Five-year change in refraction and its ocular components in the 40- to 64-year-old population of the Shahroud eye cohort study.

BACKGROUND

To assess 5-year refractive changes and their related factors in the 40- to 64-year-old population of Shahroud, Iran.

DESIGN

Prospective cohort study.

PARTICIPANTS

Of the 5190 participants of Phase I, 4737 participated in Phase II (response rate = 91.3%).

METHODS

Participants were tested by refraction, visual acuity, slit-lamp biomicroscopy, ophthalmoscopy and biometry. Myopia was defined as a spherical equivalent more negative than -0.5 dioptre (D) and hyperopia as a spherical equivalent more positive than +0.5 D.

MAIN OUTCOME MEASURES

Mean 5-year change in spherical equivalent refraction.

RESULTS

The mean 5-year change in spherical equivalent refraction was +0.24 D (95% CI: +0.22 to +0.25). After 5 years, 4.77% (95% CI: 4.08 to 5.46) of subjects developed at least 0.5 D of myopia and 22.27% (95% CI: 20.97 to 23.57) developed at least 0.5 D of hyperopia. Five-year changes in refraction included a hyperopic shift in all age groups. The greatest hyperopic shift was seen in middle-aged women. The greatest loss of lens power was observed in hyperopic women and the least in myopic men. Nuclear cataract was associated with a myopic shift in refraction. The axial length and the corneal power had very small changes during this period. Myopes showed the greatest increase in axial length. Corneal power increased by a very small amount in all refractive groups.

CONCLUSIONS

The most important biometric index related to hyperopic shifts, which were greater in magnitude in women, was loss of lens power, whereas nuclear cataract was associated with myopic shifts.