E ach year in the United States, there are more than 3.8 million cataract surgeries, more than 220,000 glaucoma surgeries and 225,000 vitrectomies performed. The total number of annual intraocular surgeries exceeds 30 million globally. Despite the rise in topical anesthesia, regional anesthesia approaches, which consists of sub-Tenon’s, peribulbar and retrobulbar blocks, remain the most common anesthetic modality employed in ophthalmic surgical procedures globally due to the greater analgesic and akinesia efficacy and the lower systemic risk profile over general anesthesia. ^, Since peribulbar block (PB) does not require an intra-operative incision of the conjunctiva and Tenon’s capsule as sub-Tenon’s does, and PB can be done in the pre-operative holding area, thereby, shortening operative time. PB has been replacing retrobulbar block over the years due to its lower risk of retrobulbar hemorrhage and globe perforation. ^,

PB is a type of extra-conal block, where local anesthetic solution is deposited outside the extraocular muscle cone. Most of the extraocular muscles, if not all, can be paralyzed in addition to anesthetizing the entire globe. ^,,, This procedure is typically performed by the surgeon or anesthesiologist and is followed by distribution of the bolus around the orbit by waiting, digital massage, or Honan balloon. ^, With this inhibition of both motor and sensory fibers, and relatively low complication rate even in patients on anticoagulants or platelet inhibitors, this technique quickly became a standard for many ocular surgeries. ^,,

The volume of regional anesthetic injected is typically determined empirically by the surgeon or anesthesiologist performing the PB. When asked, surgeons and anesthesiologists determined volume by palpating the globe for resistance or anecdotal evidence associated with the anatomical appearance. A common practice called “single injection peribulbar anesthesia” utilizes the “total upper eyelid drop” sign as the end-point indicator of the injection, which typically leads to a widely variable range of volume between 4 mL to 15 mL. Past literature indicated an extremely wide range of IOP rise following PB. Morgan et al. reported over 50 mmHg rise in 10 patients after 8 mL injection of two different anesthetic solutions. Increased IOP, even if transient, can cause vision loss in predisposed patients, particularly individuals with late-stage glaucoma who receive PB for glaucoma surgeries. However, no randomized volume-controlled study has been done. ^,,,

At our institution, the central pharmacy pre-fills 10-mL syringes with 7 mL of standard PB solution (Lidocaine MPF 1%/Bupivacaine MPF 0.375%/Hyaluronidase 5 units/mL) and delivers to all surgical centers on the same day. Our anesthesiologists perform PBs in the pre-operative holding area before transporting patients into the operating room (OR). Such practice allows time for the PB to take effect and improves OR utilization efficiency. Therefore, it is important to understand the effect of PB volume on IOP change in the modern setting with hyaluronidase containing block agents. However, the lack of evidence-based guidelines on PB best practices led to a wide range of practice patterns that are difficult to unify, which is the reason to carry out this prospective, randomized, controlled study to compare two distinctively different PB volumes in a controlled setting. Our study design is to test if the higher block volume results in higher IOP following the peribulbar block.

We conducted a masked, randomized, prospective interventional study at Massachusetts Eye and Ear (MEE). Approval for this study (protocol number 2022P003247) was obtained from the Mass General Brigham Human Research Committee of Mass General Brigham, Boston, MA, USA. All research adhered to the tenets of the Declaration of Helsinki. From March to July 2024, the patients between ages of 18 and 79 years, who had already scheduled to undergo ocular procedures under PB as previously determined by her/his surgeon, were consented and enrolled. Eyes with any previous ocular procedure or surgery, or any orbital surgery were excluded. Eyes with corneal scars or cornea edema were also excluded. If any pre-operative supplementary anesthesia was administered, the eye was disqualified from the study. The subjects were randomized into two groups; Group A received 4 mL and Group B received 7 mL block volume and were performed in one continuous injection. The participating anesthesiologists were informed of the volume immediately before administrating the block. Both the patient and the participating surgeons were masked to the volume of the block. One research assistant carried out all the IOP measurements to minimize systemic errors. For each subject eye, a baseline IOP was obtained in the pre-operative holding area while the patient was supine on the stretcher. The subjects were given ample time to acclimate in the pre-operative environment. After topical anesthesia with a drop of proparacaine solution (0.5%), a freshly calibrated Reichert Tono-Pen XL with Ocu-Film tip cover was used to measure the IOP. Two measurements were taken at each time point, and the average was used as the before-block (BB) IOP.

After consenting the subject for the peribulbar block per the standard of care protocol, the anesthesiologist was then informed of the randomized amount of volume to be used, immediately before delivering the standard PB (Lidocaine MPF 1%/Bupivacaine MPF 0.375%/Hyaluronidase 5 units/mL, per standard MEE pharmacy supply) via a BVI Visitec Peribulbar [Atkinson] 25 G x 22 mm needle in the inferotemporal periorbital space. The needle was inserted laterally over the inferior orbital rim and directed along the orbital floor under the globe. The needle may or may not have been redirected to go upwards and inwards depending on the technique once it passes the equator. After negative aspiration for blood, the PB solution was injected into the space outside of the intraconal orbital compartment. Standard IV sedation was given before the PB was administered by the anesthesiologist. Another set of two measurements were immediately obtained as the after-block (AB) IOP.

The same research assistant then provided a protocoled digital massage in a slow circular motion with the distal phalanx of the second, third, and fourth digit. Consistent pressure was applied for 10 seconds on and 5 seconds off for a total of eight times in 120 seconds, similar to the technique described by Ernest et al. A final set of after-massage (AM) IOP measurements was obtained immediately after.

Immediately after the completion of the intended surgery, Likert-Type scale (1 as the least satisfaction and 5 as the greatest satisfaction with the quality of the anesthesia) was obtained from the surgeon. Akinesia was not rated.

The sample size was determined by estimating a 4-mmHg higher mean IOP in the 7-mL group than that of the 4-mL group, a SD of 5 mmHg of mean IOP, with a significance level α = 0.05 and power (1-β) = 80%. The statistical analysis was performed with Microsoft 365 Excel. For demographics data, Welch’s t-test for continuous variables and Fisher’s Exact test and Chi-squared test for categorical variables. For surgery type analysis, a Chi-squared test for independence is used. To compare the values of groups A and B at each time point, a paired t-test for two-sample means was performed, with the two tailed P -value considered. For all other values comparing groups A and B at different time points, delta values, and anesthesia ratings, a two-sample t-test assuming unequal variance was performed with the two tailed P -value considered. Pearson correlation analysis between the IOP change and axial length was performed on eyes with known axial length. Outlier analysis was performed using IQR.

Five surgeons and five anesthesiologists participated in the trial from two ambulatory surgical centers at MEE in Boston. Fifty-one patients were enrolled and 50 eyes from 47 patients completed the study, with 25 males and 22 females. Three patients contributed one eye each on separate visits, and 44 other patients only participated with one eye each. Four eyes from 4 patients (2 from each group) were excluded from the study because supplemental block was given prior to the procedure per surgeon’s request to achieve akinesia, which prevented appropriate intra-operative evaluation of anesthesia. The surgical procedures included cataract surgery, pterygium excision, trabeculectomy, Descemet membrane endothelial keratoplasty, and anterior vitrectomy, all of which were completed under the initial peribulbar block. All 25 eyes in group A received 4 mL of block volume and all 25 eyes in group B received 7 mL of block volume. There was no statistically significant difference in the demographics between the two groups ( Table 1 ). Axial lengths were available in 21 eyes in group A and 22 eyes in group B. The average axial length of the 43 eyes was 24.2 mm, averaging 23.7 mm in group A and 24.6 mm in group B without statistically significant difference ( Table 1 ).

The BB mean baseline IOP of group A was 16.0 ± 4.2 mmHg and of group B was 17.0 ± 4.7 mmHg ( P =.40). The AB mean IOP was 15.7 ± 6.5 mmHg for group A and 18.8 ± 8.9 mmHg for group B ( P =.16). The AM mean IOP of group A was 12.8 ± 3.6 mmHg and that of group B was 14.8 ± 5.1 mmHg ( P =.11) ( Table 2 ).

Table 2

Intraocular Pressure (IOP) Before Block (BB), After Block (AB) and After Massage (AM) in Total (50 eyes), Group A (25 Eyes, 4-mL Block volume), and Group B (25 Eyes, 7-mL Block Volume).

	BB mean ± SD	AB mean ± SD	AM mean ± SD	AB-BB mean ± SD	AM-BB mean ± SD	AM-AB mean ± SD
Total (mm Hg)	16.5 ± 4.4	12.3 ± 7.9	13.8 ± 4.5	0.8 ± 6.5	−2.7 ± 3.4	−3.4 ± 5.4
p 1	0.401	0.000061
p 2	0.0000010
Group A (mm Hg)	16.0 ± 4.2	15.7 ± 6.5	12.8 ± 3.6	−0.2 ± 5.1	−3.12 ± 2.9	−2.88 ± 4.7
p 1	0.816	0.0054
p 2	0.000019
Group B (mm Hg)	17.0 ± 4.7	18.8 ± 8.9	14.8 ± 5.1	1.8 ± 7.6	−2.2 ± 3.8	−4.0 ± 6.3
p 1	0.250	0.0042
p 2	0.0074
p 3	0.396	0.163	0.114	0.273	0.340	0.481

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