Corneal parametric features and axial length (AL) were examined for correlation with high myopia. The study's findings fill the void in knowledge regarding changes in the cornea’s mechanical properties and biological parameters involved in high myopia that could expose patients to higher risk of retinal detachment, myopic maculopathy, glaucoma, and cataracts.
Study design
This was a cross-sectional comparative study performed at a single ophthalmic center in Guangzhou, China. Patients ≥50 years of age with high myopia [defined as axial length (AL) ≥26 mm] were recruited between August 2019 and October 2020. Age- and sex-matched controls also also identified. All participants underwent a comprehensive ophthalmic evaluation including slit-lamp examination, IOL Master 700, and anterior segment swept-source optical coherence tomography (SS-OCT).
Outcomes
The authors found that central corneal thickness (CCT), thinnest corneal thickness (TCT), and corneal volume (CV) had continuous negative correlations with AL. On the other hand, anterior corneal curvature (CC) decreased rapidly with AL <26 mm; however, the downward trend slowed when AL was between 26 mm and 28 mm. Interestingly, there was no significant decreasing trend when AL was >28 mm. The authors suggest that an AL of 28 mm may be the threshold for sustaining ocular mechanical stability.
Limitations
This study had several limitations. This study was cross-sectional and therefore the etiology for corneal changes could not be identified. Furthermore, because all subjects were recruited from a single center and were of Chinese origin, the study’s findings may not be generalizable to other racial or ethnic groups. Finally, the majority of the study population was generally young, and additional studies are needed to identify corneal features of patients at all ages.
Clinical significance
This study emphasizes the importance of CC in improving the accuracy of IOL calculations in patients with high myopia. In clinical practice, IOL formulas are often less accurate in individuals with AL ≥28 mm. A modification may be necessary when using formulas that employ conventional keratometry to calculate IOL power in these patients.