Refractive Errors

Myopia and Hyperopia

Normally, light enters the eye through the clear outer layer of the eye (called the cornea) and passes through a lens. These focus the light directly onto the light-sensitive tissue at the back of the eye called the retina. The retina can detect the light and send electric signals to the brain to be turned into a clear image. In some cases, the shape of the eye prevents the light from focusing directly on the retina causing blurry vision at certain distances. These are refractive errors called myopia and hyperopia.  

Myopia is a refractive error that occurs when the light focuses in front of the retina rather than directly on it like when the eye shape is too long. This makes far away objects appear blurry while closer objects are seen more clearly which is why we sometimes refer to it as “near-sightedness”. 

Hyperopia is a refractive error that occurs when the eye is shorter than normal or has a cornea (clear front window of the eye) that is too flat. As a result, light rays focus behind the retina instead of directly on it. Generally, this makes far away objects appear clearly but near objects appear blurred, hence the “far-sightedness”.


For people who are near-sighted or far-sighted, certain refractive surgery techniques can modify the curvature of the cornea. This helps improve the eye’s focusing power by making sure the light focuses closer to or directly onto the retina.


Unlike myopia and hyperopia which each have a single focal point for light, astigmatism is the result of the cornea or the lens having an irregular shape. This causes light to focus on multiple points rather than a single point on the retina.


Astigmatism can be corrected with refractive surgery techniques that reshape parts of the irregular cornea to make it smooth and symmetrical. The result is that images focus clearly on the retina rather than being distorted due to light scattering.

Presbyopia or Dysfunctional Lens Syndrome (DLS)​​

When you’re young, the lens in your eye is clear, allowing light to pass through without light scatter, glare, or blurry vision. It’s also soft and flexible, changing its shape easily, allowing you to focus on objects both close and far away. After the age of 40, the lens becomes more rigid and the lens can’t change shape as easily as it once did, making it more difficult to see at close range. This normal condition is called presbyopia or dysfunctional lens syndrome (DLS). Presbyopia literally means “aging eye” and is an age-related eye condition that makes it more difficult to see up close. 

The ability to focus on close objects is called accommodation. A healthy lens is round and can magnify objects so we can see clearly. The lens in the eye is held in place by many small fibres connected to a small muscle. When it’s relaxed, the muscles pulls on the fibres causing them to stretch the lens so it flattens out allowing us focus on things far away. When the muscle flexes, it relieves the tension on the fibres causing the lens to go back to its round shape makes it easier for us to see up close (like a magnifying glass). As we age, lenses simply lose their elasticity and don’t spring back to round as they did when we were younger.

If you feel like you’re experiencing eyestrain, headaches, feeling tired from close-up work, or find yourself holding reading materials or your phone at arm’s length in order to focus properly, these might be the effects of presbyopia. Dr. Youssef can diagnose presbyopia as part of a comprehensive eye examination.

These changes in our eyes with age are natural and since nearly everyone develops presbyopia, if a person also has myopia (near-sightedness), hyperopia (far-sightedness) or astigmatism, the conditions will combine. 

Presbyopia/DLS progresses in 3 stages:

Stage 1: Lose ability to focus on close objects

The loss of lens flexibility causes you to lose your ability to focus on close objects. From the day you’re born, your ability to focus on close objects decreases steadily and most don’t notice it at all until around age 40 when they start having trouble focusing at 14-16 inches from their eye – the distance you’d hold a book.

Stage 2: Lens Becomes Discoloured

The proteins that make up the lens become discoloured enough to cause mild glare and visual blur. Normally, the lens is completely clear, letting light shine through without an issue. As we age, the proteins break down causing the lens to go from clear to a yellow colour resulting in blurry vision and glare with night driving. For comparison, think of the way egg whites turn clear to white when heated – this is also because of proteins in the egg breaking down.

Stage 3: Cataract Forms

You lose the rest of your ability to focus and the yellowing of the lenses becomes dark enough that we call it a cataract.  If left untreated, the cataract will turn dark brown making seeing anything quite difficult until it turns completely white resulting in blindness.

How Can We Fix Presbyopia?


Reading glasses are a common and easy way to correct presbyopia symptoms and are typically worn just during close work such as reading, sewing, etc. “Readers” are can be purchased at drug stores, retail stores, or at PVSC. 

You can also opt for higher-quality eyeglasses with bifocal or progressive lenses prescribed by your eye doctor. Bifocal lenses have two different points of focus. The upper part of the lens is set for distance vision and the lower part is set near vision. Progressive lenses are similar to bifocal lenses, but they don’t have a visible line separating the prescriptions and so they offer a more seamless transition between the near and distance prescriptions.

Contact lenses also work to correct presbyopic vision. Multifocal contact lenses create multiple levels of corrective power similar to how bifocals work. Contacts can be set for monovision, in which one eye has a contact set for distance and the other has a contact set for near vision. The brain learns to adapt to using one eye or the other for different tasks.


You also have a few surgical options to treat presbyopia including:

Refractive lens exchange (RLE)

Refractive lens exchange (RLE) is often a better choice for treating presbyopia than glasses because it directly replaces the eye’s aging lens with a new one. This addresses the root cause of these conditions, offering a long-lasting solution. RLE can correct a wide range of vision issues and also prevents future cataracts, unlike cornea-based procedures (like LASIK) that reshape the eye’s surface but don’t directly fix lens-related problems.

Interested in RLE? Click here to learn more!

LASIK and cornea-based procedures

LASIK can be used to create monovision, in which one eye is corrected for near vision while the other eye is set for distance vision.

Another LASIK procedure (currently undergoing clinical trials in the U.S.) is presbyLASIK. This procedure uses an excimer laser (a laser that uses UV light) to sculpt the cornea, enabling vision at multiple distances.

Nevertheless, Dr. Youssef suggests opting for RLE surgery over cornea-based procedures as RLE addresses the defective lens, which is the underlying cause of the issue. RLE is also more suitable for patients in their 20s and 30s.