Endothelial Cell Count in Subjects who Underwent Laser Photorefractive Surgery for Myopia or Keratoplasty for Keratoconus

PICHON-RIVIERE, A.; AUGUSTOVSKI, F. A.; GARCIA MARTI, S.; GLUJOVSKY, D.; ALCARAZ, A.; LOPEZ, A.; BARDACH, A.; CIAPPONI, A

Documento de Evaluación de Tecnologías Sanitarias

IECS

Año: 2012 p. 1 - 30

1668-2793

Myopia is a highly prevalent refractive disorder of the eye and it also contributes with other morbidities such as glaucoma or retinal detachment. Treatment is usually medical but eventually a surgical correction may be performed: Refractive surgery (e.g., radial keratotomy and photo-refractive keratectomy).Also, there are stromal diseases of the cornea such as the keratoconus which may also be surgically treated and account for one third of all the indications for keratoplasty (or cornea transplant).The cornea is made up of 5 cell layers; the inner layer is the endothelial layer consisting of a monolayer of cells which does not significantly divide. With time, the cell count decreases reaching approximately 2,400 ? 3,200 cells/mm2 in adulthood. The purpose of the endothelium is to remove the cornea stromal fluid from the cornea and to keep it clear. Some diseases may damage the corneal endothelium. This may also result from traumatic lesions, many of them due to certain surgical interventions. When these cells are damaged, cell loss takes place and cell count is decreased. Recovery from the corneal edema is usually faster in those individuals whose endothelial cell count is higher, this making a big difference when the surgery is carried out in young adults or in the elderly.The use of endothelial cell count is proposed as a prognostic factor for surgeries of the cornea.TechnologySpecular microscopy is a non-invasive procedure that allows to analyze the shape of the corneal endothelium cell layer. The endothelial cell count is based on cells/mm2-average cell area (µm2) ratio.PurposeTo assess the evidence available on the efficacy, safety and issues related with coverage policies for the use of endothelial cell count in patients who underwent laser photo-refractive surgery for myopia or keratoplasty for keratoconus.MethodsA bibliographic search was carried out on the main databases: DARE, NHS EED, on Internet general search engines, in health technology evaluation agencies and health sponsors. Priority was given to the inclusion of systematic reviews; controlled, randomized clinical trials (RCTs); health technology assessments and economic evaluations; clinical practice guidelines and coverage policies of other health systems.ResultsA search was made for evidence of therapeutic strategies based on endothelial cell count in patients with keratoconus or myopia who underwent laser photoreactive surgery. Also, studies evaluating the diagnostic accuracy of endothelial cell count in this clinical setting were also sought. No studies that can be included in this report were found. Clinical practice guidelines mentioning its used were not found either.Finally, there was a search for the usefulness that endothelial cell count may have as prognostic factor in these patients. Only one model evaluating if the density or loss of endothelial cells may predict long-term progress was found but it was only applicable to patients who underwent penetrating keratoplasty or deep anterior lamellar keratoplasty.One study published in 2009 generated a multivariable regression model intended to predict long-term prognosis of corneal transplant in a cohort of 1,144 patients (and 1,144 eyes), carried out between 1992 and 2006. Up to 2002, keratoplasties were carried out in all the cases, thereafter, only when endothelial involvement was more than moderation (otherwise, deep anterior lamellar keratoplasty was carried out). Endothelial cell density was measured by wide field specular microscope. Mean follow up period was 40.5±32 months. A baseline high endothelial cell density was associated with a longer graft survival (r=0.7; p<0.01). A significant loss of endothelial cells during the first 2 years is associated with a high rate of graft failure (r=0.88; p<0.01).No additional related studies were found. Only clinical trials using endothelial cell count as success marker were found when comparing two different therapeutic strategies.ConclusionsNo studies providing scientific evidence of the usefulness of endothelial cell count in patients who undergo laser photorefractive surgeries for myopia or keratoplasty for keratoconus were found.Studies evaluating the diagnostic and predictive capability of endothelial cell count in this type of patients are required.