Experimentally increased intraocular pressure using digital forces.
OBJECTIVE
To examine the reliability of an experimental method for increasing intraocular pressure (IOP) that could be used during videokeratography.


METHODS
Two levels of digital force ("light" and "firm") were applied by each subject to the temporal sclera of the right eye through the adnexal skin. Noncontact tonometry was used to record IOP increments obtained for samples of 15 measurements with each level of digital force. The subject was advised of the IOP recorded after each measurement. Because "with-result-feedback" increments in IOP would not be possible during videokeratography, a second, "without-result-feedback" series was recorded 3 minutes later to examine the reliability of the induced IOP increments. The authors alternated the roles of subject and examiner.


RESULTS
The mean normal readings were 19.4 mm Hg (C.W.M.) and 11.7 mm Hg (G.C.B.). The mean IOPs recorded under with-result-feedback conditions for light and firm digital forces were 27.2 mm Hg and 58.3 mm Hg (C.W.M.) and 27.1 mm Hg and 52.1 mm Hg (G.C.B.), respectively. Coincidentally, light digital forces were found to induce IOP increments for G.C.B. that were similar to those that would be expected to occur during 5.5 g weighted Schiotz tonometry. The 95% confidence limits for IOP increments under with-result-feedback conditions for light and firm digital forces were 33% to 47% and 187% to 215% (C.W.M.) and 116% to 146% and 303% to 388% (G.C.B.), respectively. The means of the without-result-feedback IOP increments for the two levels of digital force, and for each subject, all fell within these 95% confidence limits.


CONCLUSIONS
For trained subjects, digital forces on the eye appear to allow an examination of the influence of IOP increments on anterior corneal surface curvature. The mean IOP increments for the two levels of digital force (+40% and +200% [C.W.M.] and +132% and +345% [G.C.B.]) appear to permit videokeratography at higher IOP levels and across a wider range than those previously examined in vivo.
McMonnies
Charles W
CW
School of Optometry and Vision Science, University of New South Wales, Kensington, Australia. c.mcmonnies@unsw.edu.au
Boneham
Gavin C
GC
D000328:Adult; D003315:Cornea / Q000502:physiology; D019781:Corneal Topography; D005246:Feedback; D005385:Fingers / Q000502:physiology*; D006801:Humans; D007429:Intraocular Pressure; D008297:Male; D014065:Tonometry, Ocular