Sudanese Journal of Ophthalmology

ORIGINAL ARTICLE
Year
: 2014  |  Volume : 6  |  Issue : 1  |  Page : 10--13

Serum Na + and K + as risk factors in age-related cataract: An Indian perspective


Adeeb A Khan1, Syed Wajahat A Rizvi1, Abadan K Amitava1, Shagufta Moin2, Ziya Siddiqui1, Faraz Yusuf1,  
1 Department of Ophthalmology, Jawaharlal Nehru Medical College, Aligarh Muslim University, Aligarh, Uttar Pradesh, India
2 Department of Biochemistry, Jawaharlal Nehru Medical College, Aligarh Muslim University, Aligarh, Uttar Pradesh, India

Correspondence Address:
Syed Wajahat A Rizvi
620/7-Rizvi Lodge, Rasalganj, Aligarh, Uttar Pradesh - 202 001
India

Abstract

Background: Recent reports suggest an association between deranged metabolism and age-related cataracts (ARC). Aim: This study was planned and carried out to evaluate some biochemical variables as possible risk factors for the different morphological types of ARC. Materials and Methods: We compared serum Na + and K + in 100 cases of ARC and 100 age- and gender-matched controls. The ARC patients were sub-grouped according to the WHO cataract grading system into posterior sub-capsular (PSC), nuclear (NC), cortical (CC) and mixed cataracts (MC). Statistical analysis was done using t-test, ANOVA, and post-hoc (Tukey) test. The 95% CI are reported; significance was set at P ≤ 0.05. Results: Although within normal range, the overall mean serum levels of Na + were significantly higher (P < 0.001; 95% CI for difference: 2.95 to 8.56) in the cases (145.39 (±3.04) mEq/L) as compared to controls (139.63 (±13.91) mEq/L). Except for the PSC group, sub-group analyses showed significantly higher Na + levels than controls (P < 0.05). There was no significant difference in serum K + levels. Importantly, serum Na + and K + levels were within the normal reference range in all the subjects. Conclusion: This study suggests that there is a tendency to have higher Na + levels in ARC as compared to non-ARC subjects, although within normal reference values.



How to cite this article:
Khan AA, Rizvi SA, Amitava AK, Moin S, Siddiqui Z, Yusuf F. Serum Na + and K + as risk factors in age-related cataract: An Indian perspective.Sudanese J Ophthalmol 2014;6:10-13


How to cite this URL:
Khan AA, Rizvi SA, Amitava AK, Moin S, Siddiqui Z, Yusuf F. Serum Na + and K + as risk factors in age-related cataract: An Indian perspective. Sudanese J Ophthalmol [serial online] 2014 [cited 2019 Aug 18 ];6:10-13
Available from: http://www.sjopthal.net/text.asp?2014/6/1/10/138844


Full Text

 INTRODUCTION



Globally, age-related cataract (ARC) accounts for 51% of blindness and remains the leading cause of visual impairment, despite improvement in surgical outcomes. [1] It is now generally believed that a number of risk factors are associated with the development of ARC. High serum glucose, usage of steroids and radiation exposure have been clearly implicated. [2],[3],[4]

Several biochemical constituents in serum have been found to be associated with cataractogenesis. While some studies have shown significantly higher concentrations of serum Na + and K + in ARC, [5],[6],[7] others have reported no association. [8]

With increasing longevity, the global burden of cataract is rising, necessitating ever increasing health expenditure. Identifying modifiable risk factors may thus help in targeting populations at risk and to delay, if not prevent cataractogenesis. Such measures may greatly reduce surgical cost, limit disability, and improve the quality of life.

Most studies in this regard were done in the west and data from Indian population has been lacking. This study is one such attempt to look for some biochemical alterations in Indian patients with age-related cataracts and to compare them with age- and gender-matched controls.

 MATERIALS AND METHODS



This study was performed in the Ophthalmology Department of Jawaharlal Nehru Medical College, Aligarh, India. After clearance from the Institutional Ethic Committee and obtaining informed consent, we recruited 200 individuals, comprising 100 cases of age-related cataract in the age group of 45-65 years with best corrected visual acuity (BCVA) between 6/24 and 3/60 (both inclusive), and 100 age- and gender-matched controls (i.e. without cataracts) with BCVA of 6/6 to 6/18. The cases were further classified into four groups, consisting of 25 cases each of posterior subcapsular cataract (PSC), nuclear cataract (NC), cortical cataract (CC) and mixed cataract (MC) using a slit lamp based modified WHO grading system. [9] Cases were labelled according to the most severe grade of the type of cataract: and in those where at least two of the types were equally severe were labelled as mixed. We excluded subjects with a history of known systemic illness (diabetes, hypertension, renal or diagnosed dyslipidemia), history of drug intake known to affect renal or liver functions (diuretics, statins, anti-hypertensives, aminoglycoside antibiotics), or any history of ocular trauma or any other ocular condition (uveitis, high myopia, glaucoma), which may have significantly contributed to cataract formation. We sampled the patients for blood urea (Berthelot method), serum creatinine (Jaffe's method) and fasting blood glucose (glucose oxidase/peroxidase method) to rule out diabetes or renal dysfunction. On the morning sample, we evaluated both serum sodium and potassium using Eschweiler ABG and electrolyte analyzer. We analyzed the results using t-test, ANOVA, and post-hoc (Tukey) test; significance was set at P ≤ 0.05 (two-tailed) and 95% CI are also reported.

 RESULTS



[Table 1] shows age and gender distribution in cases and controls. The mean age was 52.72 (±2.64) years in all cases and 52.03 (±3.35) years in controls (P = 0.108). The mean serum Na + in all cases [145.39 (±3.04) mEq/L] was significantly higher as compared to controls [139.63 (±13.91) mEq/L] (P < 0.001; 95% CI: 2.95 to 8.56) [Table 2]. There was no difference in mean serum K + between all-cases and controls (P = 0.723) [Table 2]. In subgroup analysis, the mean levels of serum Na + in NC, CC, and MC were significantly higher (P < 0.05) as compared to controls, while PSC shows no significant difference (P = 0.273) [Table 3]. Serum K + again shows no difference between subgroups and controls [Table 3].{Table 1}{Table 2}{Table 3}

 DISCUSSION



In our study, mean serum Na + in all-cases was significantly higher compared to controls (P < 0.001; 95%CI for difference of mean: 2.95 to 8.56) [Table 2], although still within the normal reference range. All cataract subtypes have higher serum Na + except for PSC, which showed no significant association (P = 0.273) [Table 3]. There was no difference in mean serum K + between all cases (P = 0.723; 95% CI for difference of mean: −0.04 to 0.07), cataract subgroups and controls [Table 2] and [Table 3].

Mansour in a study on 155 Iranian senile cataract patients versus a similar number of matched controls reported significantly higher levels of serum Na + in the cataract group (t-test; P < 0.0001). [5] Like us all his subjects had serum Na + levels within the normal reference range. In another study by the same author, on sub-group analyses of ARC cases, significantly higher levels of Na + were found in CC (P = 0.001), NC (P < 0.001), PSC (P < 0.001) and MC (P = 0.001). [6] Similar to us, no difference was found in serum K + levels, both overall and in subgroup analyses. Mansour too failed to detect any significant difference in serum K + levels. Donnelly in an Edinburg-based study on 1000 patients of senile cataract found a significantly higher serum Na + in cataract cases (P = 0.03; OR = 1.04; 95% CI: 1.0-1.08). [10] Similar to our study, they also did not find any difference of serum K + (P = 0.67; OR = 1.05; 95%CI: 0.98-1.12).

Miglior et al. conducted a case-control study in Italy [7] to evaluate risk factors for nuclear, cortical, posterior subcapsular and mixed cataract. The study group (age range: 40-75 years) comprised 385 cases and 215 controls. They classified serum Na + levels (in mEq/L) into: 138.1-141, 141.1-143, >143. They report a significantly higher risk of the first (OR 3.1; 95% CI: 1.41 to 6.59) and the third group (OR 2.14: 95%CI: 1.07 to 4.29), with CC only (defined by LOCS II), [11] but no significant association of the central group (OR 1.47: 95%CI: 0.67 to 3.24) with CC and with other cataract subgroups. In a similar fashion, they also reported the higher serum K + (OR 4.27; 95%CI: 2.21 to 10.7). Understandably they appear puzzled and suggest that the association may be spurious.

Higher serum Na + is well known to play an important role in the etiology of hypertension; [12] a few studies have shown either systolic or diastolic hypertension to be associated with cataract. Leske has shown a significantly higher proportion of hypertensives (diastolic pressure >95 mmHg) amongst patients of cortical cataracts as compared to age and gender matched non-cataract controls in a black population (OR = 1.32; 95% CI of difference: 1.01 to 1.72). [13] Paunksnis in a Lithuanian middle aged (36-64 years) population of 1282 (573 men and 709 women) individuals found higher blood pressure (>130/85 mmHg) to be significantly related to cataract in women (OR = 1.98; 95% CI of difference: 1.21-3.25). [14] Although we excluded hypertensives, we still found a significantly higher systolic BP in all-cataract group as compared to the controls (95% CI for difference: 0.89 to 4.96 mmHg), while there was no significant difference in the diastolic (95% CI for difference: −2.43 to 1.13) and mean BP (95% CI for difference: −0.99 to 2.08). This may not be of any clinical significance, but it does seem to indicate that higher Na + levels do affect BP, perhaps more the systolic component.

Any change in serum electrolytes concentration is reflected in the aqueous, and is likely to impact lens metabolism. Much like most cells in the body, the lens has high content of potassium and low content of sodium; mainly on account of the Na + -K + ATP-ase pump and lens membrane permeability. [15] However, in human age-related cortical cataracts, lens sodium is abnormally elevated, and the potassium is abnormally low. [16],[17] As a result of the osmotic disturbances caused by the ionic change, water accumulates in lens cells. Eventually this leads to cell lysis and the appearance of fluid droplets that scatter light and impair transparency. Abnormally high calcium levels accompany derangement of lens sodium and potassium in age-related human cataract. [16] The rise in calcium also leads to loss of transparency. [18],[19]

Although, the mean levels of both serum Na + and K + in ARC were found to be in the reference range, but still, the levels of serum Na + differed significantly from that of control group. The increased serum Na + levels for cortical and mixed cataract cases is reasonable since cortical cataract is known to be an osmotic cataract. No significant increase in serum Na + for PSC cataract is also reasonable. However, the increase in serum Na + for nuclear cataract cases is odd since nuclear cataracts, in contrast to cortical cataracts, have been shown previously to exhibit no changes in lens ion levels. However, the majority of human cataracts can be classified as mixed since nuclear, cortical and subcapsular opacification is evident, and it may be because of this reason that serum Na + levels spuriously seem elevated in nuclear subgroup.

We thus conclude that a gradual and persistent variation in the measured and a number of other less known parameters may be predisposing in the process of cataractogenesis. Given the present scenario of cataract, even the slightest delay in onset and progression of cataract would have major health implications, especially in the underdeveloped world.

Eventually, further large-scale studies, and perhaps a meta-analysis is needed to evaluate the potentially modifiable factors.

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