The accuracy of dynamic contour tonometry over soft contact lenses

Dynamic contour tonometry (DCT) has been shown to measure the intraocular pressure (IOP) independently of corneal thickness. This study aimed to investigate if DCT remains accurate when the IOP measurement is taken over soft contact lenses (CLs) of different thicknesses and material characteristics.

This was a prospective clinical study that included 42 patients. Subject age was 22 to 59 years (26.5 ± 6.3 years). Intraocular pressure and ocular pulse amplitude (OPA) measurements were taken under topical anesthesia without CLs and over various daily disposable CLs with -0.50, +5.00, and -5.00 diopters (D) in hydrogel (Nelfilcon A) and in silicone hydrogel (Narafilcon A) materials.

No statistically significant differences were found when comparing the IOP measurements obtained using either of the different CL powers of -0.50 or -5.00 D, irrespective of which CL material was being used. However, the difference of 0.62 mm Hg observed when the Nelfilcon A with a power of +5.00 D was used turned out to be highly statistically significant (p = 0.0002), whereas the Narafilcon A with the same power of +5.00 D, with a small difference of -0.16 mm Hg, was not. Regarding OPA measurements, no significant differences were found between measurements with and without CL neither for different materials nor for change in dioptrical power (F = 0, p = 1.000).

This study showed good reliability of IOP and OPA measurements over CLs with varying thickness profiles and different soft materials when using the DCT. Only a small but statistically significant difference of 0.62 mm Hg was found for the IOP measurement with the hydrogel CL of +5.00 D compared with "no CL."