Association of intraocular pressure and central corneal thickness with the degree of myopia

Background. In individuals with myopic refractive error—particularly high myopia—ocular anatomy undergoes changes, most notably an increase in axial length (AL) exceeding 24.5 mm. Several studies have reported alterations in the scleral shell among patients with varying degrees of myopia. Increased myopia is associated with reduced corneal hysteresis and decreased acoustic density of the sclera. Differences in intraocular pressure (IOP) between individuals with myopia, emmetropia, and hyperopia have also been described. However, the available literature provides no conclusive evidence on the relationship between intraocular pressure (IOP) and central corneal thickness (CCT) across different degrees of myopia. Purpose: To assess how intraocular pressure and central corneal thickness vary across different degrees of myopia. Materials and methods. We retrospectively analyzed medical records of 500 patients (1000 eyes) aged 18 years and older, all diagnosed with myopic refractive error. Patients were stratified into three groups based on myopia severity. The cohort included 290 females (58%) and 210 males (42%). Pachymetry was performed using the ALLEGRO Oculyzer (WaveLight Oculyzer II), autorefractometry using TONOREF (Nidek II), and IOP was measured with four tonometers: a non-contact tonometer (TONOREF Nidek II), Maklakov tonometer, Schiøtz tonometer, and Goldmann applanation tonometer. Statistical analysis was conducted using R software (version 4.2.2). Results. A statistically significant positive correlation was observed between increasing myopia and IOP measurements obtained using the non-contact tonometer TONOREF (Nidek II) (p = 0.001) and the Goldmann applanation tonometer (p < 0.001). No such association was found for IOP values measured with the Maklakov (p = 0.978) or Schiøtz (p = 0.262) tonometers. The analysis revealed a statistically non-significant (p = 0.065) trend toward increased central corneal thickness with greater myopia. Mean CCT values were 539.8 ± 32.5 µm in low myopia, 544.1 ± 33.9 µm in moderate myopia, and 546.5 ± 37.9 µm in high myopia. Conclusions. No statistically significant association was found between central corneal thickness (CCT) and the degree of myopia (p = 0.065). The effect of myopia severity on intraocular pressure (IOP) measurements varied depending on the tonometry method used. Statistically significant associations between IOP and myopia severity were observed when measured using the TONOREF (Nidek II) noncontact tonometer (p = 0.001) and the Goldmann applanation tonometer (p < 0.001). In contrast, no such association was found with the Maklakov (p = 0.978) or Schiøtz (p = 0.262) tonometers.