Resolution Visual acuity
- Resolution Acuity tests
- Electrophysiological test
Resolution Visual Acuity
Where communication is limited, or the child is very young, the patient’s looking behaviour is interpreted to assess whether they can see targets made up of increasingly fine black and white lines. These tests are called preferential looking (PL) tests.
The photograph below depicts the Cardiff Acuity Test (top) and the Keeler Acuity Cards (bottom). These are both preferential-looking tests of resolution acuity.
In hospital clinics electrophysiological measures such as the visual evoked potential (VEP) may be used. VEPs are electrical signals produced in the visual system when a target is seen. These signals are recorded with electrodes lightly attached to the scalp at the back of the head while the child watches patterns on a computer screen. These visual acuity tests measure ’resolution acuity’.
Resolution acuity tests only require the patient to look towards the black and white target. The patient doesn’t need to verbally communicate with the examiner or necessarily understand the test.
Whilst resolution acuity tests are suitable for the very young or those with whom communication is difficult, older children and those better able to communicate should be tested with more complex visual acuity tests which assess ’recognition acuity’. For more information on recognition acuity click here
When vision is reduced and when there is disease present in the eye or the visual system resolution acuity tests may overestimate vision. Measures of resolution acuity made with techniques such as preferential looking and the visual evoked potential should be interpreted with this in mind.