Study of Cataract in Relation to Axial Length and Refractivity of the Eye
Aim: To ascertain the association between different types and densities of age-related cataract with axial length and refractive state of the eye.
Methods: This prospective observational institute-based study enrolled 462 eyes of 450 patients aged 40 years or older. Eyes were classified as myopic (axial length, >25 mm), emmetropic (axial length, 21-25 mm), and hypermetropic (axial length, <21 mm). Refractive error was defined as myopia (spherical equivalent, <-0.5 D) and hypermetropia (spherical equivalent, >+0.5 D). Cataract was categorised as nuclear, cortical, or posterior subcapsular. Nuclear density was measured based on the Emery and Little Classification after slit-lamp biomicroscopy. Student t test for unpaired samples and Fisher and Yates tables were used to analyse statistical significance.
Results: Emmetropia was the most common condition (417 eyes). The most common cataract combination was nuclear with posterior subcapsular (n = 198; 44%). In the axial myopia group, nuclear cataract was the
commonest type, alone or in combination with other types (n = 33; 100%). Most eyes had refractive error of 0 to -5 D. The grade of nuclear cataract increased with increasing age (n = 48 for grade IV nuclear cataract in the 70 to 79 years age group). In all age groups, a higher grade of nuclear sclerosis was significantly associated with axial length (t = 2.2; p < 0.05). The relationship was also significant for posterior subcapsular cataract (t = 2.7; p < 0.05).
Conclusions: Nuclear cataract leads to a myopic shift in refraction. In otherwise healthy eyes, there is a gradual hypermetropic shift. The prevalence and grade of nuclear cataract increases with age. Longer axial length is associated with a higher grade of nuclear and posterior subcapsular cataract.