Khushi Kansal, M.Optom.
Optometrist, Jawahar Eye Hospital Pvt Ltd, Meerut, U.P, India
The human eye is programmed to achieve emmetropia at a young age and to maintain emmetropia as we age. Emmetropization is the result of active and passive processes. The passive method is a method in which the child’s eyes are enlarged proportionally. The proportional enlargement of the eye decreases the dioptric power of the refractive system in proportion to the increase in the axial length of the eye. The refractive power of the cornea decreases with the enlargement of the radius of curvature, and the effectiveness of the lens decreases with the depth of the anterior chamber.
When these changes are disproportionate, a refractive error occurs.(1) The bulk of emmetropization occurs in early nonage and is largely complete by age 6. thus, refractive errors that present at this age can be considered failures of emmetropization. The commonest refractive error at age 6 is hypermetropia with both anisometropia and myopia being far less common at this age. Since the frequency of myopia shows a pronounced increase in later years, only a veritably small proportion of myopic refractive errors can be attributed to a primary failure of emmetropization.
The process usually involves entering image analysis data from the retina and then adjusting the axial length of the eye. The generated image is not related to this feedback and causes negative effects. Heredity determines susceptibility to certain eye problems, while environment plays a role in influencing the results of active emmetropia. (1)
Emmetropia is preserved in adults, but growth of the lens continues with lens thickness and curvature, this is called ’emmetropia’. The lens paradox is due to the change in refractive index, which affects the increase in curvature.
These changes can be caused by differences between the nucleus and cortex or by gradient changes in the cortex. (1)
Research by Ewelina Lachowicz et al. 2010 Child Development Index. Their findings show that eye size changes significantly with age. Due to the dynamic growth of the eye, the refraction of the eye also changes.
The effect is based on the increase in the length of the eye and the change in the refractive power of the cornea and lens. The process by which the eye achieves emmetropia relies on local feedback. Total refractive power decreases after birth to maintain emmetropia in adults. (2)
It appears that the role responsible for the cooperation between the eyes and the development of emmetropia is visual. The eye appears to be able to detect and respond to its own refractive error because the refractive change and axial growth rate during emmetropization are proportional to the original refractive error. (3)
- Brown NP, Koretz JF, Bron AJ. The development and maintenance of emmetropia. Eye. 1999 Jan;13(1):83-92.
- Lachowicz E, Czepita D. Eye development in children. Part II. Eye refraction. Klinika Oczna/Acta Ophthalmologica Polonica. 2010 Jan 1;112(4):337-41.
- Mutti DO, Mitchell GL, Jones LA, Friedman NE, Frane SL, Lin WK, Moeschberger ML, Zadnik K. Accommodation, acuity, and their relationship to emmetropization in infants. Optometry and vision science: official publication of the American Academy of Optometry. 20 09 Jun;86(6):666.