Cyclotorsion measurement in laser refractive surgery

Abstract

Artigo Original | Original article INTRODUCTIONAstigmatism is a common refractive error that generates multiple focal points over the retina. It's frequently caused by an asymmetry in the corneal curvature. When the two corneal meridians are at right angle, the ametropia can be corrected with spectacles (regular astigmatism). When there are irregularities in the meridians or they are not at right angle, it's called irregular astigmatism, and does not allow correction with spectacles (1) .Mild torsional alignment errors in the astigmatism axis (greater than 3°), can lead to a clinically significant reduction in the efficiency of the laser treatment in eyes with moderate to high astigmatism (2) .The torsional movements are defined as: a) excycloversion -when the upper pole of the eye rotates to the temporal side; b) incycloversion -when the upper pole of the eye rotates to the nasal side (3) . The inferior oblique and inferior rectus muscles are responsible for the excycloversion and the superior oblique and superior rectus muscles ABSTRACT Purpose: The aim of this study was to verify the presence of cyclotorsion in eyes that underwent laser refractive surgery. Methods: This was a comparative observational study, which analyzed the medical records of 61 patients (104 eyes) who underwent laser refractive surgery and compared the axis of astigmatism of the sitting and the supine positions. Regarding the gender, 37.5% were male and 62.5% were female. The age ranged from 20 to 54 years old, with the median of 29 years. The lowest degree of astigmatism was -0.75 cylinder diopters (DC) and the highest was -6.50 DC, with a mean of -3.06 ± 1.16 DC. First, the axis of astigmatism of the seated patient was captured by the Schwind's ORK-CAM. In a second moment, inside the operating room, the axis of astigmatism of the patient in supine position was captured by the laser equipment's own camera (Schwind Amaris®), which was then compared with the previous measure. The incyclotorsion was defined by a minus sign (-) and the excyclotorsion, by a plus sign (+). Results: The maximum excyclotorsion was +7.7 and the maximum incyclotorsion was -11.0 degrees. The mean torsion (excyclo or incyclo) was 2.74 (56.7%), with a standard deviation of 2.30 degrees. There was no statistically significant change (p=0.985) in the axis of astigmatism between patients sitting versus supine. Conclusion: There was clinically significant cyclotorsion in 36.5% of the eyes submitted to laser correction.

Mobile App for Pre- and Intraoperative Assessment of Astigmatism Correction with Toric Intraocular Lenses in Cataract Surgery

“…However, the findings had important clinical relevance, since 3 degrees of IOL deviation cause an approximate loss of 10% of astigmatism correction [3]. Moreover, with an increase in astigmatism, the impact of a change in the position of the eye due to cyclotorsion on the correction is greater [12].…”

Comparison of Small Incision Lenticule Extraction Surgery With and Without Cyclotorsion Error Correction for Patients With Astigmatism

“…3–5 Studies have shown that when eye cyclotorsion is greater than 2 degrees and not compensated, cylinder correction might be adversely influenced and significant aberrations can be induced during laser treatment, especially in patients with high astigmatism. 6–8 Currently, with the rapid development of refractive surgical technology, personally designed laser platform surgery equipped with pupil-tracking or iris-registration software allows for more precise, safe, and predictable corneal ablation in refractive correction than ever before. However, no acknowledged method of cyclotorsion compensation exists for the VisuMax femtosecond laser system (Carl Zeiss Meditec, Jena, Germany).…”