This article is more than 5 years old. Information may no longer be current.
Topography-guided transepithelial surface ablation reduces astigmatism
Visual acuity and refractive outcomes were slightly better in eyes treated for myopic astigmatism than those treated for mixed astigmatism.
Click Here to Manage Email Alerts
Topography-guided transepithelial surface ablation improved vision and reduced moderate to high astigmatism, according to a study.
“The result with myopic astigmatism is better compared to the mixed astigmatism. It’s kind of like the fact that excimer laser surgery is better in the treatment of myopia than hyperopia,” Xiangjun Chen, MD, the corresponding author, told Ocular Surgery News.
Methods and measures
The retrospective study, published in the Journal of Refractive Surgery, included 206 eyes; eyes were classified according to preoperative refraction, resulting in a myopic astigmatism group (153 eyes) and a mixed astigmatism group (53 eyes).
Topography-guided transepithelial surface ablation was performed with the iRes excimer laser (iVis Technologies).
The concept of topography-guided custom ablation has an advantage of less induction of higher-order aberrations, as well as customization of a smooth transition zone to avoid regression, according to Chen. The transepithelial approach overcomes the issue with unevenly distributed epithelial thickness, which is especially important in topography-guided custom ablation. It avoids the problem caused by mismatch between topography measured with epithelium on and the stromal surface where the refractive part of the ablation is performed. The laser uses iris registration and dynamic cyclotorsional eye tracking. Furthermore, it employs automatic intraoperative illumination adjustment to keep the pupil size during the treatment at the same level as registered during the acquisition of topography, which is used for the treatment planning. That way, a possible registration error due to the pupil centroid shift between the data acquisition and the treatment is avoided.
“The combination of the elements mentioned above — topography-guided custom ablation, transepithelial approach, iris registration, dynamic cyclotorsional eye tracking and pupil size control — are all contributing to the quality of the results, which I think are comparable to the best results published or even better. So, in the future, if others analyze their results and find they are not so good or they want to improve them, they may start thinking in this direction,” Chen said.
Corneal Interactive Programmed Topographic Ablation software (CIPTA, iVis Technologies) was used to create a custom ablation plan for each eye based on subjective refraction and corneal topography. Mean optical ablation zone size was 6.24 mm in the myopic astigmatism group and 6.33 mm in the mixed astigmatism group. Total ablation zone size was 8.36 mm in the myopic astigmatism group and 8.51 mm in the mixed astigmatism group.
Patients underwent preoperative and postoperative evaluation of uncorrected and corrected distance visual acuities, slit lamp biomicroscopy, corneal topography, tomography and wavefront aberrometry.
Mean follow-up was 10.4 months in the myopic astigmatism group and 13.9 months in the mixed astigmatism group. Seven eyes required a second treatment.
Results
Postoperative uncorrected distance visual acuity was better than 20/20 in 92% of eyes in the myopic astigmatism group and 83% of eyes in the mixed astigmatism group.
No change in corrected distance visual acuity or a gain of up to two lines of corrected distance visual acuity was seen in 97% of eyes in the myopic astigmatism group and 96% of eyes in the mixed astigmatism group. No eyes lost more than one line of corrected distance visual acuity.
Residual refractive astigmatism was 0.5 D or less in 82.4% of eyes in the myopic astigmatism group and 56.7% of eyes in the mixed astigmatism group. Residual refractive astigmatism was 1 D or less in 97.4% of eyes in the myopic astigmatism group and 84.9% of eyes in the mixed astigmatism group.
Astigmatic undercorrection was slight in both groups but was more evident in the mixed astigmatism group.
Spherical equivalent refraction was within 0.5 D of the target in 83.7% of eyes in the myopic astigmatism group and 79.2% of eyes in the mixed astigmatism group. Spherical equivalent refraction was within 1 D of the target in 99.3% of eyes in the myopic astigmatism group and 94.3% of eyes in the mixed astigmatism group.
No changes in coma-type or spherical-type aberrations were reported postoperatively.
Grade 1 corneal haze was identified in 2.6% of eyes in the myopic astigmatism group and 7.5% of eyes in the mixed astigmatism group.
Drawbacks of the study included its retrospective design, 22.8% dropout rate, and lack of data on contrast sensitivity, other visual quality parameters, postoperative wound healing, postoperative epithelial thickening and corneal biomechanical changes. – by Matt Hasson
- Reference:
- Chen X, et al. J Refract Surg. 2016;doi:10.3928/1081597X-20160428-01.
- For more information:
- Xiangjun Chen, MD, can be reached at SynsLaser Kirurgi AS, Lille Grensen 7, 0159, Oslo, Norway; email: chenxiangjun1101@gmail.com.
Disclosure: Chen reports no relevant financial disclosures.
Perspective
Back to Top
Noel A. Alpins, MD
This paper discusses transepithelial treatment in the correction of moderate and high astigmatism. The conclusion is that it is safe and effective both for myopic cylinder as well as mixed astigmatism. Although the title states the paradigm is topography driven, there is some suggestion in the paper that refractive parameters also played a part, but the proportion is unclear.
The results of eyes with myopic astigmatism (153) and mixed astigmatism (53) were successful with 83% within 0.5 D of target and 99% within 1 D. Astigmatism outcomes showed a difference vector of 0.38 D (myopic) and 0.65 D (mixed).
There was a general undercorrection of astigmatism by the iVis laser by 0.96 correction index for myopia and 0.84 for mixed. The range of alignment accuracy was from 14° to +13° (myopia) and 22° to +13° (mixed). However, contrary to what is stated, misalignment is not a cause for undercorrection as the ratio SIA/TIA is not affected.
Click Here to Manage Email Alerts