Pre- and post-HD reproducibility of SFCT measurements in diabetic nephropathy patients were investigated in this study. Overall, pre-HD SFCT measurements were associated with significantly lower intra-session reproducibility values, including ICC, COV, and TRTV, compared to post-HD SFCT measurements.
The relationship between SFCT and various retinal diseases is becoming more understandable as OCT technology advances. Several studies have focused on the role of SFCT in especially diabetic retinopathy and its treatment. Farias et al ., reported choroidal thinning prior to diabetic retinopathy, as well as the association of thin choroid with microalbuminuria. By describing the short-term anatomic and functional responses to anti-VEGF therapy in patients with thicker SFCT, Rayes et al ., highlighted the significance of SFCT as a prognostic marker in the treatment of diabetic macular edema. Moreover, several factors, including AL, age, body mass index, diurnal variation, and systolic blood pressure, have been reported to affect choroidal thickness in healthy individuals [17–20].
Subfoveal CT has also been measured before and after HD in previous studies, with the majority of them reporting lower post-HD SFCT values [21–25]. This could be ascribed to a decreased osmotic gradient in serum and choroidal interstitium as a result of post-HD decreased serum osmolality. A study published by Chang et al ., reported a correlation between decreased serum osmolality, body weight and a low systolic blood pressure, and lower SFCT. In addition to a significantly lower post-HD IOP (P < 0.001), our study's findings of a significantly lower post-HD SFCT compared to pre-HD SFCT (P < 0.001) in diabetic nephropathy patients who had HD for nearly five years were in line with previous reports. An increase in post-HD SFCT, on the other hand, has been observed in another study . This finding, which is inconsistent with our study, could have resulted from misleading measurements caused by the low reproducibility of pre-HD SFCT.
Various studies have addressed SFCT reproducibility, and it has been noted that SFCT reproducibility ranges between 0.89 and 0.99, especially in healthy individuals [27, 28]. A study of neovascular age-related macular degeneration patients conducted by Hanumunthadu et al ., revealed that swept-source OCT could detect SFCT changes ≥ 57.2 µm. They also noted that SFCT changes > 35 µm in SD-OCT could be detected in the same group of patients. Further, Puigdollers et al ., reported that swept-source OCT can be used to measure SFCT with high reproducibility in patients with diabetic macular edema. Furthermore, SFCT measurements taken from the edge of choroidal stroma have been reported to be more reproducible . Contrastingly, another study found no difference in SFCT reproducibility between healthy subjects and patients with diabetic retinopathy . And, the presence of subretinal fluid has been shown to decrease CT reproducibility, which has been attributed to fluid signal attenuation and shadowing caused by the subretinal fluid . Besides, several studies have found that as choroid thickness increases, reproducibility decreases [11, 12]. Pre-HD SFCT measurements had lower reproducibility in our study. Several hypotheses have been advanced to explain the lower pre-HD SFCT measurements. As previously stated, it is possible that increasing SFCT has a negative impact on reproducibility. Another possibility is that chronic renal failure may cause an increase in extracellular fluid volume, resulting in hemodynamic instability.
We acknowledge the limitations of this study. Importantly, the size of the study population was just not high enough to improve the efficacy of our study. The measurements were carried out only horizontally. Moreover, we evaluated only the reproducibility of SFCT, which was the goal of our study. Again, residual influencing factors might have led to an unexplained analytical preference. Thus, long-term prospective studies with a larger sample size may yield clinically useful results in determining relatively accurate reproducibility of SFCT and other ocular microstructures not only before but also after HD in diabetic patients with and/or without diabetic nephropathy