prostaglandin analogues, such as latanoprost, cause benign but irreversible darkening of the iris and increased growth and thickening of the eyelashes, and the use of carbonic anhydrase inhibitors such as dorzolamide often gives rise to discomfort and altered taste (Sharts-hopko and glynn-milley 2009). carbonic anhydrase inhibitors are also contraindicated in people who are allergic to sulphur drugs. Beta blocking drugs have few adverse ocular side effects, but may have adverse systemic effects such as bradycardia, hypotension, bronchospasm and respiratory failure in older people who have asthma, chronic obstructive pulmonary disease and heart failure.