In cataract surgery (phacoemulsification; PEA), incision creation is the foundational step for all surgical stages. A properly constructed incision maintains anterior chamber stability, facilitates intraoperative maneuvers, and contributes to postoperative infection prevention and early recovery. Conversely, an inadequate wound increases the risk of intraoperative and postoperative complications such as wound leakage, endophthalmitis, and surgically induced astigmatism (SIA) 1).
Incision methods are broadly classified into clear corneal incision (CCI) and scleral incision. According to a 2003 survey by the American Society of Cataract and Refractive Surgery (ASCRS), the utilization rate of CCI reached 72%, a significant increase from 1.5% in 1992. CCI is the mainstream approach in modern cataract surgery, but scleral incisions also have inherent advantages. Additionally, the intermediate transconjunctival single-plane sclerocorneal incision is widely performed.
The width of the incision is generally around 2.4 mm, sufficient to insert the ultrasound tip and sleeve. The advent of foldable intraocular lenses (IOLs) has enabled smaller incisions, contributing to reduced SIA.
This method creates a tunnel within the corneal stroma and enters the anterior chamber. It has the following characteristics:
On the other hand, CCI has the following limitations:
This method involves incising the conjunctiva, making a half-thickness incision in the sclera about 1.5 mm posterior to the limbus, and creating a flap-like tunnel. It originated from the four-sided incision performed by Dobree in 1959 for intracapsular cataract extraction.
In a three-plane sclerocorneal incision, the first plane is made with a diamond knife along the limbus to about two-thirds of the scleral depth, the second plane creates a tunnel of at least 2 mm with a crescent knife, and the third plane enters the anterior chamber with a slit knife.
This method is intermediate between sclerocorneal and corneal incisions. A slit knife is inserted from above the conjunctiva about 0.5 mm from the limbus, advanced within the sclera along the cornea with a tunnel length similar to the incision width, and finally punctured into the anterior chamber on the cornea.
Advantages:
Disadvantages:
The ideal tunnel length is 1.75–2.0 mm. An important technique is to consciously change the angle of the slit knife in three steps: (1) hold it slightly upright against the sclera near the limbus, (2) tilt it to advance between layers, and (3) raise it slightly to puncture the endothelial side.
Clear Corneal Incision
Conjunctival preservation: Does not compromise glaucoma surgery outcomes.
Surgery time: Short. Can be performed under topical anesthesia.
Infection risk: May increase when wound closure is incomplete
SIA: Tends to be slightly larger
Sclerocorneal incision
Infection protection: Superior due to conjunctival coverage
Self-sealing: High
SIA: Small
Operability: Many steps, risk of bleeding
Transconjunctival single-plane sclerocorneal incision
Position: Intermediate between the two
Conjunctival invasion: Minimal
Infection protection: Conjunctival coverage present
Tip: Change the blade angle in three stages
| Item | Corneal incision | Sclerocorneal incision |
|---|---|---|
| Conjunctival preservation | Possible | Impossible |
| Self-sealing ability | Requires precise technique | High |
| Corneal shape change | More | Less |
Each has pros and cons; the choice should be based on the case and the surgeon’s experience. When conjunctival preservation is important, a corneal incision is preferred; to minimize infection risk, a sclerocorneal incision is chosen; and for a balance of both, a transconjunctival single-plane sclerocorneal incision is an option.
Paracentesis is an auxiliary entry route into the anterior chamber and is created for the following purposes:
Usually, two ports are created at the corneal limbus at positions 2 to 3 hours away from the main incision (10 o’clock and 2 o’clock directions). Insert at the leading edge of the conjunctival vessels, and after passing through the endothelium, advance parallel to the iris. The incision width is approximately 0.8 mm, and the tunnel length is approximately 0.8 mm.
Using a dull blade increases the risk of Descemet’s membrane detachment, so replace damaged blades with new ones.
The incision location differs in distance from the central visual axis and affects the degree of SIA.
The incision location is 0.5 to 1.5 mm anterior to the limbus. A “near-clear” corneal incision that slightly damages the surrounding limbal vessels is preferred. True clear corneal incisions without vessels have delayed fibroblast response and take longer to heal.
If preoperative corneal astigmatism exceeds 0.50 D, making the incision on the steepest meridian reduces postoperative astigmatism1).
Establishing a watertight self-sealing wound is key to infection prevention1). Methods of wound closure include the following.
The incidence of endophthalmitis after cataract surgery in the United States from 2013 to 2017 is estimated at approximately 0.04%1). Risk factors for postoperative endophthalmitis include the following.
In the ESCRS prospective multicenter study, the risk of endophthalmitis was 4.92 times higher (95% CI 1.87–12.9) when intracameral cefuroxime was not administered2). Use of silicone IOLs was also associated with increased risk (OR 3.13; 95% CI 1.47–6.67)2).
The ESCRS study reported a 5.88-fold risk increase with CCI2), but several large studies have found no significant difference between the two1). The type of incision is less important than watertight wound closure and appropriate infection prevention measures.
This is a complication that tends to occur with corneoscleral incisions. Causes include incision placement away from the limbus, and the tip of the crescent knife pointing toward the anterior chamber during lamellar dissection. It can be prevented by lifting the knife tip upward.
Failure to consider the difference in curvature radius between the sclera and cornea can result in an excessively short corneal tunnel, leading to early perforation.
This often occurs following early perforation. Intraoperative floppy iris syndrome (IFIS) and incomplete wound construction (insufficient tunnel length or short internal lip) are also causes.
Caused by friction heat between the ultrasound tip and sleeve. Causes include prolonged high-power ultrasound, insufficient irrigation, and ultrasound oscillation in an anterior chamber filled with viscoelastic material. Promote self-sealing with hydration; suture if inadequate.
Includes Descemet’s membrane detachment, corneal erosion, wound dehiscence due to minor trauma, and hyphema.
First, perform hydration (swelling of the corneal stroma by BSS injection) to promote self-sealing. If leakage persists, suture with 10-0 Prolene. If uncertain during surgery, it is safe to choose suturing.
This section explains the wound healing process and the mechanism of self-sealing.
Self-sealing in corneal incisions is achieved when the internal corneal valve is pressed against the external valve by intraocular pressure. The longer the tunnel structure, the larger the contact area between the valves and the stronger the sealing force. An intraocular pressure of at least 10 mmHg is necessary for the sealing function to work.
In multi-plane incisions, the stepped structure enhances valve interlocking, resulting in better wound closure than single-plane incisions. Incisions with a nearly square shape are less prone to valve displacement and have higher stability.
Inadequate wound closure allows inflow of extraocular fluid into the anterior chamber. Experiments using cadaver eyes have shown that India ink can penetrate into the anterior chamber through sutureless CCI, supporting the infection route via contaminated fluid inflow. Wound leakage is directly associated with the risk of endophthalmitis on the first postoperative day 1).
Vascularized “near-clear” corneal incisions promote faster fibroblast migration and enhanced healing compared to avascular “true clear” corneal incisions.
In femtosecond laser-assisted cataract surgery (FLACS), the laser can be used for main incision, relaxing incision, anterior capsulotomy, and nuclear fragmentation 1). Compared to manual CCI, it can create incisions with superior morphology and integrity, and is expected to reduce wound leakage with reverse side-cut CCI.
A 2020 meta-analysis (73 studies, 12,769 eyes in FLACS group vs. 12,274 eyes in conventional group) reported significant improvements in uncorrected and corrected visual acuity at 1–3 months postoperatively, reduced cumulative ultrasound energy, improved roundness of anterior capsulotomy, and decreased central corneal thickness 1).
However, there is still no definitive evidence of cost-effectiveness superiority. Additionally, opening the main incision created by femtosecond laser can be difficult, and many surgeons use a metal or diamond keratome only for the main port.
