Maximising the sensitivity and specificity of non-contact tonometry in glaucoma screening

Data from a glaucoma screening study involving 88.5% of the population age 50 and over of a single handed general practitioner were reanalysed to determine the effect of altering the protocol for intraocular pressure assessment and the effect of changing the referral threshold. The predictive power of the Keeler Pulsair noncontact tonometer was found to decrease from 22.5% at four pulses per eye to 12.3% when only one pulse per eye was used, with a reduction of sensitivity from 91.7% to 75%. The sensitivity of the same device fell from 91.7% if all patients with an IOP greater than 21 mmHg were deemed as having a positive screen, to 41.6% when only patients with an IOP greater than 26 mmHg were considered for referral. To create a balance between high sensitivity and acceptable predictive power of a positive result in a population where 50% of glaucoma sufferers are known prior to screening, we advise that four pulses per eye should be used with an IOP of greater than 22 mmHg used as the significant finding indicating that the patient required referral.