Report: CKD Severity Linked to Thinning of Retina, Choroid Layers

Changes in tissue thickness in the back of the eye can correlate with worsening or improvement of renal problems and could help predict who will have worsening of kidney function, a new analysis report finds. 

The research, published in the journal Nature Communications, is the first to show an association between chronic kidney disease (CKD) and the thickness of the retinal and choroidal layers in the back of the eye as measured by optical coherence tomography (OCT), a noninvasive imaging technology commonly used to evaluate eye diseases such as age-related macular degeneration (AMD), diabetic eye disease, and retinal detachments.

"These are common scans that people get at the opticians and now in many hospitals," said Neeraj Dhaun, MD, PhD, a professor of nephrology at the University of Edinburgh, Scotland. (Opticians in the United Kingdom are the equivalent of optometrists in North America.) 

CKD Severity Equals Thinner Retinas

"We scanned the back of eye of healthy people as well as patients with various types and degrees of kidney disease, and we found that two layers in the back of eye, the retina and the choroid, were thinner in patients with kidney disease compared to people who are healthy, and that the extent of this thinning predicts whether kidney function would decline going forward over a period of 2 or 3 years," Dhaun, the corresponding author of the new paper, said.

The publication is a report of four different studies. The first study measured OCT metrics in 112 patients with CKD, 92 patients with a functional kidney transplant, and 86 control volunteers. The researchers found the retina was 5% thinner in patients with CKD than in healthy controls. They also found that patients with CKD had reduced macular volume: 8.44 ± .44 mm³ vs 8.73 ± .36 mm³ (P < .001). The choroid was also found to be thinner at each of three macular locations measured in patients with CKD vs control volunteers. At baseline, CKD and transplant patients had significantly lower estimated glomerular filtration rate (eGFR) at 55 ± 27 and 55 ± 24 mL/min/1.73 m² compared with control volunteers at 97 ± 14 mL/min/1.73 m².

The second study reported on OCT measurements and kidney histologic injury in 50 patients who had a kidney biopsy within 30 days of their OCT. It found that choroidal thinning at all three macular locations was independently associated with more extensive kidney scarring. 

The third study focused on 25 patients with kidney failure who had a kidney transplant. Their eGFR improved from 8 ± 3 to 58 ± 21 mL/min/1.73 m² in the first week after the transplant. The choroid in these patients thickened about 5% at 1 week and by about 10% at 1 month posttransplant. OCT of 22 kidney donors showed thickening of the choroid a week after nephrectomy before a tendency to thinning over the next year.

The fourth study found that for patients with stable CKD, every 1 mm³ decrease in macular volume correlated to an increased odds of a decline in eGFR by more than 10% at 1 year (2.48; 95% CI, 1.26-5.08; P = .01) and by more than 20% at 2 years (3.75; 95% CI, 1.26-5.08; P = .004).

Exploring the Kidney-Eye Connection 

The potential explanation for the correlation between retinal and choroidal thickness and kidney function is unclear, Dhaun said. 

"We don't know the exact mechanisms, and these are difficult to define from studies in patients, which is why we are doing more work in animal models of kidney disease to see if we can establish the pathways that lead to the changes in the eye," he said. 

"However," Dhaun added, "what we do know is that kidney disease affects the whole body. For example, kidney disease can lead to high blood pressure and heart disease, as well as diseases in the brain, and it is these effects of kidney disease on the body as whole that we are probably picking up in the back of the eye." 

OCT has the potential to make the monitoring of patients with CKD and kidney transplant more convenient than it is now, Dhaun said. "These scanners are available in the community, and what would be ideal at some point in the future is to be able to do a patient's kidney health check in the community potentially incorporating OCT scanning alongside blood-pressure monitoring and other healthcare measures," he said.

"The findings provide an exciting example of how noninvasive retinal imaging using OCT can provide quantitative biomarkers of systemic disease," Amir Kashani, MD, PhD, the Boone Pickens Professor of Ophthalmology and Biomedical Engineering at the Wilmer Eye Institute of Johns Hopkins University in Baltimore, told Medscape Medical News. "It is striking that their findings demonstrate some potential of reversible changes in choroidal perfusion after kidney transplantation."

The finding that choroidal thickness changes in CKD are at least partly reversible with kidney transplantation is a revelation, Kashani said, and may point to a greater role for ophthalmologists in managing systemic disease. 

"Ophthalmologists can and should use their unique experience and understanding of the eye to help monitor and manage systemic conditions in collaboration with our medicine colleagues," he said. "There are many systemic diseases that can impact the eye and ophthalmologist are uniquely positioned to help interpret those findings."

Kashani noted that a particular strength of the report was the comparison of choroidal measurements in patients who had kidney transplantation and those that had a nephrectomy. "The consistent direction of changes in these two groups suggests the study findings are real and meaningful," he said.

The study was independently supported. Dhaun and co-authors report no relevant financial relationships. Kashani disclosed a financial relationship with Carl Zeiss Meditec. 

Richard Mark Kirkner is a medical journalist based in the Philadelphia area.