Axial Length: Measuring Eye Growth in Myopia Control

When your child’s prescription changes, it is natural to ask how much stronger it is. Another measurement can help explain what is happening: axial length, the distance from the front to the back of the eye. Following that measurement over time gives the doctor information about eye growth alongside the prescription and eye-health examination.

A prescription tells the doctor what correction your child needs. Axial length adds a direct measurement of the eye’s size, which is useful when monitoring myopia progression. In the sleepSEE® myopia-control program, those measurements help the provider assess the response to care and explain changes to the family. One reading is a starting point; the pattern over time is what makes monitoring useful.

This article will explain what axial length is, how we measure it, and why it's the key to protecting your child's long-term vision. We'll cover the risks associated with a longer eye and how we can slow its growth.

What is Axial Length, Really?

Myopia occurs when the eye grows too long, causing light to focus in front of the retina instead of on it. This makes distant objects blurry. The longer the eye, the worse the myopia.

Axial length records that front-to-back distance in millimeters. It gives the doctor a direct measure of eye size alongside the prescription, which can be influenced by other factors. Repeated readings help show a pattern of growth. The doctor interprets that pattern in the context of age and other findings; a single number does not establish whether growth is abnormal or whether a treatment is working.

In our clinic, serving families from Fayetteville to Fort Liberty, axial length measurement is a key part of our myopia management protocol. It allows us to shift from simply correcting blurry vision to proactively managing the underlying issue: excessive eye growth.

How We Measure It: A Look at Optical Biometry

We use an optical biometer to measure axial length. The process is quick, painless, and non-invasive. Your child rests their chin on the machine and looks at a light. A low-power laser scans the eye and provides a measurement in seconds.

This technology is accurate to a hundredth of a millimeter, which is crucial for tracking even small changes in eye growth. This data helps us determine if our treatment strategy is effective.

The Story of Growth: Normal vs. Concerning

While it's normal for a child's eyes to grow, in a myopic child, this growth is accelerated. A non-myopic child's axial length might grow by 0.1 mm per year, while a myopic child might see growth of 0.3 mm or more. This rapid growth is a major red flag.

A 1 mm increase in axial length is equivalent to a prescription change of about -2.50 to -3.00 diopters. This level of change signals the need for intervention.

We use axial length growth charts, much like the height and weight charts at your pediatrician's office, to track your child's eye growth against established data. This allows us to determine if their growth rate is normal or if they are on a trajectory toward high myopia, enabling us to intervene early.

Plotting axial length on a growth chart helps us visualize and track progression against established percentiles. This data makes the concept of 'getting more nearsighted' a measurable reality for parents.

This chart illustrates the direct relationship between the physical length of the eye and the severity of myopia. As the axial length increases, so does the level of nearsightedness, requiring a stronger prescription to achieve clear vision.

The Risks of a Longer Eye: More Than Just Thick Glasses

Uncontrolled myopia is more than an inconvenience. Excessive axial length is a significant risk factor for serious eye diseases later in life. As the eye elongates, the retina and other tissues are stretched and thinned, increasing the risk of:

• Retinal Detachment: This is a medical emergency. The retina, the light-sensitive tissue at the back of the eye, pulls away from its normal position. This can cause sudden floaters, flashes of light, and a curtain-like shadow over your field of vision. If not treated promptly, it can lead to permanent vision loss.

• Glaucoma: Often called the "silent thief of sight," glaucoma damages the optic nerve, which connects the eye to the brain. This damage is irreversible and typically starts with the loss of peripheral (side) vision. Many people don't notice the changes until the damage is significant. High myopia is a major risk factor for developing glaucoma.

• Myopic Maculopathy: This condition affects the macula, the central part of the retina responsible for sharp, detailed vision. As the eye stretches, the macula can thin and degenerate, leading to distorted or blurry central vision. This can make activities like reading, driving, and recognizing faces difficult.

• Cataracts: While cataracts are a common part of aging, high myopia can cause them to develop earlier in life. A cataract is a clouding of the eye's natural lens, which can make vision blurry, hazy, or less colorful.

• Retinal Detachment: A sight-threatening emergency where the retina pulls away from its normal position.

• Glaucoma: A disease that damages the optic nerve, leading to irreversible peripheral vision loss.

• Myopic Maculopathy: A leading cause of vision loss in highly myopic eyes, where the central part of the retina degenerates.

• Cataracts: A clouding of the eye's lens that can occur earlier in life in people with high myopia.

Studies from the American Academy of Ophthalmology show that a person with a -6.00 diopter prescription has a 22 times higher risk of retinal detachment and a 40 times higher risk of myopic maculopathy. These risks are directly tied to axial length.

This is why our mission in myopia control is not just about clear vision for your child today; it's about preserving their eye health and reducing the risk of significant vision loss for the rest of their lives. It’s a preventative healthcare strategy for their eyes.

How sleepSEE® Ortho-K Puts the Brakes on Growth

Yes, we can do something about it. Orthokeratology (Ortho-K), the cornerstone of our sleepSEE® program, involves wearing custom-designed contact lenses overnight. These lenses gently reshape the cornea while you sleep, providing clear vision during the day without glasses or contacts.

Ortho-K is also used to influence the optical signals involved in eye growth. When a child wears standard glasses or contact lenses, the central vision is corrected, but the peripheral vision is not. This creates a phenomenon called 'peripheral hyperopic defocus,' where light focuses behind the peripheral retina. It's believed that this sends a signal to the eye to keep growing longer to 'catch up' to the light. Ortho-K, on the other hand, reshapes the cornea in such a way that it creates 'peripheral myopic defocus.' This means that light focuses in front of the peripheral retina. This is thought to send a 'slow down' signal to the eye, which reduces the drive for axial elongation. [1] The provider tracks axial length to assess how the individual child responds to this change in optics.

Studies have shown that Ortho-K can slow axial length growth in myopic children by 50% or more compared to glasses. [2] This reduces the final prescription and the lifetime risk of eye disease.

The founding Fayetteville sleepSEE® Myopia Control / Management first-year program includes twice-yearly axial length monitoring and corneal topography. Individual follow-up is determined by the provider. IMI clinical management guidance. Read the program inclusions.