Wounds, OVDs and nucleus techniques

Surgical Technique: Incision Architecture & OVD Dynamics

Clear Corneal Incision (CCI) Architecture

A modern temporal clear corneal incision ($2.2\text{ to }2.4\text{ mm}$) must be constructed as a stepped, multi-planar, self-sealing tunnel:

1. Multi-Planar Architecture (2-plane or 3-plane): Begins with an initial shallow vertical groove ($300\,\mu\text{m}$), followed by a horizontal lamellar tunnel through corneal stroma ($1.5-2.0\text{ mm}$ in length), culminating in a sharp, beveled internal entry into the anterior chamber through Descemet's membrane.
2. Tunnel geometry: A suitable length-to-width relationship and multiplanar entry promote wound apposition. Published “square” rules are heuristics, not a requirement that every modern incision have an aspect ratio of at least one. Check the actual wound for leakage and suture when integrity is uncertain.
3. Stromal hydration: Local swelling can improve temporary apposition but does not guarantee closure. Confirm a stable chamber and wound seal at the end of surgery; an injured or leaking incision may require a suture.

Ophthalmic Viscosurgical Devices (OVDs)

The Arshinoff Soft-Shell Technique

Dr. Steve Arshinoff designed the soft-shell technique to exploit the mechanical advantages of both OVD classes simultaneously:

1. Step 1 (Dispersive Layer): A small bolus of dispersive OVD (Viscoat) is injected directly onto the corneal endothelium.
2. Step 2 (Cohesive Layer): A cohesive OVD (Healon) is injected beneath the dispersive layer, directly onto the anterior lens capsule.
3. Result: The cohesive OVD pushes the dispersive OVD upward, spreading it into a uniform, adherent protective blanket against the endothelium, while the cohesive agent deepens the chamber, stabilizes the iris, and flattens the capsule for capsulorhexis.

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Continuous Curvilinear Capsulorhexis (CCC)

A continuous curvilinear capsulorhexis is the cornerstone of modern phacoemulsification, transforming the capsular bag into a resilient container capable of withstanding high hydraulic forces.

Biomechanics of the Tear: Shear versus Stretch

• Shear Vector: Applying tangential traction along the circumference of the tear creates a tearing shear force, guiding the flap along a controlled circular arc.
• Stretch Vector: Pulling radially outward generates stretch vectors that direct the tear toward the equatorial zonules. As the tear approaches the zonules, zonular tension and positive vitreous pressure exacerbate outward extension.
• Capsulorhexis: An appropriately centred opening commonly around 5–5.5 mm for a 6-mm optic aims for overlap. Size and overlap do not guarantee absence of phimosis or perfect lens position.

Rescuing a Runaway Capsulorhexis

Stop traction and reform the chamber with ophthalmic viscosurgical device. Regrasp the flap near its root and redirect the tear with controlled tangential traction; the Little manoeuvre first unfolds and draws the flap back before redirecting centrally. Do not pull forcefully toward the equator. Rescue depends on visibility, tear location and chamber stability. If safe recovery fails, change the surgical plan and anticipate extension and capsular-support problems.

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Hydrodissection & Hydrodelineation

• Cortical-Cleaving Hydrodissection: A flat, angled cannula is inserted beneath the anterior capsulorhexis lip. Gentle, steady injection of BSS cleaves cortical adhesions from the inner capsular surface. Successful hydrodissection is confirmed by a visible fluid wave traversing the red reflex, slight anterior displacement of the lens, and effortless $360^\circ$ manual rotation of the nucleus.
• Hydrodelineation: The cannula tip is embedded into the mid-peripheral lens substance, and BSS is injected to cleave the central, firm endonucleus from the softer surrounding epinucleus, producing a characteristic "golden ring". The epinucleus acts as an anatomical barrier protecting the posterior capsule during high-vacuum endonuclear fragmentation.

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Nucleus Disassembly Techniques

1. Divide-and-Conquer (Gimbel / Shepard)

• Sculpt deep crossed trenches down to $90\%$ of nuclear depth using moderate ultrasound and low vacuum.
• The cross-action cracking maneuver is executed by placing the phaco tip and a second instrument (Nagahara chopper or cyclodialysis spatula) at the base of the trench and pushing in opposite lateral directions.
• The nucleus is rotated $90^\circ$ and cracked again, dividing it into four separate quadrants. Each quadrant is mobilized to the iris plane and emulsified in high-vacuum position 3.

2. Stop-and-Chop (Koch)

• Sculpt a single central trench to crack the nucleus into two heminuclei.
• The surgeon "stops" sculpting and uses a chopper to mechanically divide each heminucleus into bite-sized pie wedges. Substantially reduces cumulative dissipated energy.

3. Phaco Chop (Nagahara Horizontal vs Vertical/Quick Chop)

• Horizontal Chop: The phaco tip is embedded into the central nucleus under high vacuum (pedal position 3). The chopper is passed beneath the capsulorhexis rim, hooked around the equatorial nuclear edge, and pulled horizontally directly toward the phaco tip. A brief lateral separation cleaves the fragment.
• Vertical / Quick Chop: The phaco tip is driven deeply into the central nucleus in high vacuum. A sharp vertical chopper is plunged straight down into the nucleus immediately anterior to the embedded tip, followed by lateral instrument separation to split the nucleus.
• Efficiency: Mechanical chopping can reduce ultrasound use compared with trenching, depending on nucleus and technique; it does not guarantee a fixed energy reduction.