Device Measures Corneal Biomechanical Properties After Orthokeratology

A noncontact tonometer with an attached ultrahigh-speed Scheimpflug camera demonstrates good repeatability for measuring corneal biomechanical parameters in pediatric patients who undergo orthokeratology treatment, according to research published in Contact Lens and Anterior Eye. However, the device showed poor to moderate repeatability for measuring the length of the flattened cornea at the first and second applanations (A1L and A2L), according to the report. 

The prospective study included 51 participants with myopia (average age, 11.67±2.22 years; 24 girls, 27 boys) who underwent orthokeratology (ortho-k) treatment and returned for biomechanical measurements 3 months later. The researchers performed measurements a total of 3 times with a 5-minute interval between the hours of 9 and 11 AM to avoid diurnal variations.

With the exception of A1L and A2L values, which yielded intraclass correlation coefficient (ICC) values of 0.444 and 0.654, respectively, all ICC values were above 0.81, indicating acceptable repeatability. The ICC values for intraocular pressure (IOP; 0.902), deformation amplitude (0.918), stress-strain index (SSI; 0.917), stiffness parameter at first applanation (SP-A1; 0.937), and Ambrósio’s relational thickness horizontal (ARTh) surpassed 0.9, indicating good reliability, the report shows. 

Refraction was correlated with the time from invitation of the puff to first and second applanations (A1T and A2T), velocity of the corneal apex at first applanation (A1V), and IOP. Age demonstrated weak negative correlations with SSI, ARTh, and velocity of the corneal apex at second applanation (A2V) and a weak positive correlation with (A2V), distance of the 2 apices at time of highest concavity (peak distance). Axial length was positively correlated with SP-A1, peak distance, and A1V.

“The deformation of the cornea inevitably leads to changes in biomechanical properties,” the researchers explain. “The assessment of corneal biomechanics after orthokeratology was incomplete due to the limitations of the equipment used in previous assessments.” However, the study authors state that the device is “an appropriate device for biomechanics studies after orthokeratology treatment.” 

Study limitations include the exclusion of individuals who did not undergo orthokeratology treatment and failure to stratify participants according to corneal astigmatism.