OA Corner Part 9: Explaining spectacle prescriptions Part 1

Do you have enough of an understanding of spectacle prescriptions to be able to respond competently when a patient asks for theirs to be explained to them?

“What do all the numbers mean?” is a commonly-heard question in everyday practice; so how can you explain a patient’s prescription to them in a language they can understand?

Let’s look at the following prescription:

First of all, looking at the right eye (RE), 6/60 is the unaided vision, which is what the patient can see on the Snellen letter chart without any correction. 6/60 is the top letter on the chart, and the patient is unable to see any letters below the top one. The vision in the left eye (LE) is 6/24, which is the third line down from the top, and so the left eye sees better than the right eye when not wearing any correction. This is to be expected, as the prescription for the left eye is less myopic than the right eye.

The minus sign on the -2.50 on the right eye, and on the -1.50 on the left eye, indicates the patient is short-sighted, or myopic. This means without correction, the patient can only see clearly at a short distance, or close up. The higher the prescription, the closer this distance will be. Vision in the distance will be blurred without any correction, and it will be more blurred in the right eye than the left.

If the prescription had been a +2.50 and a +1.50, this would mean the patient is long-sighted, or hyperopic. Theoretically this means there is no clear point a patient can see clearly, although younger patients are able to add plus power by accommodating and may be able to overcome the hypermetropia. Sometimes young children who are hypermetropic will need to have drops put in their eyes to prevent them accommodating, so the true extent of the hypermetropia can be found.

The next part of the prescription for the right eye is -0.75 x 90. This is the cyl, or the cylindrical element to the prescription, and represents the degree of the astigmatism. The best way to explain this to a patient is to say that this is a common part of a prescription and means the eye needs a different correction in one meridian compared to the other.

Imagine the eye is more rugby ball shaped than football shaped, and so the curvature will be different in the two meridians, which results in two different prescriptions. These two meridians are at right angles to each other, and the precise setting is the axis element to the prescription, which in the example above will be axis 90.

The LE is -1.50DS. DS means dioptres sphere and indicates there is no cyl in the left eye. After the axis, 6/6 is the visual acuity. This is how well the patient sees on the Snellen chart with the correction in place. So in this case, 6/6 is classed as perfect vision. The visual acuity in the left eye is 6/5, which is even better than 6/6.

In next month’s OA Corner, we will look at the remaining elements of the prescription – the 2 base up and the +2.00DS Add – and how to explain these clearly and simply to the patient.

OA Corner Part 1: What makes a good OA
OA Corner Part 2: Communications
OA Corner Part 3: A question of strategies
OA Corner Part 4: Understanding bifocals
OA Corner Part 5: Our amazing eyes
OA Corner Part 6: Frame fitting basics
OA Corner Part 7: Frame styling factors
OA Corner Part 8: Single vision basics