The Effects Of Silicone Hydrogels On Intraocular Pressure Measurements.

Purpose: To determine the similarity of intraocular pressure (TOP) measurements taken
by non-contact tonometry (NCT) and Tono-Pen tonometry over a silicone hydrogel contact lens compared to Goldmann applanation tonometry (Goldmann) without a contact lens on the eye.
Methods: Twenty-six healthy volunteers (52 eyes) participated in this study. Intraocular
pressure measurements were taken first through NCT. One investigator performed all
NCT measurements. Following topical anesthesia, TOP was then taken with Goldmann
applanation tonometry and the Medtronic Tono-Pen XL. Goldmann and Tono-Pen
readings were all gathered by one investigator, although not the same as who performed
NCT. After insertion of a Ciba Focus Night and Day silicone hydrogel soft contact lens
of minimal power, measurements were repeated with NCT and Tono-Pen without
additional anesthetic.
Results: During this study, the average NCT and Tono-Pen TOP measurements without
contacts lenses were lower than Goldmann applanation tonometry measurements. When
a silicone hydrogel contact lens (Ciba Night and Day/-O.50 DS) was placed on the cornea
and pressures were taken over the contact lens using NCT and Tono-Pen, the pressure
measurements were additionally lower. Tono-Pen over a contact lens gave a reading 11.02% lower than the TOP measured by Goldmann. In comparison of Tono-Pen without
a contact lens, readings were on average 1.98% lower over the hydrogel lens. In the
same way, NCT over a contact lens measured the TOP to be an average of 13.06% lower
than Goldmann. Compared to NCT without a contact lens, NCT pressures were on
average 7.37% lower with a contact lens.
Conclusion: According to the data, tonometry readings taken with Tono-Pen over a
silicone hydrogel lens are considered similar to measurements taken with Tono-Pen
without a contact lens (p=O.l3l). Tonometry readings over a contact lens are not similar
when taken with NCT (p=.OO2) or when compared to Goldmann pressure measurements.