Reproducibility of Central Corneal Thickness Measurements in Healthy and Glaucomatous Eyes

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To the Editor:
We read with great interest the article by Realini et al1 on the reproducibility of central corneal thickness (CCT) measurements in healthy and glaucomatous eyes.
We would like to congratulate the authors for their very interesting paper because it is well known that the measurement of CCT, even if it is not the only involved parameter,2,3 is very important in the reliability of intraocular pressure measurements, both in virgin eyes4 and in those that undergo photorefractive keratectomy.5,6 Furthermore, it is also mandatory in patients with keratoconus in deciding which technique (corneal collagen crosslinking or transplant) can be more appropriate for treatment,7,8 and in keeping with the results.9,10
For these reasons the reproducibility of CCT measurements is crucial.
The authors utilized ultrasound pachymetry for such a purpose. It is true that this technique is considered to be the gold standard, but gold standard does not always mean precision. In fact, it has some limitations, among others, (1) it has to be performed by very experienced examiners, because it is almost impossible to be sure that during the different visits we are measuring the same point, and, (2) to make such measurements, anesthetic drops need to be used. In particular, the authors forgot to mention which anesthetic drops were used, and, if they were always the same, as to what was their amount, the time intervals that occurred between the anesthetic drops’ administration, and the CCT measurements, as it has been shown that some of them can produce a corneal thickening, whereas others do not.11
For these reasons, it is mandatory for this kind of study to be sure that the time interval, the drops, and their amount are the same at each follow-up visit.
In conclusion, we would like to suggest that for future studies the use of optical noncontact devices could be more reliable.
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