Author(s): Sayantan Das1, Nirmal Kumar Sasmal2, Amitava Das3
The study was designed to understand the morphological and anatomical changes in the eyeball that may directly affect the refractive (myopic) status. The role of the cornea in the appearance and progression of myopia has been the subject of study. This study is to correlate the axial length of the eyeball and curvature of the cornea with the age of the onset of myopia.
MATERIALS AND METHODS
In this prospective observational study, a total of 200 simple myopic eyes of 100 subjects with mean age of 20.06 ± 4.39 (range 10 to 30 years) consisting of 55 males and 45 females were recruited for the study. Careful history was taken in all the patients with particular attention to the age of onset of their myopic power. The patients were examined and refraction for the power, a scan biometry for axial length of the eyeball and the keratometry for the radius of curvature of the cornea were performed.
The maximum number (n=85) of eyes had myopic power less than -5.00 Dsph (Group A). Follower by 77 eyes, those belonged to the group of -5.00 Dsph to less than -10.00 Dsph (Group B). 26 eyes were selected within the range of -10.00 Dsph to <-15.00 Dsph (Group C). The high myopic power more than -15.00 Dsph were detected only in 12 eyes (Group D). The mean AL of whole study population was 24.9 ± 1.8 mm. The 111 (55.50%) number of myopic eyes had axial length within the range of 24 mm to less than 27 mm. The mean CR for the population was 7.55 ± 0.30 mm. The maximum number 179 of myopic eyes had moderate range (7.0-<8.0 mm) of radius of corneal curvature (CR). Myopia was classified as adult-onset (6-9 years) myopia in 88 eyes and as juvenile-onset (3-<6 years) myopia in 112 eyes. The values of mean AL/CR ratio obtained from this study was 3.12 ± 0.72 (Group A), 3.34 ± 0.75 (Group B), 3.57 ± 1.06 (Group C) and 3.71 ± 1.22 (Group D).
Axial lengthening is the main morphological factor in both juvenile and adult-onset types of myopia. The study observed a tendency towards smaller radii of curvature in moderate myopias. The AL and CR relation increased steadily from the lower to higher grades of myopes among the four refraction groups. The function of the cornea seems to compensate the possible myopising effects of slight increases in axial length. When increases in axial length are excessive, this effect of the cornea tends to disappear with the consequent appearance of myopia.