Intratunnel Nucleus Fragmentation
Key Points at a Glance
Section titled “Key Points at a Glance”1. What is intratunnel phacofracture?
Section titled “1. What is intratunnel phacofracture?”Intratunnel phacofracture is a new nucleus management technique for manual small-incision cataract surgery (MSICS) introduced in 2012 by Dr. Sudhir Singh of the Global Hospital Research Centre in India.
Manual small-incision cataract surgery and phacoemulsification are the most widely used cataract extraction methods. Manual small-incision cataract surgery is significantly faster and cheaper than phacoemulsification and is less dependent on technology 2). In economically disadvantaged countries, manual small-incision cataract surgery is still widely adopted due to cost-effectiveness 3). Randomized controlled trials show that phacoemulsification is superior to manual small-incision cataract surgery in terms of uncorrected distance visual acuity and complication rates, but a prospective comparative study reported no significant difference between the two 3).
Conventional manual small-incision cataract surgery techniques (Blumenthal method, viscoexpression, irrigating wire vectis, fishhook needle, etc.) all require a large incision of 7–9 mm. This large incision causes postoperative induced astigmatism. Small-incision surgery allows for easier construction of a self-sealing wound, provides greater safety during sudden movements or expulsive hemorrhage, and results in less postoperative inflammation and astigmatic change 3).
In intratunnel phacofracture, the lens nucleus is divided and removed within a sclerocorneal tunnel incision of less than 6 mm. Unlike other nucleus division methods that involve manipulation in the anterior chamber, this technique completes the nucleus removal process within the tunnel, which is its greatest feature.
Conventional manual small-incision cataract surgery requires a 7–9 mm incision and removes the nucleus as a single piece, whereas this technique divides and removes the nucleus within a tunnel through an incision of less than 6 mm. The reduced incision width decreases induced astigmatism.
2. Main symptoms and clinical findings
Section titled “2. Main symptoms and clinical findings”Subjective symptoms
Section titled “Subjective symptoms”The target of intratunnel phacofracture is cataract patients. The main subjective symptoms of cataract are as follows.
- Decreased visual acuity: The most common symptom of cataract. It gradually worsens as lens opacification progresses.
- Blurred vision: The entire field of vision appears hazy.
- Photophobia (glare): Light scattering can significantly reduce visual function in bright environments3).
- Decreased contrast sensitivity: Difficulty identifying objects in dim light.
Clinical Findings
Section titled “Clinical Findings”The difficulty of cataract surgery varies depending on the hardness and size of the nucleus. The Emery-Little classification (grades 1–5) is used to evaluate the nucleus, observing the degree of yellow opacity and size of the nucleus with a slit-lamp microscope.
| Grade | Slit-lamp Findings | Nuclear Hardness |
|---|---|---|
| Grade 1 | Clear to milky white | Soft |
| Grade 3 | Yellow | Moderate |
| Grade 5 | Brown | Very hard |
Types of cataract opacities include nuclear cataract, cortical cataract, anterior subcapsular cataract, and posterior subcapsular cataract. Age-related cataracts often present as nuclear or cortical cataracts.
3. Causes and Risk Factors
Section titled “3. Causes and Risk Factors”The cause of cataracts is age-related denaturation and coagulation of lens proteins, leading to gradual loss of transparency.
The situations in which manual small-incision cataract surgery is particularly indicated are as follows.
- Mature nuclear cataract: When the nucleus is hard and large, it may be difficult to manage with phacoemulsification 3)
- Cases with zonular weakness: When supporting tissues are weak, there is a high risk with phacoemulsification 3)
- Cases at high risk of corneal decompensation: Corneal endothelial damage from ultrasound energy can be avoided 3)
- Cataracts with corneal opacity: Surgery is possible with minimal instruments even when visibility is poor 2)
- Medical environments in developing countries: Facilities where phacoemulsification equipment is not available
4. Diagnosis and Examination Methods
Section titled “4. Diagnosis and Examination Methods”Cataract diagnosis is performed using slit-lamp microscopy. The following evaluations are important for determining surgical indications and selecting the surgical technique.
- Slit-lamp microscopy: Evaluates the type and degree of cataract and nuclear hardness. Also checks for corneal scars, anterior chamber depth, and iris condition.
- Keratometry: Measures K1 and K2 values to assess the degree of preoperative astigmatism. This is an important test that directly affects the choice of incision site in tunnel nuclear fragmentation surgery.
- Gonioscopy, anterior segment OCT, and ultrasound biomicroscopy: Useful for evaluating complex anterior segment pathologies such as narrow angles, posterior polar cataract, and lens subluxation 3).
- Macular OCT: Considered when visual acuity loss is disproportionate to the degree of cataract, to rule out concomitant retinal disease 3).
- Axial length measurement and intraocular lens power calculation: Biometry is performed to determine the appropriate intraocular lens power.
It is suitable for mature nuclear cataracts and cataracts with a hard nucleus. It can also be performed in settings where phacoemulsification equipment is unavailable, or in cases with high risk of corneal endothelial damage. The incision size is smaller than that of conventional manual small-incision cataract surgery, and a reduction in induced astigmatism is expected.
5. Standard Treatment
Section titled “5. Standard Treatment”Preoperative Preparation and Anesthesia
Section titled “Preoperative Preparation and Anesthesia”Manual small-incision cataract surgery can be performed under peribulbar anesthesia or topical anesthesia.
Incision Site Selection
Section titled “Incision Site Selection”The incision site is determined based on keratometry readings (K1 and K2).
- Difference between K1 and K2 ≤ 1.0 D: For the right eye, a superotemporal incision; for the left eye, a superonasal incision.
- K1 is steeper than K2 by ≥ 1.0 D: A superior incision is made in both eyes.
- K2 is steeper than K1 by ≥ 1.0 D: A temporal incision is made in both eyes.
To maximize the astigmatic correction effect, the incision is placed on the steeper axis.
Surgical Procedure
Section titled “Surgical Procedure”Creation of the Sclerocorneal Tunnel
Section titled “Creation of the Sclerocorneal Tunnel”A 4–6 mm sclerocorneal frown incision is made 1.5 mm from the limbus using a No. 15 blade. A funnel-shaped sclerocorneal tunnel is created with a crescent knife. Side ports are made at 90 degrees on both sides of the tunnel using a 15-degree knife. A 3.2 mm keratome is used to enter 1.5 mm into the clear cornea and puncture the anterior chamber. 2% hydroxypropyl methylcellulose (HPMC) viscoelastic is injected into the anterior chamber.
Sclerocorneal tunnel incisions provide greater wound stability compared to clear corneal incisions 2).
Anterior Capsulotomy and Hydrodissection
Section titled “Anterior Capsulotomy and Hydrodissection”A central continuous curvilinear capsulorhexis (CCC) is created with a 26-gauge needle capsulotome. The size of the CCC is 5.5–7.5 mm, adjusted according to the size of the nucleus. If the red reflex is poor, the anterior capsule is stained with trypan blue. Then, hydrodissection is performed using a 26-gauge cannula.
Dislocation of the Nucleus into the Anterior Chamber
Section titled “Dislocation of the Nucleus into the Anterior Chamber”The internal incision of the tunnel is widened laterally to 7 mm using a 5.1 mm keratome. The anterior chamber is reformed with viscoelastic, and the nucleus is rotated within the capsular bag using a sinskey hook. The CCC edge is retracted to lift one pole of the nucleus out of the bag, and the remainder is rotated to dislocate it into the anterior chamber. If the nucleus is large, 2–3 relaxing incisions are made in the CCC edge.
Intratunnel Nucleus Fragmentation (Core of This Procedure)
Section titled “Intratunnel Nucleus Fragmentation (Core of This Procedure)”Up to this point, the procedure is common to other manual small-incision cataract surgeries. This technique enters its unique steps from this stage onward.
To protect the corneal endothelium, sufficient viscoelastic is injected between the cornea and the upper surface of the nucleus, and between the nucleus and the iris. The nucleus is removed from the bag using a sinskey hook. A small Lewis lens loop is inserted through the tunnel and placed between the iris and the nucleus. The nucleus is fixed on the lens loop and slowly withdrawn from the anterior chamber while depressing the posterior lip of the tunnel.
When the nucleus becomes lodged in the tunnel, the Lewis loop is pulled posteriorly and superiorly. This causes part of the nucleus to break off and be removed, while the remainder stays in the tunnel. The remaining nucleus is pushed back into the anterior chamber with a viscoelastic cannula, aligning its long axis with the tunnel axis. Viscoelastic is injected again, and the remaining nucleus is withdrawn with the lens loop. In most cases, the residual nucleus is expelled on the second attempt. If it breaks, the procedure is repeated.
Cortex Cleanup and Intraocular Lens Insertion
Section titled “Cortex Cleanup and Intraocular Lens Insertion”Residual cortex is cleaned using a 23-gauge Simcoe irrigation/aspiration cannula. A single-piece polymethyl methacrylate (PMMA) intraocular lens with a 5.5–6.0 mm optic and 12.5 mm overall length is inserted into the capsular bag.
Wound Closure
Section titled “Wound Closure”The main port and side ports are closed by corneal stromal hydration using a 26-gauge cannula. 0.5 cc of a gentamicin-dexamethasone mixture is injected subconjunctivally, and the eye is covered with a patch.
The corneoscleral tunnel incision is self-sealing and usually does not require sutures. The port is closed by corneal stromal hydration. However, in high-risk cases (elderly, connective tissue diseases, etc.), suturing of the tunnel may be recommended 1).
6. Pathophysiology and detailed pathogenesis
Section titled “6. Pathophysiology and detailed pathogenesis”Cataract is a disease in which proteins within the lens fibers denature and coagulate, losing transparency. The mechanisms include the following patterns.
- Nuclear cataract: Pigment deposits in the lens nucleus, gradually turning yellow to brown. The nucleus hardens and enlarges, changing the refractive power.
- Cortical cataract: Increased water content between lens fibers causes opacification in the cortex.
- Subcapsular cataract: Fibrous metaplasia of the lens epithelium just beneath the anterior capsule causes anterior subcapsular cataract, and opacification beneath the posterior capsule is called posterior subcapsular cataract. It is associated with atopic dermatitis and steroid use.
The mechanical principle of tunnel nuclear fragmentation is to apply physical shearing force to the nucleus using the narrow space of the corneoscleral tunnel. When the lens loop is pulled while the nucleus is wedged in the tunnel, the tunnel wall acts as a fulcrum, applying splitting force to the nucleus. This mechanism allows the nucleus to be fragmented and removed without extensive manipulation in the anterior chamber.
In phacoemulsification, ultrasonic vibration and turbulent irrigation fluid can cause mechanical and thermal damage to the corneal endothelium 2). Manual small-incision cataract surgery does not use ultrasonic energy, thus reducing direct damage to the corneal endothelium. Especially in cases with corneal opacity or shallow anterior chamber, the ultrasonic tip may be close to the corneal endothelium during ultrasound manipulation, increasing the risk of endothelial cell damage 2).
7. Latest research and future perspectives (reports under investigation)
Section titled “7. Latest research and future perspectives (reports under investigation)”Technical improvements in manual small-incision cataract surgery
Section titled “Technical improvements in manual small-incision cataract surgery”Manual small-incision cataract surgery is expected to remain an important cataract surgery method, especially in developing countries. As a technical improvement, the use of an endoilluminator (intraocular illuminator) to enhance visibility has been reported.
Joshi (2022) performed manual small-incision cataract surgery with an endoilluminator in a cataract case complicated by corneal scarring after Hansen’s disease and a small pupil 2). With conventional coaxial illumination, visibility is significantly reduced due to light scattering from the corneal scar, but placing the endoilluminator obliquely at the limbus allowed good observation of intraocular structures. Postoperative visual acuity improved to 6/12.
Research is also progressing on the use of femtosecond lasers for creating corneal incisions, astigmatic keratotomy, capsulotomy, and nuclear fragmentation 3). However, an increased rate of posterior capsule rupture was reported during the initial introduction of femtosecond laser-assisted cataract surgery (FLACS) 3). Recent randomized controlled trials (FEMCAT trial, FACTS trial) have found no difference in posterior capsule rupture rates compared to conventional methods 3).
8. References
Section titled “8. References”- Luqman F, Qureshi V, Asad A, et al. A rare case of post-traumatic posterior chamber intraocular lens extrusion through the scleral tunnel of manual small incision cataract surgery. Cureus. 2023;15(8):e42884.
- Joshi SD. “Show me the way” – Endoilluminator-assisted manual small-incision cataract surgery in a case of corneal scar with a small pupil. Indian J Ophthalmol. 2022;70:4073-4075.
- American Academy of Ophthalmology. Cataract in the Adult Eye Preferred Practice Pattern. Ophthalmology. 2022;129(1):P1-P126.