New research published in Nature Communications examined the use of retinal optical coherence tomography (OCT) for indicating novel biomarkers to monitor and track chronic kidney disease (CKD) patients.
Let’s start with some background.
Prior studies have found that the functionality and structure of the eye and kidney are similar, with matching chorioretinal and corticomedullary oxygen gradients (respectively) just two of the resembling features.
Further, the eye is noted as being the only part of the human body in which microvascular circulation—the flow of blood through the circulatory system’s smallest vessels—can be non-invasively viewed.
And the significance of this, you may ask? Blood flow is typically affected in the presence of kidney disease.
Now this research.
Investigators from the University of Edinburgh in Edinburgh, Scotland, conducted a series of prospective cross-sectional and longitudinal studies by enrolling four categories of participants:
- Patients with pre-dialysis CKD
- Patients with kidney failure undergoing kidney transplantation
- Living kidney donors
- Healthy volunteers
These categories were divided into three groups, encompassing 300 participants:
- 112 with CKD due to a range of etiologies
- 92 with a functional kidney transplant (received on average ~7 years prior)
- 86 healthy volunteers
What studies were conducted?
Four total:
- Study 1: OCT metrics in health, CKD and post-kidney transplantation (n = 300)
- Study 2: OCT metrics and kidney histological injury (n = 50)
- Study 3: Reversal of choroidal thinning with gain of GFR + choroidal thinning with loss of GFR (n = 25)
- Study 4*: Macular volume and choroidal thickness (across three locations) independently associate with eGFR decline in CKD (n = 262)
Note: eGFR refers to estimated glomerular filtration rate, or the measure of how well the kidneys are working.
*Based on 1- and 2-year outcomes.
Let’s focus on study 1: How did the retina present in these groups?
For CKD patients, the retina was thinner compared to healthy volunteers (particularly in the central retina, by 5%).
Similarly, the macular volume was also reduced in CKD: Healthy volunteers (8.73 ± 0.36 mm3) vs. CKD (8.44 ± 0.44 mm3), p < 0.001
Both retinal thinning and macular volume were also apparent in kidney transplant recipients compared to healthy volunteers, and “were similar in magnitude to those seen in patients with CKD,” according to the investigators.
To note, retinal nerve fiber layer (RNFL) did not differ between the three groups.
Was gender indicative of anything?
Per the researchers, no. There was no difference noted in retinal thickness, macular volume, or RNFL thickness between genders.
Were macular volume and choroidal thickness impacted by eGFR?
In Study #4, OCT images indicated the mean macular volume was 8.3 ± 0.4 mm3 and mean choroidal thicknesses were 203 ± 81 μm, 276 ± 85 μm and 257 ± 77 μm at locations 1, 2, and 3, respecitvely.
eGFR declined by ≥10% at 1 year and ≥20% at 2 years in 38% (100/262) and 23% (60/262) of CKD patients, respectively.
Expert input on this?
Based on the findings, investigators concluded that eGFR is a key indicator of kidney function in patients with CKD, where, they wrote, “the greater the severity of kidney disease (reflected by a lower eGFR, the thinner the retina and choroid.”
This was dependent on age, they noted.
Any relationship between kidney disease and RNFL?
Nope, no association was found, including at any level of eGFR in kidney disease.
The researchers noted that this was in line with previous findings.
Conclusion on retinal thickness?
Patients with kidney failure undergoing a kidney transplant had a rapid thickening of the retina and choroid (suggesting improvements in vascular flow and/or function), according to the authors.
The data suggests a generalized increase in retinal thickness and, as a result, macular volume was observed, “rather than focal accumulation of intra or sub-retinal fluid, which appears more evident in central regions,” they stated.
However, the implications of this finding were noted as being “beyond the scope of our study, but will be an important part of future work as ocular disease is common in these patients.”
See here for a more in-depth look at the findings, including a breakdown of each of the four study methods and conclusions.
So what’s next?
The authors noted the need for further, longer-term clinical studies with a larger number of participants to more accurately determine the potential benefits of using such OCT imaging technology in a routine clinical setting.