Myopia: Causes, Progression, and Treatment

What is Myopia?

Myopia is a refractive error that causes distant objects to appear blurry. It is the most common cause of vision impairment in people under 40 years old. Myopia often begins in childhood but can continue to worsen into early adulthood. This is referred to as myopic progression.

Nearly half of children with progressive myopia achieve stable prescriptions by age 15. About three-quarters stabilize by age 18, and most stabilize by age 24. However, myopia can progress rapidly to high myopia if not managed properly. High myopia can lead to vision-threatening complications in adulthood.

The number of people with myopia is increasing at an alarming rate. In 2000, about 25% of the world's population was myopic. Research suggests that by 2050, about half of the world's population will be myopic.

What Causes Myopia?

Myopia occurs when the eye focuses light rays in front of the retina instead of on the retina. This makes distant objects appear blurry.

Several different factors contribute to light focusing correctly on the retina:

• The length of the eye from front to back
• The shape of the cornea and lens
• The position of the lens and cornea relative to each other inside the eye

Small changes in any of these factors can cause myopia.

Emmetropization

In early childhood, the eyes of children grow and develop rapidly. During this time, the shape of the cornea and lens along with the length of the eye balance to create clear vision.

This process is called emmetropization. When there are no refractive errors in the eye, this is referred to as emmetropia.

Most children are born hyperopic (farsighted). This is because the eye is still too short from front to back at birth.

As children grow, the process of myopization continues until they are about 6 to 8 years old. At this point, most children are slightly hyperopic, and only a small percentage are myopic.

Development and Progression of Myopia

In some cases, this process continues. When this happens, the eye develops beyond hyperopia and towards myopia. The eyeball may become too long, or the curvature of the cornea or lens may become too steep. In rare cases, the lens may move too close to the cornea.

The peak years of myopic progression are often in childhood. The development and progression of myopia at this age are influenced by several factors, including:

• Genetics
• Time spent outdoors
• Near-work activities (such as reading and screen time)

A person may be three times more at risk for myopia if one of their parents is myopic. They may be six times more at risk if both parents are myopic.

However, recent studies show strong evidence that lifestyle factors can also cause myopia. For example, prolonged near work is associated with a higher likelihood of developing myopia. Spending more time outdoors may delay the onset of myopia.

Types of Myopia

Myopia is generally divided into two types depending on the cause:

• Axial myopia is caused by an eyeball that is too long from front to back (axial length). This is the most common cause of myopia, especially in children.
• Refractive myopia can occur if the cornea or lens is too curved. It can also occur if the lens is positioned too close to the cornea, but this is very rare.

Some people may have a combination of both axial and refractive myopia.

Symptoms of Myopia

Other symptoms of myopia include:

• Squinting (partially closing the eyes)
• Needing to move closer to see objects clearly
• Difficulty with activities that require good distance vision, such as driving or playing sports
• Headaches
• Eye strain

If you experience these symptoms while wearing glasses or contact lenses, schedule an eye exam with an optometrist. You may need a stronger prescription.

Managing Myopia

Managing myopia includes all aspects of eye care that a myopic person may need. The goal is to correct blurry vision, control the progression of myopia, and reduce the risk of complications from high myopia. Myopia management includes:

• Early detection and diagnosis.
• Timely correction and control of myopia.
• Home practice measures such as the 20-20-20 rule and limiting screen time.
• Addressing any complications related to myopia.

Detecting and Diagnosing Myopia

Early detection and intervention for myopia is key to slowing its progression. However, many children with myopia will not have clear signs and may not complain of symptoms. If a child's distance vision is consistently blurry, they may not realize that anyone else sees more clearly.

• First eye exam at 6 months of age
• Another at ages 3 to 5
• Another before first grade
• Annually throughout the school years

Children with a family history of myopia or who have already been diagnosed with myopia may need more frequent eye exams.

If you or your child need corrective lenses, the optometrist will inform you of the correction needed. The prescription for myopia is written as a minus (-) sign before a number. The higher the number, the more severe the myopia.

Low myopia ranges from -0.50 to -5.75, and high myopia is -6.00 or greater. High myopia is a concern because it can lead to serious complications. Complications associated with high myopia include:

• Posterior subcapsular cataracts
• Glaucoma
• Myopic macular degeneration
• Retinal detachment

If you are at risk for high myopia, the optometrist will discuss this issue with you. They will also check for complications related to high myopia during your exam.

Adults and children diagnosed with myopia need to have regular eye exams to monitor their level of myopia. If myopia is progressing, early intervention measures are crucial. It is very important to slow the progression of myopia before high myopia develops.

Correcting Myopia

Myopia can be corrected with optical methods or surgery. Optical methods include standard prescription glasses or contact lenses. Surgical methods include refractive surgery.

Some myopic individuals need to wear glasses or contact lenses all the time. Others may only wear them for specific tasks, such as driving or looking at a blackboard.

After the eye exam, the optometrist will discuss with you the exact amount of correction you need. They will also inform you how often you need to wear corrective lenses.

Refractive surgery can reduce or even eliminate the need for glasses or contact lenses. However, this is not an option for correction until a person's myopia prescription is stable. Some more common refractive surgeries include:

• PRK
• LASIK
• Implantable lenses known as phakic IOLs

Controlling Myopia

The number of people with myopia is increasing. This means there is a lot of interest in finding ways to control the progression of myopia in children. This is especially important because high myopia can lead to serious vision-threatening complications.

Recent research shows that wearing specially designed contact lenses can slow the progression of myopia. There is evidence that these lenses can slow the axial lengthening of the eye. In other words, they can slow the rate at which the eye grows longer.

For children with progressive myopia, effective myopia control methods include:

• Myopia control glasses – Some types of bifocal, progressive addition (PAL), and other specially designed lenses can slow the progression of myopia.
• Myopia control contact lenses – Soft multifocal contact lenses and orthokeratology have both shown effectiveness in slowing the progression of myopia. Soft multifocal contact lenses were originally designed for presbyopia. Newer designs of this type of lens are being used to control myopia, with good results. Orthokeratology, also known as corneal reshaping therapy, involves wearing gas permeable (RGP) contact lenses overnight to temporarily reshape the cornea while sleeping. This helps achieve clear vision during the day without wearing glasses or contact lenses. Studies show that orthokeratology may also be effective in reducing the progression of myopia.
• Atropine eye drops – Optometrists have used atropine eye drops to help control myopia for a very long time. However, high concentrations of atropine in eye drops tend to cause side effects such as light sensitivity and headaches. Fortunately, low-dose atropine eye drops can also slow the progression of myopia in children. Lower doses can slow progression at a similar rate to higher doses with significantly fewer side effects. However, some children do not respond well to atropine eye drops.
• Lifestyle factors – Research shows that spending at least 90 minutes outdoors each day helps reduce the risk of myopia. Parents should also encourage children to take regular breaks when reading or using screens outside of school hours. The exact relationship between near work and myopia is still not well understood. But some studies suggest that prolonged near work may be a risk factor for the development and progression of myopia. Habits of holding books, screens, and other near tasks too close to the eyes may also be a factor.

Myopia control strategies can be used individually or in combination. The optometrist can advise you on which methods will have the greatest impact on the progression of myopia.

When to Get an Eye Exam for Myopia Detection

All children should have regular eye exams starting at around 6 months of age. This is important even if there are no symptoms of myopia or other eye problems.

It is important to remember that early intervention is crucial. The earlier children start myopia control strategies, the better the impact. Slowing the progression of myopia is key to reducing the risk of vision-threatening complications in adulthood.