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


METHODS
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 -15.00 D to +13.00 D 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 -15.00 D to +3.00 D (P > 0.01) but did change for lens powers +6.00 D and above (P<0.01). The least squares line describing the change in measured IOP (deltaIOP) as a function of lens power (x) has the following characteristics, deltaIOP = 0.022 + 0.591x + 0.11x2 + 0.005x3 (r = 0.985, P = 0.0001).


CONCLUSIONS
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.
Patel
S
S
Common Services Agency, Edinburgh, United Kingdom and Instituto Oftalmologico de Alicante, University Miguel Hernandez, Alicante, Spain. sudhir.patel@psd.csa.scot.nhs.uk
Illahi
W
W