Non-contact tonometry over soft contact lenses: effect of contact lens power on the measurement of intra-ocular pressure.

Abstract Purpose : To perform non-contact applanation tonometry over soft contact lenses and to examine any differences between the measured IOPs with and without the contact lens. Method : IOP was measured at one eye of eight subjects and re-evaluated through a soft lens in situ over the cornea. Seventy percent (ES70, Lunelle) water contact lenses or powers ranging from −15.00D to +13.00D were used. Results : Mean IOP without lenses was 15.2 mmHg (S.D.=±4.2) and this did not change significantly for lenses ranging from −15.00D to +3.00D ( P >0.01) but did change for lens powers +6.00D and above ( P x ) has the following characteristics, ΔIOP=0.022+0.591 x +0.11 x 2 +0.005 x 3 ( r =0.985, P =0.0001). Conclusion : Non-contact tonometry can be performed with sufficient accuracy over a soft lens on condition: (a) lens centre thickness is no more 0.30 mm and (b) power is not greater than +3D.