Phaco and corneal disease

Low endothelial cell density a challenge in cataract cases.

Dermot McGrath

Posted: Saturday, June 6, 2020

Cataract surgery in cases of low endothelial cell density remains a challenging proposition even for more experienced surgeons, according to Vincenzo Scorcia MD.

“Performing cataract surgery alone in patients with a low endothelial cell count is very challenging, mainly because of the high risk of endothelial damage from the phacoemulsification. It makes it a difficult decision for the surgeon to decide whether to proceed with cataract surgery alone or to combine it with keratoplasty,” he told delegates attending the joint ESCRS/EuCornea Symposium at the 37th ESCRS Congress.

Dr Scorcia said that there are several issues to be addressed before embarking on cataract removal in patients with pathologies such as Fuchs’ endothelial corneal dystrophy (FECD), which is the most common indication, or those who have previously undergone penetrating keratoplasty or experienced complications from anterior chamber phakic IOL implantation.

“We need to ask if the patient could improve their vision from cataract surgery alone, so we need to determine if the main problem is the cataract or the corneal disease,” he said.

Cataract-related symptoms include blurred vision and glare as well as change in refraction, which is often a myopic shift induced by cataract.

Corneal symptoms are typically represented by glare, said Dr Scorcia, University of Magna Graecia, Catanzaro, Italy. In the early stages this is characterised by an increasing number of guttata in the centre of the cornea even if the light transmission is normal, he said.

“The debilitating symptoms can occur even when there is little to no stromal or epithelial oedema and the pachymetry is relatively normal,” he said.

Light scattering starts to occur at more advanced stages of guttata, explained Dr Scorcia, and is related to increased corneal thickness and subsequent light scattering caused by separation of the collagen fibrils of the cornea.

“At this point the patients usually complain of a degradation of visual acuity and this problem is more prevalent in the morning,” he said.

Once the surgeon decides to proceed with phacoemulsification, the next key issues are to assess the risk of corneal decompensation after cataract surgery and then to determine which preoperative parameters should be considered as risk factors for corneal failure, said Dr Scorcia.

He pointed out that the threshold number of endothelial cells necessary to main corneal deturgescence, which is the state of dehydration necessary to maintain the transparency of the cornea, is currently unknown. Furthermore, non-uniform endothelial cell loss often results in sampling errors.

“We know that peripheral endothelial cells have a higher density than in the central part of the cornea, yet the cells are usually counted only in the central zone so we are lacking a lot of valuable information about the reservoir of cells in the periphery,” he said.

Dr Scorcia added that it is also difficult to obtain an accurate count of endothelial cells in the presence of corneal oedema, which leads to poor specular microscopy images.

Another key parameter is preoperative central corneal thickness (CCT), which above a threshold of 640 microns is usually considered predictive of corneal decompensation in FECD patients.

“We should perhaps treat this as a guide rather than a strict rule, since we still do not know what the normal thickness value should be and there is poor reliability of ultrasound pachymetry readings. There is also a very high diurnal variation of CCT in patients with FECD, which hinders identification of true corneal thickening,” he said.

Previous studies have shown up to 90% of Fuchs’ patients who underwent cataract surgery did not need corneal transplants and achieved a postoperative best-corrected visual acuity of 20/35, said Dr Scorcia.

“In a large number of cases, opting for cataract extraction alone despite endothelial pathology may be a good option because the patients are often satisfied with less than perfect visual outcomes and it avoids the potential complications associated with endothelial keratoplasty,” he said.