Impact of corneal biomechanical features on the results of tonometric measurements

Relevance Glaucoma is one of the main causes of low vision in the world. The level of intraocular pressure (IOP) is the only modifiable factor influencing the development of glaucomatous optic neuropathy [1]. In clinical practice, IOP is assessed using indirect tonometry, which is based on the assessment of corneal deformation under external mechanical influence (flattening, indentation, etc.) using a tonometer [2–4]. Therefore, when performing tonometry, it is necessary to take into account measurement errors associated with the individual characteristics of the fibrous membrane of the eye [5]. Objective To study the effect of peripheral corneal thickness (PCT) and its curvature on the results of tonometric measurements. Material and methods Forty-nine patients (49 eyes) who were indicated for antiglaucoma surgery were examined. Using bidirectional applanation tonometry, we obtained the following parameters: IOPcc (corneal-compensated IOP), IOPg (IOP according to Goldman), the difference (delta) of IOP (IOPcc-IOPg), CH (corneal hysteresis), CRF (corneal resistance factor). During keratotopography, we examined the central and peripheral corneal thickness (CCT) in four meridians, the curvature of the anterior and posterior surfaces of the cornea, and the depth of the anterior chamber. The influence of the studied parameters on the difference in IOP was assessed. Results IOP delta correlates with CRF (r = –0.652), CH (r = –0.873), central corneal thickness (r = –0.293), PTR at all distances except 5 mm (r = –0.297; –0.287; –0.302; –0.303), with the strong and weak meridians of the anterior corneal surface (r = 0.328; r = 0.315), with the strong and weak meridians of the posterior surface, as well as the average curvature of the posterior surface (r = 0.307; r = 0.332; r = 0.328). Conclusion It can be assumed that the tonometry error is determined not by the thickness or curvature of the cornea as such, but by its biomechanical properties. Although corneal thickness and curvature can affect its biomechanical parameters, CRF and CH are more comprehensive indicators of its properties than individual indicators of its linear dimensions. Keywords: glaucoma; tonometry; peripheral corneal thickness; corneal curvature; intraocular pressure