Ocular problems have been reported to exist in patients with end-stage renal disease (ESRD). Discounting ageing itself, which is a known risk factor for glaucoma, older patients with ESRD on haemodialysis (HD) are more likely to have glaucoma. Intraocular pressure (IOP) is a major risk factor for the development and progression of glaucomatous disease, and transient changes in IOP have been reported during HD in patients. This topic is controversial in the literature; whereas elevated IOP is reported in most of the studies as a risk factor for glaucoma development and progression, some results have shown no changes or a decrease in IOP during an HD session. A possible hypothesis that explains the serious increase of IOP during HD involves a potential connection with the rapid decrease in serum osmolarity during dialysis, resulting in an osmotic gradient between the plasma and intraocular fluids due to the presence of the blood-ocular barrier, which can draw water from the plasma into the eye. In eyes that have an obstructed aqueous outflow pathway, it is not possible to have a good aqueous humour drainage, which results in IOP elevation. In addition, it was suggested that the change in IOP during HD correlated with the change in plasma colloid osmotic pressure and bodyweight.¹
This cross-sectional study was designed to evaluate the effects of one session of HD on IOP and its relationship with ultrafiltration rate. The authors’ population consisted of 67 patients, 35% of which were female, with a mean age of 53.2±11.5 years and who were under conventional intermittent HD for at least 3 months. Patients receiving glaucoma treatment, with corneal abnormalities, history of corneal surgery, allergy to topical anaesthetic agents, or a current eye infection, were excluded. Measurements were made at two time points, using a pneumotonometer with the patient in a seated position: approximately 15 minutes before starting HD (T1), and approximately 15 minutes after ending HD (T2).² Pre-HD and post-HD plasma osmolarity were also analysed. Plasma osmolarity was calculated as: plasma osmolarity = 2(Na) + [(glucose)/18] + [(SUN)/2.8], where Na indicates plasma sodium ion concentration (mMol/L), glucose indicates plasma glucose concentration (mg/dL), and SUN indicates levels of serum urea nitrogen (mg/dL). The authors multiplied by 0.0555 and 0.3570, respectively, to convert glucose and SUN to mMol/L.2
Blood pressures were also measured at these times. In addition, ultrafiltration rate was calculated for each patient. Echocardiographic studies were performed prior to and 30–60 minutes following the dialysis session. Mean inferior vena cava diameter (IVCD) was expressed as (IVCD in inspiration + IVCD in expiration)/2. IVCD was adjusted for body surface area.
During evaluation, the authors found that laterality of the eyes (right or left) had no significant effect on the pre-dialysis and post dialysis IOP values. Significant increases in IOP and decreases in plasma osmolarity, systolic blood pressure, and IVCD were found post-dialysis session (p<0.012, p<0.034, p<0.39, and p<0.45, respectively). Changes in the IOP correlated with ultrafiltration rate (correlation coefficient [r]=-0.5; p<0.01) and differences in IVCD (r=0.4; p<0.01). However, there was no significant correlation between changes in IOP and plasma osmolarity (r=-0.2; p>0.2).
In conclusion, these results indicate a relationship between HD, ultrafiltration rate, and IOP in ESRD patients. Higher ultrafiltration rate may predict increased risk for glaucoma in HD patients so scheduled ophthalmic examination should be a regular protocol for HD management. For patients evaluated to be at a high risk, longer or more frequent dialysis sessions should be considered to prevent the deleterious consequences of excessive body fluid expansion.
