Abstract
Abstract: :
Purpose: Determine the effect of contact lenses (CL) on the measurement of corneal hysteresis (CH), intraocular pressure (IOP) and excess ocular pressure (EOP) as measured by the Reichert ocular response analyzer (ORA). Determine the effect of contact lenses on the "normality" line derived from the regression of CH vs. IOP. Methods: Corneal hysteresis (CH), intraocular pressure (IOP), excess ocular pressure (EOP), corneal curvature (CC – Reichert KR) and spherical equivalent refractive error (SE – Reichert KR) were measured three times for 28 eyes, 14 normal subjects both with CL and without CL. Time interval between the with and without CL measurements was 0.5 hrs. Results: Mean values between with–without CL: CH 5.48 – 5.47 mmHg, IOP 13.8 – 14.2 mmHg, EOP 0.5 – 0.1 mmHg. Correlations of with–without CL: CH – R2=0.76, IOP – R2=0.88, EOP R2 =0.3. Average of with–without CL right–left eye correlation : CH R2=0.88, IOP R2=0.88, EOP R2=0.44. Average right–left SE without CL is –4.65 D. Average right–left SE with CL is – 0.19 D. Correlation of average right–left IOP change with curvature R2=0.01. Normality line without CL: R2=0.77, slope 0.71mmHg, offset –4.6mmHg. Normality line with CL: R2=0.74, slope 0.70mmHg, offset –4.3mmHg. Conclusions:Mean values for CH and IOP are not affected by contact lens status within instrument noise level. The low with–without CL EOP correlation is consistent with the negligible normality line parameter with–without CL changes. Right–left eye correlation is very strong and unaffected by contacts. Small reductions in IOP with CL are insignificant and could be due to average curvature reduction of 4.46 D, but low IOP change correlation with curvature change indicates otherwise. Independence of CH and IOP from contact lenses status provides reinforcement of the claim that the ORA corneal parameter depends primarily on corneal viscoelasticity.
Keywords: cornea: basic science • contact lens • intraocular pressure