Protection of corneal endothelium during cataract surgery is critical for achieving good visual outcomes. Maintenance of corneal clarity relies heavily upon the functionality of healthy endothelial cells and an intricate pumping system designed to remove fluid from the corneal stroma. It is well known that some degree of endothelial cell loss will be present after any cataract surgery [1–3,4▪,5,6]. Significant loss of endothelial cells during cataract surgery may lead to prolonged corneal edema and, in severe cases, may result in corneal decompensation often associated with decreased vision. In this era, where expectations for favorable visual results following cataract surgery have continued to increase, the preservation of corneal endothelium becomes even more important.
Cataract surgery has evolved greatly in recent decades. New surgical techniques and instrumentation have made cataract surgery less invasive, with more rapid visual rehabilitation. But, how have these advances reduced the stress to the corneal endothelium during surgery? Comparing intracapsular cataract extraction with conventional large-incision extracapsular cataract extraction, the rate of endothelial cell loss after intracapsular extraction has been reported to be between 11.6 and 17.1% compared with 13.6–17.0% following conventional extracapsular surgery [1,2]. An early publication in 1984 compared corneal endothelial cell loss after phacoemulsification versus conventional extracapsular cataract surgery and found no significant difference in endothelial cell loss between the two groups (10.7% cell loss for extracapsular and 10.0% cell loss for phacoemulsification) . A recent publication of a randomized controlled trial in India revealed similar endothelial cell loss between phacoemulsification and the small-incision extracapsular cataract surgery (SICS) 6 weeks after the procedure (15.5% in the phaco group versus 15.3% in the SICS group) with comparable final visual results in both groups [4▪]. A similar reduction in endothelial cell count after SICS was also validated in another publication . Another study by Bourne et al. compared phacoemulsification to conventional extracapsular cataract extraction and their impact on corneal endothelial cell loss. No significant difference in overall corneal endothelial cell loss was found between these two procedures (16.2% in phaco group versus 14.1% in extracapsular group). These authors reported an increased risk of severe corneal endothelial cell loss with phacoemulsification in patients with dense cataracts (52.6% with phaco versus 23.1% with extracapsular extraction). Interestingly, other studies have reported more favorable figures, estimating the rate of endothelial cell loss after phacoemulsification to be between 1.2 and 12% [7–9].
When performing phacoemulsification, different surgical approaches may dictate the amount of ultrasound energy used and, therefore, its impact on corneal endothelium. Park et al. evaluated the difference in endothelial cell loss in both the stop-and-chop technique, as well as the phaco-chop technique. They also compared the use of ultrasound energy in both groups and determined that the phaco-chop technique required lower ultrasound energy than the stop-and-chop technique on dense cataracts. Nonetheless, the endothelial cell loss was similar in both groups. When comparing the phaco-chop technique versus the divide-and-conquer technique, a 3-month follow-up study did not reveal any statistically significant difference in the endothelial cell loss after cataract surgery using either technique, although the phaco-chop technique required less phaco power . Furthermore, Faramarzi et al. demonstrated that, when performing the stop-and-chop technique, the position of the phaco tip may influence the rate of endothelial cell loss after cataract surgery. They report that after phaco surgery the rate of corneal endothelial cell loss was statistically higher when the phaco tip was in the bevel-down position than when the tip was in the conventional bevel-up position (13.6 versus 5.9%, respectively).
Then the question arises concerning what intrinsic patient factors may influence endothelial cell loss after cataract surgery. Diabetes mellitus, with its induced metabolic stress, has been proposed as a possible risk factor for increased endothelial damage after cataract surgery [13▪▪,14]. Recent data comparing endothelial cell count 3 months after phacoemulsification surgery in diabetic and nondiabetic patients revealed a significant increase in the rate of endothelial cell loss in the diabetic patients group (6.2% in diabetics versus 1.4% in nondiabetics) [13▪▪]. A similar conclusion was established in another study looking at endothelial cell loss in manual SICS in diabetic patients . In this study, a statistically significant difference between the diabetic and the age-matched nondiabetic group was demonstrated, the diabetic group notably presenting with a greater decrease in endothelial cell count (16.58 vs. 19.24%). Another group of patients deserving special consideration during cataract surgery are the patients with low corneal endothelial cell density preoperatively, who are more susceptible to any endothelial cell loss. This group includes patients with Fuchs corneal dystrophy, patients with previous viral or syphilitic keratitis, and patients with previous intraocular inflammation or trauma, among others . Hayashi et al. compared the rate of endothelial cell loss in patients with low preoperative endothelial cell density (<1000 cells/mm2) versus patients with normal endothelial cell density and discovered no significant difference in the percentage of cell loss between the two groups (5.1%, low-density group; 4.2%, control group). Seitzman et al. evaluated the use of preoperative pachymetry measurements in patients with Fuchs corneal dystrophy who underwent cataract surgery to predict the need of future corneal transplant for persisting corneal edema after cataract surgery. They concluded that patients with Fuchs and a preoperative pachymetry of 640 μm had an increased risk of corneal edema and deterioration in vision after cataract surgery, and for this reason they recommended to perform combined corneal transplant and cataract extraction in this group of patients.
Interestingly, the difference in rate of endothelial cell loss after cataract surgery is well documented in patient populations having undergone previous corneal transplant. A recent publication evaluated endothelial cell loss in patients undergoing cataract surgery by phacoemulsification after penetrating keratoplasty versus after deep anterior lamellar keratoplasty (DALK) [17▪▪]. They also evaluated the rate of endothelial cell loss after cataract surgery in patients without previous corneal surgery. This study demonstrated an increase in the rate of endothelial cell loss in patients with previous penetrating keratoplasty (43.99%) when compared with normal corneas (12.39%) and patients with previous DALK (11.22%) after a 1-year follow-up. These findings may indicate that preservation of the patients’ endothelium in DALK surgery may help not only graft survival but also may provide greater safety for the corneal endothelium in the case of future anterior segment surgery. Similar results were presented previously by Kim and Kim  comparing endothelial cell loss after cataract surgery in patients with previous penetrating keratoplasty (58.1%) versus patients with normal corneas (14.98%) after a 2-year follow-up.
These aforementioned findings then beg the question, what can be done to protect the corneal endothelium during phacoemulsification? The use of viscoelastic materials during cataract surgery has been described since the 1970s. They have been used primarily for stabilization of the anterior chamber space during crucial steps of the surgery, such as during capsulorhexis and intraocular lens implantation, as well as protection of intraocular structures during phacoemulsification. Viscoelastic materials are commonly divided into two major groups, cohesive and dispersives based on their properties. Various publications have evaluated the efficacy of different viscoelastic materials in protecting corneal endothelium during phacoemulsification. Using a rabbit model, recently Ben-Eliahu et al. demonstrated that the use of the soft-shell technique (in which a dual layer of dispersive viscoelastic in contact with the corneal endothelium and cohesive viscoelastic maintaining the anterior chamber) provided better protection for corneal endothelium when compared with the use of a cohesive viscoelastic alone. Another recent study in humans revealed that, in uneventful cataract surgery, the use of a dispersive viscoelastic led to a reduction of endothelial cell density of 1.2% compared to 9.6% associated with the use of a cohesive viscoelastic .
Modifications in phacoemulsification technology, like the use of torsional ultrasound energy, have introduced newer, more effective modalities of cataract extraction, in comparison to the conventional longitudinal ultrasound. Compared with the jackhammer motion in conventional phaco, the torsional oscillation sheers the lens material with virtually no repulsion, thereby improving the flow of nuclear material into the phacoemulsification tip [20▪]. The rate of corneal endothelial cell loss with the use of torsional ultrasound has been compared to the conventional phaco. In two different studies, Kim et al. and Bozkurt et al. reported a reduction in endothelial cell loss with the use of torsional ultrasound (3.19–4.2%) compared to conventional ultrasound (6.7–7.9%), but they could not demonstrate statistical significance in their findings [21,22]. On the other hand, Fakhry et al. reported a statistically significant reduction of corneal endothelial cell loss with the use of pure torsional ultrasound when compared with combined torsional and longitudinal ultrasound for eyes with hard cataracts .
Endothelial cell loss after cataract surgery is an inevitable consequence of the procedure. Nonetheless, important steps taken during cataract surgery and the perioperative period may influence the rate of endothelial cell loss and thus potentially improve the visual outcome of this common surgical intervention. Proper patient selection and education, meticulous surgical technique, and good postoperative care are important for maintaining a clear cornea with excellent visual potential.
The authors would like to acknowledge Landon Meekins.
Conflicts of interest
N.A.A. receives research funding from Research to Prevent Blindness.
The authors do not report any conflicts of interest.
REFERENCES AND RECOMMENDED READING
Papers of particular interest, published within the annual period of review, have been highlighted as:
- ▪ of special interest
- ▪▪ of outstanding interest
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