gms | German Medical Science

Purpose: Nowadays, refractive surgery became very popular. It affects the central corneal thickness and corneal biomechanics. Hence corneal tonometry has the limitation when using after keratorefractive surgery. An accurate IOP-measurement without corneal contact would be preferable. Transpalpebral transscleral tonometry is not directly influenced by corneal surgery and it has been shown to provide reliable IOP-measurement results. The aim of the current study was to evaluate the clinical use and the reliability of transpalpebral transscleral tonometry in patients with refraction anomaly before and after keratophotorefractive surgery.

Methods: 98 individuals (age: 18 – 53 years) with ametropia of different grades were included in the retrospective study. 38 subjects (age: 18 – 50 years) underwent excimer laser correction of vision with different durations of post-surgery period from 7 days to 4 years. Other 59 subjects (age: 19 – 53 years) from the cohort had no history of keratophotorefractive interventions. IOP was assessed with Goldmann Applanation Tonometry (GAT) and non-corneal tonometry (Diaton transpalpebral transscleral tonometer, Tonom GmbH) in both eyes of each patient.

Results: In patients after keratophotorefractive correction GAT IOP amounted to 11.8 (10.0 – 14.0) mmHg, CCT corrected GAT IOP was 14.3 (12.8 – 16.3) mmHg and transpalpebral IOP (tpIOP)was 15.0 (13.4 – 17.5) mmHg. Individuals unaffected by the surgery showed GAT IOP of 18.0 (15.0 – 19.0) mmHg [median (1^st quartile – 3^rd quartile)], CCT corrected GAT IOP of 17.2 (14.9 – 18.4) mmHg tpIOP of 14.5 (12.5 – 16.0) mmHg. GAT IOP showed strong correlation with CCT: r = 0.606; p<0.001, while CCT corrected GAT IOP (r = 0.095; p = 0.355) and tpIOP (r = -0.125; p = 0.224) did not correlate with CCT. Bland-Altman plots show a good agreement between CCT corrected GAT and tpIOP.

Conclusions: The results of IOP measurement using transpalpebral transscleral tonometry were independent from biomechanical properties of the cornea, while Diaton IOP values before and after corneal surgery remain stable. GAT IOP-measurement results were dependent on corneal properties. CCT corrected GAT IOP values before and after corneal surgery differ from each other. In the whole group CCT corrected GAT and transpalpebral IOP-values showed a good agreement. This study confirms the advantages of the clinical application and reliability of transpalpebral transscleral tonometry after photorefractive surgery.