Femtosecond-Assisted Arcuate Keratotomy for the Correction of Postkeratoplasty Astigmatism: Vector Analysis and Accuracy of Laser Incisions

Management of post-keratoplasty ametropia

Even after a successful corneal transplant, patients experience severe refractive errors, impeding their rehabilitation and satisfaction. Refractive errors can be caused by recipient pathology and corneal thickness, as well as intraoperative factors such as donor-host discrepancy, recipient's eccentric trephination, vitreous length, wound apposition, technique of suturing, and suture material. Also, wound healing and the interim between keratoplasty and suture removal contribute to astigmatism. Lamellar keratoplasty outperforms penetrating keratoplasty in terms of endothelial cell loss and endothelial graft rejection, yet the risk of developing refractive errors is comparable. Nonsurgical interventions such as spectacles and lenses fail to provide desirable vision in cases with high astigmatism and corneal irregularity. When these limitations are encountered, surgical interventions including incisional keratotomy, wedge resection, laser refractive surgeries, intracorneal segments, and intraocular lens implantation are employed. However, occasionally, none of these approaches deliver the desired effects, leading to the need for a repeat keratoplasty.

Transepithelial or intrastromal femtosecond laser arcuate keratotomy to manage corneal astigmatism at the time of cataract surgery

PURPOSE

The aim of this study was to compare the results of intrastromal arcuate incisions (AIs) and transepithelial AIs to treat corneal astigmatism during femtosecond laser-assisted cataract surgery (FLACS).

METHODS

This retrospective study included 20 patients with corneal astigmatism between 0.70 and 2.00 diopters (D) who underwent FLACS with concurrent intrastromal AIs in one eye and transepithelial AIs in the fellow eye. The main outcomes measures at 2-3 months of follow-up were the difference between pre-operative and postoperative keratometric corneal cylinder (Kcyl), the correction index (CI) and the percentage of overcorrection.

RESULTS

The mean difference between preoperative and postoperative Kcyl revealed a mean value of 0.36 ± 0.37 D in the transepithelial group and 0.53 ± 0.42 D in the intrastromal group (p < 0.001). The mean CI was 0.83 ± 0.71 in the transepithelial group and 0.68 ± 0.29 in intrastromal group (p = 0.17). Five eyes (25 %) had an astigmatism overcorrection in the transepithelial group and 1 eye (5%) in the intrastromal group.

CONCLUSIONS

Both intrastromal and transepithelial AIs showed potential for mild to moderate astigmatism correction and appeared to be a safe procedure. Despite transepithelial AIs presented a higher CI, the intrastromal AIs results were more predictable.

Two-year outcomes after full-thickness astigmatic keratotomy combined with small-incision lenticule extraction for high astigmatism

Background

To evaluate clinical outcomes after full-thickness astigmatic keratotomy (FTAK) combined with small-incision lenticule extraction (SMILE) in eyes with high astigmatism.

Methods

This study comprised 75 eyes of 43 patients with over 4.0 diopters (D) of astigmatism who were treated with SMILE after FTAK. Visual acuities and refractive measurements were evaluated at 1 month after FTAK, and 1, 6, 12, and 24 months after SMILE. Vector analysis of the astigmatic changes was performed using the Alpins method.

Results

Twenty-four months after the combined procedure, the average spherical equivalent was reduced from − 6.56 ± 2.38 D to − 0.36 ± 0.42 D (p < 0.001). The uncorrected and corrected distance visual acuities improved from 1.54 ± 5.53 to − 0.02 ± 0.09 and from − 0.03 ± 0.07 D to − 0.07 ± 0.08 D (both p < 0.001), respectively. The preoperative mean astigmatism was − 5.48 ± 1.17 D, which was reduced to − 2.27 ± 0.97 D and − 0.34 ± 0.26 D at 1 month after FTAK and 24 months after SMILE, respectively (p < 0.001). The surgically-induced astigmatism after FTAK, SMILE, and FTAK and SMILE combined was 3.38 ± 1.18 D, 2.22 ± 0.84 D, and 5.39 ± 1.20 D, respectively. Furthermore, the correction index of FTAK, SMILE, and FTAK and SMILE combined was 0.63 ± 0.17, 0.90 ± 0.40, and 0.98 ± 0.06, respectively. There were no intraoperative or postoperative complications.

Conclusion

Our surgical procedure combining FTAK and SMILE showed good and stable clinical outcomes during two-year follow-up for the treatment of high astigmatism.

Transepithelial or intrastromal femtosecond laser arcuate keratotomy to manage corneal astigmatism at the time of cataract surgery

PURPOSE

The aim of this study was to compare the results of intrastromal arcuate incisions (AIs) and transepithelial AIs to treat corneal astigmatism during femtosecond laser-assisted cataract surgery (FLACS).

METHODS

This retrospective study included 20 patients with corneal astigmatism between 0.70 and 2.00 diopters (D) who underwent FLACS with concurrent intrastromal AIs in one eye and transepithelial AIs in the fellow eye. The main outcomes measures at 2-3months of follow-up were the difference between preoperative and postoperative keratometric corneal cylinder (Kcyl), the correction index (CI) and the percentage of overcorrection.

RESULTS

The mean difference between preoperative and postoperative Kcyl revealed a mean value of 0.36±0.37D in the transepithelial group and 0.53±0.42D in the intrastromal group (P<.001). The mean CI was 0.83±0.71 in the transepithelial group and 0.68±0.29 in intrastromal group (P=.17). Five eyes (25%) had an astigmatism overcorrection in the transepithelial group and 1eye (5%) in the intrastromal group.

CONCLUSIONS

Both intrastromal and transepithelial AIs showed potential for mild to moderate astigmatism correction and appeared to be a safe procedure. Despite transepithelial AIs presented a higher CI, the intrastromal AIs results were more predictable.

Astigmatic correction by intrastromal astigmatic keratotomy during femtosecond laser-assisted cataract surgery: Factors in outcomes

PURPOSE

To evaluate the 6-month outcomes of femtosecond laser astigmatic keratotomy (AK) combined with femtosecond laser-assisted cataract surgery and identify factors affecting the efficacy of astigmatic correction.

SETTING

Seoul St. Mary's Hospital, Catholic University of Korea, Seoul, South Korea.

DESIGN

Retrospective case series.

METHODS

Femtosecond laser AK was performed during femtosecond laser-assisted cataract surgery. The keratometric astigmatism, refractive cylinder, corneal hysteresis (CH), and corneal resistance factor (CRF) were measured preoperatively and postoperatively at 1 week, 2 months, and 6 months. Vector analysis to evaluate the 6-month outcomes of femtosecond laser AK and univariable regression analysis to determine the factors influencing the correction index were performed.

RESULTS

The study enrolled 89 eyes of 89 patients. The stigmatism type, CH, CRF, and absolute angle of error showed significant correlations with the correction index (P = .041, P = .029, P = .044, and P < .001, respectively). There was a significant difference in the correction index and no difference in keratometric astigmatism between with-the-rule (WTR), against-the-rule (ATR), and oblique astigmatism (P = .044). The keratometric astigmatism with ATR and oblique astigmatism (0.66 diopter [D] ± 0.42 [SD] and 0.46 ± 0.27 D, respectively) was significantly lower than the refractive cylinder (0.92 ± 0.56 D and 0.78 ± 0.43 D, respectively) (P < .05); this was not the case for WTR astigmatism.

CONCLUSIONS

The efficacy of femtosecond laser AK was affected by the biomechanical properties of the cornea and astigmatism type. Further studies incorporating the individual biomechanical properties of the cornea and total corneal astigmatism in a nomogram are recommended.

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.

Comparison of manual and femtosecond laser arcuate keratotomy procedures for the correction of post-keratoplasty astigmatism

Purpose

To compare the effectiveness of femtosecond laser (FSL) assisted and manual arcuate keratotomy (AK) procedures for the correction of postkeratoplasty astigmatism.

Methods

Fifty-two eyes (52 patients) were treated with FSL assisted AK and 53 eyes (51 patients) with manual AK for post-keratoplasty astigmatism. The main outcome measures included preoperative and postoperative manifest refraction, uncorrected and corrected distance visual acuity (UDVA, CDVA), corneal topography and complications.

Results

In FSL group, UDVA changed significantly from 0.90 ± 0.43 preoperatively to 0.60 ± 0.39 at last follow-up (p = 0.001). In manual group, preop- (0.87 ± 0.35) and post-operative UDVA (0.93 ± 042) were comparable (p = 0.535). CDVA improved from 0.30 ± 0.18 preoperatively to 0.20 ± 0.14 at last follow-up visit in FSL group (0.014) and 0.28 ± 0.15 preoperative to 0.23 ± 0.19 at last postoperative visit (0.074) in manual group. Postoperative UDVA and CDVA were comparable between both the groups (p > 0.05). The mean preoperative refractive cylinder was 6.38 ± 3.73 and 7.15 ± 132, decreasing significantly to 5.06 ± 2.06 and 5.19 ± 2.25 after manual and FSL assisted AK procedures respectively. Mean change in the refractive cylinder was −1.10 ± 4.11 in manual AK group and −2.19 ± 2.35 in FSL group (p = 0.134). Perforation, overcorrection and regression occurred in respectively 3 eyes (5.8%), 12 eyes (23.07%) and 1 eye (1.92%) in FSL group and 1 eye (1.9%; macro-perforation), 7 eyes (13.21%) and 8 eyes (15.09%) in manual group. Additionally, in the manual group, severe ectasia occurred in 1 eye (1.9%).

Conclusion

FSL assisted AK procedure is comparable or to a certain extent better regarding safety and efficacy than manual AK procedure. Postoperatively, FSL resulted in better outcomes of UCVA, BCVA, refractive cylinder and keratometric astigmatism compared to the manual AK procedures; although, the difference between the groups was not statistically significant.

Intraocular lens bicylindric power calculation method: Using both flat and steep K readings to improve intraocular lens power prediction

PURPOSE

To compare and analyze the accuracy of the refractive outcomes obtained in intraocular lens power calculation using the classical calculation method with mean keratometry (K) and the calculation method with both K meridians presented in this article.

METHODS

A total of 62 eyes of 62 subjects who were undergoing cataract surgery were included in this study. Optical biometry was performed using mean K and Haigis formula for classical intraocular lens calculation methods to achieve intraocular lens power; 4 weeks after surgery, prior to medical discharge, subjective refraction was made. Alternatively, intraocular lens power was calculated with bicylindric method using both keratometry readings, obtaining spherocylindrical refractive expected outcomes. Finally, results obtained with intraocular lens calculation methods, bicylindric method, and Haigis formula were compared.

RESULTS

Spherical equivalent calculated by classical intraocular lens calculation methods using Haigis formula (H-SE) was -0.027 ± 0.115 D and using bicylindric method (B-SE) was -0.080 ± 0.222 D. Achieved spherical equivalent obtained 4 weeks after surgery (A-SE) was -0.144 ± 0.268 D. Difference between H-SE and A-SE was -0.117 D (p = 0.002). Difference between B-SE and A-SE was not significant (-0.054 D, p = 0.109). Analysis in refraction groups showed a positive correlation between A-SE confronted to B-SE and H-SE (r = 0.313; p = 0.013 and r = 0.562; p < 0.001, respectively). This indicated a reliability in ametropic group prediction of 0.767 in H-SE and 0.843 in B-SE.

CONCLUSION

Intraocular lens calculation with bicylindric method could be more accurate and had more reliability than classical intraocular lens calculation method. Bicylindric method adds astigmatism control and provides a reliable expected spherocylindrical refraction.

Femtosecond laser-assisted astigmatic keratotomy: a review

Background

Astigmatic keratotomy (AK) remains an accessible means to correct surgically induced or naturally occurring astigmatism. The advantages of femtosecond laser-assisted astigmatic keratotomy (FSAK) over conventional methods have been recognized recently.

Main text

This review evaluates the efficacy, complications, and different methods of FSAK for correction of astigmatism in native eyes and those that underwent previous penetrating keratoplasty (PKP).

The penetrating and intrastromal FSAK (IFSAK) techniques can reduce post-keratoplasty astigmatism by 35.4% to 84.77% and 23.53% to 89.42%, respectively. In native eyes, the penetrating and IFSAK techniques reduce astigmatism by 26.8% to 58.62% and 36.3% to 58% respectively, implying that the magnitude of the astigmatic reduction is comparable between the two FSAK procedures. Nonetheless, IFSAK offers the additional advantages of almost no risk of infection, wound gape, and epithelial ingrowth. The use of nomograms, anterior-segment optical coherence tomography, and consideration of posterior cornea and corneal biomechanics are helpful to enhance the efficacy and safety of FSAK. The complications of FSAK in eyes that underwent PKP include overcorrection, visual loss, microperforations, infectious keratitis, allograft rejection, and endophthalmitis. The reported difficulties in native eyes include overcorrection, anterior gas breakthrough, and suction loss.

Conclusions

In eyes that underwent PKP, FSAK effectively reduces high regular or irregular astigmatism, with rare and manageable complications. Nevertheless, the drawbacks of the procedure include the potential loss of visual acuity and low predictability. For native eyes undergoing femtosecond laser-assisted cataract surgery, IFSAK is a good choice to correct low astigmatism (< 1.5 diopters). The refractive effect of astigmatism from the posterior cornea needs to be considered in the nomograms for native eyes undergoing refractive cataract surgery. To further improve the efficacy of FSAK, more large-scale randomized studies with longer follow-up are needed.

Post-keratoplasty astigmatism management by relaxing incisions: a systematic review

Postoperative visual acuity can be limited by post-keratoplasty astigmatism, even with a clear corneal graft. Astigmatism management can be performed by selective suture removal, adjustment of sutures, optical correction, photorefractive procedures, wedge resection, intra-ocular lens implantation, intracorneal ring segments, relaxing incisions with or without compression sutures and repeated keratoplasty. Relaxing incisions can be made in the graft, graft-host interface or host cornea. Despite the unpredictability of the method because the flat and steep meridians are usually not orthogonal after penetrating keratoplasty, with asymmetric power distribution, all the studies showed an overall reduction of refractive, keratometric or topographic astigmatism, ranging from 30% to 72% with manual or femtosecond-assisted techniques. Most patients with astigmatism higher than 6 diopters had residual cylinder less than or equal to 3 diopters, which can be treated by laser excimer ablation or secondary intraocular lens implantation.