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| Year : 2011 | Volume
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| Issue : 6 | Page : 1142-1148 |
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| Changes of serum calcium, phosphorus, and parathyroid hormone concentrations and ocular findings among patients undergoing hemodialysis |
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Farzad Pakdel1, Hamidreza Samimagham2, Amin Shafaroodi2, Mehrdad Sheikhvatan3
1 Department of Ophthalmology, Hormozgan University of Medical Sciences, Bandarabbas, Iran
2 Department of Nephrology, Hormozgan University of Medical Sciences, Bandarabbas, Iran
3 Tehran University of Medical Sciences, Tehran, Iran
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| Date of Web Publication | 8-Nov-2011 |
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 Abstract | | |
There are various reports of ocular abnormalities in metabolic disorders. This study was done with the aim to investigate the relationships between the amounts of serum calcium, phosphorus, and parathyroid hormone concentrations and ocular findings in patients undergoing hemodialysis. Fifty eight patients with end stage renal failure undergoing hemodialysis were randomly selected and enrolled in this prospective study. Demographic data, history of diabetes mellitus and hypertension, and duration of hemodialysis were recorded. Serum calcium, phosphorus, alkaline phosphatase (ALP), and parathyroid hormone (PTH) concentrations were measured. Also, blood urea nitrogen (BUN) and weight of the patient was measured just before and three minutes after the hemodialysis. Patients also underwent a complete ocular examination including visual acuity, intraocular pressure (IOP), biomicroscopic examination, and fundoscopy. In univariate analysis, adverse relationships were found between the ocular hypertension and ALP concentration (P = 0.017) and also between the visual acuity and phosphorus concentration (P = 0.033). However, in multivariate regression analysis and with regard to the patients' characteristics and medical history in a multivariate model, no relationships were found between ocular findings and serum calcium, phosphorus, ALP, and PTH concentrations. No relationships were found between the serum concentrations of calcium, phosphorus, ALP, and PTH and ocular findings in patients with end stage renal failure undergoing hemodialysis.
How to cite this article:
Pakdel F, Samimagham H, Shafaroodi A, Sheikhvatan M. Changes of serum calcium, phosphorus, and parathyroid hormone concentrations and ocular findings among patients undergoing hemodialysis. Saudi J Kidney Dis Transpl 2011;22:1142-8 |
How to cite this URL:
Pakdel F, Samimagham H, Shafaroodi A, Sheikhvatan M. Changes of serum calcium, phosphorus, and parathyroid hormone concentrations and ocular findings among patients undergoing hemodialysis. Saudi J Kidney Dis Transpl [serial online] 2011 [cited 2022 Aug 12];22:1142-8. Available from: https://www.sjkdt.org/text.asp?2011/22/6/1142/87213 |
| Introduction | |  |
It has been clearly shown that various underlying factors can affect the eye, such as hemodialysis treatment. [1] The most important ocular changes seen among hemodialysis patients' are the retinal vascular complications such as hypertensive retinopathy, anterior optic ischemic neuropathy, central retinal artery occlusion, and diabetic retinopathy. [2] Another important problem in these patients is the occurrence of hyperphosphatemia that has a central role in ectopic calcifications caused by an abnormal balance of calcium and phosphorus metabolism. [3],[4] These calcifications can be seen in the conjunctiva occurring due to the deposition of calcium phosphate salts which is thought to be the cause of inflammatory reaction leading to painful and irritable red eyes. [5],[6] Furthermore, the relationship between intraocular pressure changes and hemodialysis has been evaluated for almost 40 years and in the majority of patients, a significant rise in intraocular pressure was noted after hemodialysis. [7],[8]
However, some of the previously reported findings, theories, and conclusions have not been confirmed about the relationship between the ocular changes and metabolic disorders especially calcium and phosphorus changes related to hemodialysis. [1],[9],[10] The main goal of this study was to investigate the possible relationships between the levels of serum calcium, phosphorus, and parathyroid hormone concentration and ocular findings in patients undergoing hemodialysis.
| Materials and Methods | | |
Fifty eight patients with chronic renal failure undergoing hemodialysis in the dialysis unit of Shahid Mohammadi Hospital were enrolled in this prospective study. None of the patients had a history of malignancy or primary hyperparathyroidism. All patients were under treatment with calcium carbonate and Rocaltrol. The duration of CRF in these patients ranged from four to 180 months. All patients were on hemodialysis three times a week, for two to four hours each time. The protocol was approved by the research ethicscommittee of the hospital and the written informed consent was obtained from all the patients.
Demographic data, history of diabetes mellitus and hypertension, duration of hemodialysis, total fluid loss after hemodialysis, blood urea nitrogen (BUN) before and after hemodialysis, and solute clearances (Kt/V, normalized creatinine clearances) were determined in all patients. Serum calcium, phosphorus, and alkaline phosphatase concentrations were measured by commercial kits and serum parathyroid hormone (PTH) concentration was measured by DSL-8000 kit done randomly before the hemodialysis. Patients' weight and BUN were also measured just before and three minutes after hemodialysis. They also underwent a complete ocular examination including visual acuity, intraocular pressure (IOP), biomicroscopic examination, and fundoscopy.
Results were reported as mean ± standard deviation (SD) for the quantitative variables and percentages for the categorical variables. The groups were compared using the Student's "t" test or Mann-Whitney U test for the continuous variables. Regression analysis was used for the consideration of correlations between quantitative variables. Predictors exhibiting a statistically significant relation with complications in univariate analyses were taken for stepwise multivariate logistic regression analysis to determine the effects of serum chemical indices on ocular findings after adjustment for patients' age and sex, history of diabetes mellitus, history of hypertension, Kt/V, and duration of dialysis. P values of 0.05 or less were considered statistically significant. All the statistical analyses were performed using SPSS version 13 (SPSS Inc., Chicago, IL, USA).
| Results | | |
Demographic data, measured criteria, and ocular findings in all the studied patients are shown in [Table 1]. Almost half of them are men and the mean age of patients was 48.1 ± 16.9 (range 10 to 80 years old). The majority of patients had the history of hypertension. The most common ocular findings were hypertensive retinopathy (73.7%), cataract (60.3%), and conjunctive calcification (24.1%). | Table 1: Demographic characteristics, measured criteria and ocular findings in all studied patients undergoing hemodialysis.
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Relationships between ocular findings in the studied patients and the concentrations of serum chemical indices are shown in [Table 2] and [Table 3]. The results showed that in univariate analysis, significant correlation was found only between serum phosphorus concentration and right visual acuity (Standardized Beta= -0.316, P = 0.033). Also, a positive relationship was found between the occurrence of ocular hypertension and ALP concentration. However, multivariate regression analysis did not confirm these relationships. | Table 2: Relationships between the serum chemical components and ocular findings.
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 | Table 3: Relationships between the serum chemical components and ocular findings (continued).
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In comparison between diabetic and non-diabetic patients, the incidence of conjunctival calcification (P = 0.016), cataract (P<0.001), and retinopathy (P<0.001) were higher in diabetics. However, serum concentrations of studied chemical criteria were similar between the two groups before and after hemodialysis. Also, among post-dialysis ocular findings, hypertensive retinopathy was more prevalent in hypertensive compared to normotensive subjects (P = 0.015). In patients with shorter duration of hemodialysis (≤2 months), serum concentration of calcium before dialysis was higher than other patients (P = 0.019), whereas the concentrations of alkaline phosphatase (P = 0.043) and parathyroid hormone (P = 0.033) were lower in the first group. There were significant correlations between the change of alkaline phosphatase and duration of hemodialysis (Standardized Beta = -0.394, R square = 0.155, P = 0.006) and also between parathyroid hormone concentration and duration of dialysis (Standardized Beta = 0.420, R square = 0.177, P = 0.003).
In the diabetic group, positive relationships were found between the calcium concentration and hypertensive retinopathy (P = 0.043) and also between the phosphorus concentration and the incidence of glaucoma (P = 0.027); however, these relations were not observed in non-diabetics. In patients with shorter duration of hemodialysis (≤2 months), a positive correlation was found between the phosphorus concentration change after dialysis and intraocular pressure (Standardized Beta = 0.488, R square = 0.238, P = 0.021). Besides, in the patients with longer duration of hemodialysis (>2 months), an inverse relationship was found between the calcium concentration change after dialysis and visual acuity (Standardized Beta = -0.483, R square = 0.233, P = 0.027). However, these relationships were not statistically significant between other variables and in other studied groups.
| Discussion | | |
In the present study, we tried to determine the effects of various serum chemical components such as calcium, phosphorus, ALP, and PTH on ocular findings in the patients undergoing hemodialysis. In our study, we found no significant relationships between these criteria and ocular findings after adjustment for patients' demographic characteristics, risk factors, and duration of dialysis. The results of similar studies were different. In a study by Aktaş et al, serum calcium and phosphate levels presented as important prognostic factors for the ocular findings and symptoms in patients with chronic renal failure. [11] However, Dursun et al, found no relation between the severity of conjunctival changes and presence of calcium deposition. [9] Also, in a study by Vrabec et al, no correlation of ocular calcification and parathyroid hormone (PTH) levels or calcium and phosphate product were observed. [12] Owing to the differences in the obtained results, we feel that the pathophysiology of the impact of chemical components such as calcium and phosphorus and their regulator factors such as PTH should be investigated in further and larger studies.
In the present study, the presence of diabetes mellitus had relationships with the incidence of cataract and conjunctival calcification. Diabetes itself has been associated with both age-related cataract and cortical cataract. [13],[14] Both the National Health and Nutrition Examination Survey (NHANES) and the Framingham study demonstrated an increased risk of age-related cataract development in diabetics less than 65 years old. Other epidemiological studies indicate an even greater relative risk associated with diabetes between the ages of 50 and 79 years. Diabetes mellitus appears to shift the prevalence of cataract toward a younger age and toward cortical and posterior subcapsular cataracts. [15] However, some investigators have not distinguished between known diabetics and those found as a result of cataract. In a study by Xu et al, diabetes mellitus was not significantly associated with the presence of cataract, although there was a significant correlation with higher intraocular pressure. [16] Biochemical markers of early eye changes in diabetic microangiopathy and progressive development of cataract are not completely understood. The current hypothesis of diabetic cataract formation considers it to be a consequence of non-enzymatic glycosylation of lens proteins. In addition, an enhanced rate of formation of fluorescent advanced glycation end-products formation might play an important role in the pathogenesis of diabetic cataract. [17]
Also, we found that the mean alkaline phosphatase concentration before dialysis had negative correlation with the duration of dialysis and the correlation between serum parathyroid hormone and duration of dialysis was a positive one. However, no significant difference was found between the mean of calcium concentration and dialysis duration. Reported results in previous articles about the effects of duration dialysis and serum mineral and hormones concentrations were different. Al-Hejaili et al indicated that the mean gain or loss of calcium is related to both dialysate calcium concentration and to the duration of dialysis, [18] whereas in a study by Oprisiu et al, plasma PTH concentrations were negatively correlated to dialysis duration and to plasma concentrations of aluminum, calcium, and 25 OH vitamin D, but not to those of phosphate and bicarbonate. [19] It is clear that secondary hyperparathyroidism is quite common in patients with chronic kidney disease receiving hemodialysis. [20],[21] The disorder is characterized by persistently elevated levels of parathyroid hormone and complicated by major disturbances in mineral metabolism and among dialysis patients, these complications should be closely monitored. [22]
In the present study, it was found a positive correlation between the mean phosphorus concentration before dialysis and intraocular pressure. Serum phosphorus concentration has a main role in maintaining serum osmolarity. Therefore, the variations of the intraocular pressure post-dialysis may be explained by some modifications of the osmolarity. [23] Thus, the changes of blood osmolarity due to the change of phosphorus concentration may result in intraocular pressure and may lead to glaucoma.
Also, in our study, positive relationship was found between the calcium concentration and hypertensive retinopathy among diabetic patients. About 25 years ago, researchers observed that calcium might be inversely related to the development and severity of hypertension. Besides, hypertensive retinopathy has been noted as a common condition in diabetic patients characterized by a spectrum of retinal vascular signs in people with elevated blood pressure and retinal vasoconstriction and reduced retinal blood flow, which precede the onset of diabetic retinopathy. [24] However, the direct role of serum calcium concentration in the pathogenesis of hypertensive retinopathy especially in the patients undergoing dialysis has not been clearly determined and needs more studies on this topic.
In conclusion, no relationships were found between serum concentrations of calcium, phosphorus, ALP, and PTH and ocular findings in patients with end stage renal failure undergoing hemodialysis. Furthermore, the change of serum calcium concentration due to hemodialysis can lead to the hypertensive retinopathy and visual acuity disturbance. Also, the change of serum phosphorus concentration can change the intraocular pressure and result in glaucoma. However, we could not demonstrate the effect of serum parathyroid hormone concentration and pathological ocular findings during hemodialysis.
| Acknowledgements | | |
The authors would like to thank Farzan Institute for Research and Technology for technical assistance.
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Correspondence Address:
Hamidreza Samimagham
Department of Nephrology, Hormozgan University of Medical Sciences, Bandarabbas
Iran
 Source of Support: None, Conflict of Interest: None  | Check |
PMID: 22089771 
[Table 1], [Table 2], [Table 3] |
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