Sir,

We have read with interest the excellent work by Kamiya et al,1 which investigated the corneal biomechanical properties in eyes undergoing phototherapeutic keratectomy (PTK) for the treatment of granular corneal dystrophy. In the study, corneal hysteresis (CH) was measured with an ocular response analyser before and 3 months after surgery. One of their main results was that the CH was significantly decreased from 10.2±2.2 to 8.7±1.8 mmHg after PTK.

Previous studies have investigated the relationship between CH and intraocular pressure (IOP). Kamiya et al2 found that eyes with higher IOP are more predisposed to having lower CH. In another study, González-Méijome et al3 reported that average changes in CH over time correlated well with the changes in IOP values. Although the relationship between CH and IOP has not been fully investigated, the current literature implies that IOP levels may affect the measurement of CH.

Kamiya et al1 in their study mentioned that steroidal medications were topically administered postoperatively. The use of the medications may potentially lead to the elevation of IOP. The authors did not mention the IOP levels in eyes before and after PTK. On account of the potential effects of IOP levels on CH measurements, the decrease of CH may be because of the elevation of IOP. Thus, we suggest that the authors show IOP data and make a comparison of IOP levels before and after PRK.