Sir,

Communication is greatly facilitated by mobile phones (cell phones) and their use is now commonplace among doctors. The current restrictive policy in ophthalmic departments seems to be unjustified given the absence of evidence. There is no published work relating to such departments or their equipment, and the studies available suggest that there is minimal risk to most hospital equipment.

Mobile networks operate by receiving and transmitting their signals via relay stations at carrier frequencies between 900 and 1800 MHz. Electromagnetic interference occurs where the mobile, which is an intentional radio transmitter, causes an electronic piece of equipment to act as an unintentional radio receiver. Global System for Mobile communication (GSM) employs a cellular structure in which a base station is used to provide access over a narrow bandwidth. The telephone senses how close it is to the cellular network antenna and increases or decreases its own energy in order to adapt to its environment (adaptive energy), altering the absolute degree interference of individual telephones in any one place. Interference is highest at the initial stages of an outgoing or incoming call.

The issue of mobile phone interference in hospitals first came to attention in the United Kingdom in 1994 when the UK Medical Devices Agency (MDA) issued a safety notice that prompted a detailed study published in 1997.1 Only 4% of 178 devices examined suffered interference from mobile phones, with less than 0.1% showing serious effects. They recommended that phones should be switched off in areas where sensitive devices may be used (including operating theatres). None of the devices tested are routinely used in the ophthalmology setting. Irnich and Tobisch2 tested more than 220 electronic medical devices in a hospital environment (predominantly intensive care related) and were able to demonstrate a greater than 98% safety when mobile phones were maintained at a distance greater than 1 m. The recommended safe distance of 1 m has become known as the ‘arm's length rule’. In one study, a CO2 airway adapter and haemoglucostix meter suffered interference,3 while another study demonstrated adverse effects in a physiological monitor along with other equipment, but none was affected by the fields over 1 m.4 Effects on physiological monitors, defibrillators and pacemakers have been described,1, 5, 6, 7, 8 but were transitory and occurred only in close proximity (tens of centimetres). Other studies with implantable defibrillators found no interference at all,9 or concluded that ‘although interference can happen it would rarely be clinically important.10

In light of the evidence available, perhaps a relaxation of mobile phone restrictions in the ophthalmology department should be considered for doctors, especially as forthcoming advances in telecommunications are likely to herald the advent of medical data transfer on these devices. Further, ophthalmology departments do not routinely utilize critical care equipment. Many eye units are located out of the main path of core hospital equipment, and even for those that are near risk areas (intensive care, operating theatres, and cardiac units, for example), or have their own operating theatres interference would be highly unlikely given the range at which it occurs (<1 m). A precautionary measure would be to have all phones switched off (mobile-free zones) within these risk areas with clearly defined borders analogous to no smoking areas. It has been suggested that many already ignore the total ban usually present.11

If the restriction of mobile phone use in the ophthalmology setting is to continue, a more justified reason might be that of social disturbance as proposed by the city of New York.