Eye Surgery Peribulbar Block Volume: 4 mL Versus 7 mL

A recent randomized prospective study published in the American Journal of Ophthalmology examined an important practical question: how much local anesthetic volume is appropriate for peribulbar (PB) anesthesia? The study randomized 50 eyes to receive either 4 mL or 7 mL of peribulbar anesthetic. Importantly, the study does not compare 3 mL with 7 mL; it compares 4 mL with 7 mL.

The concern with a larger PB volume has traditionally been a possible rise in intraocular pressure (IOP). In this study, however, there was no statistically significant difference in IOP change between the 4-mL and 7-mL groups. Mean IOP after the block was 15.7 mmHg in the 4-mL group and 18.8 mmHg in the 7-mL group, with no significant between-group difference. After two minutes of digital massage, IOP fell further in both groups.

Interestingly, the 7-mL group received significantly higher surgeon satisfaction scores: 4.8 compared with 4.3 for the 4-mL group. The operations included cataract surgery as well as pterygium surgery, trabeculectomy, DMEK and anterior vitrectomy, and these procedures were completed under the initial PB block.

Safe PB for Long Eye Surgery

The practical message is reassuring: sometimes it is safe and reasonable to use peribulbar anesthesia for a long eye surgery, rather than assuming that a prolonged procedure automatically requires another form of anesthesia. A well-performed PB can provide adequate analgesia and akinesia, and in this study the 7-mL volume did not produce a significantly greater IOP rise than 4 mL.

However, this should not be interpreted as meaning that any volume is universally safe. The study was small, involving only 50 eyes, and three eyes had marked IOP elevations after PB. Two of these responded to digital massage, while one patient with glaucoma remained elevated. The authors specifically noted that the upper safe limit of PB volume remains unknown.

Bottom Line

This study provides useful evidence that 4 mL and 7 mL PB can both be used safely in appropriately selected patients, with 7 mL providing better surgeon-rated anesthesia in this trial. Clinical judgment and IOP monitoring remain important, particularly in glaucoma and other high-risk eyes.

Source: Alam BER et al., “The Effect of Peribulbar Block Volume on Intraocular Pressure Change: A Randomized Prospective Study,” American Journal of Ophthalmology, 2026;289:1–6. DOI: 10.1016/j.ajo.2026.05.010.