Changes of intraocular pressure during experimental vitrectomy

Dynamic Pressure Measurements During Vitrectomy in a Model of the Eye

Purpose

To accurately evaluate pressure changes during vitrectomy in a rigid model of the vitreous chamber and to test the efficiency of the EVA phacovitrectomy system (Dutch Ophthalmic Research Center) in terms of compensation of intraocular pressure variations.

Methods

We tested 23-, 25-, and 27-gauge double-blade vitreous cutters in both vented global pressure control and automatic infusion compensation (AIC) modes in a vitreous chamber model, mimicking the real surgical procedure. Balanced salt solution and artificial vitreous, similar to the real vitreous body, were used. We tested both standard-flow (SF) and high-flow (HF) infusion systems, varying the infusion pressure between 20 and 40 mm Hg. In each experiment, flow rate was also measured.

Results

Pressure drop was rapidly and efficiently compensated when 23- and 25-gauge cutters were used in AIC mode, with infusion pressures ranging between 30 and 55 mm Hg. The 27-gauge cutter was less efficient in compensating pressure variations. Pressure fluctuations related to the high-frequency motion of the cutter blade were small compared to the overall pressure variations. The use of the HF infusion system resulted in larger flow rates and lower pressure changes compared to the SF infusion system.

Conclusions

Despite the rigid material of the model, the present pressure measurements are in line with previous studies performed on porcine eye. The use of AIC mode compensates intraoperative pressure drops efficiently, with both 23- and 25-gauge cutters. The HF infusion system is more efficient than the SF infusion system.

Translational Relevance

The AIC infusion mode efficiently compensates intraoperative pressure drops, in both 23- and 25-gauge experimental vitrectomy. The HF infusion system resulted in larger flow rate and lower pressure changes.

Ex Vivo Comparison of Intraocular Pressure Fluctuation During Pars Plana Vitrectomy Performed Using 25- and 27-Gauge Systems

INTRODUCTION

The purpose of this study was to compare intraoperative intraocular pressure fluctuation using different aspiration systems and 25- and 27-gauge vitreous surgery probes.

METHODS

Ex vivo, pars plana, 25- and 27-gauge vitreous surgery was performed on four porcine eyes, and IOP fluctuations were evaluated. We performed three-port vitrectomy using the Constellation® Vision or the EVA® Phaco-Vitrectomy system. Each 20-s experiment was conducted five times for each set of conditions, each with the same substituted balanced salt solution. Real-time intraoperative intraocular pressure measurement was performed at the distal end of the infusion tube. Intraocular pressure was measured during core vitrectomy; core vitrectomy with fluid aspiration; peripheral vitreous shaving with scleral indentation; and fluid-gas exchange. The Mann-Whitney U test was used to evaluate statistical significance.

RESULTS

Mean ± standard deviation intraoperative intraocular pressure fluctuation during 25- and 27-gauge core vitrectomy were 15.9 ± 1.6 mmHg and 11.9 ± 1.4 mmHg, respectively (P < 0.05), using the Constellation system; 23.2 ± 1.4 mmHg and 14.1 ± 0.7 mm Hg, respectively (P < 0.001), using the EVA vacuum mode; and 15.0 ± 0.5 mmHg and 11.5 ± 1.4 mmHg, respectively (P < 0.05), using the EVA flow mode. The smallest intraoperative intraocular pressure fluctuations during core vitrectomy with fluid aspiration, peripheral vitreous shaving with scleral indentation, and fluid-gas exchange, were all achieved using the 27-gauge EVA flow mode; these values were 14.2 ± 0.4 mmHg, 35.7 ± 0.9 mmHg, and 6.4 ± 0.2 mmHg, respectively.

CONCLUSION

Regardless of the aspiration system, intraoperative intraocular pressure fluctuation was lower during 27-gauge than during 25-gauge vitrectomy. The 27-gauge EVA flow mode produced optimal intraoperative intraocular pressure stability.

Influence of Surgical Procedures and Instruments on the Incidence of Suprachoroidal Hemorrhage during 25-gauge Pars Plana Vitrectomy

PURPOSE

To evaluate the influence of surgical procedures and instruments that are associated with intraocular pressure (IOP) fluctuations on the incidence of suprachoroidal hemorrhage (SCH) during 25-gauge pars plana vitrectomy (25G-PPV), and to investigate the clinical features of SCH during 25G-PPV.

DESIGN

Retrospective, comparative case series.

PARTICIPANTS

A total of 3034 cases that underwent initial 25G-PPV at a single surgical center.

METHODS

Univariate analysis was performed to evaluate the relationships between the incidence of SCH during 25G-PPV and the surgical procedures and instruments that were associated with IOP fluctuations. The participants were divided into 4 groups that underwent the following procedures: neither fluid-air exchange nor vitreous shaving under scleral depression (group 1, n = 1144); fluid-air exchange alone (group 2, n = 463); vitreous shaving under scleral depression alone (group 3, n = 639); and both procedures (group 4, n = 788). The incidence of SCH in each group was compared. The clinical features and surgical outcomes of SCH during 25G-PPV were also investigated.

MAIN OUTCOME MEASURES

The incidence of SCH during 25G-PPV and the clinical features and surgical outcomes of SCH during 25G-PPV.

RESULTS

The incidence of SCH was significantly higher in cases that underwent fluid-air exchange (P = 0.0047) or vitreous shaving under scleral depression (P = 0.0157). There were no significant relationships between the incidence of SCH and the use of surgical instruments. The incidence of SCH in group 4 (8/788, 1.02%) was significantly higher than that in groups 1 (1/1144, 0.09%), 2 (0/463, 0%), and 3 (0/639, 0%) (P = 0.01). Almost all SCH cases were localized, and there were no cases of SCH involving the posterior pole. Of all the SCH cases, only one case required reoperation for retinal redetachment. No cases required secondary surgical management for SCH.

CONCLUSIONS

There remains a slight risk of SCH during 25G-PPV in cases that require both fluid-air exchange and vitreous shaving under scleral depression. Even if SCH occurs during 25G-PPV, the surgical outcomes after SCH may not be substantially worse.

In vivo intraocular pressure monitoring during microincision vitrectomy with and without active control of infusion pressure

PURPOSE

To evaluate intraocular pressure (IOP) fluctuation during vitrectomy, we directly monitored IOP in vivo using 2 vitrectomy machines with or without constant infusion pressure monitoring and control.

METHODS

Among 61 eyes of 61 consecutive patients, 32 were assigned to the Accurus system (group 1) and 29 were assigned to the Constellation system (group 2) in this prospective case series. The IOP fluctuations were evaluated during routine vitrectomy procedures.

RESULTS

The initial IOP before vitrectomy was 20.3 ± 2.4 mm Hg in group 1 using a conventional vented gas forced infusion system and 20.0 ± 0.0 mm Hg in group 2 using active IOP control at 20 mm Hg (p = 0.532). However, the average IOP change during core vitrectomy was -8.6 ± 4.3 mm Hg in group 1 and -0.8 ± 1.1 in group 2 (p<00.001). Maximum IOP was significantly decreased in group 1 (-17.0 ± 2.6 mm Hg) compared with that in group 2 (-4.1 ± 2.2 mm Hg) (p<00.001). Partial ocular collapse was observed during vitrectomy only in group 1 (78.1%). Peak IOP significantly increased during scleral compression and gas and fluid injection but was not significantly different between the groups (all p≥0.147). The IOP fluctuation range was 50-70 mm Hg in both groups.

CONCLUSIONS

The IOP fluctuated significantly during routine vitrectomy using both systems. Hypotony and partial ocular collapse were more frequently observed during vitrectomy with the Accurus system than with the Constellation system. Both systems were vulnerable to IOP surge during indentation and intravitreal injection.

INTRAOCULAR PRESSURE CHANGES DURING VITRECTOMY USING CONSTELLATION VISION SYSTEM'S INTRAOCULAR PRESSURE CONTROL FEATURE

PURPOSE

To evaluate intraocular pressure (IOP) changes during experimental vitrectomy and the efficacy of Constellation Vision System's IOP control (IOPc) feature in reestablishing baseline pressure.

METHODS

Using a pressure transducer in freshly enucleated porcine eyes, a broad range of parameters (baseline pressures, aspiration levels, and cut rates) were tested with 23- and 25-gauge probes and IOPc turned ON versus OFF.

RESULTS

IOPc turned ON was significantly more effective than IOPc turned OFF in controlling IOP drop and stabilizing pressure during vitrectomy using a wide range of baseline pressures (20-70 mmHg). The 23-gauge system consistently presented a reduced drop from baseline compared with the 25-gauge system. The overall average drop for the 23- and 25-gauge systems was 12.79 mmHg and 21.17 mmHg, respectively. Both gauge sizes reestablished baseline pressure approximately 1.6 seconds after the initial pressure drop generated at the beginning of aspiration. A peak of IOP (overshooting) was observed when the pressure was returning to baseline using both 23- and 25-gauge systems.

CONCLUSION

Using IOPc feature turned ON, 23- and 25-gauge probes were effective in reestablishing and sustaining baseline infusion pressures, although 23-gauge probes showed less IOP fluctuation than did 25-gauge probes.

Long-term trends in intraocular pressure after combined vitrectomy with sub-tenon injection of triamcinolone acetonide

PURPOSE

To evaluate the long-term effect of vitrectomy by itself and combined vitrectomy with sub-Tenon injection of triamcinolone acetonide (TA) on intraocular pressure (IOP).

METHODS

In a retrospective cohort study, the medical records of 56 eyes of 56 patients who underwent nonemergent vitrectomy and were followed up for at least 24 months were reviewed. Thirty-two eyes of 32 patients underwent combined vitrectomy with sub-Tenon injection of TA. Twenty-four eyes of 24 patients underwent vitrectomy only. Increased IOP of >4 mmHg from the baseline, change in IOP from the baseline, and preoperative and postoperative measured IOPs were recorded and compared between the two groups, and with fellow eyes.

RESULTS

Minimum follow-up period was 24 months. Except the IOP at postoperative 1 day, there were no significant differences between vitrectomized eyes and nonvitrectomized fellow eyes. There were also no differences between vitrectomized eyes and eyes that underwent combined vitrectomy with sub-Tenon injection of TA. And in the comparison of the vitrectomy-only eye group and the vitrectomy with sub-Tenon TA eye group, there was also no significant difference during the whole follow-up period.

CONCLUSION

Vitrectomy by itself or combined vitrectomy with sub-Tenon injection of TA does not seem to increase IOP in the long term.

Intraoperative assessment of intraocular pressure in vitrectomized air-filled and fluid-filled eyes

PURPOSE

To ascertain the difference of intraocular pressure (IOP) measurement between vitrectomized air-filled and fluid-filled eyes.

METHODS

Thirty-one eyes of 31 consecutive patients who underwent conventional vitrectomy and intraocular gas tamponade were assessed. After vitrectomy, IOP of the fluid-filled eyes was measured by Tono-Pen. Thereafter, fluid-air exchange was performed, and IOP of the air-filled eyes was measured again. The IOP within each fluid- and air-filled eye was varied by selecting settings on the vitrectomy system, from 10 to 50 mmHg with 5-mmHg increments. Postoperatively, IOP was assessed by both Tono-Pen and Goldmann applanation tonometry (GAT). Linear and nonlinear regression analyses were conducted between intraoperatively measured Tono-Pen readings and actual IOPs. Bland-Altman plot was used to assess the agreements between postoperatively measured Tono-Pen readings and GAT readings.

RESULTS

The discrepancy between Tono-Pen readings and actual IOP in fluid-filled eyes was not significant, except for the profound high pressures over 45 mmHg. However, Tono-Pen readings in air-filled eyes were significantly lower than actual IOPs in all ranges, and Tono-Pen increasingly underestimates IOP at higher levels. Intraoperative Tono-Pen readings were correlated significantly with actual IOP and a quadratic equation evidenced the best fit (R(2) = 0.996). Postoperatively, difference of the measurements between Tono-Pen and GAT was not significant.

CONCLUSION

Tono-Pen and GAT significantly underestimate actual IOP in air-filled eyes. It should be considered that actual IOP would be greater than the measured IOP in gas-filled eyes, even though the IOP is measured as normal.

Intraocular pressure fluctuation during microincision vitrectomy with constellation vision system

PURPOSE

To investigate intraocular pressure (IOP) fluctuation during various vitrectomy maneuvers using the vitrectomy system (Alcon Constellation Vision System).

DESIGN

An experimental study as laboratory investigation.

METHODS

In porcine eyes, 23- and 25-gauge vitrectomy was performed, and IOP fluctuations were evaluated in vitreous cutting mode, in aspiration mode, and during scleral compression. The measurements were performed with the IOP control setting turned on or off.

RESULTS

Using the 23-gauge system with the IOP control setting turned on, IOP decreased from 30 to 23.7 mm Hg after starting vitreous cutting, and then returned to 30 mm Hg in 2.6 seconds. When the IOP control setting was turned off, IOP decreased to 19.1 mm Hg in 0.9 seconds, and remained at that pressure. Under aspiration at 650 mm Hg without cutting, IOP showed a sharp depression from 30 to 12.2 mm Hg, and then returned to 30.6 mm Hg in 2.6 seconds with the IOP control setting turned on. When the IOP control setting was turned off, IOP decreased to 2.2 mm Hg in 9.7 seconds, and did not recover. When the sclera was compressed without aspiration, IOP rapidly increased to 70-100 mm Hg, and then slowly decreased to 30 mm Hg in 3.5-4.0 seconds, with or without the IOP control system. Similar data were obtained with 25-gauge vitrectomy.

CONCLUSIONS

The IOP control system can attenuate IOP fluctuations during vitrectomy maneuvers. There was no significant difference in IOP fluctuations between 23- and 25-gauge systems.