Oct. 15, 2016
In a prospective cohort study conducted at Mayo Clinic's campus in Rochester, Minnesota, researchers found that patients' visual acuity continued to improve through five years after Descemet stripping endothelial keratoplasty (DSEK) for Fuchs' endothelial corneal dystrophy (FECD) and was associated with evidence of optical and anatomic repair.
"Prior studies have been retrospective. This study, however, assessed standardized visual function, optical quality and anatomic properties of eyes with FECD through five years after primary DSEK," says Sanjay V. Patel, M.D., Ophthalmology chair at Mayo Clinic in Rochester, Minnesota. Study outcomes were published by Katrin Wacker, M.D., and others in an issue of Ophthalmology in 2016.
In DSEK, abnormal host Descemet membrane and endothelium are removed and replaced by donor Descemet membrane and endothelium with a variable thickness of donor corneal stroma. Because DSEK does not disrupt the anterior corneal surface, visual function and quality of life improve quickly for patients after DSEK. Many patients also experience better uncorrected distance visual acuity and less astigmatism after the treatment, compared with penetrating keratoplasty. Five-year graft survival also is comparable. As a result, vision (as well as graft survival) is now a primary outcome measure of corneal transplantation.
Structural change assessment
The impact and reversibility of structural changes in the host cornea on optical long-term outcomes after endothelial keratoplasty are unknown. Changes may include residual anterior corneal haze, increased anterior surface high order aberrations and subepithelial ﬁbrosis, which begin in the early stages of FECD.
To assess those structural changes, researchers determined associations between visual function (acuity and disability glare) and anatomic changes (corneal and graft thickness, and corneal haze). They hypothesized that the remodeling of anatomic structures was associated with visual rehabilitation. They also evaluated graft survival and endothelial cell loss through five years.
The study included 52 eyes of 45 patients with FECD undergoing primary DSEK between October 2006 and March 2010. Participants were examined before surgery and at ﬁxed intervals through 60 months. At each visit:
- Graft survival was determined by slit-lamp examination.
- Best spectacle-corrected visual acuity was measured using the electronic Early Treatment Diabetic Retinopathy Study protocol.
- Total anterior corneal high order aberrations were derived from corneal topography.
- Corneal backscatter, corneal thickness and endothelial cell density were measured from confocal microscopy images. Corneal thickness was also measured by ultrasonic pachymetry.
"Best spectacle-corrected visual acuity continued to improve between one and five years after DSEK to a mean of 20/25," says Dr. Patel. "This change was accompanied by improvements in corneal backscatter and optical aberrations, suggesting gradual repair of the host cornea after resolution of corneal edema, and with mean total corneal thickness being approximately 700 µm." Several factors may be related to the continued vision improvement:
- Visual acuity is affected by high order aberrations that degrade the center of the retinal image point-spread function, and thus the modest improvement in anterior corneal high order aberrations may be one explanation for improvement in visual acuity.
- Increased anterior corneal high order aberrations may result from anatomic abnormalities in the subepithelial zone, such a subepithelial fibrosis, and may also be associated with anterior corneal haze in these eyes.
Endothelial cell loss
The greatest endothelial cell loss occurred by one month after DSEK (24 percent). Researchers found endothelial cell loss of 32 percent at one year. Thereafter, the annual rate of cell loss was approximately 7 to 9 percent, resulting in cell loss of 55 percent at five years.
The annual rate of endothelial cell loss between three and five years after DSEK (9.3 percent) was similar to that between three and five years after penetrating keratoplasty (8.8 percent) and was markedly different than the rate in healthy unoperated eyes.
An Australian Corneal Graft Registry study, published by Douglas J. Coster, M.D., and others in Ophthalmology in 2014, suggests worse graft survival with endothelial keratoplasty compared with penetrating keratoplasty. "Our research also found that late endothelial failure for FECD in otherwise healthy eyes still occurs, and accelerated endothelial cell loss persists in the remaining grafts, similar to after penetrating keratoplasty," says Dr. Patel. "The likelihood of corneal clarity 10 or more years after endothelial keratoplasty appears similar or no worse to that after penetrating keratoplasty, and graft longevity is an important consideration if evolving allograft techniques lead to earlier surgical intervention."
For more information
Wacker K, et al. Descemet stripping endothelial keratoplasty for Fuchs' endothelial corneal dystrophy. Ophthalmology. 2016;123:154.
Coster DJ, et al. A comparison of lamellar and penetrating keratoplasty outcomes: A Registry study. Ophthalmology. 2014;121:979.