What Are Refractive Errors?

Refractive errors are a common ocular condition (eye condition) that affects millions worldwide. These errors result from imperfections in the shape of the eye, causing light to focus either in front of or behind the retina, leading to blurred or distorted vision. Think of it like a camera trying to capture a clear image but being slightly out of focus, causing the picture to appear blurred or distorted. In this article, we will look at types of refractive errors, their causes, symptoms, diagnosis, and treatment options for effective management.

The science of vision

Before we dive into the details of refractive errors, it's essential to understand the science behind our vision. Vision is not just about opening our eyes and seeing the world. It involves a series of complex processes which involve the eye's optical system.¹ This system consists of several optical components that work together to focus light onto the retina. These components include:

• Cornea: The transparent, curved front surface of the eye. It plays a vital role in refracting light as it enters the eye.
• Lens: Located behind the cornea, the lens is adjustable and fine-tunes the focusing process. It helps accommodate different distances, allowing you to shift your focus from near to far objects.
• Retina: The innermost layer of the eye, covered in light-sensitive cells called photoreceptors. The retina acts like a camera's film, capturing and transmitting the visual information to the brain.

Light is the key player in the visual process. When you see an object, it's because light from that object travels into your eye. As light passes from one medium, like the air, into another, such as the cornea of the eye, it changes direction, a phenomenon known as refraction. This bending of light is critical for the formation of a clear image on the retina.

To achieve clear vision, the focal point of light must align perfectly with the retina. When light focuses directly on the retina, the brain processes it into a sharp, well-defined image. However, if the light happens to pass through in any other way, this leads to blurred vision and refractive errors.

Types of refractive errors explained

There are four types of refractive errors, each associated with a unique problem in the eye's optical system, which is explained in detail below:

Myopia (Nearsightedness)

Myopia or near/short-sightedness is quite common, affecting nearly 42% of Americans.² It occurs when the cornea is too steep or the eyeball is too long. This causes light to focus in front of the retina rather than directly on it. Those with myopia can clearly see objects directly in front of them or nearby but struggle to see objects far away. They often need to squint or move objects closer to their eyes to focus properly and see more clearly.

Hyperopia (Farsightedness)

Hyperopia or far/long-sightedness occurs when the cornea is too flat, or the eyeball is too short. This causes light to focus behind the retina.³ Individuals with hyperopia have difficulty seeing objects close to them but have no trouble seeing objects far away. Those with this condition might experience eyestrain or blurred vision when performing close-vision tasks.

Astigmatism

arises when the cornea or lens inside the eye has an irregular shape. Unlike myopia and hyperopia, astigmatism causes light to focus on multiple points in the eye instead of directly on the retina. This leads to issues with clarity and seeing objects that are both far and near. It can create a sense of double vision or ghosting (shadowing) of images.⁴ 

Presbyopia

A study by The Global Burden of Disease estimated that approximately 510 million people worldwide have visual impairment from uncorrected presbyopia.⁵ Unlike the other three refractive errors, presbyopia is an age-related condition. As people age, the eye's lens naturally becomes less flexible, making it difficult for the eye to focus on close-up objects. Presbyopia typically becomes noticeable around the age of 40. 

Refractive error symptoms

Identifying symptoms or how refractive errors impact vision is vital for effectively addressing the challenges they pose. It marks the critical first step in diagnosis and seeking appropriate treatment to ensure clear and comfortable vision. Below, we look at the symptoms of each refractive error:

What causes refractive errors?

Refractive errors can develop due to:

• Changes to your cornea
• Eyeball length (i.e., the eyeball grows too short or too long)
• Ageing of the eye’s lens
• Cataract surgery

What are the risk factors for refractive errors?

It is possible for anyone to develop refractive errors during any point in their life. However, if you have family members who wear glasses/contact lenses, you may have an increased risk. The onset of most refractive errors (e.g., myopia and hyperopia) occurs during childhood, whereas presbyopia is more commonly found in adults at age 40 or above.

Consult with your eye care specialist about your risks of getting refractive errors, and how often you need to get an eye exam.

Diagnosing refractive errors

Eye care professionals use a variety of assessments and tools to determine the nature and extent of refractive errors. These include:

Visual acuity test 

This is one of the first assessments used to determine the presence of refractive errors. It typically involves reading letters or symbols on a chart from a specific distance to measure how well you can see. The results are usually expressed as a fraction, such as 20/20, where the first number represents the distance you are tested, and the second number represents the distance at which an individual with normal vision can see the same line.⁶

Refraction test

A refraction test is performed to determine the precise prescription needed for eyeglasses or contact lenses. The optometrist or ophthalmologist uses a phoropter, a device with a series of lenses, to evaluate which combinations provide the clearest vision. This test can identify the specific refractive error and its magnitude.⁷

Retinoscopy

Retinoscopy is a technique where the eye care professional uses a beam of light to evaluate the reflection from the retina. By observing how the light reflects, the practitioner can estimate the prescription needed to correct refractive errors.⁸

Autorefractors and aberrometers

Autorefractors and aberrometers are automated instruments that provide objective measurements of the eye's refraction and aberrations. They are especially useful for diagnosing refractive errors in young children or individuals who have difficulty responding during the refraction test.⁹

Correcting and treating refractive errors

The good news is that refractive errors are highly treatable, and various options are available to help individuals regain clear vision. Let's look at some of them below:

Eyeglasses

One of the most common and non-invasive solutions is the classic spectacles or eyeglasses. These work by compensating for the eye's imperfections by redirecting incoming light so that it focuses exactly on the retina. Eyeglasses can be tailored to address myopia, hyperopia, astigmatism, and presbyopia, making them a versatile and effective option for vision correction.¹⁰

Contact lenses

Another non-invasive and effective option is contact lenses. These are placed directly on the cornea (the clear front surface of the eye) and work to correct vision impairment. Like eyeglasses, they provide a clear path for light to reach the retina. Contacts offer the advantage of being discreet and providing a wider range or field of vision than glasses. They are available in various types, including daily disposables, extended wear, and toric lenses for astigmatism.¹¹

Refractive surgery

Refractive surgery, such as LASIK (laser eye surgery), offers a more permanent solution for certain refractive errors. During LASIK, a laser reshapes the cornea to enhance its ability to focus light onto the retina. This procedure can effectively correct myopia, hyperopia, and astigmatism and reduce the dependence on glasses or contact lenses.¹²

Other surgical options

Alternative surgical procedures may be recommended for individuals with extreme refractive errors or unique eye conditions. These may include photorefractive keratectomy (PRK), implantable collamer lenses (ICL), or clear lens exchange (CLE), among others. The suitability of these procedures is determined by the eye's specific needs and the patient's preferences.¹³ 

Monovision and multifocal lenses

Monovision and multifocal contact lenses are typically recommended for those with presbyopia or a combination of refractive errors. Monovision lenses correct each eye separately — one for near vision and the other for distance, allowing the brain to adapt and select the appropriate eye for the task at hand. Multifocal lenses have multiple prescriptions built into one lens, providing clear vision at various distances.¹⁴ 

Summary

Refractive errors affect individuals of all ages, making understanding their impact on vision, the science involved, and available treatments crucial. Myopia, hyperopia, astigmatism, and presbyopia each bring unique challenges. Fortunately, clear and healthy eyesight is within reach with options like eyeglasses, contact lenses, refractive surgery, and more.

Consulting with an eye care professional is essential to determine the best treatment for your specific refractive error. Early detection via regular eye exams is key to maintaining vision and potentially preventing more severe eye conditions. Enjoy a world in sharp focus with the right care and intervention.