Intraocular pressure after myopic laser refractive surgery measured with a new Goldmann convex prism: correlations with GAT and ORA

Abstract

Background The purpose of this study is to describe measurements using a newly developed modified Goldmann convex tonometer (CT) 1 year after myopic laser refractive surgery. Intraocular pressure (IOP) measurements were compared with IOP values obtained by Goldmann applanation tonometer (GAT), and Ocular Response Analyzer (ORA). Methods Prospective double-masked study performed on thirty eyes of thirty patients that underwent laser in situ keratomileusis (LASIK; n = 19) or photorefractive keratectomy (PRK; n = 11). IOP was measured before and 3 and 12 months after surgery. Intraclass correlation coefficient (ICC) and Bland-Altman plot were calculated to assess the agreement between GAT, CT, IOPg (Goldmann-correlated IOP) and IOPcc (corneal-compensated IOP) from ORA. Results Twelve months after LASIK, IOP measured with CT showed the best correlation with IOP measured with GAT before surgery (GATpre) (ICC = 0.886, 95% CI: 0.703–0.956) (15.60 ± 3.27 vs 15.80 ± 3.22; p < 0.000). However, a moderate correlation was found for IOP measured with IOPcc and CT 12 months after LASIK (ICC = 0.568, 95% CI: − 0.185 – 0.843) (15.80 ± 3.22 vs 12.87 ± 2.77; p < 0.004). Twelve months after PRK, CT showed a weak correlation (ICC = − 0.266, 95% CI: − 3.896 – 0.663), compared to GATpre (17.30 ± 3.47 vs 16.01 ± 1.45; p < 0.642), as well as poor correlation (ICC = 0.256, 95% CI: − 0.332 – 0.719) with IOPcc (17.30 ± 3.47 vs 13.38 ± 1.65; p < 0.182). Conclusions Twelve months after LASIK, IOP measured with CT strongly correlated with GAT before surgery and could therefore provide an alternative method for measuring IOP after this surgery. More studies regarding this new convex prism are needed to assess its accuracy.

Evaluation of Intraocular Pressure in Eyes After Femtolasik Surgery

“…Thus, trauma to Bowman's layer during flap creation, collagen deposition during flap making, collagen deposition during the healing process, and increased accumulation of water in the stroma due to increased proteoglycans and hyaluronic acid can alter the normal rigidity of the cornea 10,13,14 . So, consequently, decreasing corneal stiffness will make it easier for applanation-type tonometer to flatten the cornea, so less force will be required to flatten the cornea and IOP readings will decrease 4,10 .…”

“…Myopia is the most common refractive error 2 and its prevalence is expected to increase in such a way that it could affect up to 1 billion people with high myopia by 2050 (7.5 times more than in 2000) 3 . Keratorefractive procedures are very popular in correcting these ametropias, with Laser in situ keratomileusis (LASIK) being the most popular corneal refractive surgery performed in the last decades, with approximately one million myopic patients undergoing LASIK every year 4 . Intraocular pressure (IOP) is the main risk factor for the development and progression of open-angle glaucoma (OAG) 5 .…”

“…The IOP can be evaluated using techniques such as applanation -Goldmann applanation tonometry (GAT) and surface correction (CATS, Reichert, USA)), indentation pneumotonometer (Pneumotonometer, Reichert, USA), both applanation and indentation (Tono-Pen, Reichert, USA), rebound (i-Care, USA), dynamic contour (dynamic contour tonometer (DCT), Pascale, Switzerland) and non-contact type (air breath tonometers such as Corvis ST (CVS, Oculus , Germany ) and ocular response analyzer (ORA, Reichert, USA) 7 . GAT is still the gold standard for measuring IOP in normal corneas 4 . Applanation tonometry is based on the Imbert-Fick law 8 which only applies to a sphere with an infinitely thin, perfectly flexible, elastic and dry limiting membrane, neither of which is true in the human eye 7,9 .…”

“…Femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) involves the creation of a corneal flap by femtosecond laser and corneal reshaping by excimer laser to remove tissue from the underlying stromal bed. Thus, these changes in corneal morphology and biomechanics may affect IOP measurement by several methods patients 4,5,6,7,11 .…”

Refractive surgery for the glaucoma suspect

“…Another recent study from Iglesias et al [35 ▪ ] assessed a new Goldmann convex prism and compared its measurements to GAT and ORA after myopic laser refractive surgery. They found a high correlation between preoperative IOP measurements from GAT and post-LASIK IOP measurements from the new convex prism at 3 and 12 months.…”