Types of Myopia

There are Three Types of Myopia2

  1. Pathologic myopia: Caused by abnormal and extreme elongation of the axial length of the eye that doesn’t change (before 6 years old)
  2. School-age myopia: Occurs between 6-18 years of age. Stabilization is expected by late teens to early twenties
    • Associated with higher IQ scores
    • More time spent reading
    • Less exposure to sunlight compared to non-myopic patients
    • More common in urban and industrialized countries
    • In Singapore, more time spent in academia correlates to magnitude of myopia
  3. Adult onset: Early adult is considered 20 to 40 years old; late adult is over 40 years old. Affected by accommodative anomalies and near vision dominated occupations
To control myopia, the rate of eye growth must be slowed. The average age for this is 16 years.2

Speed of Myopia Progression

chart - speed of myopia progression
  1. Gifford, P., & Gifford, K. L. (2016). The Future of Myopia Control Contact Lenses. Optometry and Vision Science. 93(4): 336-343.

  2. Peripheral Hyperopia explanation summarized from:
      • Gifford, P., & Gifford, K. L. (2016). The Future of Myopia Control Contact Lenses. Optometry and Vision Science, 93(4), 336-343.
      • Smith, E. L., Kee, C., Ramamirtham, R., Qiao-Grider, Y., & Hung, L. (2005). Peripheral Vision Can Influence Eye Growth and Refractive Development in Infant Monkeys. Investigative Ophthalmology & Visual Science. 46(11): 3965.
      • Cooper, J., Schulman, E., Jamal, N. (2012). Current Status on the Development and Treatment of Myopia. Optometry. 83(5):179-199.
  3. Flitcroft, D. (2012). The complex interactions of retinal, optical and environmental factors in myopia aetiology. Progress in Retinal and Eye Research. 31(6): 622-660.

Simple Definitions

Emmetropic eyes do not require vision correction. Emmetropia is a state in which the eye is relaxed and focused on an object more than 6 meters or 20 feet away. The light rays coming from that object are essentially parallel, and they come to perfect focus on the retina without effort.3

Nearsightedness: Also known as myopia, nearsightedness is a condition in which nearby objects are seen clearly, but distant ones are blurred. Nearsightedness can be inherited and is often discovered during childhood. However, nearsightedness can also develop in early adulthood. When myopia develops in early adulthood, it typically isn’t severe.3

Peripheral retina describes the area beyond the roughly 6 mm around the fovea – the central retina. It stretches to the ora serrata, 21 mm from the center of the retina (fovea).4

Peripheral hyperopia, or peripheral hyperopic defocus, occurs when the peripheral vision is focused behind the back of the eye’s light receptors located in the retina, regardless of where the central focus is located.5

    • Some studies have shown that the peripheral retina has more influence than the macula than emmetropization and ocular growth, causing axial elongation6
    • It is hypothesized that the eye shape, associated with peripheral hyperopia, is one of the factors influencing axial eye growth7
    • Correcting the hyperopic peripheral defocus could eliminate the local retinal signal for elongation – blocking the signal may slow or stop myopia progression8

An Unfortunate by-product of Myopia Correction may be Peripheral Hyperopia¹

myopia_peripheral_hyperopia

Uncorrected/Corrected Myope

Minus lenses correct at the center of the retina for clear vision.

However, peripheral light rays at the edge of the eye are now moved behind the retina.

myopic eye vs normal eye

Myopic/Normal Eye

This may re-establish a growth signal and lead to the lengthening of the eye.

  • The eye growth repeats itself over and over

  • Resulting in higher and higher amounts of myopia

    1. Overview. https://en.wikipedia.org/wiki/Emmetropia. Accessed 3 July 2017.
    2. Cooper, J., Schulman, E., Jamal, N. (2012). Current Status on the Development and Treatment of Myopia. Optometry. 83(5):179-199.
    3. Emmetropia and Refractive Errors. https://www.verywell.com/what-is-emmetropia-vision-3421548. Accessed 3 July 2017.
    4. WebVision: Simple Anatomy of the Retina by Helga Kolb. http://webvision.med.utah.edu/book/part-i-foundations/simple-anatomy-of-the-retina/. Accessed 3 July 2017.
    5. Myopia Prevention and Control: Definitions. http://www.myopiaprevention.org/definitions.html. Accessed 3 July 2017.
    6. Myopia Research: From the Margins to the Mainstream by Annie Stuart. https://www.aao.org/eyenet/article/myopia-research-from-margins-to-mainstream. Accessed 3 July 2017.
    7. Mutti DO, Hayes JR, Mitchell GL et al. Refractive Error, Axial Length, and Relative Peripheral Refractive Error Before and After the Onset of Myopia. Invest Ophthalmol Vis Sci 2007 June;48(6):2510-2519.
    8. Smith EL, Hung Li-Fang, Huang J. Relative Peripheral Hyperopic Defocus Alters Central Refractive Development in Infant Monkeys. Vision Res 2009 Sept.;49(19):2386-2392.