Vertical diplopia following local anaesthetic cataract surgery: predominantly a left eye problem?

Vertical diplopia is an uncommon but disappointing complication of otherwise successful local anaesthetic cataract surgery. We studied strabismus patterns in a group of such patients to identify the nature and extent of extraocular muscle involvement.

A retrospective review identified 15 cases of vertical diplopia following local anaesthetic cataract surgery between July 1994 and January 1998. Peribulbar anaesthesia was used in all cases and given by right-handed professionals.

All cases had otherwise successful cataract surgery (mean age 80.5 years; median pre-operative VA 6/18; median post-operative VA 6/9). The mean level of vertical diplopia was 7.2 prism dioptres (PD) in the primary position (range 2-25 PD). The left inferior rectus (IR) was paretic in 6 cases and restricted in 5 cases. The left superior rectus (SR) was not affected in any of the cases. The right IR was restricted in a single case. The right SR was paretic in 2 cases and restricted in a single case. None of the cases had clinical involvement of the oblique muscles. Eleven of the cases were managed successfully with prisms. Two of the cases required strabismus surgery.

The incidence of left eye extraocular muscle involvement was greater than right eye involvement, although this did not reach statistical significance (73% vs 27%; p = 0.075). This may be due to the more difficult access of right-handed individuals giving left eye peribulbar injections with the needle tract being directed more closely to the muscle cone. The IR muscle is more commonly affected than the SR (80% vs 20%; p = 0.019). An equal incidence of paretic and restricted rectus muscle pathology was found in this study (53% vs 47%; p = 0.818). The exact aetiology of muscle injury is unknown but could be due to direct muscle or nerve trauma, anaesthetic toxicity, periocular haemorrhage or a combination of these.