Study shows impact of age on SMILE outcomes
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Even though small incision lenticule extraction is deemed a safe, effective and reliable procedure in patients older than 40 years, outcomes may not be as good as in the younger population, according to a study.
“In our older than 40 years group, we had overall good results but with a clear tendency toward worse refractive and visual outcomes as compared with the younger than 35 years group. Refractive patients are highly demanding, and in this older group, unless there are contraindications such as a limited ocular surface, in our view LASIK offers a higher patient satisfaction and lower enhancement rate need,” Jorge Alió del Barrio, MD, said in an interview with Ocular Surgery News.
The study was a retrospective, comparative analysis of two groups of myopic patients with or without astigmatism treated with SMILE (Carl Zeiss Meditec) at the Vissum Institute in Alicante, Spain, between 2016 and 2019. Fifty-one consecutive eyes of patients aged 40 years or older were matched with 51 eyes of patients aged 35 years or younger. The difference in preoperative spherical equivalent for each pair of eyes was within 0.25 D, and lenticule diameter and cap thickness were comparable.
At 6 months, a significantly higher mean residual astigmatism was observed in the older group. Both groups gained lines of corrected distance visual acuity, but the improvement was significantly better in the younger population. The efficacy index was 0.97 in the older group vs. 1.07 in the younger group, and the safety index was 1.04 vs. 1.11, respectively. Predictability was also better in the younger population, with 76% of eyes within +0.13 D of spherical equivalent compared with 50% in the older group.
Decreased remodeling capacity
“We set up this study because we observed that SMILE outcomes in pre-presbyopic and presbyopic people were not as sharp as they should be, and this was mainly related to residual postoperative astigmatism due to undercorrection or occasionally surgical-induced astigmatism that did not exist preoperatively. This resulted in a higher rate of enhancement in patients over the age of 40 years,” Alió del Barrio said.
In a previous study by Liu and colleagues, age older than 35 years was a significant risk factor for enhancement after SMILE. The current study supports this finding, leading to the hypothesis that such suboptimal outcomes may be due to a diminished remodeling capacity in response to the lenticule extraction in relation to the increased corneal stroma stiffness that occurs with age.
“The stiffness of corneal stroma increases with age. That is the reason why keratoconus halts in the older population and corneal cross-linking is usually not necessary over the age of 40 years because the cornea by itself gets stiffer with time. SMILE is a pure intrastromal procedure, and the stroma needs to reshape to provide the required visual outcomes. It is likely that younger, more elastic corneas have a better ability to remodel than older and stiffer corneas in response to the lenticule extraction,” Alió del Barrio said.
SMILE in selected cases
It is not uncommon for patients to undergo refractive surgery after they have reached the age of 40 years, Alió del Barrio said. Many younger people cannot afford the procedure unless they have family support or an early start in their career. In addition, the onset of presbyopia leads to a further worsening of vision, which is often the decisive push for wanting to get rid of spectacles.
“Tear film quality also decreases, particularly in women, and contact lenses are less tolerated and often become a struggle,” he said. “People at this stage of their life have the money and may decide to undergo surgery. In my practice, the over-40s who come for refractive surgery are about 20%.”
SMILE is an excellent procedure with remarkable advantages, Alió del Barrio said, as it is proven to have less impact to the ocular surface and dry eye risk. However, if the ocular surface is proven to be unremarkable, he prefers LASIK in this older population. Enhancements are easier and probably less frequent with LASIK. Moreover, monovision can be used to compensate for presbyopia, and if it is not well tolerated, it is easy to reverse if LASIK was originally performed.
“You just lift the flap and do the treatment, with a quick recovery and discharge, while with SMILE you would have to either convert to LASIK or do a PRK, which involves a higher extra cost to the clinic either in relation with the surgical cost or a long recovery in case of PRK,” he said. “It is not a strict recommendation, but according to the outcomes of our study, personally I prefer LASIK when dealing with this older population.”
However, there are patients in this age group for whom Alió del Barrio would rather perform SMILE, for example, those with a doubtful ocular surface stability or those with high ametropia and insufficient corneal thickness to consider LASIK.
“By doing SMILE, you can remain within safety limits and avoid the long recovery time of PRK. If there is a real advantage that outweighs the slightly worse refractive outcomes and the chances of reversing a monovision, then let’s go for a SMILE,” he said. “Outcomes will still be very good, though likely not as sharp as in younger corneas.” – by Michela Cimberle
- Reference:
- Liu YC, et al. Ophthalmology. 2017;doi:10.1016/j.ophtha.2017.01.053.
- For more information:
- Jorge Alió del Barrio, MD, can be reached at Vissum – Miranza Group, Avenida de Denia, s/n, 03016 Alicante, Spain; email: jorge_alio@hotmail.com.
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