Corneal Complications of Intraocular Surgery

Epithelial Complications

Epithelial defects are a common complication after surgical trauma or toxicity of medications and antiseptics. Excessive dryness can occur with prolonged preoperative use of topical anesthetics. Patients with dry eye syndrome, exposure keratopathy, anterior basement membrane dystrophy, diabetes mellitus, and those undergoing vitrectomy are at increased risk for developing epithelial defects, especially with minor trauma to the corneal surface.

Epithelial edema may present intraoperatively in patients with a history of dry eyes, surgical trauma, elevated intraocular pressure, prolonged surgical times, and endothelial injury. Epithelial edema can result in an irregular light reflex and decreased clarity of intraocular structures, requiring central corneal epithelial debridement. Filamentary keratitis may also develop postoperatively in patients with ptosis or dry eyes.

Management involves frequent lubrication with artificial tears, gels, ointments, or therapeutic soft contact lenses. Scleral contact lenses may also play a role in management of epithelial injuries. A tarsorrhaphy and/or amniotic membrane graft may be necessary to treat chronic epithelial defects. , Use of autologous serum may decrease time to reepithelialization by 40%. Patients at risk may benefit from preoperative use of lubricants and topical cyclosporine or lifitegrast and intraoperative use of viscoelastics on the corneal surface. Meibomian gland dysfunction and the associated evaporative dry eye is common in cataract population and should be evaluated and treated preoperatively as well as postoperatively. Cenegermin (recombinant human nerve growth factor) eye drops have recently become available for treatment of neurotrophic keratitis and may allow for prevention and treatment of perioperative epithelial defects. Most epithelial defects resolve promptly but may result in infectious keratitis, corneal scarring, and neovascularization with loss of vision, especially after retinal surgery.

Thermal Burns

Thermal burns to the cornea can occur with use of cautery and phacoemulsification ultrasonic handpieces. Coagulation of corneal tissue results in collagen shrinkage with focal opacification, scar tissue formation, and induction of astigmatism. Central corneal injury has more significant sequelae as compared to peripheral burns. The phacoemulsification handpiece generates significant heat due to friction between the vibrating needle and silicone sleeve with the use of ultrasound energy, which must be adequately cooled by the flow of irrigation fluid. Constriction of the silicone sleeve, disruption of this irrigation, and prolonged phacoemulsification times can result in a sudden thermal burn to the incisional corneal tissue, resulting in corneal contraction, wound gape, and leaky incisions ( Fig. 96.1 ). Thermal burns during phacoemulsification can occur due to hydration of an incision during surgery resulting in a tight entrance wound, during lens fragment removal, and with dense nucleus removal requiring high degrees of ultrasound energy.

Prevention and early recognition of thermal injury is essential to minimizing morbidity associated with thermal burns. Phacoemulsification must be discontinued with loss of irrigation flow or tight incisions. Improvements in phacoemulsification technology and cataract extraction techniques have significantly reduced thermal wound injuries. , Hyperpulse and microburst settings as well as torsional phacoemulsification handpieces generate less heat when compared to longitudinal handpieces, which can reduce the risk of thermal burns during surgery. , A survey of cataract surgeons in the United States and Canada showed that high surgical volume was the strongest independent variable relating to decreased rates of corneal contracture injury. Ophthalmic viscoelastic device (OVD) selection was also an important independent variable in the survey, not only because more viscous OVDs have the potential to disrupt intraoperative fluid dynamics, retain heat, and lead to thermal burns and endothelial damage, but also because certain OVDs, such as 2.3% sodium hyaluronate (Healon 5), have been shown to be exothermic when in contact with the phacoemulsification tip. Consequently, the importance of OVD irrigation and aspiration prior to the initiation of phacoemulsification cannot be overstated.

Femtosecond laser technology has also been implicated as a potential mechanism to decrease phacoemulsification time and thus reduce thermal burns. The femtosecond laser was introduced into cataract surgery in 2008. Numerous studies have now shown that femtosecond laser assisted cataract surgery (FLACS) allows physicians to make more precise anterior capsulotomies and reduce phacoemulsification time by using the laser to prefragment the lens nucleus. , Prefragmentation reduces ultrasound time, thus decreasing the heat generated by the phacoemulsification tip and reducing the incidence of thermal burns and early endothelial cell loss. These benefits are conferred because of the short laser pulse duration (10 ⁻¹⁵ seconds) resulting in minimal collateral damage to the surrounding tissues. Furthermore, femtosecond lasers have been shown to be effective for creating corneal wounds and arcuate incisions that potentially may reduce postsurgical astigmatism.

Descemet Membrane Tear/Detachment

Small tears in the Descemet membrane occur frequently, especially adjacent to corneal incisions; however, they usually remain localized and do not result in vision loss. Small Descemet tears can enlarge during surgery to become detachments associated with corneal edema and vision loss. Descemet membrane detachments (DMDs) have been reported with cataract extraction, but also after a wide variety of ophthalmic procedures, including cyclodialysis, iridotomy, , trabeculectomy, , penetrating keratoplasty, full-thickness lamellar keratoplasty, endothelial keratoplasty (EK), pars plana vitrectomy, holmium laser sclerostomy, and viscocanalostomy. Risk factors for DMD have changed since the days of intracapsular cataract surgery where α-chymotrypsin and cryo probe tip contact with the endothelium were major factors. Today, blunt knife entry, oblique insertion of instruments, and entry of instruments and viscoelastics into a false plane above the Descemet membrane represent the most common risk factors. Alternative risk factors for DMD include a history of ocular conditions disrupting the Descemet membrane such as congenital glaucoma, birth forceps injury, keratoconus, and Terrien marginal degeneration ( Fig. 96.2 ). Clear corneal phacoemulsification incisions have an increased association with Descemet tears when compared to scleral tunnel incisions with extracapsular cataract extraction, due to repeated insertion and removal of the phacoemulsification probe with high-flow irrigation and a tight incision, which can strip the Descemet membrane. The detachment can be noted in the immediate postoperative period or weeks later.

DMDs can spontaneously reattach with medical treatment alone, with a mean resolution time of 9.8 weeks. , With large detachments or slow resolution, descemetopexy with air, sulfur hexafluoride (SF ₆ ), , , perfluoropropane 14% (C ₃ F ₈ ) gas injections, sodium hyaluronate, , or through-and-through corneal mattress sutures may help and can be repeated. , , Bullous keratopathy or corneal scarring may occur, requiring endothelial or penetrating keratoplasty in 11%–13% of cases. ^{19,36,38,49–52}

Infectious Keratitis

Infectious keratitis with permanent corneal scarring can occur with clear corneal surgery, with bacterial keratitis and fungal keratitis presenting in the early and late postoperative period, respectively. Infectious keratitis is more commonly seen adjacent to the corneal incision site, with use of sutures, after intrastromal ring insertion and in association with endophthalmitis. Herpes simplex keratitis can flare in patients with a previous history of herpetic disease. Long-term follow-up and early recognition of infectious keratitis allow for better resolution. Corneal cultures can help guide treatment of the keratitis and possible associated endophthalmitis. Prophylaxis with povidone-iodine (PI) and intracameral and topical postoperative antibiotics may reduce risk of endophthalmitis and keratitis. Patients with a history of herpes simplex keratitis may need oral antiviral prophylaxis to reduce the risk of reactivation. Additionally, adhesive bandages can be used for closure of clear corneal incisions, which may further limit suture-induced complications, such as infective keratitis and suture-induced astigmatism after cataract surgery ( Fig. 96.3 ). However, it remains to be seen if physicians will shift away from hydration and suture closure of clear corneal incisions.