Aim: To assess the effectiveness of the Keeler crowded logMAR visual acuity test in comparison with the Snellen test and to establish the optimum visual acuity threshold, using the Keeler crowded logMAR, for referral from the orthoptic secondary screening service to the ophthalmologist. Methods: A retrospective audit was carried out of community and hospital records of all referrals from the secondary vision screening clinics over the 2-year period from 31 July 2007 to 1 August 2009. In total, notes of 1035 patients were reviewed for this audit. The age at referral, visual acuity, vision test and primary diagnosis were recorded. Data were excluded if the patient: had records that were incomplete, had poor cooperation during assessment, had no formal visual acuity testing, or had been tested using the Cardiff Acuity Test or Kay Pictures. All Snellen visual acuities were converted into alogMAR equivalent to allow for direct comparison. Frimley Park Hospital’s visual acuity criterion for referral from the secondary screening service was a uniocular Snellen equivalent of poorer than 6/6 (equivalent) vision. Since the introduction of the Keeler logMAR tests, the criterion has been set at less than 0.100 for the crowded logMAR. Results: The false-positive referral rate was 15.094% (n = 32) for the Snellen test whereas for the crowded logMAR it was 17.949% (n = 7) at the established referral level of visual acuity. Conclusion: Such a high false-positive rate is attributable to our high visual acuity threshold referral criterion. Analysing the data available using different threshold levels of acuity for referral, it was found that accuracy can be improved, whilst maintaining maximum sensitivity, by adopting 0.175 on the crowded logMAR test as the visual acuity referral criterion and also ensuring that all patients with an intraocular difference of 0.100 logMAR are referred.