Sir,

We applaud the authors for attempting to address the issue of mobile phone use around ophthalmic equipments. The paper concludes that ‘devices are unlikely to be significantly affected by electromagnetic interference’ and questions the need for a complete ban of mobile telephones in ophthalmic departments. Although probably true, it appears that the methods used may not be robust enough to draw these conclusions.

The study did not address the phones' energy emissions when observing for effects on the tested equipment; thus, these results are valid only for the exact time, place, and handsets used. This is because a mobile phone increases or decreases its energy output depending on its proximity to the base station (a phenomenon known as ‘adaptive energy’), the state of the call (standby, connecting or connected), and there is further variability in energy output between individual handsets and networks. Therefore, electromagnetic interference testing without simultaneous energy or power measurements can be dangerous as it may lead to a false conclusion of relative safety. One such example is where there happens to be a base station in close proximity to the test site resulting in the phones emitting only a fraction of their potential energy.

Although the results are encouraging, we feel that caution should be exercised when drawing conclusions from these data.