Lens and Peripheral Retinal Relationships During Vitrectomy: Comparison of 23-, 25-, and 27-Gauge Vitrectomy and Curved Endolaser Probes

Abstract

Purpose:

This work aims to compare spatial relationships between the crystalline lens and vitrectomy instruments of different gauges.

Methods:

Eight phakic eyes recovered from deceased donors were used after fixation. Valved trocars (27-gauge, 25-gauge, and 23-gauge) were sequentially placed in the superotemporal quadrant 4 mm posterior to the limbus in each eye. Intraocular relationships of vitrectomy and curved endolaser probes were measured for each gauge.

Results:

There were no significant differences in maneuverability between instruments of different gauges. The mean distance from instrument to lens at the geometric center of the globe was 5.5 mm. Vitrectomy probes of all gauges could access the peripheral retina on both sides of the sclerotomy in the 3 to 4 o’clock position adjacent to the sclerotomy without touching the lens. The instruments could be advanced without lens touch to contact the retina within at least 2 mm of the ora serrata 180° away from the insertion site.

Conclusions:

Vitrectomy and curved endolaser probes achieved similar maneuverability relative to the lens regardless of gauge. This study confirms that small-gauge vitrectomy instruments have a considerable range of safe access to the peripheral retina in phakic eyes from a single sclerotomy.

Introduction

Since the first description of pars plana vitrectomy by Machemer in 1971, advances in wide-angle viewing systems have improved the visibility of the periphery, which allows for peripheral vitrectomy. ¹ Peripheral vitrectomy is important for treatment of proliferative fibrovascular disease, trauma, and rhegmatogenous retinal detachment. However, adequate vitreous excision risks damaging the lens. Lens touch has been reported to occur in 1% to 9% of vitrectomy cases. ^2,3 Lens touch during vitrectomy induces early cataract and posterior capsule rupture in subsequent surgery.

The range of peripheral access to the vitreous was experimentally assessed previously to delineate the lens’s and peripheral retina’s relationship during vitrectomy with a 20-gauge vitrectomy probe. ⁴ In that study, the authors quantitated intraocular spatial relationships between the lens and vitrectomy instruments for various sclerotomy positionings. Sclerotomy sites 4 mm posterior to the limbus in phakic eyes were demonstrated to be advantageous, as surgeons had intuited, compared with more anterior sites.

Micro-incision vitrectomy surgery introduced smaller-gauge (23-, 25-, and 27-gauge) vitrectomy instruments; however, their potential impact on the relative margin of safety for avoiding lens touch in phakic eyes has not been examined. The present study evaluates the spatial relationships between the lens and vitrectomy instruments of different gauges.

Methods

Institutional review board (IRB) approval was waived because no human participants were involved in this pathology study. Trocar cannulas, vitrectomy cutters, and endolaser probes used in the study were commercially available components of the Alcon Constellation vitrectomy system (Alcon Inc). We paralleled the procedure previously reported for 20-gauge instruments. ⁴ Eight phakic deceased-donor eyes that were fixed in formalin 2 to 5 days post mortem were obtained from the Lions Eye Bank (Miami, FL).

A sharp cutting blade was used to remove a superior cap from each globe to allow for direct observation. The normal anatomic intraocular relationships were maintained. Each eye had a 27-gauge valved trocar cannula placed in the superotemporal quadrant 4 mm posterior to the limbus. We used a freehand beveled incision technique to place the trocars. The trocar blade entered at a 45° angle to the sclera. With the blade at the halfway point of entry, the angle was adjusted to perpendicular to the sclera for the remaining half of the blade. Standard calipers were used to measure the axial lengths, ora serrata diameters, and intraocular distances to the nearest 1.0 mm. Statistical analyses were conducted using the Kruskal-Wallis and Wilcoxon tests.

The first measurement (Figure 1A) involved introducing a 27-gauge vitrectomy probe toward the geometric center of the globe and measuring the distance between the shaft and the crystalline lens at its closest separation. The second measurement (Figure 1B) involved advancing the instrument tip along the ora serrata from the meridian of sclerotomy circumferentially until the lens was contacted; the chord length, or the length from the sclerotomy to the tip of the instrument, was measured, and using standard trigonometry, the circumferential arc of the instrument’s access to the ora serrata on both sides of the sclerotomy was calculated. The third measurement (Figure 1C) involved directing the instrument toward the equatorial retina 180° away from the sclerotomy site. The tip was advanced anteriorly until it touched the lens; the distance between the instrument’s tip and the ora serrata in the diametrically opposed meridian was measured.

Figure 1.

(A)The instrument was introduced to the geometric center of globe. The arrow notes the distance between the shaft and proximal edge of the crystalline lens. (B) The instrument was positioned so the tip overlaid the ora serrata in the same meridian as the sclerotomy. The instrument’s tip was moved along the ora serrata until the instrument touched the lens. The arrow depicts the chord length from the sclerotomy to the tip of the instrument. (C) The instrument was directed toward the equatorial retina 180° away from the sclerotomy site. The tip was advanced until the instrument touched the lens. The arrow shows the distance between the instrument’s tip and the ora serrata in the meridian opposite the sclerotomy site.

Each of these measurements was repeated for each eye with a 27-gauge, curved endolaser probe. Once all 27-gauge measurements were recorded, the same procedure was repeated for each eye using 25- and 23-gauge trocar cannula and instruments.

Results

The average length of the 8 eyes was 23.6 mm (SD = 1.4 mm; range, 21.0-26.0 mm), and the average diameter of the ora serrata was 17.3 mm (SD = 1.7 mm; range, 14.0-20.5 mm).

Lens-Probe Distance

The average distances from all instruments to the lens at the geometric center of the globe are recorded in Table 1.

Table 1.

Distance From Instrument to the Lens at Geometric Center of the Globe.

	Vitrectomy cutter, mm		Endolaser, mm		Vitrectomy cutter compared with endolaser
	Mean (SD)	P a	Mean (SD)	P a	P b
23-Gauge	5.4 (0.8)	.83	5.7 (0.9)	.72	.55
25-Gauge	5.6 (1.0)		5.5 (1.1)		.96
27-Gauge	5.7 (0.4)		5.6 (0.6)		.78

^aKruskal-Wallis test.

^b Wilcoxon rank-sum test.

The mean distances ranged from 5.4 mm to 5.7 mm. There was no significant difference found among the vitrectomy cutters (P = .83) or among the curved endolasers (P = .72). There was no significant difference between the 23-, 25-, and 27-gauge cutters and lasers (P = .55, P = .96, and P = .78, respectively).

Arc Length

The average arc lengths for vitrectomy cutters of all gauges are recorded in Table 2.

Table 2.

Arc Length of Vitrectomy Cutter Access to the Peripheral Retina on Both Sides of the Sclerotomy.

	Vitrectomy cutter
	Mean degrees (SD)	Mean clock hours	P a
23-Gauge	112 (23)	3.7	.16
25-Gauge	129 (20)	4.3
27-Gauge	127 (14)	4.2

^aKruskal-Wallis test.

The mean arc lengths ranged from 112 to 129 degrees. There were no significant differences in arc length among cutters of different gauges (P = .16).

Distance to Ora Serrata at Lens Touch

The average distances from all instruments to the ora serrata at lens touch in the meridian 180° from the sclerotomy are recorded in Table 3.

Table 3.

Distance From Instrument to the Ora Serrata at Lens Touch in the Meridian 180° From the Sclerotomy.

	Vitrectomy cutter, mm		Endolaser, mm		Vitrectomy cutter compared with endolaser
	Mean (SD)	P a	Mean (SD)	P a	P b
23-Gauge	1.8 (0.9)	.27	1.0 (1.5)	.93	.11
25-Gauge	1.6 (0.9)		0.5 (0.8)		.03
27-Gauge	1.0 (0.8)		0.8 (1.1)		.50

^aKruskal-Wallis test.

^b Wilcoxon rank-sum test.

The mean distances ranged from 0.5 mm to 1.8 mm. There was no significant difference found among cutters (P = .27) or among the curved endolasers (P = .93). There was no significant difference between the 23-gauge (P = .11) and 27-gauge (P = .50) cutters and lasers. The 25-gauge curved laser was able to get significantly closer to the ora serrata insertion site compared with the 25-gauge cutter (P = .03).

Conclusions

Vitrectomy and curved endolaser probes achieved similar ranges of safe excursion relative to the lens regardless of gauge in this study of eyes recovered from deceased donors. There was substantial access for the cutter on both sides of the sclerotomy, indicating that maneuvers to access the areas of peripheral retina and vitreous in the 3 to 4 o’clock position adjacent to the sclerotomy were generally safe in phakic eyes. Furthermore, cutters and endolaser probes could be safely advanced in the meridian 180° from the sclerotomy to the retina within 2.0 mm of the opposite ora serrata. These findings indicated a significant margin of safety in advancing a probe to the equatorial region even 180° from the insertion site. The 25-gauge endolaser demonstrated better access to the ora serrata than the cutter, indicating that curved instruments are safer than rigid probes.

The findings of this study were consistent with a prior study. ⁴ Similar to our results, they found that from a sclerotomy site at 4.0 mm posterior to the limbus, the distance from lens to instrument at the geometric center of the globe ranged from 5.4 mm to 5.7 mm. We used a sclerotomy site of 4.0 mm posterior to the limbus, because in the prior study this distance was found to give a wider range of accessibility to the anterior retina circumferentially from the sclerotomy site as well as on the opposite side of the sclerotomy. The results of our study were also consistent with a prior study that evaluated both curved and straight instruments and found that curved probes outperformed straight probes in accessing the peripheral retina. ⁵ From a sclerotomy site of 4.0 mm posterior to the limbus, they found that the straight vitrectomy probe and endolaser could access the diametrically opposed peripheral retina at 2.4 mm and 0.5 mm, respectively, from the ora serrata in the meridian 180° from the sclerotomy site. Furthermore, the curved vitrectomy and endolaser probes were able to access peripheral retina beyond the ora serrata.

Intraoperative conditions will affect ocular anatomy and change the intraocular spatial relationships between eye structures and instruments. Cycloplegia shifts the lens-iris diaphragm posteriorly, likely decreasing the probe—lens separation. Conversely, higher perfusion pressure may increase or dynamically change intraocular relationships. The lens-iris diaphragm tends to be displaced anteriorly by vitrectomy infusion pressure, but that should increase the safe excursion ranges. However, incidental hypotony could have the reverse effect, implying that high aspiration rates should be avoided when working at these margins. In addition, circumferential freehand beveling of trocars may be a potential risk of lens touch, particularly in an eye that is hypotonus. Surgical technique could also affect eye anatomy, as some surgeons will tilt the eye or apply torque to the sclera to improve access to the vitreous.

One limitation to this study is that all measurements were taken from a trocar insertion site at 4 mm posterior to the limbus because this distance was previously shown to be most favorable for peripheral vitrectomy. We used Alcon instruments for this study while many other vitrectomy instrumentation systems are available; however, one would expect similar geometric relationships regardless of manufacturer. Another limitation of this study is the small sample size. The 8 eyes were analyzed within a specific time frame, during which extra vitreoretinal instruments were available for experimentation. Thus, the study was not necessarily powered to detect statistical differences. Finally, using a vitreous substitute for the experimentation theoretically could have offered the advantage of improved globe uniformity when taking measurements. However, we opted to instead fix deceased-donor eyes in formalin immediately on receipt by our eye bank to minimize risk of tissue degradation and preserve tissue anatomy until sufficient eyes were collected to allow experimental procedures and measurements on all eyes in a single sitting.

In conclusion, this study confirms that small-gauge vitrectomy instruments allow considerable access to the peripheral retina without significant advantage or disadvantage when comparing 23-, 25-, and 27-gauge instrumentation for safety in phakic eyes. Vitreoretinal surgeons should still exhibit caution when using instruments in the periphery of phakic eyes because of risk of iatrogenic lens trauma.