The Science Behind Myopia: What Happens Inside the Eye?

The Science Behind Myopia: What Happens Inside the Eye?

Introduction to Myopia

What Is Myopia?

Myopia, commonly known as nearsightedness, is a refractive error of the eye in which close objects appear clear but distant objects look blurry. It is one of the most common vision problems worldwide and is increasing rapidly, especially among children and teenagers.

In a healthy eye, light rays entering the eye focus directly on the retina — the light-sensitive layer at the back of the eye. In myopia, however, light focuses in front of the retina instead of directly on it. This improper focusing leads to blurred distance vision.

Understanding the science behind myopia requires a basic knowledge of how the eye works and what changes occur in its structure.

How Normal Vision Works

Structure of the Eye

The human eye functions much like a camera. It has several important parts that work together to produce clear vision:

1. Cornea – The transparent front surface of the eye that bends (refracts) incoming light.
2. Pupil – The opening that allows light to enter.
3. Lens – A flexible structure that fine-tunes the focus of light.
4. Retina – The inner lining at the back of the eye that converts light into electrical signals.
5. Optic Nerve – Carries visual information to the brain.

The Process of Focusing Light

When light enters the eye:

1. It first passes through the cornea.
2. The cornea bends the light.
3. The lens further adjusts the focus.
4. Light rays converge exactly on the retina.
5. The retina sends signals to the brain.
6. The brain interprets these signals as clear images.

For distant objects, the light rays are almost parallel. A properly shaped eye brings these parallel rays to a precise focus on the retina.

What Happens in Myopia?

Light Focuses in Front of the Retina

In myopia, the eye does not focus light correctly. Instead of landing on the retina, light rays converge in front of it. By the time they reach the retina, the rays have already started spreading out again, resulting in a blurred image.

This is the core scientific problem behind myopia.

The Main Scientific Causes of Myopia

1. Elongated Eyeball (Axial Myopia)

The most common cause of myopia is an elongated eyeball. The eye becomes longer from front to back than normal.

Because of this increased length:

• Light travels a longer distance.
• It focuses before reaching the retina.
• Distant vision becomes blurry.

This condition is called axial myopia.

2. Excessive Curvature of the Cornea (Refractive Myopia)

Sometimes, the cornea is too curved. When this happens:

• The cornea bends light too strongly.
• Light focuses too quickly.
• The focal point forms in front of the retina.

This is known as refractive myopia.

Understanding Refraction: The Core Concept

What Is Refraction?

Refraction is the bending of light when it passes from one medium to another (for example, from air into the cornea).

The amount of bending depends on:

• The shape of the cornea
• The power of the lens
• The length of the eyeball

In myopia, the refractive power of the eye is too strong for its length.

The Role of the Retina

Why the Retina Is Important

The retina contains specialized cells called:

• Rods – Help in low-light vision.
• Cones – Responsible for color and detailed vision.

If light does not focus directly on the retina, these cells cannot produce a sharp image. Even though the retina itself may be healthy in simple myopia, the image formed is unclear because of improper focusing.

Why Distant Objects Become Blurry

Parallel Light Rays and Distance Vision

When looking at distant objects:

• Light rays enter the eye nearly parallel.
• In a normal eye, these rays meet exactly on the retina.
• In a myopic eye, they meet before reaching the retina.

As a result:

• The retina receives a defocused image.
• The brain interprets it as blurry.

Why Near Objects Appear Clear

Converging Light Rays from Nearby Objects

When looking at nearby objects:

• Light rays spread out more.
• The eye naturally adjusts (accommodation).
• The focal point shifts backward.

In many cases, this allows the light to land correctly on the retina in a myopic eye, making close objects appear clear.

This is why myopia is called nearsightedness.

Accommodation and Myopia

What Is Accommodation?

Accommodation is the process by which the lens changes shape to focus on near objects.

In a myopic eye:

• The eye is already focused for near objects.
• Less accommodation is needed.
• Near tasks feel easier than distance viewing.

However, prolonged near work may increase eye strain.

The Role of Genetics

Is Myopia Inherited?

Genetics plays a major role in the development of myopia.

If:

• One parent is myopic → Child has higher risk.
• Both parents are myopic → Risk increases significantly.

Scientists have identified multiple genes associated with eyeball growth and refractive development.

Environmental Factors and Eye Growth

How Lifestyle Influences Eye Shape

Research shows that environmental factors strongly influence myopia progression.

Key factors include:

• Excessive screen time
• Prolonged reading at close distance
• Limited outdoor exposure
• Reduced sunlight exposure

The Theory of Eye Growth Regulation

The eye continues to grow during childhood. Visual signals from the retina guide this growth.

If the retina consistently receives blurred images (especially during development), it may signal the eye to grow longer. This elongation worsens myopia.

The Biology of Axial Elongation

Why Does the Eye Become Longer?

Axial elongation occurs due to changes in:

• The sclera (white outer layer of the eye)
• Collagen structure
• Biochemical signaling pathways

Growth factors influence the stretching of the sclera, increasing the eye's length.

Once the eye elongates significantly, the condition becomes permanent.

Types of Myopia

1. Simple Myopia

• Mild to moderate.
• Common in school-aged children.
• Usually stabilizes in early adulthood.

2. High Myopia

• Severe degree (often more than -6.00 diopters).
• Associated with longer axial length.
• Higher risk of complications.

3. Pathological Myopia

• Progressive and severe.
• Can lead to retinal thinning.
• May cause vision-threatening complications.

Measuring Myopia

What Are Diopters?

Myopia is measured in diopters (D).

• A negative number (e.g., -2.00 D)
• Higher negative numbers indicate stronger correction needed.

The measurement represents the optical power required to bring light focus back onto the retina.

How Glasses Correct Myopia

Concave (Diverging) Lenses

Glasses for myopia use concave lenses.

These lenses:

• Spread out incoming light rays slightly.
• Move the focal point backward.
• Allow light to focus directly on the retina.

This restores clear distance vision.

Contact Lenses and Laser Surgery

Contact Lenses

Contact lenses sit directly on the cornea and:

• Adjust the focusing power.
• Provide a wider field of view.
• Offer cosmetic convenience.

Laser Surgery

Laser procedures reshape the cornea by:

• Flattening it slightly.
• Reducing excessive curvature.
• Correcting refractive error.

However, surgery does not change the elongated eyeball in axial myopia.

Long-Term Structural Changes in Myopia

What Happens in High Myopia?

In severe cases:

• The retina becomes stretched.
• Risk of retinal detachment increases.
• Macular degeneration may develop.
• Glaucoma risk rises.

The stretched eye tissues become thinner and more fragile.

The Myopia Epidemic

Why Is Myopia Increasing?

Globally, myopia rates are rising rapidly.

Contributing factors:

• Increased academic pressure
• Digital device usage
• Reduced outdoor play
• Urban lifestyle changes

Some projections suggest that nearly half the world’s population may be myopic by 2050.

Can Myopia Be Prevented?

The Role of Outdoor Light

Studies show that spending at least 1–2 hours outdoors daily may reduce myopia risk.

Natural sunlight stimulates dopamine release in the retina, which helps regulate eye growth.

Healthy Visual Habits

• Follow the 20-20-20 rule (every 20 minutes, look 20 feet away for 20 seconds).
• Maintain proper reading distance.
• Limit continuous screen exposure.
• Ensure adequate lighting.

The Future of Myopia Research

Advanced Treatments Under Study

Researchers are exploring:

• Atropine eye drops to slow progression.
• Specialized contact lenses to control eye growth.
• Orthokeratology lenses worn overnight.
• Genetic therapies targeting growth signals.

The goal is not only to correct myopia but also to prevent its progression.

Conclusion

Myopia is not just a simple vision problem—it is a complex interaction between eye shape, light refraction, genetics, and environmental influences. The core issue lies in how light focuses in front of the retina due to either elongation of the eyeball or excessive curvature of the cornea.

Understanding what happens inside the eye helps us appreciate why distant objects become blurry and why early intervention is important. As research continues, better strategies for prevention and management are emerging, offering hope for controlling the global rise of myopia.

Clear vision depends on precise optical alignment, and even small structural changes inside the eye can significantly affect how we see the world.