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Saudi Journal of Kidney Diseases and Transplantation
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Table of Contents   
ORIGINAL ARTICLE  
Year : 2011  |  Volume : 22  |  Issue : 6  |  Page : 1142-1148
Changes of serum calcium, phosphorus, and parathyroid hormone concentrations and ocular findings among patients undergoing hemodialysis


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 Publication8-Nov-2011
 

   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 2019 Aug 18];22:1142-8. Available from: http://www.sjkdt.org/text.asp?2011/22/6/1142/87213

   Introduction Top


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 Top


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 Top


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 Top


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 Top


The authors would like to thank Farzan Institute for Research and Technology for technical assistance.

 
   References Top

1.Diaz-Couchoud P, Bordas FD, Garcia JR, et al. Corneal disease in patients with chronic renal insufficiency undergoing hemodialysis. Cornea 2001;20:695-702.  Back to cited text no. 1
    
2.Popa M, Nicoarä S. Ocular changes in dialysis patients. Ofthalmologia 2000;50(1):65-7.  Back to cited text no. 2
    
3.Cupisti A, Morelli E, D'Alessandro C, Lupttis Barsotti G. Phosphate control in chronic ure­mia: Don't forget diet. J Nephrol 2003;16(1): 29-33.  Back to cited text no. 3
    
4.Block GA. Prevalence and clinical consequences of elevated Ca product in hemodialysis patient. Clin Nephrol 2000;54(4):318-24.  Back to cited text no. 4
    
5.Klaassen-Broekema N, van Bijsterveld OP. Red eyes in renal failure. Br J Ophthalmol 1992;76:268-71.  Back to cited text no. 5
    
6.Maurer KH, Schumacher HR. Hydroxyapatite phagocytosis by human polymorphonuclear leucocytes. Ann Rheum Dis 1979;38:84-8.  Back to cited text no. 6
    
7.Sitprija V, Holmes JH, Ellis PP. Intraocular pressure changes during artificial kidney therapy. Arch Ophthalmol 1964;72:626-31.  Back to cited text no. 7
    
8.Dujiæ M, Markoviæ P, Jovanoviæ D, Dragiæeviæ P, Radovanoviæ LJ. Changes in intraocular pressure during dialysis. Srp Arh Celok Lek 1997;125(9-10):257-60.  Back to cited text no. 8
    
9.Dursun D, Demirhan B, Oto S, Aydin P. Im­pression cytology of the conjunctival epithetlium in patients with chronic renal failure. Br J Ophthalmol 2000;84(11): 1225-7.  Back to cited text no. 9
    
10.Pavloviæ D, Vatavuk Z, Vrabec R, et al. Ocular changes in hemodialysis patients. Ther Apher Dial 2005;9:70-9.  Back to cited text no. 10
    
11.Aktaº Z, Ozdek S, AsliDinç U, et al. Alte­rations in ocular surface and corneal thickness in relation to metabolic control in patients with chronic renal failure. Nephrology (Carlton) 2007;12(4):380-5.  Back to cited text no. 11
    
12.Vrabec R, Vatavuk Z, Pavloviæ D, et al. Ocular findings in patients with chronic renal failure undergoing hemodialysis. Coll Antropol 2005; 29(Suppl 1):95-8.  Back to cited text no. 12
    
13.Georgi ME, Carlisle MS, Smiley LE. Giar­diasis in a great blue heron (Ardeaherodias) in New York State: Another potential source of water borne giardiasis. Am J Epidemiol 1986; 123:916-7.  Back to cited text no. 13
    
14.Harding JJ, Egerton M, van Heyningen R, Harding RS. Diabetes, glaucoma, sex, and cataract: Analysis of combined data from two case control studies. Br J Ophthalmol 1993;77: 2-6.  Back to cited text no. 14
    
15.Hennis A, Wu SY, Nemesure B, Leske MC. Risk factors for incident cortical and posterior subcapsular lens opacities in the Barbados Eye Studies. Arch Ophthalmol 2004;122:525-30.  Back to cited text no. 15
    
16.Xu L, Xie XW, Wang YX, Jonas JB. Ocular and systemic factors associated with diabetes mellitus in the adult population in rural and urban China. The Beijing Eye Study. Eye 2009;23(3):676-82  Back to cited text no. 16
    
17.Sensi M, Pricci F, Pugliese G, et al. Role of advanced glycation end-products (AGE) in late diabetic complications. Diabetes Res Clin Pract 1995;28(1):9-17.  Back to cited text no. 17
    
18.Al-Hejaili F, Kortas C, Leitch R, et al. Noc­turnal but not short hours quotidian hemodialysis requires an elevated dialysate calcium concentration. J Am Soc Nephrol 2003;14: 2322-8.  Back to cited text no. 18
    
19.Oprisiu R, Bolosiu H, Boca I, et al. Renal osteodystrophy during the developing stage of maintenance dialysis in Transylvania. Early development of periarticular calcifications and beta 2 microglobulin amyloidosis in spite of a relatively good prevention of secondary hyperparathyroidism. Ann Med Interne (Paris) 1998;149(2):67-75.  Back to cited text no. 19
    
20.Salem MM. Hyperparathyroidism in the hemialysis population: A survey of 612 patients. Am J Kidney Dis 1997;29:862-5.  Back to cited text no. 20
    
21.Owda A, Elhwairis H, Narra S, Towery H, Osama S. Secondary hyperparathyroidism in chronic hemodialysis patients: Prevalence and race. Ren Fail 2003;25:595-602.  Back to cited text no. 21
    
22.Slatopolsky E, Brown A, Dusso A. Pathogenesis of secondary hyperparathyroidism. Kidney Int 1999;73:S14-9.  Back to cited text no. 22
    
23.Moþa E, Davidescu L. Changes in the ocular tension of dialysis patients. Ofthalmologia 1997;41(1):15-8.  Back to cited text no. 23
    
24.Wong TY, Mitchell P. Hypertensive retinopathy. N Engl J Med 2004;351:2310-7.  Back to cited text no. 24
    

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Correspondence Address:
Hamidreza Samimagham
Department of Nephrology, Hormozgan University of Medical Sciences, Bandarabbas
Iran
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PMID: 22089771

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