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Femtosecond laser astigmatic keratotomy effective before or after cataract surgery
The correction of astigmatism resulted in significantly improved visual acuity and corneal cylinder.
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Astigmatism, an optical defect that results in blurred vision secondary to an inability to sharply focus an object onto the human retina, often has to be dealt with by the clinician by way of non-surgical approach, namely glasses or contact lenses, or by the ophthalmic surgeon, especially during cataract surgery with manual diamond knife limbal relaxing incisions, a toric IOL or femtosecond laser arcuate incisions, or during excimer laser vision correction such as LASIK or PRK.
In a U.S. study that included 2,523 children, about 28.4% of children aged 5 to 17 years had astigmatism, with significant differences among ethnic groups: Asians (33.6%) and Hispanics (36.9%) had the highest prevalence of astigmatism, while the lowest prevalence was among African-Americans (20%) and Caucasians (26.4%).
The two major types of astigmatism are regular and irregular. In regular astigmatism, there are two regular radi, one larger than the other and perpendicular to each other, and it arises from the cornea or the crystalline lens, while irregular astigmatism can often be secondary to corneal scar or due to scattering within the crystalline lens. Regular astigmatism can be with-the-rule, in which the vertical meridian is steepest; against-the-rule, in which the horizontal meridian is steepest; or oblique, in which the steepest curve is between 30° and 60° or 120° and 150°. Astigmatism can be simple, compound or mixed, depending on the focus of the principal meridians. Significant astigmatism can cause headaches, squinting, eyestrain, difficulty driving at night and blurred vision.
In this column, Padilla and Ambati describe their surgical technique of Intra-Lase astigmatic keratotomy during or after cataract surgery.
Thomas “TJ” John, MD
OSN Surgical Maneuvers Editor
The purpose of this interventional case series is to illustrate the effectiveness of the IntraLase iFS laser system (Abbott Medical Optics) in performing astigmatic keratotomy concurrently with cataract extraction.
The optimization of refractive outcomes in cataract patients necessarily entails precise astigmatic management, which has been one of the principal drivers of adoption of new femtosecond laser systems and/or toric IOLs. One study found that in preoperative examination, 64% of cataract surgery patients had between 0.25 D and 1.25 D of corneal astigmatism. Due to the fact that the prevalence and incidence of both cataracts and astigmatism are so high, a common practice is to surgically correct both at the same time. Currently there are multiple astigmatism-correcting devices and techniques available to ophthalmologists. Traditional diamond blade limbal relaxing incision (LRI) surgery has been observed to reduce cylinder by an average of 60%, while toric IOLs have been advertised to decrease cylinder by 58.4%. We propose that astigmatic keratotomy using the IntraLase iFS laser system is a safe, precise and highly effective method of surgically correcting astigmatism.
Methods
Patients with both cataracts and corneal astigmatism were identified in the clinic of Dr. Ambati at the Moran Eye Center. Corneal astigmatism measurements were made preoperatively by taking an average of three measuring devices (Oculus Pentacam, Carl Zeiss Meditec IOLMaster and Humphrey Atlas Corneal Topography System). Once these astigmatism values were averaged, 21 eyes of 12 patients who met inclusion criteria were treated with a150 KHz IntraLase iFS laser system, which was used to make the initial intrastromal cuts for astigmatism correction. Immediately after the laser astigmatic keratotomy procedures, the patients underwent phacoemulsification cataract surgery. The patients were examined preoperatively and postoperatively for visual acuity, refraction and corneal topography. Postoperative examinations were performed 1 month after surgery.
Results
The initial mean preop best corrected visual acuity for patients set to distance was 20/47 (0.37 ± 0.29 logMAR); the mean postop uncorrected visual acuity was 20/24 (0.08 ± 0.10 logMAR) (P = .002), and the mean postop BCVA was 20/20 (0.007±0.03 logMAR) (P = .0003).
Figure 1. In a representative case, the cylinder and axis were averaged, and the resulting value was entered into the IntraLase laser for calculations. The red lines illustrate the degrees and positions of the laser cuts. In this patient, using a depth of 600 µm and a ring size of 9 mm to 9.5 mm, the IntraLase laser made incisions from 50° to 100° and 230° to 280°.
Images: Padilla M, Ambati BK
Figure 2. This is a postoperative photo of the patient from Figure 1. Astigmatic keratotomy incisions were made in the patient’s left eye using the IntraLase-enabled keratoplasty setting and the topographic data from Figure 1. This patient’s topographic astigmatism went from 1.68D @ 71° preop to 0.39D @ 57° postop, which is a 77% decrease in corneal cylinder. After surgery, this patient’s refraction improved from –13.75 +2.50 × 60 to plano.
Figure 3. A second case had severe corneal astigmatism after penetrating keratoplasty 30 years prior. The initial astigmatic corneal cylinder was 9.16 D, which exceeded the astigmatic correction provided by an SN6AT5 lens (Alcon) inserted in 2009.
Figure 4. Astigmatic keratotomy incisions were created by the IntraLase at a 7-mm optical zone to treat the astigmatism observed in Figure 3. Postoperatively the patient had 1 D of residual refractive cylinder.
Figure 5. Postoperative topographic measurements revealed that patient 2 had a corneal cylinder improvement from 9.16 D to 1.44 D, which was an 84% decrease in cylinder. Distance vision improved from a BCVA of 20/40 before surgery to 20/25 postop.
Figure 6. This image shows intraoperative formation of the astigmatic keratotomy incision using the IntraLase laser in a different patient. The incision can be visualized at approximately the 12 o’clock region. This corneal arcuate incision was performed at a depth of 80% of corneal thickness.
Figure 7. After the IntraLase LRI astigmatic keratotomy incision, the incision was opened using a Sinskey hook.
Patients set for near had a mean preop BCVA of 20/47 (0.37 ± 0.15 logMAR); mean postop near UCVA was 20/24 (0.08 ± 0.08 logMAR) (P = .005), and mean postop BCVA was 20/20 (0.02 ± 0.04 logMAR) (P = .00535).
The mean preop topographic cylinder was 2.01 ± 0.7 D, while mean postop topographic cylinder was 0.83 ± 0.57 D (P = .003). The mean preop axis was 91.3 ± 47.5°, and mean postop axis averaged 81.6 ± 48.8°, which was not statistically significant.
Average refractive error for patients set to distance changed from a mean preop sphere of –4.7 ± 4.7 D to –0.03 ± 0.47 D postop (P = .002). In patients set for near, the refractive sphere changed from an average of 0.71 ± 2.51 D preop to –0.96 ± 0.68 D postop, which was not statistically significant.
The average preop refractive cylinder was 1.50 ± 1.40 D, while postop it was 0.38 ± 0.42 D (P = .0013)
Conclusion
Astigmatic keratotomy using the IntraLase iFS laser system immediately before or after cataract surgery allowed for an effective and safe correction of astigmatism. Mean preoperative topographic cylinder was 2.01 D, while mean postoperative topographic cylinder was 0.83 D and mean postoperative refractive cylinder, arguably the more clinically relevant outcome, was 0.38 D. These outcomes compare favorably to other femtosecond laser systems, toric IOLs or manual LRIs. Visual outcomes were excellent. The results of astigmatic keratotomy using the IntraLase iFS laser were successful in patients with a surgical history of phacoemulsification cataract surgery, keratoplasty and LASIK. The significantly improved visual acuity and corneal cylinder, along with a lack of complications in the postoperative period, suggest that this is a safe and effective treatment that can be achieved using an existing femtosecond laser without having to procure an expensive new femtosecond laser platform.