[The nuclear hardness and associated factors of age-related cataract]

To determine the nuclear hardness and associated factors of age-related cataract.

Forty-seven eyes of 47 patients with age-related cataract aged > 50 years were studied. The opacity of lenses was assessed and classified by the LOCS II pre-operatively. The lens nucleus obtained during extracapsular cataract extraction (ECCE) was measured. By means of a fine conical probe and dynamometer, the resistance to penetration of different lens layers was transferred to an electric signal and recorded by a function recorder. The hardness to the penetration of different lens layers was calculated. Multivariate regression analysis was applied to the parameters including age, color of the nucleus, duration of symptoms and other factors.

The mean force required to penetrate the lens was (0.51 +/- 0.29) Newtons (N) for grade I, (1.41 +/- 0.35) N for grade II and (1.95 +/- 0.42) N for grade III; it increased to (2.96 +/- 0.62) N for grade IV. The hardest part of the lens was located at the nucleus center. Multivariate analysis of the data showed that 85% of the variation in hardness could be explained in terms of color and opacity. The patients with myopia and diabetics had an increased incidence of grading IV nuclear sclerosis. Regression analysis revealed a positive correlation between nucleus color and weight (r = 0.4565), diameter (r = 0.5263), thickness (r = 0.5552) and hardness (r = 0.8969), P < 0.001. There was a weak positive correlation between age and the weight of nucleus (r = 0.3239, P < 0.05).

The results indicate that the color can be used more reliably to predict physical characteristics of lens nucleus, the preoperative knowledge of which would help the surgeon in planning small-incision surgery including phacoemulsification.