Evaluation of Femtosecond Laser Intrastromal Incision Location Using Optical Coherence Tomography

Outcome of astigmatism correction using femtosecond laser combined with cataract surgery: penetrating vs intrastromal incisions

PURPOSE

To compare the effectiveness of penetrating vs intrastromal femtosecond laser corneal relaxing incisions (CRI) in reducing corneal astigmatism during cataract surgery.

SETTINGS

Baylor College of Medicine and Mercy Clinic Eye Specialists.

DESIGN

Prospective randomized study.

METHODS

Subjects were randomly assigned to undergo paired penetrating (8-mm optical zone (OZ) at one center and 9-mm OZ at the other) or intrastromal CRIs (8-mm OZ at both centers). The lengths of the CRIs were based on published nomograms but modified to take into account posterior corneal astigmatism. Vector analysis was performed, and net corneal changes along the CRI meridian were calculated. Multiple regression analysis was performed to assess factors contributing to net corneal changes.

RESULTS

Preoperatively, 9-18% of eyes had corneal astigmatism of ≤ 0.5 D, and 76-93% of eyes had postoperative refractive astigmatism of ≤ 0.5 D (P<0.05). Both penetrating and intrastromal CRIs produced significant mean net corneal changes along the CRI meridian (-0.49 D to -1.21 D), and 71% - 84% of eyes had postoperative astigmatism vector prediction errors of ≤0.50 D. The 8-mm penetrating CRIs induced greater net corneal changes but more eyes with overcorrection than did the intrastromal and 9-mm penetrating CRIs (all P<0.05). Greater net corneal changes occurred with longer CRI length, higher preoperative corneal astigmatism magnitude, and preoperative against-the-rule corneal astigmatism. Nomograms based on anterior and total corneal astigmatism are proposed.

CONCLUSIONS

Both penetrating and intrastromal CRIs were effective in reducing corneal astigmatism during cataract surgery.

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.

Correcting astigmatism at the time of cataract surgery: Toric IOLs and corneal relaxing incisions planned with an image-guidance system and intraoperative aberrometer versus manual planning and surgery

PURPOSE

To compare the outcomes of the combination of an image-guided system and intraoperative aberrometer with the surgeon's standard of care in correcting astigmatism using toric intraocular lenses (IOLs) or corneal incisions.

SETTING

Single site in United States.

DESIGN

Prospective case series.

METHODS

Contralateral eyes of patients having uncomplicated bilateral cataract surgery and astigmatism correction were randomly assigned to Group A or Group B. Group A received the surgeon's preferred standard of care. Group B had preoperative planning using an image-guidance system (VERION), intraoperative aberrometry (ORA System with VerifEye+), and femtosecond laser-assisted cataract surgery. The primary endpoint was the residual refractive astigmatism at 3 months.

RESULTS

Thirty-eight eyes were treated with toric IOLs and 40 eyes with corneal astigmatic incisions. On average, toric IOLs resulted in almost 0.25 diopter (D) less cylinder than corneal astigmatic incisions (P < .01), with no difference between groups (P = .41). There was no statistically significant difference in the mean spherical equivalent refraction by group (P = .51). At 3 months, the IOL in 4 eyes (11%) (2 in Group A and Group B each) was more than 10 degrees of absolute orientation from the intended orientation. The mean keratometry was 0.16 D higher with the image-guided system compared with optical biometry (Lenstar). The vector difference between the 2 measurements was 0.5 D or lower in all eyes.

CONCLUSIONS

The combined use of an image-guided system and intraoperative aberrometer did not significantly improve outcomes compared with the surgeon's standard of care. Based on keratometry, there was good agreement in corneal astigmatism measurements between the image-guided system and the optical biometer.

Architecture evaluation of the main clear corneal incisions in femtosecond laser-assisted cataract surgery by optical coherence tomography imaging

Purpose

To assess the stability and reliability of femtosecond laser-assisted cataract surgery (FLACS) incisions design and dimensions using anterior segment optical coherence tomography (AS-OCT) imaging.

Setting

Renato Ambrósio Ophthalmologic Study Center from Hospital Oftalmológico de Brasília, Brasília, Brazil.

Design

Prospective nonrandomized controlled case series.

Methods

Eyes undergoing FLACS with triplanar main temporal clear corneal incision (CCI) were evaluated at the end of the case. Eyes that required any incision hydration, surgical complications or lacked follow-up were excluded. The AS-OCT was performed after femtosecond delivery; at the end of the case; at 1 day and at 30 days after surgery. Data of pachymetry, endothelial and epithelial gaps, Descemet detachment and CCI architecture were compared.

Results

Eleven eyes from 11 patients completed follow-up. Corneal thickness was statistically different between after femtosecond delivery and the end of the case (P-value <0.05), but without difference compared to 30 days evaluation. There was an increase of Descemet detachments (P-value <0.05) and endothelial gaps (P-value =0.0133) at the end of the case compared to post-femtosecond delivery. As for the architecture of the CCI, significant difference was found between the parameters of entry angle and exit angle measured with AS-OCT and the programmed.

Conclusion

The AS-OCT was capable of visualizing changes in the cornea at the CCI. Despite the stress caused by manipulation, results indicated good stability of incision and reproducibility of tunnel length.

Synopsis

Difference of corneal thickness at the CCI between after femtosecond and after phacoemulsification measurements (P-value <0.05), with increase of endothelial gaps (P-value =0.0133) and Descemet detachments (P-value <0.05).

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.