In the management of patients with glaucoma, the appropriate care over the patient’s lifespan will involve a strategy with multiple contingencies should the disease worsen. When faced with aggressive disease, we escalate therapy from eye drops to laser and then on to incisional surgery. Since some glaucoma surgical therapies have an average lifespan of five years or less, sequential surgeries may be required.
While the optic nerve may be the primary victim of glaucoma, the cornea may receive collateral damage, particularly from glaucoma surgery. Of course many patients with glaucoma may have endothelial disease at the time of diagnosis, particularly those with shallow anterior chambers, extended periods of elevated pressure or secondary glaucomas. There has been some data to suggest that laser iridotomy (with Nd:Yag or argon laser) may damage the corneal endothelium.1-2 A recent prospective longitudinal study in which patients with bilaterally occludable angles underwent unilateral iridotomy demonstrated that the endothelial cell count decreased similarly in both lasered eyes and the unlasered fellow eyes over 3 years, indicating that the narrow angle may be the primary cause of endothelial loss.3 Interestingly, there appears to be no significant endothelial cell loss from selective laser trabeculoplasty.4,5 Standard cataract extraction results in a loss of 5-10% of the endothelial cell count.6 Complicated cataract surgery, which occurs frequently in eyes with certain types of glaucoma (e.g., the exfoliation syndrome), can result in a significantly compromised corneal endothelium. Additionally, data has shown that both trabeculectomy and glaucoma shunt surgeries can result in endothelial decompensation, particularly if the glaucoma surgery is the second surgery for the eye. In the tube versus trabeculectomy study, 9% of trabeculectomy eyes and 16% of tube shunt eyes ended up with persistent corneal edema after 5 years, making this complication the most common.7 In other words, for patients with glaucoma requiring surgery, the risk of reduced visual function from corneal decompensation is second only to the risk of vision loss from optic nerve damage. Of course corneal edema can be reversed with a variety of surgeries. However, such interventions inevitably threaten the stability of the glaucoma.
What then is to be done to protect the cornea in our glaucoma patients? I believe that for patients with glaucoma that may require future surgical management, we should develop a corneal preservation strategy early on. For me, this includes a careful baseline corneal examination often along with a baseline endothelial cell count (and of course corneal thickness measurement) prior to the patient’s first surgical procedure in eyes that appear to be at risk. Depending on that patient's risk and baseline cell count, surgical techniques and perioperative management may be altered in favor of corneal preservation. In some cases, involving a cornea specialist prior to the next surgery may help with surgical planning.
In summary, corneal endothelial disease is common in surgical glaucoma patients. Taking a proactive approach to preserving the cornea could reduce an important, and perhaps preventable, cause of vision loss in glaucoma patients.
1. Wu SC, Jeng S, Huang SC, Lin SM. Corneal endothelial damage after neodymium: YAG laser iridotomy. Ophthalmic Surg Lasers. 2000 Sep-Oct;31(5):411-6.
2. Wilhelmus KR. Corneal edema following argon laser iridotomy. Ophthalmic Surg. 1992 Aug;23(8):533-7.
3. Kumar RS, Baskaran M, Friedman DS, Xu Y, Wong HT, Lavanya R, Chew PT, Foster PJ, Aung T. Effect of prophylactic laser iridotomy on corneal endothelial cell density over 3 years in primary angle closure suspects. Br J Ophthalmol. 2013 Mar;97(3):258-61.
4. Lee JW, Chan JC, Chang RT, Singh K, Liu CC, Gangwani R, Wong MO, Lai JS. Corneal changes after a single session of selective laser trabeculoplasty for open-angle glaucoma. Eye (Lond). 2014 Jan;28(1):47-52.
5. Ong K, Ong L, Ong LB. Corneal Endothelial Abnormalities After SLT. J Glaucoma. 2013 Apr 29.
6. Faramarzi A, Javadi MA, Karimian F, Jafarinasab MR, Baradaran-Rafii A, Jafari F, Yaseri M. Corneal endothelial cell loss during phacoemulsification: bevel-up versus bevel-down phaco tip. J Cataract Refract Surg. 2011 Nov;37(11):1971-6.
7. Gedde SJ, Schiffman JC, Feuer WJ, Herndon LW, Brandt JD, Budenz DL; Tube versus Trabeculectomy Study Group. Treatment outcomes in the Tube Versus Trabeculectomy (TVT) study after five years of follow-up. Am J Ophthalmol. 2012 May;153(5):789-803.
Dr. Nathan M. Radcliffe is the director of the glaucoma service and a clinical assistant professor at
New York Univeristy Langone Ophthalmology Associates and is a cataract and glaucoma surgeon at
the New York Eye Surgery Center.