Sir,

We thank you for providing us an opportunity to respond to the letter by Cate and Broadway1 concerning our paper on patterns of adherence to hypotensive therapy that was recently published in Eye.2 Our paper tried to address the issue of adherence in a way that was clinically more meaningful than simple percentage figures that are commonly reproduced in the literature. As part of this project we also collected pre- and post-treatment IOPs although we did not report on them within the Eye paper.

In their letter Cate and Broadway highlight that the routine use of an electronic dosing monitor is unrealistic (especially so now that Alcon has discontinued the supply of such aids) and asks whether a measure of IOP reduction can be used as a surrogate measure for adherence. We have now undertaken an analysis of pre- and post-treatment IOPs and can report that there is no relationship between IOP reduction and adherence (see Figure 1).

Figure 1
figure 1

The relationship between adherence to hypotensive medication and IOP reduction measure at the time of a clinic appointment.

Full size image

We do not find this surprising. The post-treatment IOP measured at a clinical appointment reflects whether or not the medication has been taken in the last few days rather than long-term adherence. Patients attending a hospital appointment are reminded to medicate and pre-clinic appointment adherence is likely to be very high. The short-term hyperaemia that often accompanies the onset of prostaglandin treatment is not an uncommon sign at follow-up appointments and suggests the recent re-introduction of medication.

Although patients tend to overestimate their adherence (for which data are supplied in our paper), simple non-judgemental questioning is likely to give a better estimate of adherence than an analysis of IOP data collected at follow-up appointments.