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Indian J Ophthalmol. 2017 February; 65(2): 170.
PMCID: PMC5381300

Comment on: Comparison of serum sodium and potassium levels in patients with senile cataract and age-matched individuals without cataract

Sir,

We congratulate Mathur and Pai for their interesting article entitled, “Comparison of serum sodium and potassium levels in patients with senile cataract and age-matched individuals without cataract,”[1] in which they noted significantly higher mean serum sodium levels in individuals above 50 years of age with cataract than in age-matched individuals without cataract; however, mean serum potassium levels were not significantly different. The authors concluded that a high level of serum sodium contributes to cataract formation and that diets with high sodium content could be a risk factor for senile cataract formation.[1] We wish to offer a few comments:

  1. The mean serum values of sodium and potassium in the cases (cataractous eyes) versus controls (noncataractous eyes) are given without standard deviations (SDs)/standard errors of the mean (SEM); the means in the two groups are stated to be within the normal range, and “P values” are given to validate the findings. The SD/SEM values should have been provided to allow readers to independently perform relevant statistical tests and draw their own conclusions
  2. Although the authors state that nonparametric tests – Kruskal–Wallis/Mann–Whitney U-test – were performed for statistical analysis, details are not discussed
  3. The authors also state that “alteration in cation concentration of aqueous humor, which is attributed to alterations in serum cation concentration, can be known as a risk factor for cataract formation;” however, this sequence of events has not been proven to occur in the article cited by the authors (Clayton et al. 1980). Moreover, Mathur and Pai made no attempt to document aqueous humor levels of sodium and potassium
  4. The authors conclude (both in the abstract and text) that “diets with high sodium contents are a risk factor for senile cataract formation and dietary modifications can possibly reduce the rate of progression; a high level of serum sodium in turn contributes to cataract formation.” The first conclusion is highly speculative and unsubstantiated since they presumably did not compare the sodium content of diets consumed by their cases (patients with cataract) versus diets of their controls (individuals without cataract). The statement “a high level of serum sodium in turn contributes to cataract formation” contradicts their own findings “the means in the two groups (cataract cases vs. controls) were within the normal range” (emphasis ours).

The electrolyte composition of the lens resembles that of other human cells, with a high potassium and low sodium and chloride concentrations.[2] The aqueous bathing the lens closely reflects the ionic composition of the plasma, with high concentrations of sodium and chloride but low levels of potassium.[2] Potassium loss from the lens, which occurs during cataract formation, probably results from interruption of the ion pump within the cell membrane; potassium complexes thus break down and diffuse outward.[2]

Interestingly, Consul et al. reported that although mean aqueous humor levels of sodium, potassium, and chloride were slightly lower in eyes with senile cataract than those in normal eyes, the differences were not statistically significant, leading them to suggest that this was “just another manifestation of senility.”[3]

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

References

1. Mathur G, Pai V. Comparison of serum sodium and potassium levels in patients with senile cataract and age-matched individuals without cataract. Indian J Ophthalmol. 2016;64:446–7. [PMC free article] [PubMed]
2. Olson L. Anatomy and embryology of the lens. In: Duane TD, Jaeger EA, editors. Clinical Ophthalmology. Vol. 1. Philadelphia, USA: Harper and Row; 1986. pp. 1–8.
3. Consul BN, Taunk JP, Mathur GB. Human aqueous electrolytes (a study of sodium, potassium and chloride in normal and cataractous eyes) J All India Ophthalmol Soc. 1969;17:52–4. [PubMed]

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