Cornea & Ocular Surface

Corneal Biomechanical Properties Altered by Refractive Surgical Procedures

Avatar photoCourtney Dryer, OD
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New Vision clinic, main center for refractive surgery in France, with cutting-edge technology for all eye laser operations. Eye operation using the SMILE, Small Incision Lenticule Extraction, laser technique. It is a new generation of treatment which enables short-sightedness to be corrected without removing the superficial layer of the cornea, nor opening it. The SMILE technique involves producing with the Femtosecond laser, a lenticule, thin slice, in 3D in the thickness of the cornea, and removing it with a micro incision in the shape of a smile. The worse the short-sightedness, the thicker the lenticule. (Photo by: BSIP/Universal Images Group via Getty Images)
Researchers compare post-surgical biomechanical properties between patients undergoing small-incision lenticule extraction and photorefractive keratectomy.

Both small-incision lenticule extraction (SMILE) and photorefractive keratectomy (PRK) procedures alter corneal biomechanical properties 3 months following surgery, according to a study published in Cornea. However, these changes are more prominent after SMILE.

Researchers enrolled 74 patients receiving either PRK (72.9% women; mean age, 31.06 ±8.57 years) or SMILE (64.9% women; mean age, 32.31±6.72 years) in the analysis. Corneal biomechanical properties between the 2 groups were recorded through Scheimpflug imaging and noncontact tonometry pre-surgically and during a 3-month post-surgical follow-up visit.

According to the report, both groups experienced significant increases in deformation amplitude (DA) ratio, maximum inverse radius (InvRadMax), maximum deflection amplitude (DeflAmpMax), velocity 1, and peak distance following their surgeries. Both groups experienced a post-operative decrease in stiffness parameter A1 (SP-A1), Ambrosio relational thickness (ARTH), intraocular pressure (IOP), A1 length, A1 time, highest concavity (HC) radius, and A2 length.

Patients in the PRK group demonstrated improved DA ratio (P =.03), InvRadMax (P= .02), and A2 time (P =.03). 

The mean changes in DA ratio, HC radius, InvRadMax, and ARTH were significantly higher in the SMILE group (1.19±0.46; -1.11±0.59 millimeters (mm); 2.60±0.89/mm; -2.42.78±75.75, respectively) compared with those of the PRK group (P <.05 for all). 

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In both groups, the change in central corneal thickness (CCT) was significantly correlated with changes in DA ratio and InvRadMax (P <.05 for both). 

“Research into corneal biomechanical properties has many potential applications such as improved diagnosis and staging of corneal ectasia, enhanced screening of laser refractive surgery candidates, customization of interventions such as intrastromal ring segment implantation, and a more comprehensive understanding of biomechanics-modulating interventions such as corneal crosslinking and corneal transplantation,” according to the researchers. 

Study limitations include a small sample size, lack of randomization, and short duration.

Reference

Zarei-Ghanavati S, Jafarpour S, Hassanzadeh S, et al. Changes in corneal biomechanical properties after small-incision lenticule extraction and photorefractive keratectomy, using a noncontact tonometer. Cornea. 2022;41(7):886-893. doi:10.1097/ICO.0000000000002888 

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