Corneal Endothelial Cell Loss After Trabeculectomy Versus Combined Trabeculectomy Phakoemulsification and IOL Implantation

Corneal endothelial cells health and pumping function is crucial to permit corneal optical clarity by keeping the cornea in a relatively dehydrated state.1 The corneal endothelium is a single layer of hexagonal cells with uniform size and shape in normal conditions. When endothelial cell density diminishes, the remaining cells increase in size to cover the empty spaces left by the dead cells, and therefore there is a change in the size (polymegathism) and morphology (pleomorphism) of the remaining cells. Trauma or other insults often cause endothelial cell death, which is irreparable because these cells lack division capacity.2,3,4 Corneal endothelial damage has been associated with most types of intraocular surgeries including glaucoma and cataract surgeries.5,6,7,8 Cataract and glaucoma are the most common causes of visual impairment worldwide.9,10

Phacoemulsification and Intraocular lens (IOL) insertion, the most commonly performed method of cataract extraction in the developed world, was first described in 1967.11 This technique allows rapid visual rehabilitation postoperatively and low induced astigmatism.11 The reported average loss of central corneal endothelial cells after phacoemulsification vary between 4% and 25%.8 Trabeculectomy, introduced by Cairns in 1968 12, is the most commonly performed incisional glaucoma procedure worldwide and has become the glaucoma filtering procedure of choice in glaucoma patients 5,13,14 with advanced glaucoma or poor tolerance or uncontrolled IOP despite of multiple topical or systemic medications with the goal of preserving vision and reducing the likelihood and rate of visual field loss and optic nerve changes in susceptible patients by reducing the intra ocular pressure (IOP) as the major risk factor.15,16 The use of anti-metabolites specifically Mitomycin C (MMC) as a supplement to trabeculectomy with more favorable effect on the outcome was reported by Chen 17 and Palmer 6 in the early 1990s5 showing eyes treated with MMC-augmented trabeculectomy have lower intraocular pressure (IOP) than eyes treated with trabeculectomy only.12 About 8.7% loss in central endothelial cells was reported after 3 months follow up in patients with Trabeculectomy with augmented Mitomycin C (MMC).7 Combined Trabeculectomy with Cataract surgery (Phacoemulsification and IOL insertion) can be performed based on the need to restore cataract-impaired visual acuity in trabeculectomy candidates.9,18 Given available results of previous studies on the effects of each of above mentioned procedures on corneal endothelial cells7,8, it is presumed that combined trabeculectomy with phacoemulsification and IOL insertion would have a cumulative effect on central corneal endothelial cell loss.

Specular microscopy is a non-invasive technique to assess the structure and function of the corneal endothelium by permitting visualization of the corneal endothelial mosaic.19 It is the standard method of endothelial cell analysis worldwide. By counting the number of the cells in measured areas of the cornea, an estimate of endothelial cell density can be made.

There is only one retrospective study available comparing central corneal endothelial cell loss after Trabeculectomy versus combined Trabeculectomy, Phacoemulsification and IOL insertion.2 There is also very limited data available to determine whether the expected damage is a non-progressive short-term effect or a progressive consequence which can lead to corneal endothelial decompensation. The investigator's aim is to evaluate and compare the effects of above mentioned procedures on central corneal endothelial cells health and density. The results of this study could help glaucoma surgeons make proper decisions in performing combined versus single surgeries in patients with initial risk factors for corneal decompensation.

3. Hypothesis The hypothesis of this study is that combined trabeculectomy, phacoemulsification and IOL implantation has more effect on corneal endothelial cell loss than trabeculectomy alone.