Intraocular pressure measurement in patients with instrastromal corneal ring segments

PURPOSE: To study the measurement of intraocular pressure after implantatio n of Intacs (ICRS) intrastromal corneal ring segment, a device that is posi tioned circumferentially in the peripheral corneal stroma to correct myopia . The device changes the corneal curvature by shortening are length. Since the ring segments are made of polymethylmethacrylate, this may cause locali zed changes in corneal elasticity so intraocular pressure measurement may b e affected. METHODS: We measured the intraocular pressure of 12 eyes in which the ICRS had been in place longer than 6 months. We used Goldmann applanation and To ne-Pen tonometers over the central corneal and the paracentral corneal area s. We also measured the intraocular pressure with the Tono-Pen applanated d irectly over the intrastromal corneal ring segments. RESULTS: The resulting intraocular pressure measurements were similar for t he Tone-Pen tonometer readings over the central cornea, paracentral cornea, and the Goldmann applanation tonometer readings over the central cornea (P <.01). Our measurements using the Goldmann applanation tonometer on the pa racentral corneal area showed artificially elevated intraocular pressure in the 40 to 60 mmHg range. We were not able to obtain consistent results whe n we measured the intraocular pressure using the Tone-Pen on the corneal ar ea directly overlying the intrastromal corneal ring segment implants. CONCLUSION: Consistent intraocular pressure measurements on eyes with the I CRS can be obtained with the Goldmann applanation tonometer over the centra l corneal area or with the Tono-Pen tonometer over the central or paracentr al corneal areas.