series.

METHODS

Preoperative evaluation included optical biometry using IOLMaster 500 and corneal tomography using Pentacam HR. The corneal tomography measurements were repeated at 3 months postoperatively. The change of spherical equivalent due to SMILE was calculated by the manifest refraction at corneal plane (SMILE-Dif). A theoretical model, involving the virtual implantation of the same IOL before and after SMILE, was used, and the IOL power calculations were performed using ray tracing (OKULIX, version 9.06) and third- (Hoffer Q, Holladay 1, and SRK/T) and fourth-generation (Haigis-L and Haigis) formulas. The difference between the IOL-induced refractive error at corneal plane before and after SMILE (IOL-Dif) was compared with SMILE-Dif. The prediction error (PE) was calculated as the difference between SMILE-Dif-IOL-Dif.

RESULTS

The study included 204 eyes that underwent SMILE. The PE with ray tracing was -0.06 ± 0.40 diopter (D); Haigis-L, -0.39 ± 0.62 D; Haigis, 0.70 ± 0.48 D; Hoffer Q, 0.84 ± 0.47 D; Holladay 1, 1.21 ± 0.51 D; and SRK/T, 1.46 ± 0.54 D. The PE with ray tracing was significantly smaller compared with that of all formulas (P ≤ .001). The PE variance with ray tracing was σ2 = 0.159, being significantly more homogenous compared with that of all formulas (P ≤ .011, F ≥ 6.549). Ray tracing resulted in an absolute PE of 0.5 D or lesser in 81.9% of the cases, followed by Haigis-L (53.4%), Haigis (35.3%), Hoffer Q (25.5%), Holladay 1 (6.4%), and SRK/T (2.9%) formulas.

CONCLUSIONS

Ray tracing was the most accurate approach for IOL power calculation after myopic SMILE.

Trifocal diffractive intraocular lens implantation in patients after previous corneal refractive laser surgery for myopia

Background

With the difficulties in IOL power calculation and the potential side effects occurring postoperatively, multifocal IOL implantation after previous corneal refractive surgery are rarely reported especially for the trifocal IOL. Herein we report the clinical observation of trifocal IOL implantation in patients with previous myopia excimer laser correction. In this study, a multi-formula average method was performed for the IOLs power calculation to improve the accuracy. Visual and refractive outcomes were analyzed, and the subjective quality of patients’ life was evaluated by questionnaires survey.

Methods

This retrospective case series included patients with previous myopia excimer laser correction who underwent femtosecond laser assisted phacoemulsification and trifocal IOL (AT LISA tri 839 MP) implantation. Follow-up was done at 1-day, 1-month and 3-month to assess the visual outcomes. Outcome measures were uncorrected distance, intermediate and near visual acuity (UDVA, UIVA, UNVA), manifest refraction, defocus curve, and subjective quality of vision.

Results

Twenty-one Eyes from sixteen patients (14 eyes with previous laser in situ keratomileusis and 7 eyes with previous photorefractive keratectomy) were included. Mean postoperative spherical equivalent (SE) at 3-month was − 0.56 D ± 0.49 SD, wherein, 10 eyes (47.6%) were within ±0.50 D of the desired emmetropia and 19 eyes (90.5%) were within ±1.0 D. Mean monocular UDVA, UIVA and UNVA (logMAR) at last visit were 0.02 ± 0.07, 0.10 ± 0.10, and 0.15 ± 0.11 respectively. Three patients (19%) reported halos and glare in postoperative 3 months, two of them needed to use spectacles to improve the intermediate visual acuity. Fifteen patients (94%) reported a satisfaction score of ≥3.5 out of 4.0, without any difficulty in daily activity. Thirteen patients (81%) did not need spectacles at all distances, while the other 3 patients (19%) used spectacles for near-distance related visual activity. Mean composite score of the VF-14 questionnaire was 95.00 ± 7.29 out of 100.

Conclusions

Trifocal IOL implantation after myopia excimer laser correction could restore good distance, intermediate visual acuity and acceptable near visual acuity, and provide accurate refractive outcomes as well as high spectacles independence rate.

Comparison of the accuracy of intraocular lens power calculation formulas for eyes after corneal refractive surgery

Background

In cataract surgery, calculating intraocular lens (IOL) power in patients who have previously received corneal refractive surgery on the same eye presents a clinical challenge. This study aims to compare the accuracy of the Haigis-L, Barrett True-K, and Shammas-PL formulas in predicting the IOL power in eyes following corneal refractive surgery.

Methods

This study analyzed 32 eyes belonging to 28 patients who underwent cataract surgery and IOL implantation after previously undergoing myopic corneal refractive surgery. The IOL power was calculated using the Haigis-L, Barrett True-K, and Shammas-PL formulas, and the accuracy of the three formulas was compared.

Results

The Haigis-L, Barrett True-K, and Shammas-PL formulas had a mean arithmetic IOL prediction error of -0.65, -0.39, and -0.46, respectively. The mean numerical errors of the three formulas were significantly different from zero (P<0.001). The smallest median absolute refraction prediction error (median =0.40) belonged to the Barrett True-K formula, which was significantly smaller than that of the Haigis-L formula (median =0.57, P<0.05) but similar to that of the Shammas-PL formula (median =0.49, P>0.05). There was no significant difference in the percentage of eyes within either ±0.50 D or ±1.00 D of the predicted refraction error across the three formulas.

Conclusions

The Barrett True-K formula can predict IOL power in eyes that have previously undergone myopic corneal refractive surgery better than the Haigis-L formula.

Intraocular lens power calculation in eyes with previous corneal refractive surgery

Background

This review aims to explain the reasons why intraocular lens (IOL) power calculation is challenging in eyes with previous corneal refractive surgery and what solutions are currently available to obtain more accurate results.

Review

After IOL implantation in eyes with previous LASIK, PRK or RK, a refractive surprise can occur because i) the altered ratio between the anterior and posterior corneal surface makes the keratometric index invalid; ii) the corneal curvature radius is measured out of the optical zone; and iii) the effective lens position is erroneously predicted if such a prediction is based on the post-refractive surgery corneal curvature. Different methods are currently available to obtain the best refractive outcomes in these eyes, even when the perioperative data (i.e. preoperative corneal power and surgically induced refractive change) are not known. In this review, we describe the most accurate methods based on our clinical studies.

Conclusions

IOL power calculation after myopic corneal refractive surgery can be calculated with a variety of methods that lead to relatively accurate outcomes, with 60 to 70% of eyes showing a prediction error within 0.50 diopters.

Intraocular Lens Power Calculation in Eyes After Laser In Situ Keratomileusis or Photorefractive Keratectomy for Myopia

Intraocular power calculation is challenging for patients who have previously undergone corneal refractive surgery. The sources of prediction errors for these eyes are well known; however, the numerous formulas and methods available for calculating intraocular lens power in these cases are eloquent testimony to the absence of a definitive solution. This review discusses some of the available methods for improving the accuracy for predicting the refractive outcome for these patients. It focuses mainly on the methods available on the American Society of Cataract and Refractive Surgery (ASCRS) online calculator and provides some practical guidelines for cataract surgeons who encounter these challenging cases.

Accuracy of formulae for secondary intraocular lens power calculations in pediatric aphakia

Purpose

To compare the accuracy of axial length vergence formulas versus refractive vergence formulas for secondary intraocular lens (IOL) implantation in pediatric aphakia.

Methods

This retrospective comparative study, evaluated 31 eyes of 31 patients aged ≤3.5 years, who had undergone secondary IOL implantation. The median absolute error (MedAE) was compared between axial length vergence formulas (Hoffer Q, Holladay I, SRK II, and SRK/T) and refractive vergence formulas (Lanchulev, Holladay R, Mackool, and Khan) as well as between formulas within the same vergence.

Results

There was a significant difference (P = 0.010) between MedAE for axial length vergence formulas [1.19 Diopter(D)] and MedAE for refractive vergence formulas (2.48 D). The MedAE of axial length vergence formulas were comparable as to Hoffer (1.59 D), Holladay (1.27 D), SRK/T (1.23 D), and SRK II (1.30 D). Among refractive vergence formulas, Lanchulev (5.00 D) and Holladay R (2.51 D) had significantly larger MedAE as compared to Khan (2.06 D) and Mackool (2.15 D).

Conclusion

Axial length vergence formulas performed significantly better than refractive vergence formulas; however, axial length vergence formulas were comparable within the same vergence.

Bilateral cataract surgery in a 56-year-old man following presbyopia laser in situ keratomileusis: A case report

We describe a case of bilateral cataract surgery in a 56-year-old man following presbyopia laser in situ keratomileusis. The preoperative refraction was −2.00 in the right eye and −0.75 × 105 in the left eye. On the last examination, the uncorrected distance visual acuity was 20/80 that can be corrected to 20/20 in the right eye with a refraction of −2.25 and 20/20 in the left eye, whereas the visual acuity for reading was 20/40 in the right eye and 20/80 in the left eye with a refraction of +2.25. His monovision surgery design of previous cornea surgery was also taken into consideration for the phacoemulsification and posterior chamber intraocular lens (IOL) implantation. Two-step surgery is helpful for predicting an accurate IOL degree.

Intraocular lens calculations after laser vision correction

PURPOSE OF REVIEW

This article describes different strategies for corneal measurements and/or intraocular lens (IOL) calculations and proposes a systematic approach for IOL selection in patients who have undergone laser corneal refractive surgery.

RECENT FINDINGS

Corneal measurements and IOL calculations cannot be obtained accurately with the standard measuring technologies and formulas in patients with history of laser corneal refractive surgery; therefore a variety of methods and formulas, some of which required prerefractive surgery data, have been proposed to improve the accuracy of measurements and calculations. Formulas that do not rely on prerefractive data seem to be as accurate as those that do; therefore the lack of prerefractive data no longer presents an obstacle for accurate IOL selection in these patients.

SUMMARY

Postrefractive patients undergoing cataract extraction and IOL implantation should have corneal measurements and IOL calculations that take into account and compensate for the limitations in accurate measurements and calculations. IOL selection should also aim to compensate for induced spherical aberration according to the ablation pattern.

Intraocular lens power calculation following laser refractive surgery

Refractive outcomes following cataract surgery in patients that have previously undergone laser refractive surgery have traditionally been underwhelming. This is related to several key issues including the preoperative assessment (keratometry) and intraocular lens power calculations. Peer-reviewed literature is overwhelmed by the influx of methodology to manipulate the corneal or intraocular lens (IOL) powers following refractive surgery. This would suggest that the optimal derivative formula has yet been introduced. This review discusses the problems facing surgeons approaching IOL calculations in these post-refractive laser patients, the existing formulae and programs to address these concerns. Prior published outcomes will be reviewed.

IOL power calculation after corneal refractive surgery

PURPOSE

To describe the different formulas that try to overcome the problem of calculating the intraocular lens (IOL) power in patients that underwent corneal refractive surgery (CRS).

METHODS

A Pubmed literature search review of all published articles, on keyword associated with IOL power calculation and corneal refractive surgery, as well as the reference lists of retrieved articles, was performed.

RESULTS

A total of 33 peer reviewed articles dealing with methods that try to overcome the problem of calculating the IOL power in patients that underwent CRS were found. According to the information needed to try to overcome this problem, the methods were divided in two main categories: 18 methods were based on the knowledge of the patient clinical history and 15 methods that do not require such knowledge. The first group was further divided into five subgroups based on the parameters needed to make such calculation.

CONCLUSION

In the light of our findings, to avoid postoperative nasty surprises, we suggest using only those methods that have shown good results in a large number of patients, possibly by averaging the results obtained with these methods.

The accuracy of the double-K adjustment for third-generation intraocular lens calculation formulas in previous keratorefractive surgery eyes

PURPOSE

To evaluate the effect of the double-K (DK) modification on third-generation formulas.

METHODS

Thirty-eight previously myopic and 24 previously hyperopic eyes that underwent phacoemulsification with intraocular lens (IOL) insertion after Laser in situ keratomileusis (LASIK) were evaluated. Pre-LASIK refraction and keratometry, post-LASIK topography, axial length (AL), IOL type and power, and 1-month postphacoemulsification refraction were recorded spherical equivalent after phacoemulsification (SE(postphaco)). Measured corneal power was adjusted using published and validated methods for postmyopic and posthyperopic LASIK. For each eye, and using SE(postphaco), different DK-IOL formulas were used to calculate the corresponding IOL power, the outcome measure, which was compared with the implanted IOL.

RESULTS

DK-Holladay 1 yielded the highest Pearson correlation coefficient (PCC), 0.955 for myopes and 0.943 for high myopes (AL>26 mm). Mean error (ME) and mean absolute error (MAE) for myopes for DK Sanders-Retzlaff-Kraff theoretical formula [DK-SRK/T] were 0.44±0.84 D and 0.75±0.61 D for DK-SRK/T compared with -0.04±0.67 D and 0.52±0.40 D for DK-Holladay 1 (P<0.001 and P=0.016, respectively), and 0.03±0.88 and 0.64±0.58 for DK-Hoffer Q. For high myopes, ME and MAE were 0.75±0.81 D and 0.84±0.69 D for DK-SRK/T, and -0.05±0.74 D (P<0.0001) and 0.57±0.45 D (P=0.019) for DK-Holladay 1. About 29% of DK-SRK/T eyes with large AL had MAE>1.5 D, compared with 0% for DK-Holladay 1 and 14% for DK-Hoffer-Q. Eyes with previous hyperopic LASIK faired similarly for all formulas, with similar PCCs, and only 8% in each category with MAE>1.5 D.

CONCLUSIONS

DK-SRK/T overestimates IOL power in eyes with large AL, especially with concomitant steep pre-lasik keratometry. Among third-generation formulas, DK-Holladay 1 seems more accurate to use in postmyopic LASIK eyes.

New factor to improve reliability of the clinical history method for intraocular lens power calculation after refractive surgery

PURPOSE

To determine whether the refractive error in an eye developing cataract after refractive surgery represents actual regression or is cataract related and whether the method to gather this information would allow the use of history-related formulas in intraocular lens (IOL) power calculation after refractive surgery.

SETTING

Second University of Naples, Naples, Italy.

DESIGN

Case series.

METHODS

The refractive effects, axial length (AL), and mean keratotomy (K) values were evaluated in eyes before and 6 months after photorefractive keratectomy for myopia or for myopic or mixed astigmatism.

RESULTS

The study evaluated 257 eyes of 166 patients (93 women). Before surgery, there was a high correlation between refractive error and the product of AL and K (AL × K) (r(2) = 0.8213). In patients with refractive results close to emmetropia, the mean AL × K was 1005.91 ± 25.88 (SD), meaning that in the range of 954 and 1058, there was a 95% possibility that the patients were almost fully corrected. The following regression formula was obtained to calculate the amount of refractive error independent of cataract onset: Refractive error = -0.0157 × (AL × K) + 16.437.

CONCLUSIONS

The regression formula determined whether the refraction depended on the onset of cataract and estimated the amount of undercorrection or overcorrection that occurred after refractive surgery, leading to improved estimation of the power of the IOL to be implanted. It may allow the use of history-related formulas in IOL power calculation for eyes that have had corneal refractive surgery.

Intraocular lens power calculation after myopic excimer laser surgery: clinical comparison of published methods

PURPOSE

To compare results of intraocular lens (IOL) power calculation methods after myopic excimer laser surgery.

SETTING

Private practice.

METHODS

In this prospective study, eyes having phacoemulsification after myopic excimer laser surgery were classified into Group 1 (preoperative corneal power available, refractive change known), Group 2 (preoperative corneal power available, refractive change uncertain), and Group 3 (preoperative corneal power unavailable, refractive change known even if uncertain). The IOL power was calculated using the following methods: clinical history, Awwad, Camellin/Calossi, Diehl, Feiz, Ferrara, Latkany, Masket, Rosa, Savini, Shammas, Seitz/Speicher, and Seitz/Speicher/Savini.

RESULTS

The lowest mean absolute errors (MAEs) in IOL power prediction in Group 1 (n = 12) and Group 2 (n = 11), respectively, were with the methods of Seitz/Speicher/Savini (0.51 diopter [D] +/- 0.44 [SD] and 0.55 +/- 0.50 D), Seitz/Speicher (0.58 +/- 0.47 D and 0.54 +/- 0.45 D), Savini (0.60 +/- 0.44 D and 0.65 +/- 0.63 D), Masket (0.82 +/- 0.49 D and 0.69 +/- 0.51 D), and Shammas (0.77 +/- 0.43 D and 1.11 +/- 0.50 D). In Group 3 (n = 5), the lowest MAEs were with the methods of Masket (0.23 +/- 0.27 D), Savini (0.49 +/- 0.86 D), Seitz/Speicher/Savini (0.68 +/- 0.36 D), Shammas (0.84 +/- 0.98 D), and Camellin/Calossi (0.91 +/- 0.84 D).

CONCLUSIONS

When corneal power is known, the Seitz/Speicher method (with or without Savini adjustment) seems the best solution to obtain an accurate IOL power prediction. Otherwise, the Masket method may be the most reliable option.

Calculation of intraocular lens power using Orbscan II quantitative area topography after corneal refractive surgery

PURPOSE

To present the prospective application of the Orbscan II central 2-mm total-mean corneal power obtained by quantitative area topography in intraocular lens (IOL) calculation after refractive surgery.

METHODS

Calculated and achieved refraction and the difference between them were studied in 77 eyes of 61 patients with previous radial keratotomy (RK), RK and additional surgeries, myopic LASIK, myopic photorefractive keratectomy (PRK), or hyperopic LASIK who underwent phacoemulsification without complications in 3 eye centers. All IOL calculations used the average from the central 2-mm Orbscan II total-mean power of maps centered on the pupil without the use of previous refractive data. Six IOL styles implanted within the bag were used.

RESULTS

Using the SRK-T formula, the overall calculated refraction was -0.64+/-0.93 diopters (D). The overall achieved spherical equivalent refraction (-0.52+/-0.79 D; range: -3.12 to 1.25 D; 95% confidence interval [CI]: -0.70/-0.34 D) was +/-0.50 D in 53% of eyes, +/-1.00 D in 78% of eyes, and +/-2.00 D in 99% of eyes. The overall difference between the calculated and achieved refraction (0.12+/-0.93 D, P=.27; range: -2.18 to 2.62 D; 95% CI: 0.09/0.33 D) was +/-0.50 D in 39% of eyes, +/-1.00 D in 77% of eyes, and +/-2.00 D in 96% of eyes. This difference was +/-1.00 D in 77% of eyes with RK (P=.70), 82% of eyes with myopic LASIK (P=.34), and 90% of eyes with myopic PRK (P=.96). In eyes with RK followed by LASIK, a trend toward undercorrection was noted (P=.03). In eyes with hyperopic LASIK, a trend toward overcorrection was noted (P=.005).

CONCLUSIONS

In eyes with previous corneal refractive surgery, IOL power calculation can be performed with reasonable accuracy using the Orbscan II central 2-mm total-mean power. This method had better outcomes in eyes with previous RK, myopic LASIK, and myopic PRK than in eyes with hyperopic LASIK or RK with LASIK.

Cataract surgery after refractive surgery

PURPOSE OF REVIEW

To review recent contributions addressing the challenge of intraocular lens (IOL) calculation in patients undergoing cataract extraction following corneal refractive surgery.

RECENT FINDINGS

Although several articles have provided excellent summaries of IOL selection in patients wherein prerefractive surgery data are available, numerous authors have recently described approaches to attempt more accurate IOL power calculations for patients who present with no reliable clinical information regarding their refractive history. Additionally, results have been reported using the Scheimpflug camera system to measure corneal power in an attempt to resolve the most important potential source of error for IOL determination in these patients.

SUMMARY

IOL selection in patients undergoing cataract surgery after corneal refractive surgery continues to be a challenging and complex issue despite numerous strategies and formulas described in the literature. Current focus seems to be directed toward approaches that do not require preoperative refractive surgery information. Due to the relative dearth of comparative clinical outcomes data, the optimal solution to this ongoing clinical problem has yet to be determined. Until such data are available, many cataract surgeons compare the results of multiple formulas to assist them in IOL selection for these patients.

Clinical evaluation of the intraoperative refraction technique for intraocular lens power calculation

OBJECTIVE

To evaluate clinically the intraoperative refraction technique for intraocular lens (IOL) power calculation using 2 existing formulas proposed by Ianchulev and Leccisotti and to derive alternative formulas for this technique.

DESIGN

Comparative case series.

PARTICIPANTS

One hundred eighty-two eyes from 182 patients with cataract.

METHODS

Recruited patients were separated into a normal cornea group and a special group that included eyes with surgically altered corneas. Phacoemulsification was carried out for all cases. Intraoperative aphakic autorefraction using a portable autorefractor was performed. An IOL with power calculated before surgery then was implanted. In each eye, postoperative refraction was obtained. The IOL power that would have achieved emmetropia was calculated retrospectively. Aphakic autorefraction readings obtained during surgery were used to calculate the aphakic spherical equivalent (SE). The 2 formulas incorporating aphakic SE were applied to calculate the target IOL power. Comparison then was made to determine the accuracy of the formulas.

MAIN OUTCOME MEASURES

A difference (referred to as IOL difference) was calculated by subtracting the adjusted emmetropic IOL power determined by postoperative refraction from the emmetropic IOL power calculated by the 2 formulas using intraoperative aphakic SE.

RESULTS

One hundred forty-four patients were in the normal cornea group and 18 were in the special group. In the normal group, the Ianchulev formula showed a relatively accurate prediction for IOL power to achieve emmetropia over almost the full range of axial length except in extremely long eyes. The Leccisotti formula tended to overestimate IOL power and worked particularly poorly in short eyes. It worked best in long eyes. In the special group, neither of the 2 formulas was able to show superiority universally. Using data from the normal group, alternative formulas for IOL power calculation were derived. These new formulas then were validated on the special group that showed good estimation.

CONCLUSIONS

The Ianchulev formula could be applied to most eyes, with the exception of those in highly myopic subjects. The Leccisotti formula showed good performance in myopic patients. For eyes falling into the special group, an alternative formula, correction factor, or both, may be required. The new formulas reported herein may be an option.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Practical method to calculate post-LASIK corneal power: the Actual K(a+p) method

AIM

To evaluate the accuracy of a practical method (the Actual K(a+p) method) of corneal power measurement for post-LASIK eyes undergoing cataract surgery.

METHODS

Ten eyes of 7 patients (4 male, 3 female, average age 50.10±4.01 years, with -11.01±3.55D mean refraction before LASIK), underwent post-LASIK phaco+IOL cataract surgery. We used the posterior corneal curvature as measured by the Pentacam in a method we named Actual K(a+p) to calculate the post-LASIK corneal power for IOL calculation. The refractive outcomes after cataract surgery were evaluated. The Actual K(a+p) was compared with the back- calculated corneal power (BCK), which was thought to be the benchmark of true corneal power. The corneal power estimated by other published methods, including Maloney, Shammas, Koch-Maloney, Savini, and McCulley, together with the true net power and equivalent K reading (EKR) as found by the Pentacam were also compared with the BCK.

RESULTS

All eyes achieved satisfied refractive status after cataract surgery. The difference between the postoperative refraction and the target refraction was 0.04±0.40D, range from -0.63D and +0.85D. Among all the methods we studied, although the Bonferroni multiple comparison tests did not detect significant differences between any two of them, the Actual K(a+p) yielded the highest agreement with the BCK, with 80% of the eyes falling within ±0.5D and 100% within ±1.0D from the BCK values.

CONCLUSION

The Actual K(a+p) method can provide encour- aging results in post-LASIK eyes undergoing cataract surgery.

Intraocular lens power adjustment nomogram after laser in situ keratomileusis

PURPOSE

To develop a nomogram for improving the accuracy of intraocular lens (IOL) power calculation at the time of cataract surgery based on the manifest refraction spherical equivalent (MRSE) change produced by laser in situ keratomileusis (LASIK).

SETTING

University-based clinical practice, Jules Stein Eye Institute, Los Angeles, California, USA.

METHODS

This was a retrospective review of the records of consecutive patients who had cataract surgery after LASIK. Spherical equivalent refractive data before and after LASIK and cataract surgery were recorded. The differences between the targeted postoperative refractive errors after cataract surgery and the achieved refractive errors were plotted against the LASIK-induced MRSE change, yielding postoperative refractive errors to target during IOL power calculation to achieve emmetropia.

RESULTS

Thirty-two eyes of 23 patients were identified; 25 eyes had myopic LASIK and 7, hyperopic LASIK. Regression analysis yielded the following polynomial relationship: target postoperative refractive error (D) to achieve emmetropia during IOL power calculation = -0.018(MRSE Change)(2) + 0.192(MRSE Change) - 0.062. The outcomes in 97% of eyes fell within +/-1.00 D of the value predicted by this formula.

CONCLUSIONS

A 2nd-order polynomial relationship was found between LASIK-induced MRSE change and the MRSE error after cataract surgery. From this equation, a simple adjustment nomogram was generated and put into a look-up table format. The formula and nomogram should improve IOL power calculation accuracy in post-LASIK eyes when the MRSE change is known.

Intraocular lens power calculation after previous laser refractive surgery

Methods to attempt more accurate prediction of intraocular lens power in refractive surgery eyes are many, and none has proved to be the most accurate. Until one is identified, a spreadsheet tool is available and can be used. It automatically calculates all the methods for which data are available on a single sheet for the patient's chart. The various methods and how they work are described.

Correction of residual hyperopia after cataract surgery using the light adjustable intraocular lens technology

PURPOSE

To determine whether residual hyperopia could be corrected postoperatively using the light adjustable lens technology in patients undergoing cataract surgery and light adjustable lens implantation.

DESIGN

Prospective, nonrandomized clinical trial.

METHODS

Fourteen eyes of 14 patients were studied. The manifest refraction, uncorrected visual acuity (UCVA), and best-corrected visual acuity (BCVA) were determined with follow-up time to determine the achieved refractive corrections and their stability.

RESULTS

Of 14 eyes, 13 eyes (92.9%) achieved +/- 0.25 diopters (D) of the target refraction at one day post lock-in, with 100% of the eyes achieving the targeted refractive adjustment within 0.5 D or better up to six months postoperative follow-up. All eyes treated show no change in manifest spherical refraction >0.25 D between one day post lock-in, and three and six months postoperative visits. The data demonstrate the stability of the achieved refractive change after the adjustment and lock-in procedures. The mean rate of change was 0.006 D per month, which is six times more stable than that of refractive procedures.

CONCLUSIONS

Residual hyperopia errors in the range of +0.25 to +2.0 D were successfully corrected with precision and significant improvement in UCVA and without compromising BCVA using the light adjustable intraocular lens technology.

Theoretical evaluation of the cataract extraction-refraction-implantation techniques for intraocular lens power calculation

PURPOSE

To evaluate theoretically three previously published formulae that use intra-operative aphakic refractive error to calculate intraocular lens (IOL) power, not necessitating pre-operative biometry. The formulae are as follows: IOL power (D) = Aphakic refraction x 2.01 [Ianchulev et al., J. Cataract Refract. Surg.31 (2005) 1530]; IOL power (D) = Aphakic refraction x 1.75 [Mackool et al., J. Cataract Refract. Surg.32 (2006) 435]; IOL power (D) = 0.07x(2) + 1.27x + 1.22, where x = aphakic refraction [Leccisotti, Graefes Arch. Clin. Exp. Ophthalmol.246 (2008) 729].

METHODS

Gaussian first order calculations were used to determine the relationship between intra-operative aphakic refractive error and the IOL power required for emmetropia in a series of schematic eyes incorporating varying corneal powers, pre-operative crystalline lens powers, axial lengths and post-operative IOL positions. The three previously published formulae, based on empirical data, were then compared in terms of IOL power errors that arose in the same schematic eye variants.

RESULTS

An inverse relationship exists between theoretical ratio and axial length. Corneal power and initial lens power have little effect on calculated ratios, whilst final IOL position has a significant impact. None of the three empirically derived formulae are universally accurate but each is able to predict IOL power precisely in certain theoretical scenarios. The formulae derived by Ianchulev et al. and Leccisotti are most accurate for posterior IOL positions, whereas the Mackool et al. formula is most reliable when the IOL is located more anteriorly.

CONCLUSION

Final IOL position was found to be the chief determinant of IOL power errors. Although the A-constants of IOLs are known and may be accurate, a variety of factors can still influence the final IOL position and lead to undesirable refractive errors. Optimum results using these novel formulae would be achieved in myopic eyes.

Intraocular lens calculation by intraoperative autorefraction in myopic eyes

BACKGROUND

The purpose was to provide a formula to calculate intraocular lens (IOL) power by intraoperative autorefraction in myopic refractive lens exchange (RLE).

METHODS

This was a prospective, noncomparative consecutive case series, including 82 eyes of 82 patients with age superior to 45 years and mean preoperative spherical equivalent (SE) -12.84 diopters (D) [standard deviation (SD) 6.24, range -3 to -27]. Autorefraction was performed by a hand-held instrument during phacoemulsification after cortex removal and the IOL power calculated from the resulting aphakic SE by two existing restricted formulas (personal for high myopia and Ianchulev for low myopia). In each eye, subjective refraction 2 months postoperatively and implanted IOL were used to retrospectively calculate the IOL power achieving plano (predicted final adjusted IOL power). The relation between aphakic SE at intraoperative autorefraction (x, independent variable) and predicted final adjusted IOL power (y, dependent variable) was studied.

RESULTS

A relation between SE at intraoperative autorefraction and predicted final adjusted IOL power for the whole series range was expressed by the parabola y=0.07x(2)+1.27x+1.22. Previous restricted formulas achieved a good predictability in their specific range with a mean postoperative SE of -0.58 D (SD 0.73, range -3 to 0.75) and a mean defocus equivalent of 0.69 D (SD 0.62, range 0 to 3).

CONCLUSION

The parabolic relation accounts for previous different regression lines in different myopic ranges. Intraoperative autorefraction is a reliable alternative to standard biometry in myopic eyes. A table for clinical use is provided.

Intraocular lens power calculation after radial keratotomy: Estimating the refractive corneal power

PURPOSE

To evaluate the most accurate method for corneal power determination in patients with previous radial keratotomy (RK).

SETTING

University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, USA.

METHODS

A retrospective review of data for 16 eyes of 14 patients with a history of RK and subsequent phacoemulsification and posterior chamber intraocular lens (IOL) implantation was performed. Outcome measures included axial length, postoperative topography, type and power of IOL implanted, and postoperative spherical equivalent (SE) refraction at 3 to 6 months. Average central corneal power (ACCP) was defined as the average of the mean powers of the central Placido rings. For each eye, simulated K-readings and different values of ACCP computed corresponding to different central corneal diameters were used in each case, along with the implanted IOL power, to back-calculate the SE refraction (Ref) via the double-K adjusted Holladay 1 IOL formula. The predicted refractive error was hence computed as (Ref - SE), both in algebraic and absolute values.

RESULTS

The ACCP over the central 3.0 mm (ACCP(3mm)) yielded the lowest absolute predicted refractive error (0.25 +/- 0.38 diopters [D]), which was statistically lower than the error for ACCP(1mm) (P<.001) and for the simulated K-value (P = .033). It also resulted in 87.5% of eyes being within +/-0.50 D and 100% within +/-1.00 D of the actual postoperative refraction.

CONCLUSIONS

Corneal refractive power after RK was best described by averaging the topographic data of the central 3.0 mm area. Applying this method, together with a double-K IOL formula, achieved excellent IOL power predictability.

Präoperative Berechnung der Stärke intraokularer Linsen bei Problemaugen

The removal of the opaque crystalline lens in cataract surgery and its replacement by an artificial lens has become the most successful surgical intervention in the history of medicine. Modern intraocular lenses, today's micro-incision approach and high-end measurement and computational techniques provide restoration of good visual acuity in the majority of cases. Patients with problem eyes not allowing standard procedures for intraocular lens power calculation require special attention. Among them are highly ametropic subjects with very short or long eyes or patients, whose corneal structures are different from normal due to preceding refractive surgery. The special problems for measurement and lens power calculations in these eyes are dealt with in detail. Based on hitherto unpublished clinical data, causes and possible solutions for the existing problems are discussed. Generally, the best available measurement techniques should be applied in these cases. With respect to the algorithms used it has to be made sure that no additional errors are introduced by the algorithms themselves. The popular SRK II formula should therefore not be used any more. If errors are minimized this way, gross postoperative refractive surprises should be avoided even in problem eyes.

No-history method of intraocular lens power calculation for cataract surgery after myopic laser in situ keratomileusis

PURPOSE

To prospectively evaluate the no-history method for intraocular lens (IOL) power calculation in 15 cataractous eyes that had previous myopic laser in situ keratomileusis (LASIK) and for which the pre-LASIK K-readings were not available.

SETTING

Private practice, Lynwood, California, USA.

METHODS

The predicted IOL power was calculated in each case. Also calculated were the mean arithmetic and absolute IOL predictor errors, range of the prediction errors, and number of eyes in which the error was within +/-1.00 diopter (D).

RESULTS

The mean arithmetic IOL prediction error was -0.003 D +/- 0.63 (SD), and the mean absolute IOL prediction error was 0.55 +/- 0.31 D (range -0.89 to +1.05 D). Fourteen eyes (93.3%) were within +/-1.00 D. The results of the Shammas post-LASIK formula compared favorably to the results obtained with the optimized Holladay 1 (P = .42), Hoffer Q (P = .25), Haigis (P = .30), and Holladay 2 (P = .19) formulas and were better than the results obtained with the optimized SRK/T formula (P = .0005).

CONCLUSION

The no-history method is a viable alternative for IOL power calculation after myopic LASIK when the refractive surgery data are not available.