A Comparative Analysis Of The Effects Of Prk, Lasik And Smile On Corneal Biomechanics
Published 2023 - 41st Congress of the ESCRS
Reference: FP11.01 | Type: Free paper | DOI: 10.82333/62cn-jc42
Authors: Abby Wilson* 1 , Dan Reinstein 2 , Timothy Archer 3 , John Marshall 4
1Mechanical Engineering,University College London,London,United Kingdom;UCL Institute of Ophthalmology,University College London,London,United Kingdom, 2Reinstein Vision,London Vision Clinic,London,United Kingdom;Irving Medical Centre,Columbia University,New York,United States;Biomedical Science Research Institute,Ulster University,Coleraine,United Kingdom, 3Reinstein Vision,London Vision Clinic,London,United Kingdom, 4UCL Institute of Ophthalmology,University College London,London,United Kingdom
Purpose
Several refractive surgery procedures are now available including; PRK, LASIK and SMILE. For some cases, any one of these procedures is suitable, as such controversy exists regarding their biomechanical implications and which should be the preferred method of vision correction. PRK and SMILE, being flapless procedures, are hypothesized to better maintain the mechanical integrity of the cornea relative to LASIK, with variables such as flap thickness, or lenticule depth and thickness offering further potential for optimisation. Here, we performed an interferometric study to spatially analyse changes to corneal strain distributions after PRK, LASIK and SMILE.
Setting
Sample preparation and imaging was performed by Abby Wilson at UCL Mechanical Engineering, Torrington Place, London, UK. All surgeries were performed by Dan Reinstein at London Vision Clinic, Harley Street, London, UK.
Methods
Porcine corneal-scleral specimens (<48hrs post-mortem) were fixed into a chamber filled with phosphate-buffered saline solution to exert a pressure (baseline 17.0mmHg) on the posterior cornea to simulate normal IOP. Surface deformation of the specimens in response to pulsatile pressure variations (17.0 to 17.5mmHg) over 50 cycles was evaluated by speckle interferometry. All corneas were imaged prior to surgery, all surgeries were -3.00D, including PRK, LASIK (depth 160µm, 200µm), SMILE (depth 160µm, 200µm). Minimum 6 specimens per procedure. Imaging was repeated for all corneas post-surgery. Pre-surgery and post-surgery displacement maps were compared for individual corneas to evaluate spatial changes to corneal deformation after surgery.
Results
For all procedures the profile of surface deformation changed post-surgery indicating changes to corneal stress-strain distributions induced by the procedures. In all cases displacement was increased in the treatment zone, with LASIK corneas showing particularly high displacement concentrated at the flap boundaries. PRK showed the lowest increase in total surface displacement (+2%) with LASIK (depth 200µm) the highest (+33%). The increase in surface displacement in SMILE was greater when performed at 200µm vs 160µm (+23% and +11% respectively).
Conclusions
When evaluated immediately following surgery PRK was shown to best preserve the biomechanical integrity of the cornea. SMILE appears to have biomechanical advantages over LASIK with further benefits gained when performed at a shallower depth. Further work is now required to establish the biomechanical effects after a period of wound healing at the interface in llamelar procedures; to determine the optimum depth for SMILE surgery to best preserve corneal biomechanics; and to confirm these findings in human tissue.