Integrity of Intrastromal Arcuate Keratotomies Performed by Femtosecond Laser

The Impact of Different Optical Zone Diameter on Corneal Astigmatism Correction Using Femtosecond Laser Corneal Relaxing Incisions: 8 mm vs 9 mm

PURPOSE

To compare the impact of 8 mm versus 9 mm optical zone (OZ) diameters on corneal astigmatism correction and to evaluate the impact of incision depth percentage after femtosecond laser corneal relaxing incisions (CRIs) combined with cataract surgery.

METHODS

Thirty-nine eyes from 39 patients were enrolled and randomly assigned to two groups based on the OZ diameter: 8 mm and 9 mm. Corneal astigmatism and CRI depth were measured using Pentacam and anterior segment optical coherence tomography. Vector analysis was performed using Alpins method.

RESULTS

In the 8 mm group, postoperative corneal astigmatism was reduced by 0.77 ± 0.61 diopters (D), significantly greater than the reduction of 0.42 ± 0.40 D in the 9 mm group (p < 0.05). The 8 mm group exhibited greater surgically induced astigmatism (SIA), net corneal changes, and a smaller angle of error (AE) (p < 0.05). At 3 months postsurgery, the correction index (CI) values were 0.84 ± 0.39 for the 8 mm group, exceeding the 0.52 ± 0.32 observed in the 9 mm group (p < 0.05). The mean incision depth percentage was significantly higher in the 9 mm group (79.30 ± 10.76%) compared to the 8 mm group (72.58 ± 8.73%) (p < 0.05). In the 8 mm group, CI values closer to 1.00 were associated with lower percentages of incision depth.

CONCLUSIONS

CRIs with an 8 mm OZ diameter demonstrated superior efficacy in correcting corneal astigmatism with shallower incision depths compared to those with a 9 mm diameter.

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.

Evaluation of Femtosecond Laser Intrastromal Incision Location Using Optical Coherence Tomography

PURPOSE

To use optical coherence tomography (OCT) to evaluate the femtosecond laser intrastromal incisions made during cataract surgery to reduce corneal astigmatism.

DESIGN

Retrospective case series.

PARTICIPANTS

Seventy-seven eyes of 77 patients.

METHODS

Paired intrastromal incisions were created using the Catalys femtosecond laser (Abbott Medical Optics, Inc., Santa Ana, CA). The planned intrastromal incision parameters were 20% uncut anterior, 20% uncut posterior, midpoint depth of 50%, and 90° side cut angle. Optical coherence tomography scans were obtained 3 weeks or more after surgery to assess these 4 parameters, and actual values were compared with intended values.

MAIN OUTCOME MEASURES

Percentages of uncut anterior and posterior tissue, midpoint depth, and degrees of side cut angle.

RESULTS

The mean values were 17.2±5.8% (range, 7.2%-36.9%) for uncut anterior, 32.5±8.8% (range, 6.0%-57.9%) for uncut posterior, and 42.3±6.6% (range, 25.5%-65.4%) for midpoint depth, which all were significantly different from the planned parameters (all P < 0.05). The mean side cut angle was 88.5°±5.6° (range, 71°-114°) and was significantly different from the planned side cut angle of 90° (P < 0.05). In 50 eyes that had paired intrastromal incisions scanned by the OCT, there was no correlation between the paired incisions for midpoint depth and side cut angle (correlation coefficient, r = -0.063 and -0.067, respectively; P > 0.05).

CONCLUSIONS

The intrastromal incision midpoint depth was significantly more anterior than the planned depth of 50%. The locations of paired intrastromal incisions in each eye were not correlated. Further improvements are needed to ensure the precise location of the intrastromal incisions made with this device.