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Single Incision Wagon Wheel Phaco

Department of Ophthalmology, Bradford Teaching Hospitals NHS Foundation Trust, Duckworth Lane, Bradford, UK

Correspondence: Mahiul MK Muqit,
Email: mmmk3{at}aol.com Department of Ophthalmology, Bradford Teaching Hospitals NHS Foundation Trust, Duckworth Lane, Bradford, United Kingdom. Tel: 01274 542200 Fax: 01274383153

Date of acceptance: 1 Jun 2008

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Introduction

The "one-handed" phacoemulsification technique using a single incision/single instrument technique has been described by Kershner.1 There have been a variety of techniques reported to manage soft cataracts, including chip and flip2 and, tilt and tumble.3 These techniques are two-handed approaches and the potential for side-port wound leakage4 exists due to excessive instrumentation when manipulating soft cataracts. Carousel and merry-go-round phaco techniques have been described for soft cataract extraction. These techniques may firstly increase zonular stresses during nuclear rotations in the horizontal plane. Secondly, excessive manipulation may occur within the capsular bag and lead to posterior capsular fracture. We propose a wagon wheel technique for the removal of soft-to-semisoft cataract (Figure 1a) using single-site phacoemulsification.

Surgical technique

A two-step 2.75mm clear corneal wound is constructed at 100°, and the soft-shell technique5 is employed using Duovisc® (Alcon). A continuous curvilinear capsulorhexis is performed with a diameter of 5mm, followed by hydrodissection at the 6 o'clock position. This is followed by hydrodelineation that produces a double golden ring sign (Figure 1b). The inner ring confirms circumferential division of the endonucleus, and the outer ring confirms that the presence of an epinuclear shell. The phaco machine (Alcon Legacy 20,000) settings are adjusted to ultrasound power 30%, burst mode at 100ms interval, linear vacuum 400 mmHg, and bottle height 110cm.

In order to help prevent surge, it is important to keep the inflow of fluid greater than the outflow of fluid at all times. Our initial setting for the peristaltic-based system is a high bottle height to ensure a sufficient inflow of fluid into the eye. We utilize a high vacuum level with the wagon wheel technique. There is a risk of post-occlusion surge when fluid outflow from the eye outstrips the inflow. Surge will lead to anterior chamber (AC) collapse, and possible posterior capsule fracture. Our single-site approach reduces incisional leak from a side-port, and the high bottle height maintains AC stability.

The core of endonucleus is debulked with the tip bevel down using high vacuum aspiration. The phaco tip is then embedded into the endonucleus at the edge of the central golden ring at the 5 o'clock meridian (Figure 1c). The endonucleus is engaged with high vacuum and rotated centrally to the level of the capsulorhexis. With the nucleus in the vertical plane, the phaco tip is positioned bevel down within the endonucleus. The high vacuum engagement allows the nucleus to be lifted upwards and off the epinuclear shell in order to reduce mechanical pressure on the posterior capsule. The nucleus is now in the wagon wheel position (Figure 1d), and removed with high vacuum and burst phaco. The epinuclear shell keeps the capsular bag on stretch, and helps to cushion any endonucleus contact during the wagon wheel emulsification. The nucleus spins towards the phaco tip in the vertical plane, and the vacuum maintains engagement until the nucleus is completely removed (Figure 1e).

After endonuclear removal, the subincisional cortex and epinucleus remain. The removal of these two components safely is aided by using high vacuum and burst mode. The epinucleus is gripped with high vacuum and trimmed in one quadrant, and the subincisional cortex will flow around the quadrant and into the phaco tip. Special attention should be made at this stage to prevent early flipping of the epinucleus. In this situation, a residual cortical bowl will remain behind, and removal may be associated with posterior capsule trauma. During high vacuum removal of the initial quadrant, the floor of the epinuclear shell may be pushed back and this manoeuvre will keep the capsular bag on stretch. The next two epinuclear quadrants are removed in a similar fashion, to leave the fourth quadrant. At this final stage, the high vacuum keeps the epinuclear edge held at the phaco tip, and the quadrant is flipped and then removed in a controlled manner with burst mode. The remaining cortical material will be aspirated with the epinuclear quadrant. The effective phaco time may be reduced to less than 2 seconds using our technique. At the end of surgery, the corneal wound is hydrated and the central cornea remains clear (Figure 1f).

Discussion

Soft-to-semisoft cataracts (grades 1 to 2 based on the Emery-Little classification of nucleus hardness) are recognised to be difficult to crack, and excessive manipulations within the central groove may increase the risk of posterior capsule fracture and zonular dehiscence. This type of cataract may be especially challenging for trainee ophthalmologists. Our wagon wheel technique avoids this problem by moving the nucleus to the capsulorhexis plane and lifting it away from the posterior capsule. As the lens is removed in the wagon wheel position, the nuclear volume decreases as the lens spins centrifugally towards the phaco tip. This manoeuvre minimises mechanical pressure on the posterior capsule and zonules. Our technique uses the hydro forces of burst phaco to disassemble the nucleus and high vacuum removes the cataract. This strategy of burst phaco power may reduce the total amount of ultrasound energy used within the eye. In the wagon wheel position, a layer of Viscoat® protects the corneal endothelium and minimal phaco energy is generated using both burst mode and high vacuum aspiration of the soft-to-semisoft lens. During the first week postoperatively, the cornea appears clear with minimal anterior chamber reaction.

Our single site technique combined with wagon wheeling avoids the intracapsular nuclear rotations associated with conventional one-handed phaco. The wagon wheel technique may be used in a number of clinical settings where avoidance of zonular and capsular stresses is important. Examples may include posterior polar cataract, traumatic posterior subcapsular cataract, high myopia, and clear soft lens extraction.

Our wagon wheel technique reduces damage to intracameral structures, and allows soft-to-semisoft cataracts to be safely removed. The single site approach eliminates side port complications and permits low energy phaco to be performed with minimal instrumentation within the eye.

References