Comparison of visual acuity charts identifying visual impairment among older people outside the eye clinic.

Purpose: Evaluate the construct validity and describe sensitivity, specificity and predictive value of two short charts of visual acuity (VA) and examine whether these can identify and detect signs of visual impairment among older people.

Method: The study included 43 persons, >65 years, with age related eye disease, living in their own homes. An ophthalmologist assessed the individuals' VA at an eye clinic with the 5 m KM chart. A research assistant assessed individuals' VA by the 1 m KM chart and the Visual Acuity Screening Test in their home environment.

Results: All persons with a VA level of <0.5 were correctly identified by both instruments. The instruments have good positive and negative predictive values for the 1 m KM chart (73% and 100%) and for the Visual Acuity Screening Test (69% and 100%). The construct validity between the instruments was good, but the assessment at the eye clinic assessed the participants as having higher VA level.

Conclusions: Both instruments have good construct validity, considering they were carried out in poorer lighting conditions and a good predictive value for screening out VA levels <0.5. The 1 m KM chart showed the best agreement with the 5 m KM chart.