We read with great interest the article by Altan-Yaycioglu et al. Their efforts in evaluating the ocular side-effects of tolterodine and oxybutynin is greatly appreciated. We would be most grateful if the authors can share with us their thoughts in regard to the following points.
First, accommodation amplitude declines with advancing age as a result of sclerosis of the crystalline lens fibres and changes in its capsule , giving rise to the condition of presbyopia, the inability to focus near objects. As a rule of thumb, people 40–50 years of age will usually have ∼1.0 diopter (D) of presbyopia, while those over 60 years of age may have 3.0 D or more. In fact, it is common for people to start experiencing presbyopia after 40 years of age. This appears to coincide with the age range of patients having overactive bladder – in this study, the mean ages in the tolterodine and oxybutynin treated groups were 40.2 years and 42.2 years, respectively. These patients were likely to have started using presbyopic glasses for near visual tasks. Furthermore, the accommodation amplitude changes induced by tolterodine (0.41 D) and oxybutynin (0.38 D) can be easily compensated for by their presbyopic glasses. Therefore, from this point of view, the potential benefit of the two drugs in the treatment of overactive bladder should not be undermined as the accommodation amplitude deficit is fully correctable.
Secondly, the pupillary diameter was measured by the ruler of a slit-lamp. This may cause inaccuracy especially when measuring the scotopic pupillary diameter as the dimmed slit lamp light will still shine directly into the pupil. We suggest using a pupillometer. Studies have found that the automated pupillometer is more accurate and reliable than manual examination in measuring pupil size and reactivity .
Thirdly, the authors concluded ‘both oxybutynin and tolterodine reduced aqueous tear secretion markedly’. However, there were no significant differences between the baseline and day 28 findings for Schimer I-values in either group. It is only the mean tear-break-up-time (TBUT) that was significantly shorter after 28 days of treatment. The precorneal tear film consisted of three layers: lipid, aqueous and mucin. The TBUT time is a measure of the mucin tear layer, and not the aqueous tear layer, which is a function of the Schimer I-values.
We agree with the authors that for individuals already having dry eye, an ophthalmologist consultation may be appropriate before prescribing anticholinergics. This may be especially true for those patients having a severe pre-existing dry eye, or sicca, with complications such as significant corneal epithelial erosions or corneal thinning.
We would like to commend the authors for conducting this excellent prospective randomized study. We hope that the issues raised here will help broaden the discussion on the topic.