I’ve been criticised for not noting the patient’s working distance when I measure the near reading print size. I don’t understand why the working distance is required.

In my role as an expert witness for medico-legal and fitness to practise cases and hearings, I have to read a lot of other eye specialists’ clinical records. It is very common for the near reading distance to be absent from the clinical records.

When we measure distance visual acuity we include information on the size of the letter the patient can see and the distance the letter was viewed at. For example, the measurement 6/24 means that a ‘24’ sized letter was viewed at 6 m. In the UK, where I do most of my clinical work we still use N notation for recording reading print size. N notation is based on font size. N5 is the smallest and N8 is about the size of newspaper column print.

Sadly, in my experience, it is very common for eye specialists to note the letter size in the clinical records, for example, N8 without a note of the reading distance and without a note of what each eye, in turn, can read. This is akin to noting only ‘24’ when recording a distance visual acuity of 6/24 and also only noting distance visual acuity with both eyes together and not with each eye in turn.

A note of the N size on its own is not a measure of reading visual acuity. It is simply the size of the print the patient could read. In order for the N size managed by the patient to be equivalent to a reading acuity it has to be accompanied by the working distance; the distance the reading material was held at by the patient when the print was being read. N5 read at 20 cm is a totally different clinical value from N5 read at 45 cm. By not noting the working distance in the records valuable clinical information is lost. This is a shame because it would take around 5 seconds to measure the working distance with a tape measure and around 10 seconds to measure monocular reading acuity values.

A note of the reading visual acuity for each eye is important. Conditions affecting the macula such as age-related macular degeneration can affect near reading acuity more than distance visual acuity. If the test is conducted with both eyes together, a reduced near reading visual acuity in one eye could be missed as the normal level in the unaffected eye may mask the reduced value in the affected eye. Subtle changes in macular function could be missed if monocular reading visual acuity is not measured and this may result in delayed treatment.

Every patient deserves their monocular reading visual acuity to be measured and recorded.