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Editor,

We agree with Tan et al. (2005) on the clinically relevant association between patients' frightening visual experiences during cataract surgery and their intraoperative morbidity as well as overall patient dissatisfaction.

Irrespective of the mode of anaesthesia, recent studies have consistently found that most patients retain some form of light perception during cataract surgery, with the majority of them also reporting a broad spectrum of additional visual experiences (Au Eong et al. 1999, 2000a, 2000b; Prasad et al. 2003; Tranos et al. 2003; Wickremasinghe et al. 2003). However, the proportion of patients undergoing phacoemulsification who experience fear has ranged from 3% to 16.2% in the case of sub-Tenon's anaesthesia (Prasad et al. 2003; Tranos et al. 2003; Wickremasinghe et al. 2003), compared to 7.1% and 11.1% with retrobulbar and peribulbar anaesthesia, respectively (Au Eong et al. 2000a; Tranos et al. 2003). It is also interesting to note that a higher percentage of patients with topical anaesthesia experienced fear with preoperative oral diazepam (15.4%) than without (9.1%) (Au Eong et al. 2000b; Tranos et al. 2003).

Wickremasinghe et al. (2003) demonstrated a correlation between lower volumes of anaesthetic using a sub-Tenon mode of delivery and frightening visual perception, most likely due to the direct anaesthetic effect or from mechanical compression of the optic nerve within the sub-Tenon space. Although topical anaesthesia does not impair optic nerve function, our study found that, although it was not statistically significant, topical anaesthetic gave more favourable results than sub-Tenon's or peribulbar anaesthetic (Tranos et al. 2003). Prasad et al. (2003) also produced fewer reports of fear with sub-Tenon's (3%) compared to retrobulbar anaesthetic (7.1%), suggesting the importance of factors other than the differential blockade of optic nerve function. This is further supported by Ropo et al. (1992), whose studies of visual evoked potentials (VEPs) demonstrated that less than 50% of cases of retrobulbar anaesthetic blocked optic nerve function completely.

A significant association has been shown between fear and visual sensations such as colours and flashes during surgery (Au Eong et al. 2000b). This suggests that vivid visual phenomena are more likely to be distressing to the patient. We would agree that although the other varied types of visual symptoms described previously are associated with fear, it is predominantly the unexpected nature of the intraoperative sensations rather than the experience per se that results in distress.

Although our study did not demonstrate any statistical significance between intraoperative fear and age or previous cataract surgery in the fellow eye, we found that younger patients (< 65 years) tended to find the visual experience more frightening, possibly due to the combination of a greater level of awareness and less dense cataracts (Tranos et al. 2003). We agree with Tan et al. that it may be possible that prior cataract surgery, by way of reducing the uncertainty of the event, may alleviate some of the anxiety associated with the visual experience.

There is little doubt that fear caused by intraoperative visual sensations can have a marked impact on subsequent patient perception of the experience. It has been reported that 7.7% of patients who underwent cataract surgery under topical anaesthesia would have chosen retrobulbar or peribulbar techniques in order to reduce visual impressions, despite being warned of the potentially higher risk of complications (Au Eong et al. 2000b). However, it would be interesting to determine whether a detailed preoperative explanation of possible visual phenomena might have had any effect on the results.

There is a substantial body of evidence to suggest that the reduction or elimination of intraoperative fear in a significant proportion of patients can result in a considerable decrease in intraoperative and postoperative morbidity. As many patients associate their final operative outcome with their intraoperative emotional experience, this can also serve to improve patient satisfaction. In order to allay fears during surgery, the process of informed consent should include a detailed explanation of possible intraoperative visual sensations, especially in patients aged below 65 years and those undergoing first eye cataract surgery. Comprehensive preoperative counselling and the elucidation of relevant factors associated with intraoperative fear are extremely valuable in terms of minimizing patient anxiety and will lead to an uneventful operation.

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