Where does SMILE monovision fit in?

Small-incision lenticule extraction (SMILE, Carl Zeiss Meditec) monovision could be a valid option to manage presbyopia in patients with myopia, said Sheetal Brar, MD.

She presented outcomes from 6 months of follow-up in a study that included 18 myopic patients who underwent SMILE bilaterally. All patients had right eye dominance and were targeted for emmetropia in their right eye and for myopia ranging from -1.00 to -1.75 D in their non-dominant left eye, depending on their tolerance and reading requirement.

“After 6 months of follow-up, we found that SMILE monovision provides satisfactory visual outcomes for near, intermediate, and distance vision and is associated with minimal side effects of nighttime halos and glare,” said Dr. Brar, Nethradhama Eye Hospital, Bangalore. India.

“However, SMILE monovision is a relatively new treatment modality,” she said. “Therefore, longer follow-up is needed to establish the benefits of this modality over other laser-based presbyopic procedures.”

Patients included in the study had a mean age of 46 years (range 44 to 52 years). Preoperative evaluations included a check for ocular dominance and assessments of monovision tolerance, suppression, and fusion.

“All patients were found to be suitable candidates for SMILE based on topography,” Dr. Brar said. “They all demonstrated good tolerance to anisometropia and good suppression and fusion.”

Patients were also counseled preoperatively that SMILE monovision would reduce dependence on reading glasses, but that they may still need glasses for fine tuning of near vision. The preoperative counseling also set expectations for needing a period of adaptation after surgery.

Outcomes at 6 months

Mean SE preoperatively was -6.14 D in the dominant eyes and -5.55 D in the non-dominant eyes. Residual SE at 6 months was -0.14 D in the dominant eyes and -1.36 D in the non-dominant eye.

Monocular testing in the dominant eye showed no significant difference between the preoperative logMAR corrected distance visual acuity (CDVA) and the postoperative uncorrected distance visual acuity (UDVA), 0.02 versus 0.05, respectively.

As expected, however, the non-dominant eyes that were treated with a myopic target had a drop in distance visual acuity comparing the preoperative CDVA and postoperative UDVA, -0.015 versus 0.136, respectively. In binocular testing, UDVA was 6/6 or better in 15 (83%) patients; 16 (89%) patients had uncorrected near visual acuity of N6 or better.

Intermediate visual acuity was checked at 40, 60, and 80 cm with an ETDRS chart. At all distances, there were no significant differences comparing the preoperative corrected and postoperative corrected outcomes.

Postoperative uncorrected visual acuity at 40 and 60 cm was also not significantly different than the preoperative corrected visual acuity, but postoperative uncorrected visual acuity at 80 cm was significantly better than the preoperative corrected vision.

Functional vision was also assessed with the Salzburg reading desk, and the results for testing at 40, 60, and 80 cm showed no significant differences comparing the reading speeds measured preoperatively with correction versus the results obtained both with and without correction at 6 months.

“We also checked the defocus curves from -2.5 to +2.5 D and found the procedure gives a depth of field of about 1.5 D, which is quite satisfactory,” Dr. Brar said.

Evaluation of fine stereoposis showed no significant differences comparing the values obtained preoperatively with correction and the postoperative results from testing performed with and without correction.

High satisfaction

All patients completed a questionnaire at 6 months asking about satisfaction with vision at different distances and visual symptoms. The results showed 16 of the 18 patients were happy with their distance vision, 17 were happy with their near vision, and all patients were happy with their intermediate vison. No patients had been prescribed glasses.

“Only two patients still complained of mild halos and glare at 6 months, and no patient complained of headaches, nausea, or diplopia,” Dr. Brar said.

Dr. Brar suggested that good candidates for SMILE monovision include presbyopic patients who are myopic with a high refractive error, those who have moderate-to-severe dry eye or who have been long-term contact lens users, and individuals who play a lot of contact sports.

She noted that compared with LASIK monovision, SMILE has several potential advantages.

“SMILE may work better than LASIK monovision because there is better control of aberrations with SMILE with its more natural prolate corneal treatment profile,” Dr. Brar said. “In addition, SMILE uses a larger optical zone than LASIK and avoids any problems from fluence projection errors.

“With SMILE, there is autocentration on the visual axis, and it is also associated with less postoperative dry eye,” she said.

Dr. Brar has no relevant financial interests to disclose.