Abstract
PurposeTo analyze changes in corneal topographic measurements and higher-order aberrations (HOAs) after horizontal muscle surgery for exotropia.DesignRetrospective, observational study.MethodsA total of 131 eyes of 121 patients who had undergone surgery for exotropia were included. The eyes with unilateral lateral rectus (ULR) or bilateral lateral rectus (BLR) recession(s) were assigned to group A, and those with unilateral lateral rectus recession & medial rectus resection (R&R) to group B. Corneal topographic measurements and HOAs were compared between the preoperative and postoperative periods using a Placido-dual Scheimpflug analyzer (Galilei 2TM, Ziemer, Port., Switzerland) for each group.ResultsIn group A, simulated keratometery (sim K) was significantly changed until 3 months postoperatively relative to the preoperative value (postoperative 1 week, p = 0.017; 1 month, p = 0.037; and 3 months, p = 0.023, respectively). All steep K (steep sim K, steep-Kpost, and TCP-steep K) parameters also were significantly changed at postoperative 1 month (p<0.001, p = 0.015, p<0.001, respectively), but not at 3 months. Among the higher-order aberrations, spherical aberration (Z40) and secondary horizontal astigmatism (Z42) at postoperative 1 week had significantly changed from the preoperative values, as had horizontal quadrafoil (Z44) at 1 month. However, in group B, only vertical quadrafoil (Z4-4) showed statistically significant changes, at postoperative 1 and 3 months. None of the other postoperative parameters was significantly different from the corresponding preoperative value.ConclusionLateral rectus recession induced changes in both corneal topographic measurements and HOAs, whereas R&R did so only in HOAs. These changes might explain some patients' complaints about poor quality of vision.
Highlights
Surgical correction of exotropia, to restore the normal ocular position by weakening the lateral rectus muscle with/without strengthening the medial rectus muscle through changing the orientation of their action plan, has been the main treatment for deviations [1]
Among the higher-order aberrations, spherical aberration (Z40) and secondary horizontal astigmatism (Z42) at postoperative 1 week had significantly changed from the preoperative values, as had horizontal quadrafoil (Z44) at 1 month
Most changes of this kind have been thought to be related to changes in corneal curvature secondary to the reduction in the tension of the recessed extraocular muscle transmitted via the sclera to the cornea [4, 6,7,8,9,10]
Summary
To restore the normal ocular position by weakening the lateral rectus muscle with/without strengthening the medial rectus muscle through changing the orientation of their action plan, has been the main treatment for deviations [1]. Recession of a single rectus muscle typically effects a decrease of corneal curvature in the meridian of the recessed muscle, though paradoxically, it occasionally increases the focusing power along this meridian [4, 6,7,8,9,10]. OrbscanTM (Bausch & Lomb, Rochester, NY), which uses Placido disk technology to display conventional corneal topography, was the first commercially viable hybrid system [12]. The dual-camera system derives images from both sides, which minimizes the effect of decentration due to eye movements on corneal pachymetry and posterior corneal curvature measurements [15]
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