A recent clinical study conducted at Farabi Eye Hospital has shed light on the effectiveness of two different centration strategies in photorefractive keratectomy (PRK) for patients battling myopia and astigmatism. The trial focused on comparing symmetric offset (SO) and asymmetric offset (AO) techniques, examining essential outcomes that define sight quality after refractive surgery.
This extensive research took place between May and August 2022, where forty candidates for refractive surgery participated. These individuals were randomly assigned to each centration strategy for one eye while the other eye underwent the alternative treatment. Over a follow-up period averaging 114 days, results revealed promising outcomes for both methods.
One of the study’s striking findings is that 95% of the eyes treated with the AO method and 93% with the SO approach achieved uncorrected distance visual acuity (UDVA) of 20/20 or better within four months postoperatively. Despite the different methods of ablation, the final visual outcomes did not significantly differ between groups, providing further evidence of PRK's efficacy in correcting refractive errors.
Patients in the study also exhibited similar metrics regarding the effective optical zones (EOZ) of the surgeries, measured at 6.05 ± 0.64 mm for SO and 6.05 ± 0.68 mm for AO. Notably, the effective optical zone reflects the area where significant changes in corneal shaping occur, critically influencing surgical outcomes and patient satisfaction.
The trial also highlighted important statistical findings regarding the minimum ablation depths associated with each centration method. The SO technique resulted in a minimum ablation depth of 0.03 ± 0.03 mm, compared to 0.01 ± 0.01 mm for the AO. This notable difference, supported by a significant P-value of < 0.001, indicates that the SO strategy might allow for slightly deeper corneal corrections compared to AO.
However, the postoperative mean manifest spherical equivalent (MRSE) indicated no significant difference between groups, remaining at ± 0.08 D in both cases, demonstrating that both methods are equally viable for correcting myopic astigmatism while preserving corneal integrity.
The researchers also evaluated higher-order aberrations (HOAs), which can pose challenges to visual quality following refractive surgery. Encouragingly, no significant variations in postoperative mean RMS of HOAs arose between the AO and SO groups, reinforcing the reliability of both strategies in maintaining sight clarity.
This progressive study is a response to ongoing discussions within the ophthalmic community regarding optimal centration techniques in laser vision correction. Traditionally, methods either align with the corneal vertex or center around the pupil, with many opting for symmetric approaches that are believed to align better with the visual axis of the eye.
Asymmetric offset centration, introduced more recently, aims to blend these strategies by optimizing ablation areas to enhance visual outcomes. This trial marks one of the first significant comparisons specifically assessing these two methods in patients with low to moderate myopic astigmatism.
The outcomes of this study promise potential implications for future refractive surgical strategies, giving surgeons essential insights into which centration technique might be more effective under varied patient circumstances. As Dr. Farhad Salari and his team concluded, symmetric and asymmetric offset strategies exhibit safe and effective refractive correction capabilities in myopic astigmatism patients.
The continued evaluation of these methods reflects the dynamic nature of refractive surgery, where advancements hinge on evidence-based research guiding clinical practice. As technology evolves, the aim remains to enhance patient care and satisfaction through improved surgical outcomes.
