Understanding the Varieties: Exploring Different Types of Myopia

Imagine a world where all those distant landscapes and faces one longs to see remain a mystery. That is how many perceive the world without spectacles, especially children having myopia. Myopia or nearsightedness affects millions, and it's essential to shed light on the diverse dimensions of this common eye condition.

Understanding myopia

When a person has myopia, their eyeball is longer than normal from front to back, or the cornea (the clear window at the front of the eye) is too steeply curved.¹ As a result of this, light focuses in front of the retina instead of directly on it. Thus, things that are far away appear to be blurry.2 Having myopia can increase the chances of developing eye problems later, such as cataract, glaucoma and retinal detachment.

Myopia often can be corrected with eyeglasses or contact lenses. Apart from these, refractive surgery for myopia is also a commonly explored treatment option.¹ One often scours the internet with the quest to find the most suitable myopia lens type. While comprehending the various treatment options for managing myopia is crucial, it's equally important to understand the different types of myopia. Accordingly, myopia can be classified into different types based on cause, the rate of progression or even changes to the eye resulting from it.

Classifying myopia based on cause

There are 2 different types of myopia: Axial myopia and Refractive myopia.

1. Axial myopia is the most common type of myopia observed in clinical practice and is caused by an increase in the axial length of the globe. This means, the axial length of the eye is too long when measured from the cornea to the back of the eye. Evern a 1-mm increase in the axial length correlates with a myopic shift of 3 D, also known as spherical myopia.^3,4

2. Refractive myopia occurs when the focusing power of the eye is abnormally strong and focuses the image in front of the retina.4 It can be attributed to changes in the structure or location of the image-forming structures of the eye, i.e. the cornea and/or lens.⁵

While myopia here was classified as the cause, it is not the only way to understand the different types of myopia.

Classifying myopia based on numbers

Did you know that myopia, or near-sightedness, can be measured with numbers? It's just like using math to understand how well the eyes can see things far away. However, before we get to the different types of myopia based on numbers, it is important to understand the basics.

Myopia is discussed using the measure of lens power called the Dioptre (D). When it comes to myopia correction lens type, we always use negative numbers to denote the power, as the lens used for vision correction is a concave lens. If the prescription says -1.00, that means your child could have one dioptre of near-sightedness, which is a fairly mild amount of near-sightedness. If the number is -4.25, that means they have 4 and 1/4 dioptres of near-sightedness. This is more nearsighted than -1.00 and requires stronger (thicker) lenses. The further away from zero the number, the worse the eyesight and more vision correction (stronger prescription) is needed for your child.⁶

Accordingly, the 4 different types of myopia are as follows:⁵

1. Myopia: When the eyes can't see things far away very well, characterized by a number that is less than -0.5.

2. Low Myopia: Myopia that is between -0.5 and -6.00 dioptres.

3. High Myopia: If the number is lesser than -6.00 dioptres, which means it's even harder to see faraway things. It is a severe form of myopia, also called as pathological myopia or degenerative myopia in which the eye grows too long, causing problems in the posterior or back part of the eye such as posterior staphyloma (bulging in the back part of the eye), issues with the central vision area or damage to the optic nerve, which can reduce the sharpness of vision even with glasses or lenses.

4. Pre-myopia: A refractive state of an eye close to emmetropia in children where a combination of baseline refraction, age, and other quantifiable risk factors provide a sufficient likelihood of the future development of myopia. Hence, one may need to take necessary steps to prevent it.

Classifying myopia based on environmental influences⁷

Apart from this, myopia or near-sightedness can be influenced by various environmental factors. Accordingly, below are the 2 different types of myopia:

1. Night myopia: Sometimes, people might find it harder to see things clearly at night. This is called "night myopia." It happens because low light conditions make it challenging for the eyes to focus correctly. Additionally, the pupils become larger in the dark, allowing more unfocused light to enter the eye. 2. Pseudo myopia: Also known as "false myopia," occurs due to excessive close-up work. Distance vision becomes temporarily blurred due to overuse of the eye's focusing mechanism. Usually, resting the eyes restores clear distance vision, however, prolonged visual stress could lead to permanent reduction in distance vision over time.

Thus, myopia is not just a single condition; it comes in different forms and can be influenced by various factors. Whether it's the way our eyes react to low light, the consequences of excessive close-up work, or the numerical measurements that define its severity, there's a lot to learn about myopia.

Seeking prompt advice from an eye care specialist is important. By being informed and taking proactive steps, you can protect your child’s vision so that they get to experience a world that is bright and clear.

References:

1. Porter D. Myopia control in children [Internet]. 2022 [cited 2023 Nov 15]. Available from: https://www.aao.org/eye-health/diseases/myopia-control-in-children

2. Nearsightedness (myopia) [Internet]. U.S. Department of Health and Human Services; [cited 2023 Nov 15]. Available from: https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/nearsightedness

3. Subudhi P, Agarwal P. Myopia. [Updated 2023 Mar 31]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-.

4. Recko M, Stahl ED. Childhood myopia: epidemiology, risk factors, and prevention. Missouri medicine. 2015 Mar;112(2):116.

5. Flitcroft DI, He M, Jonas JB, Jong M, Naidoo K, Ohno-Matsui K, Rahi J, Resnikoff S, Vitale S, Yannuzzi L. IMI - Defining and Classifying Myopia: A Proposed Set of Standards for Clinical and Epidemiologic Studies. Invest Ophthalmol Vis Sci. 2019 Feb 28;60(3):M20-M30.

6. WebMD [Internet]. What Is Acuity of Vision?; [cited 2023 Nov 15]. Available from: https://www.webmd.com/eye-health/what-is-acuity-of-vision

7. Myopia [Internet]. [cited 2023 Nov 15]. Available from: https://www.aoa.org/healthy-eyes/eye-and-vision-conditions/

FAQs

Q1) What are 3 types of myopia?

Ans: There are 2 different types of myopia: Axial myopia and Refractive myopia.

Q2) What is the most common type of myopia?

Ans: Axial myopia is the most common type of myopia observed in clinical practice and is caused by an increase in the axial length of the globe. This means, the axial length of the eye is too long when measured from the cornea to the back of the eye. Evern a 1-mm increase in the axial length correlates with a myopic shift of 3 D, also known as spherical myopia.

Q3) What is myopia classification?

Ans: While comprehending the various treatment options for managing myopia is crucial, it's equally important to understand the different types of myopia. Accordingly, myopia can be classified into different types based on cause, the rate of progression or even changes to the eye resulting from it.

Q4) What is high myopia called?

Ans:High Myopia: If the number is lesser than -6.00 dioptres, which means it's even harder to see faraway things. It is a serious form of myopia, also called pathological myopia or degenerative myopia in which the eye grows too long…

Q5) What is serious myopia?

Ans:It is a severe form of myopia, also called as pathological myopia or degenerative myopia in which the eye grows too long, causing problems in the posterior or back part of the eye such as posterior staphyloma (bulging in the back part of the eye), issues with the central vision area and damage to the optic nerve, which can reduce sharpness of vision even with glasses or lenses.