Corneal wound hydration is a technique used at the end of cataract surgery to assist in closing the clear corneal incision (CCI). Ophthalmic irrigation solution (BSS) is injected into the side walls of the CCI or the corneal stroma, causing the corneal tissue to swell and the roof of the wound to adhere to the floor. The technique using a blunt cannula was first reported clinically.
CCI is currently the most common incision method in cataract surgery. It requires no sutures, shortens surgical time, and induces less astigmatism. However, with the widespread use of CCI, it has been suggested that the incidence of postoperative endophthalmitis may have slightly increased 2). Reports indicate that wound leakage on the first postoperative day increases the risk of endophthalmitis by 44 times, making secure wound closure essential.
It is important to perform wound hydration at the end of cataract surgery to ensure secure closure. In particular, leakage from side ports is easily overlooked, so irrigation fluid should be injected into the anterior chamber to confirm no leakage.
If wound closure after hydration is insufficient, the following findings may be observed.
Positive Seidel test: Fluorescein staining confirms aqueous humor leakage from the wound. May be accompanied by hypotony.
Shallow anterior chamber: Continuous aqueous leakage from the wound causes the anterior chamber to become shallow.
Corneal edema: Caused by excessive hydration or Descemet’s membrane detachment. Increased corneal thickness can be confirmed by anterior segment OCT.
Descemet’s membrane detachment: Observed as wrinkles on the posterior corneal surface. Extensive detachment can form a double anterior chamber and cause severe corneal edema.
QIs it normal for the cornea to become white and cloudy after hydration?
A
Mild corneal opacity immediately after hydration is due to stromal swelling and is usually transient. However, if the opacity is severe and persistent, suspect Descemet’s membrane detachment or corneal endothelial damage, and further examination with anterior segment OCT is necessary.
Inappropriate incision creation: If the incision is too large, the anterior chamber becomes unstable. If too small, friction with the ultrasound tip can easily cause wound burn 2).
Wound burn: Occurs when the temperature around the ultrasound tip reaches 60°C or higher. The incidence is approximately 0.043% 2). Prolonged ultrasound oscillation for hard nuclei or insufficient perfusion are causes.
Postoperative external force on the eye: Rubbing the eye or insufficient scleral rigidity may cause the closed wound to reopen after surgery 2).
Children and young adults: Tissues are more extensible, making self-sealing difficult.
Relationship Between Wound Leakage and Endophthalmitis
An incomplete wound can lead to postoperative wound leakage, hypotony, and endophthalmitis2). Whether there is a difference in endophthalmitis risk between clear corneal incisions and scleral incisions remains inconclusive, but watertight wound closure is essential for any incision method 2). The incidence of postoperative endophthalmitis after cataract surgery in the United States is estimated at 0.04% 2).
Place a hydrodissection needle (30G or 34G) or a blunt cannula perpendicular to the CCI and inject BSS into the corneal stroma. The cornea becomes swollen and opaque, and the wound self-seals.
Basic Steps
Cannula insertion: Place the tip of a blunt cannula or hydrodissection needle against the side wall of the CCI. Keep it within the corneal stroma, not entering the anterior chamber.
BSS injection: Inject irrigation fluid into the corneal stroma to swell the cornea. It is basic to hydrate both sides of the wound.
Additional hydration if closure is insufficient: If both sides do not close, add hydration near the center of the wound. However, doing it forcefully may cause Descemet’s membrane detachment.
Confirmation of closure: Use a cotton swab to check for aqueous humor leakage from the anterior chamber. Also check for leakage from side ports.
Precautions
Inject within the tunnel: Keep the tip of the cannula within the tunnel (corneal stroma) and avoid injection near the inner valve (near Descemet’s membrane).
Check intraocular pressure: Confirm that there is no aqueous humor leakage at an appropriate intraocular pressure before finishing the surgery.
Decision to suture: If hydration does not close the wound, suture with 10-0 nylon. When in doubt, suture.
Another method is to apply the I/A tip to the wound and perform hydration. This method is said to be less disruptive to the wound architecture.
Anterior stromal pocket hydration method: A modification that hydrates the corneal stroma just anterior and central to the CCI. In a study of 66 eyes, this method was reported to reduce the leakage rate under direct pressure compared to the conventional method.
Infusion port method: A technique reported by Suzuki et al. using the infusion port during phacoemulsification. It is said to be less likely to damage surrounding tissues such as Descemet’s membrane.
Incision-over-pocket method (Wong method): A pocket is created overlapping the inner side of the CCI, and hydration is performed at the end of surgery.
Regarding the effects of stromal hydration, OCT examinations have shown that corneal thickness and wound length increase for up to 2 weeks postoperatively. On the other hand, some studies have found no significant difference in endothelial or epithelial gaping or wound misalignment with or without hydration. Another study reported that hydration with a 2.2 mm wound actually thinned the cornea and increased the incidence of endothelial gaping. Furthermore, it has been shown that even after stromal hydration, 67% of CCIs still exhibit wound leakage with external manipulation (simulated blinking).
QCan hydration completely prevent wound leakage?
A
No, it cannot be completely prevented. Leakage may still occur if external force is applied after hydration. If wound integrity is questionable, sutures should be added.
Inadvertent injection of irrigation fluid during hydration can cause Descemet’s membrane detachment. Some studies report a higher incidence of Descemet’s membrane detachment in eyes that underwent hydration compared to those that did not, while others find no significant difference.
To prevent Descemet’s membrane detachment, it is important to keep the cannula tip within the tunnel (corneal stroma) and avoid injection near Descemet’s membrane. Localized detachment within 1 mm can be observed, but for extensive detachment, air injection into the anterior chamber should be attempted to reposition it.
In the literature, 9 cases of intraocular injury due to cannula dislodgement during hydration have been reported. Injuries include corneal perforation, retinal detachment, vitreous hemorrhage, hyphema, and iris laceration. The incidence is estimated at 0.88 per 1000 procedures per year.
As preventive measures, the use of a Luer-lock syringe, confirmation of cannula fixation, holding the cannula base, and not directing the tip toward the posterior pole are recommended.
Lamprogiannis et al. (2024) reported a case of complete iridodialysis (iris prolapse) occurring during hydration after uneventful cataract surgery in an 86-year-old woman 1). It was inferred that transient intraocular pressure elevation during hydration and reopening of the wound caused the iris to prolapse out of the anterior chamber. Corrected visual acuity of 20/50 was maintained at 4 months postoperatively.
Particular caution is needed in elderly patients, those with zonular weakness, and cases where iris prolapse occurred intraoperatively 1). In patients with risk factors for intraoperative floppy iris syndrome (IFIS), gentle manipulation of the iris and avoidance of rapid intraocular pressure fluctuations are important 1).
QCan wound burn be closed by hydration?
A
When corneal tissue degenerates and contracts due to wound burn, closure may be difficult with hydration alone. In such cases, suturing with 10-0 nylon is necessary. If the burn is extensive, 3 to 5 sutures may be required.
6. Mechanism of action and structural background of the cornea
Injecting BSS into the corneal stroma increases the water content within the stroma, causing the cornea to swell. Proteoglycans (keratan sulfate and chondroitin sulfate) filling the spaces between collagen fibers in the corneal stroma have a very strong water-absorbing pressure and retain the injected fluid. This swelling presses the roof of the wound against the floor, achieving physical closure.
At the same time, the pump function of corneal endothelial cells pumps excess water into the anterior chamber, exerting a force that pulls the roof of the wound toward the floor. This physical adhesion and the pump mechanism work together to assist wound closure.
Structure of the corneal stroma and regulation of water content
The corneal stroma accounts for about 90% of corneal thickness and consists of regularly arranged collagen fibers. Corneal transparency is maintained by the uniform spacing between collagen fibers. When the water content in the stroma increases, the spacing becomes irregular and transparency decreases. The temporary clouding of the cornea immediately after hydration is due to this mechanism.
Corneal endothelial cells have a barrier function that limits water penetration and a pump function that actively removes water. If the corneal endothelium is healthy, temporary corneal edema from hydration resolves within hours to days.
7. Latest research and future perspectives (reports at research stage)
Cyanoacrylate adhesives can be used for CCI closure, but there are risks of toxicity, lack of flexibility, and inflammation. Fibrin glue is more flexible and biodegradable, and is reported to provide better closure than sutures in CCI, but there is a potential risk of prion or virus transmission.
Polyethylene glycol (PEG)-based liquid adhesive ocular bandages (such as OcuSeal® and ReSure®) have been reported to provide better closure than hydration alone, with less astigmatism and less foreign body sensation than sutures. When using ocular bandages, further investigation is needed regarding the necessity of stromal hydration.
Femtosecond lasers can provide stable and reproducible incisions. Compared to manual incisions, there is less epithelial wound gaping, Descemet’s membrane detachment at the incision site, endothelial misalignment, and astigmatic variation. Whether this method leads to better wound closure and a reduction in postoperative endophthalmitis remains to be studied.
Lamprogiannis L, Syam PP, Patel A, et al. Iris avulsion during corneal wound hydration after uneventful cataract extraction. Cureus. 2024;16(11):e74807.
American Academy of Ophthalmology. Cataract in the Adult Eye Preferred Practice Pattern. Ophthalmology. 2022;129:P1-P126.
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