The Effect of Scleral Buckle Surgery on Tonographic Outflow Facility, Positional Intraocular Pressure, and Ocular Biomechanics

PURPOSE

To investigate the in vivo effect of scleral buckle surgery on ocular biomechanics and aqueous humor dynamics.

DESIGN

Prospective observational cross-sectional study.

PARTICIPANTS

Nine patients with unilateral 360 degree encircling scleral buckles without vitrectomy for rhegmatogenous retinal detachments, between 3 and 39 months postoperative.

METHODS

All measurements were performed in both eyes of all participants. Intraocular pressure (IOP) was measured in the seated and supine positions using pneumatonometry. Outflow facility was measured using 2-minute weighted pneumatonography. Ocular rigidity coefficient was determined from the Friedenwald equations based on the difference in IOP with and without a weighted tonometer tip. The percentage change in IOP upon transitioning from seated to supine was calculated. Measurements for buckled and nonbuckled eyes were compared using paired Student t test of means.

MAIN OUTCOME MEASURES

Sitting and supine IOP and percentage difference between the 2 positions; outflow facility; ocular rigidity coefficient.

RESULTS

Seated IOP was similar between buckled and nonbuckled eyes (16.1 ± 2.5 vs. 16.7 ± 2.7 mmHg; P = 0.5) whereas supine IOP was lower in buckled eyes compared with nonbuckled eyes (18.7 ± 2.6 vs. 21.3 ± 2.5 mmHg; P = 0.008). The percentage increase in IOP upon change in body position from seated to supine was greater in nonbuckled eyes (17.4 ± 9.4% vs. 27.6 ± 9.5%; P = 0.005). Ocular rigidity coefficient was lower in buckled (9.9 × 10-3 ± 1.4 × 10-3 μL-1) vs. nonbuckled eyes (14.4 × 10-3 ± 3.1 × 10-3 μL-1; P = 0.006). Outflow facility was not significantly different in buckled and nonbuckled eyes.

CONCLUSIONS

Scleral buckling decreases ocular rigidity but does not affect outflow facility. This change in ocular biomechanics likely results in the attenuated IOP change from seated to supine position. Decreased ocular rigidity may also reduce IOP fluctuations and potentially reduce the risk for glaucoma progression.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Development and testing of a metabolic chamber for effluent collection during whole eye perfusions

Ocular hypertension is caused by dysregulated outflow resistance regulation by the conventional outflow (CO) pathway. The physiology of the CO pathway can be directly studied during ex vivo ocular perfusions. In addition to measuring outflow resistance generation by the CO tissues, perfusion media that is conditioned by CO pathway cells can be collected upon exiting the eye as effluent. Thus, contents of effluent include factors contributed by upstream cells that report on the (dys)functionality of the outflow tissues. Two methods have been used in the past to monitor effluent contents from perfused eyes, each with their limitations. To overcome these limitations, we designed and printed a metabolic chamber to accommodate eyes of different sizes during perfusions. To test this new chamber, human eyes were perfused for 4 h at constant flow rate of 2.5 μl/min, while pressure was continuously monitored and effluent was collected every hour. Facility was 0.28 ± 0.16 μl/min/mmHg for OD eyes and 0.33 ± 0.11 μl/min/mmHg for OS eyes (n = 3). Effluent samples were protein rich, with protein concentration ranging from 2700 to 10,000 μg/ml for all eyes and timepoints (N = 3). Effluent samples expressed proteins that were actively secreted by the TM and easily detectible including MYOC and MMP2. Taken together, our model provides a reliable method to collect effluent from ex vivo human eyes, while maintaining whole globe integrity.

Ahmed glaucoma valve in vitrectomized eyes: An implantation technique to minimize early postoperative fluid-loss hypotony

PURPOSE

To describe the application of a modified Ahmed glaucoma valve (AGV) surgical implantation technique in vitrectomized eyes, in order to minimize the risk of early postoperative hypotony, which leads to hemorrhagic complications.

MATERIALS AND METHODS

Data of patients implanted with AGV using the surgical technique described were retrospectively reviewed. Inclusion criterion: glaucomatous eyes with previous history of pars plana vitrectomy. Intraocular pressure (IOP) measurement and ophthalmic examination were performed preoperatively and postoperatively weekly for 1 month for the detection of early hypotony, choroidal effusion/detachment, intraocular hemorrhage. The surgical technique consisted in creating a 5 mm long scleral tunnel with a 23 G needle reaching the anterior chamber at the iridocorneal angle, in which the Ahmed glaucoma valve tube was inserted.

RESULTS

Ten eyes of 10 patients were included. Median preoperative IOP was 30.5 mmHg [interquartile range (IQR) 28.3-33.0]; median postoperative IOP was 12.0 mmHg (IQR 9.3-13.0) at 1 week, and 12.5 mmHg (IQR 11.0-15.0) at 1 month. In no cases postoperative IOP was <8 mmHg. On the first postoperative day, five (50%) eyes showed few blood clots in the anterior chamber. On the second-week appointment, moderate choroidal effusion was observed in two eyes (20%). No hemorrhagic complications were observed.

CONCLUSIONS

The creation of a long intrascleral tunnel with a 23 G needle for AGV implantation in vitrectomized eyes could be effective in decreasing leakage through the space between the valve tube and the sclerocorneal tissue. This technique is safe, easy to perform, feasible and fast. Due to its advantages and good postoperative results, it could also be adopted in non-vitrectomized eyes.

Needling revision with marking maneuver to locate the scleral flap

PURPOSE

To report a variation of the classical needle revision maneuver with an external marking of the scleral flap, augmented with mitomycin C (MMC) in failed non penetrating deep sclerectomy (NPDS).

METHOD

This observational prospective pilot study included five consecutive patients who underwent an MMC needling revision of failed NPDS with the external marking of the scleral flap. All participants underwent a complete ophthalmologic examination and data were collected preoperatively as well as 1 day, 1 week and 1 month after the surgery. The surgical site was also evaluated during the procedure.

RESULTS

A significant reduction of IOP and antiglaucomatous medication from preoperative levels was detected at the end of the follow-up period. Regarding the surgical site, we succeed in locating the scleral flap and observing the bleb formation in all cases. No significant subconjunctival bleeding was detected.

CONCLUSION

This variation of the classical needling technique seems to improve intrasurgical visualization and reduces complications, which might lead to an improvement in surgical success.

Consensus recommendations for trabecular meshwork cell isolation, characterization and culture

Cultured trabecular meshwork (TM) cells are a valuable model system to study the cellular mechanisms involved in the regulation of conventional outflow resistance and thus intraocular pressure; and their dysfunction resulting in ocular hypertension. In this review, we describe the standard procedures used for the isolation of TM cells from several animal species including humans, and the methods used to validate their identity. Having a set of standard practices for TM cells will increase the scientific rigor when used as a model, and enable other researchers to replicate and build upon previous findings.

Assessment of Aqueous Humor Dynamics in the Rodent by Constant Flow Infusion

Mice and rats are being increasingly used in glaucoma research and much useful data have been generated from them. One aspect of using these animals for this purpose involves assessment of aqueous humor dynamics. Several techniques have been described in the literature for the determination of one or more of these parameters in rodents, in both living animals and eyes perfused ex vivo. Here, we describe the practical details for a technique for the determination of all principal parameters of aqueous humor dynamics (intraocular pressure (IOP), aqueous humor formation rate (Fin), uveoscleral outflow rate (Fu), aqueous outflow facility (C), and episcleral venous pressure (Pe)) in the living rat and mouse eye, in a single experimental session.

Unconventional aqueous humor outflow: A review

Aqueous humor flows out of the eye primarily through the conventional outflow pathway that includes the trabecular meshwork and Schlemm's canal. However, a fraction of aqueous humor passes through an alternative or 'unconventional' route that includes the ciliary muscle, supraciliary and suprachoroidal spaces. From there, unconventional outflow may drain through two pathways: a uveoscleral pathway where aqueous drains across the sclera to be resorbed by orbital vessels, and a uveovortex pathway where aqueous humor enters the choroid to drain through the vortex veins. We review the anatomy, physiology and pharmacology of these pathways. We also discuss methods to determine unconventional outflow rate, including direct techniques that use radioactive or fluorescent tracers recovered from tissues in the unconventional pathway and indirect methods that estimate unconventional outflow based on total outflow over a range of pressures. Indirect methods are subject to a number of assumptions and generally give poor agreement with tracer measurements. We review the variety of animal models that have been used to study conventional and unconventional outflow. The mouse appears to be a promising model because it captures several aspects of conventional and unconventional outflow dynamics common to humans, although questions remain regarding the magnitude of unconventional outflow in mice. Finally, we review future directions. There is a clear need to develop improved methods for measuring unconventional outflow in both animals and humans.