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Assessment of Pascal dynamic contour tonometer in monitoring IOP after LASIK

2005; Lippincott Williams & Wilkins; Volume: 31; Issue: 3 Linguagem: Inglês

10.1016/j.jcrs.2005.02.021

1873-4502

Christoph Kniestedt, H. Kanngiesser, Robert L. Stamper,

Corneal Surgery and Treatments

We read with great interest the article by Siganos and coauthors1 about dynamic contour tonometry (DCT). Our studies also strongly suggest that contour-matching tonometry is less dependent on corneal rigidity than applanation tonometry. However, we want to clarify that in the article, our studies were cited incorrectly and we did not use noncontact air tonometry. In a comparative study of human cadaver eyes,2 we compared the recently introduced dynamic contour tonometer and manometric reference pressure. We concluded that at all intraocular pressure (IOP) levels (5 mm Hg to 58 mm Hg), DCT readings were significantly closer to the real intracameral IOP than both pneumatonometry and Goldmann applanation tonometry. Unfortunately, it was not possible to correlate IOP readings with corneal thickness since human cadaver corneas are structurally altered and extremely hydrated starting very shortly after death. However, in the study cited in the text (Kniestedt et al.), we compared tonometers at varying stages of corneal hydration.3 We performed DCT measurements on maximally hydrated and dehydrated eyes and found that DCT appears to be independent of corneal thickness changes produced by altering corneal hydration. This is clinically relevant since corneal edema is a relatively frequent occurrence and accurate IOP measurements are necessary to determine causation and management. Thus, corneal thickness as an inherited trait was not and could not be examined in any of our cadaver eye studies and citing our studies as having determined this is incorrect. The second citation in our article (Kanngiesser et al.) refers to a study in which we described the theoretical model and compared the mathematical and geometrical results with actual DCT readings in cadaver eyes. It is true that within the limited boundaries of the in vitro study, corneal thickness (chemically thinned), corneal astigmatism, and corneal radius do not seem to influence the accuracy of DCT. To draw any conclusion that in a clinical setting DCT is independent of innate corneal thickness would not be accurate. That DCT may actually be independent of corneal thickness was suggested by a recently completed clinical study using DCT and applanation tonometry, in which no correlation between corneal thickness and DCT readings was found, whereas applanation tonometry according to Goldmann was indeed correlated with central corneal thickness.4 Proof that DCT is independent of corneal thickness can only be obtained by comparing DCT to manometric readings in living, normal eyes—a study that would be difficult to perform.5–7 Christoph Kniestedt MD Hartmut Kanngiesser PhD Robert L. Stamper MD aWintherthur, Switzerland bPort, Switzerland cSan Francisco, California, USA