Effect of astigmatic keratotomy on spherical equivalent: results of the Astigmatism Reduction Clinical Trial

Refractive Coupling Effects in Keratorefractive Lenticule Extraction Procedures: A Machine Learning-Assisted Approach

PURPOSE

To evaluate the impact of refractive couplings in myopia and myopic astigmatism with two different keratorefractive lenticule extraction (KLEx) systems.

METHODS

This was a retrospective evaluation of refractive outcomes with two different lasers studying 2,841 eyes undergoing small incision lenticule extraction (SMILE) (VisuMax 500; Carl Zeiss Meditec) and 2,528 eyes undergoing SmartSight (ATOS; SCHWIND eye-tech-solutions GmbH). Coupling effects (derived from the ratio between partial slopes) were determined for sphere and cylinder and for spherical equivalent, cardinal, and oblique astigmatism separately.

RESULTS

Statistically significant coupling effects were observed for both the VisuMax and ATOS systems, as indicated by P values less than .05. For the VisuMax, a coupling effect of 8% of cylinder into sphere and a 2% coupling of sphere into cylinder was found. For the ATOS, the coupling effect of sphere into cylinder was 1%. A 3% coupling effect of oblique astigmatism into cardinal astigmatism in the VisuMax, and conversely, a 0.1% coupling effect of defocus into oblique astigmatism in the ATOS were found. In cases with no astigmatism plan, sphere had a 2% effect on induced astigmatism in the VisuMax and 0.6% in the ATOS. In high astigmatism plans, sphere had a significant 16% impact on cylinder in the VisuMax. Additionally, the effect of defocus on cardinal astigmatism was 6% in the VisuMax and 0.8% on oblique astigmatism in the ATOS.

CONCLUSIONS

Despite the P values less than .05 indicating statistical significance, the observed coupling effects were consistently low, with magnitudes below 10%, even for astigmatism exceeding 2.50 diopters. These couplings may be partly attributed to cross-effects of torsional eye movements. Coupling values for KLEx were markedly lower than those reported for non-aspheric excimer laser ablations. The results suggest that surgical results may be refined further by optimizing nomograms to mitigate coupling effects. [J Refract Surg. 2024;40(10):e706-e715.].

Toric intraocular lens implantation vs. femtosecond laser-assisted arcuate keratotomy for correction of moderate astigmatism in cataract surgery

PURPOSE

To compare toric intraocular lens (TIOL) implantation and femtosecond laser-assisted arcuate keratotomy (FSAK) during phacoemulsification surgery in correction of moderate astigmatism.

SETTING

Clinical research study.

DESIGN

Prospective randomized comparison study.

METHODS

Patients with age-related cataract and moderate preoperative corneal astigmatism of 1.25 to 3.0 diopters (D) were randomized into a TIOL implant group and an FSAK group with symmetrical paired corneal arcuate keratotomies. The preoperative evaluation included corrected distance visual acuity (CDVA), corneal topography, autokeratometry and ocular biometry. Postoperative examinations were performed at 1 and 3 months and included CDVA and uncorrected distance visual acuity (UDVA), manifest refraction, autokeratometry and corneal topography. Vector analysis of astigmatic changes was performed using the Alpins vector method.

RESULTS

This study comprised 75 eyes from 67 patients. Mean residual refractive astigmatism at 3 months was -0.63 ± 0.55 D in the TIOL group and -0.90 ± 0.53 D in the FSAK group (P = 0.037) and was ≤ 1.00 D in 32 eyes (84%) and 25 eyes (64%), respectively. There were no statistically significant differences in difference vector (DV), angle error (AE), magnitude error (ME) or correction index (CI) in the 3-month follow-up. The index of success (IS) was 0.32 ± 0.33 D in the TIOL group and 0.48 ± 0.29 D in the FSAK group (P = 0.029).

CONCLUSION

TIOL implantation showed better results in correcting moderate astigmatism. Despite this, FSAK is shown to be a safe technique for reducing astigmatism.

Vector Analysis of Femtosecond Laser-Assisted Arcuate Keratotomy for Post-Keratoplasty Astigmatic Correction

PURPOSE

To study the astigmatic correction of high post-keratoplasty astigmatism using Femtosecond laser (FSL)-assisted Arcuate Keratotomy (FS-AK).

METHODS

A prospective interventional cohort study. We enrolled 17 eyes with high degree of irregular astigmatism, scheduled for FS-AK. FSL was used to perform paired arcuate incisions 1.00 mm inside the graft. Patients' uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), and astigmatic change were recorded and followed up to 1 year after surgery. Vector analysis using Alpins' method was done to analyze the astigmatic correction.

RESULTS

FS-AK reduced the refractive astigmatism at final follow-up visit at 12 months (p = 0.0008, repeated-measures analysis of variance [ANOVA]). The procedure improved the UCVA over the follow-up period (p = 0.007, repeated-measures ANOVA), with a similar effect on the BCVA (p = 0.046, repeated-measures ANOVA). There was a mild correlation between the target-induced astigmatism and the surgically induced astigmatism (R2 = 0.245) with a tendency to overcorrect more than under correct the astigmatism. A constant rotational error in the counterclockwise direction was also detected.

CONCLUSIONS

FS-AK improves the visual outcome and reduces the refractive cylinder in post-penetrating keratoplasty astigmatism. The predictability of astigmatism correction was variable in reducing post-keratoplasty astigmatism. Refinement of the treatment nomogram for such cases is highly recommended.

A novel nomogram for the treatment of astigmatism with femtosecond-laser arcuate incisions at the time of cataract surgery

Purpose

The purpose of this study was to determine an arcuate incision (AI) nomogram to treat astigmatism during femtosecond laser-assisted cataract surgery.

Methods

This is a retrospective, cohort study. Femtosecond laser (FSL)-assisted transepithelial AIs were created at a 9.0 mm optical zone, 80% depth, centered on the limbus. We modified the manual Donnenfeld limbal relaxing incision nomogram to 70% for with-the-rule (WTR), 80% for oblique (OBL), and 100% for against-the-rule (ATR) astigmatism. The correction index (CI) equaled AI-induced astigmatism/target-induced astigmatism. Measures included preoperative keratometric corneal cylinder (Pre Kcyl), postoperative Kcyl (Post Kcyl), and postoperative residual refractive astigmatism (Post RRA).

Results

Mean Pre Kcyl and 1–2 months Post RRA in 161 eyes of 116 patients were 0.626±0.417 diopters (D) (range 0.5–2 D), and 0.495±0.400 D (range 0–1.5 D), respectively. Mean absolute astigmatic changes (Pre Kcyl–Post Kcyl) without accounting for axis change in the WTR, ATR, and OBL groups were 0.165±0.383 D (P<0.001), 0.374±0.536 D (P<0.001), and 0.253±0.416 D (P=0.02), respectively. Mean absolute astigmatic changes using RRA as the postoperative measurement (Pre Kcyl–Post RRA) without accounting for axis change were 0.440±0.461 D (P<0.001), 0.238±0.571 D (P<0.05), 0.154±0.450 (P=0.111) in WTR, ATR, and OBL groups, respectively. CIs for WTR, ATR, and OBL were 0.53, 1.01, and 0.95, respectively. There were no intraoperative or postoperative complications related to the AIs.

Conclusion

Transepithelial FSL-AIs using the modified Donnenfeld nomogram show potential for management of mild to moderate corneal astigmatism. An increase in the magnitude or reduction of the optical zone size for the treatment of WTR and ATR astigmatism for this nomogram may further improve refractive accuracy.

Tomographic Analysis of Anterior and Posterior and Total Corneal Refractive Power Changes After Femtosecond Laser-Assisted Keratotomy

PURPOSE

To analyze the effect of penetrating femtosecond laser-assisted keratotomy (pFLAK) during laser lens surgery on anterior and posterior corneal astigmatism and total corneal refractive power (TCRP) astigmatism (CA_ant, CA_post, CA_TCRP) measured with Scheimpflug tomography.

DESIGN

Prospective, interventional case series.

METHODS

This institutional study included 27 eyes of 23 patients (aged 65 ± 8 years) with low-to-moderate CA_TCRP determined with Scheimpflug tomography (Pentacam HR; Oculus, Wetzlar, Germany) after penetrating femtosecond laser-assisted keratotomy (pFLAK) and laser lens surgery. The CA_ant, CA_post, and CA_TCRP were determined before and 1 and 3 months after surgery. Vector analysis according to the Alpins method was used to calculate surgically induced astigmatism (SIA).

RESULTS

The mean preoperative CA_ant (0.97 ± 0.30 diopter [D]) was significantly reduced to 0.63 ± 0.34 D (P < .001). SIA_ant was 0.71 ± 0.37 D. The CA_post showed no significant change, from preoperative 0.26 ± 0.12 D to 0.26 ± 0.10 D postoperatively (P = .625). In line with this finding, SIA_post was low (0.12 ± 0.07 D). The CA_TCRP showed similar results as CA_ant.

CONCLUSION

pFLAKs planned according to Scheimpflug-based CA_TCRP result in a significant reduction of the CA_ant and CA_TCRP, but do not affect the posterior corneal curvature significantly, as measured by Scheimpflug tomography. Further research is required to develop a new valid nomogram for laser-assisted lens surgery.

Femtosecond astigmatic keratotomy for postkeratoplasty astigmatism

PURPOSE

To evaluate the initial outcomes of femtosecond laser arcuate keratotomies (AK) to correct high astigmatism after keratoplasty.

METHODS

This retrospective non-comparative interventional study included 52 consecutive patients (52 eyes) who underwent Intralase-enabled arcuate keratotomies. Changes in uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BCVA), mean refractive and keratometric astigmatism, preoperative and postoperative manifest refraction and complications were the main outcome measures.

RESULTS

The mean follow-up period was 13.77 ± 4.17 months. Mean BCVA and UCVA improved statistically significantly from 0.30 ± 0.18 LogMAR and 0.90 ± 0.43 LogMAR preoperatively to 0.20 ± 0.14 and 0.60 ± 0.39 postoperatively respectively (P < 0.05, all comparisons). Mean subjective cylinder decreased statistically significantly from 7.15 ± 1.32 D preoperatively to 5.19 ± 2.25 D at the last postoperative visit (P = 0.0002). Two eyes (4%) lost one line or more of BCVA. Three patients (5.8%) had corneal perforation and only one eye required resuturing of the AK wound. Twelve patients (23%) were overcorrected.

CONCLUSIONS

AK performed with the femtosecond laser was relatively easy to perform, safe, and effective for treating post-keratoplasty astigmatism. There was a significant improvement in UCVA and BCVA with a very low rate of complications. A larger series is required to refine the nomogram to achieve a greater reduction in cylinder.

Full-Thickness Astigmatic Keratotomy Combined With Small-Incision Lenticule Extraction to Treat High-Level and Mixed Astigmatism

PURPOSE

To explore the clinical effects of combined full-thickness astigmatic keratotomy and small-incision lenticule extraction (SMILE) in patients who are inoperable using SMILE alone.

METHODS

We included 13 eyes of 9 patients with high-level or mixed astigmatism who underwent full-thickness astigmatic keratotomy followed by SMILE (secondarily) to correct the residual refractive error.

RESULTS

Six months after SMILE, the spherical equivalent was reduced from -4.83 ± 3.26 D to -0.17 ± 0.38 D (P < 0.001), and the astigmatism was reduced from 5.12 ± 0.96 D to 0.21 ± 0.22 D (P < 0.001). The uncorrected and corrected (CDVA) distance visual acuities improved from 1.07 ± 0.62 to 0.02 ± 0.13 (P < 0.001) and from 0.08 ± 0.14 to -0.01 ± 0.14 (P = 0.002), respectively. The CDVA improved by 1 or 2 Snellen lines in 8 cases (61.5%), and there was no loss in CDVA. All procedures were completed without intraoperative or postoperative complications.

CONCLUSIONS

This combined procedure was effective and safe for the treatment of high-level or mixed astigmatism.

Corneal coupling of astigmatism applied to incisional and ablative surgery

PURPOSE

To redefine measures of corneal coupling for use with incisional and ablation procedures for astigmatism.

SETTING

Private clinics, Melbourne, Victoria, Australia.

DESIGN

Retrospective nonrandomized study.

METHODS

The measures known as the coupling ratio (CR) and coupling constant (CC) were redefined to ensure validity in most cases of incisional procedures and laser vision correction procedures. In addition, a new measure--the coupling adjustment (CAdj)--was developed to quantify the amount of spherical adjustment that must be applied to compensate for coupling that occurs as a result of astigmatism treatment. These quantitative measures of coupling were applied to retrospective data to show their applicability.

RESULTS

Pure myopic, compound myopic, and compound hyperopic astigmatism excimer laser treatments showed a CR close to zero, a CC close to 0.5, and a CAdj close to zero. Incision LRIs showed a CR close to 1.0 and a CC close to zero. In all cases, the coupling measures were consistent for treatments with a larger astigmatic component (>1.0 diopter) but variable when the astigmatic component of the treatment was smaller.

CONCLUSIONS

The revised definitions of CR and CC can be used with incisional and ablative surgery. Incorporating the CAdj into the planning of spherocylindrical treatments allows one to factor in the effect of the astigmatic treatment on the spherical component and thus to more accurately target the desired spherical equivalent.

FINANCIAL DISCLOSURE

Dr. Alpins and Mr. Stamatelatos have a financial interest in the Assort software program. Dr. Ong is an employee of Assort.

Toric intraocular lens implantation versus astigmatic keratotomy to correct astigmatism during phacoemulsification

PURPOSE

To compare toric intraocular lens (IOL) implantation and astigmatic keratotomy (AK) in correction of astigmatism during phacoemulsification.

SETTING

Tertiary care hospital.

DESIGN

Prospective randomized trial.

METHODS

Consecutive patients with visually significant cataract and moderate astigmatism (1.25 to 3.00 diopters [D]) were randomized into 2 groups. Temporal clear corneal 2.75 mm phacoemulsification with toric IOL implantation was performed in the toric IOL group and with 30-degree coupled AK at the 7.0 mm optic zone in the keratotomy group. The uncorrected (UDVA) and corrected (CDVA) distance visual acuities, refraction, keratometry, topography, central corneal thickness, and endothelial cell density were evaluated preoperatively and 1 day, 1 week, and 1 and 3 months postoperatively.

RESULTS

The study enrolled 34 eyes (34 patients), 17 in each group. There was no difference in UDVA or CDVA between the 2 groups at any follow-up visit. The mean preoperative and postoperative refractive cylinder was 2.00 D ± 0.49 (SD) and 0.33 ± 0.17 D, respectively, in the toric IOL group and 1.95 ± 0.47 D and 0.57 ± 0.41 D, respectively, in the keratotomy group (P=.10). The mean residual astigmatism at 3 months was 0.44 ± 1.89 @ 160 in the toric IOL group and 0.77 ± 1.92 @ 174 in the keratotomy group (P=.61). All eyes in the toric IOL group and 14 eyes (84%) in the keratotomy group achieved a residual refractive cylinder of 1.00 D or less (P=.17).

CONCLUSION

Toric IOL implantation was comparable to AK in eyes with moderate astigmatism having phacoemulsification.

Bilateral femtosecond laser-enabled intrastromal astigmatic keratotomy to correct high post-penetrating keratoplasty astigmatism

A 35-year-old man presented with bilateral high astigmatism following penetrating keratoplasties performed for advanced keratoconus. Femtosecond laser-enabled intrastromal astigmatic keratotomy was performed, resulting in a significant reduction in corneal astigmatism. At 4 months, the corneal astigmatism continued to decrease. The visual acuity, refraction, and serial corneal topographic data are presented.

Simultaneous phacoemulsification and graft refractive surgery in penetrating keratoplasty eyes

Purpose. To report outcomes of graft refractive surgery (GRS) along with clear-cornea phacoemulsification and intraocular lens (IOL) implantation in penetrating keratoplasty (PKP) eyes. Methods. Fourteen eyes of 13 patients who had received PKP underwent simultaneous GRS (relaxing incisions with or without counter-quadrant compression sutures) and clear-cornea phacoemulsification with IOL implantation. To calculate IOL power, preoperative keratometry readings and the SRK-T formula were used. Results. Mean patient age and follow-up period were 50.5 ± 14.4 years and 14.6 ± 7.1 months, respectively. A significant increase was observed in best spectacle-corrected visual acuity (from 0.55 ± 0.18 logMAR to 0.33 ± 0.18 logMAR, P = 0.001). There was a significant decrease in vector keratometric astigmatism by 6.22 D (P = 0.03). Spherical equivalent refraction was reduced from −3.31 ± 3.96 D to −1.69 ± 2.38 D (P = 0.02) which did not significantly differ from the target refraction (−0.76 ± 0.14 D, P = 0.20). No complications developed and all the grafts remained clear at the final examination. Conclusion. Simultaneous phacoemulsification and GRS is a safe and effective method to address post-PKP astigmatism and lens opacity. IOL power can be calculated from preoperative keratometry readings with an acceptable accuracy. However, patients should be informed about the possibility of high refractive errors postoperatively.

Long-term refractive stability following combined astigmatic keratotomy and phakoemulsification

BACKGROUND

To determine whether combined astigmatic keratotomy and cataract surgery induces a sustained reduction in astigmatism.

METHODS

Patients who had previously undergone combined cataract surgery and astigmatic keratotomy for naturally occurring astigmatism were identified and their notes reviewed. Mean final follow-up was 34 months (30-42 months). Fourteen eyes of 11 patients were eligible for study. Arcuate corneal incisions had been employed using the Buzard nomogram. Using power vector analysis, the post-operative refractive change at 6 months and final follow-up was determined.

RESULTS

The mean preoperative manifest cylindrical refractive error was 2.88 D (1.50-5.50 D). The mean postoperative manifest cylindrical refractive error was 1.89 and 1.79 D at 6 months and final follow-up, respectively. Power vector analysis demonstrated a significant postoperative reduction in refractive blur at 6 months and final follow-up (P = 0.006, P = 0.004, respectively): mean preoperative blur strength was 2.90 D and mean postoperative blur strength was 1.33 and 1.25 D at 6 months and final follow-up, respectively. Sustained postoperative reduction in astigmatism was noted in 12 of 14 eyes at final follow-up.

CONCLUSIONS

Astigmatic keratotomy is a well-established treatment for astigmatism. In this series, the refractive benefit from combined astigmatic keratotomy and cataract surgery is maintained for several years. No surgical complications were observed.

Biometry and formula accuracy with intraocular lenses used for cataract surgery in extreme hyperopia

PURPOSE

To audit intraocular lens (IOL) power predictions for cataract surgery in extreme hyperopia and to compare the accuracy across different biometry formulae and IOL types.

DESIGN

A retrospective analysis of 76 eyes from 56 patients undergoing cataract surgery with IOLs ranging in power from 30 to 35 diopters (D).

METHODS

Axial lengths, corneal powers and anterior chamber depths were measured with ultrasound or optical methods, and the IOLMaster (Carl Zeiss Meditech, Inc, Dublin, California, USA) software was used to predict the refractive outcome for each IOL used. Differences between the predicted and actual postoperative refraction were then analyzed for each formula.

RESULTS

In practice, 55% of patients were within +/-1.0 D of the refraction predicted by their surgeon. In theory, the Haigis formula would have given the smallest mean refractive error (+0.51 +/- 0.12 D), followed by the Hoffer Q (-0.70 +/- 0.14 D), Holladay 1 (-1.11 +/- 0.13 D), and SRK/T formulae (-1.45 +/- 0.14 D). The Haigis formula overpredicted the lens power required, which would have generated a myopic result. The other formulae underpredicted the lens power required and would have generated a hyperopic result. There was a significant difference between lens designs: the Haigis was more accurate for open-loop, whereas the Hoffer Q was more accurate for plate-haptic lenses. The anterior chamber depth measurement could also be used to predict changes in intraocular pressure after surgery.

CONCLUSION

This represents the largest published series to date of biometry predictions for cataract surgery in extreme hyperopia and confirms the Haigis formula to be the most accurate. A consistent difference between open-loop and plate-haptic lenses suggests that haptic design may influence the effective lens position in very small eyes. We further propose a simple formula to optimize the Haigis and Hoffer Q formulae in patients with extreme hyperopia.

Conductive Keratoplasty and the Coupling Phenomenon

PURPOSE

To determine whether changes in corneal astigmatism with astigmatic conductive keratoplasty (CK) treatment obey Gaussian coupling (i.e., the steepening of the flat axis associated with the flattening of the steep axis) and to measure the coupling ratio and the coupling constant to determine the effect of astigmatic CK treatment on spherical equivalent.

METHODS

Retrospective review of 33 eyes in 24 patients who had undergone CK for hyperopia and who were treated intraoperatively for induced astigmatism. Induced astigmatism was determined by comparison of keratometric readings before and after CK.

RESULTS

The coupling ratio was calculated according to two equations: clinical coupling ratio (1.61 +/- 0.81 diopters) and coupling ratio of the surgically induced refractive change (1.57 +/- 1.16 diopters). Values of the coupling ratio between 0.72 and 1.88 indicate coupling.

CONCLUSIONS

The cornea does not behave according to Gauss's law of elastic domes. The targeted flat axis and steep axis 90 degrees away are affected by CK in opposite but not equal amounts. Therefore, when correcting surgically induced astigmatism with CK, the overall spherical equivalent of the patient will change because the coupling ratio is not equal to 1.

Repeat keratoplasty for correction of high or irregular postkeratoplasty astigmatism in clear corneal grafts

PURPOSE

To evaluate the functional results of repeat penetrating keratoplasty in clear corneal grafts with high/irregular postkeratoplasty astigmatism.

DESIGN

Retrospective, longitudinal, single-center, consecutive clinical case series.

METHODS

We studied 17 eyes (16 keratoconus, 1 Fuchs' dystrophy) of 16 patients (age, 54.9 +/- 12.6 years). They were treated with repeat PK, performed using the 193-nm Zeiss-Meditec MEL-60 excimer laser using round metal masks (diameter, 7.5-8.0 mm), and employing double running sutures. main outcome measures: Subjective refractometry, standard keratometry, and corneal topography (Tomey TMS-1) were used to assess best-corrected visual acuity (BCVA), spherical equivalent (SEQ), keratometric and topographic central corneal power (CP), refractive, keratometric and topographic astigmatism, surface regularity index (SRI), surface asymmetry index (SAI), and potential visual acuity (PVA) preoperatively, before and after first suture removal (1.1 year), and after second suture removal (1.8 years).

RESULTS

Visual acuity improved significantly (BCVA from 0.2-0.5, P = .04 or better) for all postoperative measurements. CP decreased significantly, but SEQ did not change. All measures of astigmatism and SRI and SAI values showed postoperative improvement with sutures in place; however, astigmatism increased significantly after second suture removal.

CONCLUSIONS

With all-sutures-in, BCVA and astigmatism improve significantly after repeat PK for high/irregular astigmatism. However, to present significant increase in astigmatism, final suture removal should be postponed as long as possible in such eyes.

Bitoric laser in situ keratomileusis for astigmatism

PURPOSE

To evaluate the efficacy, predictability, and safety of bitoric laser in situ keratomileusis (LASIK) for the correction of mixed astigmatism.

SETTING

Instituto Oftalmológico de Alicante, Alicante, Spain.

METHODS

This prospective study included 28 eyes of 21 patients with mixed astigmatism who had bitoric LASIK using the Hansatome microkeratome (Bausch & Lomb Surgical) and the Chiron Technolas 217 excimer laser (Bausch & Lomb Surgical). The main outcome measures were uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), defocus equivalent, blur strength, and refraction.

RESULTS

Six months after bitoric LASIK, the mean UCVA was 0.70 +/- 0.23 (SD). The percentage of eyes with a UCVA of 20/40 or better was 78.6% and of 20/20, 21.4%. There was a statistically significant increase in the mean BCVA from 0.71 +/- 0.19 before surgery to 0.83 +/- 0.15 at 6 months (P =.0004). Three eyes (10.7%) lost 1 line of BCVA; 19 eyes (67.9%) gained 1 or more lines. The mean preoperative astigmatism of -4.04 +/- 1.13 diopters (D) was reduced to -0.67 +/- 0.79 D after surgery. The defocus equivalent was less than 1.00 D in 75.0% of eyes and less than 0.50 D in 64.3%. Vector analysis showed that the mean achieved correction was 97.4% of the intended correction.

CONCLUSIONS

Bitoric LASIK was a safe, effective, and predictable procedure in the treatment of mixed astigmatism. It is a means to improving BCVA in a significant percentage of patients.

Correction of astigmatism with short arc-length intrastromal corneal ring segments: preliminary results

OBJECTIVE

To evaluate the refractive effect of 130 degrees short arc length intrastromal corneal ring segments (ICRS) designed to correct myopia concurrent with astigmatism.

DESIGN

Prospective, nonrandomized, comparative (self-controlled) trial.

PARTICIPANTS

Ten eyes of 6 patients from one surgical center with manifest refraction spherical equivalent between -1.00 and -6.00 diopters (D), manifest cylinder correction between 1.00 and 6.00 D, and best spectacle-corrected visual acuity of 20/20 or better.

INTERVENTION

The patients were assigned to receive 1 of 6 ICRS thicknesses, ranging from 0.25 to 0.50 mm by 0.05 mm increments, with an arc length of 130 degrees.

MAIN OUTCOME MEASURES

Vector analysis of astigmatic correction. Efficacy was assessed by uncorrected visual acuity and by deviation of postoperative spherical and cylindrical refractive error from predicted correction. Safety was assessed by maintenance or loss of preoperative best spectacle-corrected visual acuity. Measurements were made before surgery and after surgery at days 1 and 7 and months 1, 2, 3, and 6.

RESULTS

At 6 months, uncorrected visual acuity was 20/20 or better in 80% of eyes (8/10) and 20/40 or better in all eyes. Eight of 10 eyes (80%) were within +/-0.25 D of plano spherical equivalent manifest refraction. There was no loss of best spectacle-corrected visual acuity, and 6 of 10 eyes (60%) gained a line. Reduction of keratometric cylinder by ICRS thickness was statistically significant (P = 0.039).

CONCLUSIONS

Preliminary results of visual and refractive performance after correction of compound myopic astigmatism using short arc length ICRS are promising.

Intraoperative Arcuate Transverse Keratotomy With Phacoemulsification

PURPOSE

To evaluate the efficacy of paired intraoperative arcuate transverse keratotomy at a 7-mm-diameter zone along with a 3.5-mm clear corneal phaco tunnel in the steeper axis to correct pre-existing astigmatism.

METHODS

A prospective randomized case-control study was conducted on 34 eyes of 28 patients with immature senile cataract. They were divided into two groups; in one group (17 eyes) intraoperative arcuate keratotomy was coupled with phacoemulsification in the steeper meridian (arcuate keratotomy group; mean preoperative astigmatism 2.28 +/- 0.89 D) and the other group (17 eyes) phacoemulsification was performed in the steeper meridian without arcuate keratotomy (control group; mean preoperative astigmatism 2.04 +/- 0.50 D). The patients were examined at 1 day, and 1, 4, and 8 weeks postoperatively. Correction of keratometric astigmatism, surgically induced refractive changes, magnitude and axis of cylinder, spherical equivalent refraction, with and against the wound change, and coupling ratio were evaluated.

RESULTS

Mean reduction in keratometric astigmatism in the keratotomy group was 1.26 +/- 0.54 D (P = .0067) and in the control group was 0.48 +/- 0.60 D (P = .0423). The difference in reduction of keratometric astigmatism between the two groups was statistically significant (P = .0296). Surgically induced refractive change at 8 weeks follow-up was 2.15 +/- 1.13 D in the keratotomy group and 1.50 +/- 1.32 D in the control group (P = .046). Coupling ratio was -1.10 +/- 0.43 in the keratotomy group at 8 weeks after surgery while the control group was -0.82 +/- 0.38.

CONCLUSION

A combination of intraoperative arcuate keratotomy with steep axis phacoemulsification incision is more effective than steep axis phacoemulsification incision alone in reducing pre-existing astigmatism.

Factors that influence the surgical effects of astigmatic keratotomy after cataract surgery

OBJECTIVE

To determine the factors affecting the surgical effect of astigmatic keratotomy (AK) when against-the-rule astigmatism is present following cataract surgery.

DESIGN

Prospective interventional noncomparative case series.

PARTICIPANTS

Twenty eyes of 19 patients from four medical centers who had against-the-rule astigmatism following cataract surgery.

INTERVENTION

AK with a 6 mm optical zone, two linear 3-mm length incisions (T-cut) and a depth of 90% of the central thickness was performed on all subjects.

MAIN OUTCOME MEASURES

Vector analysis of astigmatic correction. Multiple regression analysis for seven covariates including age, spherical equivalent of the manifest refraction, preoperative astigmatism, corneal diameter, corneal thickness, mean radius of corneal curvature and axial misalignment.

RESULTS

Multiple regression analysis showed that the preoperative astigmatism (p = 0.014) and the axis deviation (p = 0.005) were significantly correlated with the surgical effects.

CONCLUSIONS

Even with a uniform surgical procedure, the surgical effects of AK in eyes with against-the-rule astigmatism can be affected by the amount of preoperative astigmatism and the intraoperative axis misalignment. Adding the amount of preoperative astigmatism to the nomogram and improvement of surgical procedures will be required to obtain better surgical predictability of AK following cataract surgery.

Prospective evaluation of a plate haptic toric intraocular lens

PURPOSE

Standard intraocular lenses (IOL) only correct the spherical component of aphakic refractive error. This study describes clinical experience with a foldable, injectable, toric IOL.

METHODS

Keratometric, refractive and visual data were collected on patients listed for cataract surgery. Toric IOLs were offered where keratometric cylinder was greater than 1.5 dioptres. Small-incision phacoemulsification surgery was performed and the IOL implanted with its long axis along the steep corneal axis. Post-operative refractive data were compared with pre-operative and expected refraction using vector analysis software.

RESULTS

Results of 22 eyes of 16 consecutive patients implanted with toric IOLs are reported. Two IOLs rotated more than 30 degrees in the first 24 h and were re-dialled surgically. Two further IOLs (9%) rotated more than 30 degrees during follow-up. In 21 of 22 eyes (95%) the refractive astigmatism was reduced, with a mean 73% of planned correction (vector analysis) achieved.

CONCLUSIONS

The toric IOL is a useful surgical tool to reduce the refractive effects of pre-existing corneal astigmatism. Design modification to prevent IOL rotation would make results more predictable.

Advances in refractive surgery: 1975 to the present

PURPOSE

To review the major advances in the field of refractive surgery occurring over the past 25 years.

METHODS

Literature review.

RESULTS

The major developments in refractive surgery over the past 25 years are reviewed.

CONCLUSIONS

The past 25 years have witnessed great changes in refractive surgery. As a result of advancements in technology, instrumentation, and technique, we have seen improvements in the treatment of all types of ametropias. In this article, we review some of the successes and failures of the past quarter-century.