Introduction

Globally, vision impairment remains a pressing concern, affecting over 2.2 billion individuals. Notably, nearly half of these cases - comprising of at least 1 billion people - could have been prevented or managed with timely intervention. Among these, are conditions such as cataracts, refractive errors, age-related macular degeneration, glaucoma, and diabetic retinopathy, which stand as the most significant contributors to vision impairment and blindness.^1,2

Vision impairment significantly impacts the quality of life for adults, leading to lower employment rates and increased levels of depression and anxiety. Severe early childhood vision impairment can cause developmental delays and lifelong consequences, while school-aged children with vision issues may struggle academically. Among older adults, it exacerbates social isolation, compromises mobility, heightens the risk of falls and fractures, and accelerates the need for nursing or care home placement. These underscore the urgency of understanding and addressing common eye diseases and conditions.

Proactive measures are essential in safeguarding one's eye health. By embracing a healthy lifestyle and prioritising regular visits to eye care professionals, individuals can take proactive steps to preserve their vision and address any gradual or sudden changes in their vision. Through understanding and action, we can collectively work towards reducing the burden of vision impairment and ensuring better eye health.²

Anatomy of the eye

In order to understand the most prevalent eye diseases, it will be helpful to understand how a healthy eye works. 

The eye comprises several essential components that work together to enable vision. At its front, the cornea serves as a transparent shield, focusing incoming light. Positioned behind the cornea, is the iris, with its colourful pigmentation, which regulates the amount of light entering through the adjustable pupil. The lens, located behind the pupil, further focuses the light onto the retina, a light-sensitive layer lining the back of the eye. The retina contains photoreceptor cells - rods for low-light vision and cones for colour perception - that convert light into electrical signals. These signals are then transmitted through the optic nerve and into the brain, where visual information is interpreted as images. Each part plays a crucial role in the intricate process of sight, from light reception to perception, so any defects in any structure or function lead to eye diseases that are discussed below.³

By understanding how these diseases affect different parts of the eye, individuals can recognise symptoms early and seek appropriate treatment in a timely manner, which is what distinguishes minor vision abnormalities from total vision loss (blindness).

Common eye conditions

Refractive errors

Refractive errors are a common vision problem resulting from irregularities in the shape of eye components such as the cornea or lens, which disrupt the correct focusing of light onto the retina, the eye's light-sensitive layer. This condition leads to difficulties in achieving clear vision. With more than 150 million Americans affected, refractive errors stand as the most prevalent vision issue in the United States.⁴ 

There are 4 main types of refractive errors: 

• Myopia (nearsightedness) - objects far away appear blurry 
• Hyperopia (farsightedness) - nearby objects appear blurry
• Astigmatism - all objects appear distorted or blurry irrespective of distance
• Presbyopia - difficulty in seeing or focusing on things up close in middle-aged or older individuals

The primary symptom of refractive errors is blurry vision, accompanied by a range of additional symptoms. These may include double or hazy vision, seeing a glare or halo around bright lights, and frequently squinting. Individuals may also report headaches, eye strain (characterised by tired or sore eyes), and difficulty focusing when reading or using a computer.⁴

Following an eye exam, the most common corrective measures for refractive errors include glasses, contact lenses, and surgical interventions. Glasses are a straightforward and safe option which involves an optician prescribing the appropriate lenses to optimise vision. Contact lenses, which rest on the eye's surface, also correct refractive errors and are custom-fitted by your eye doctor. Additionally, surgical procedures such as laser eye surgery can alter the cornea's shape to address refractive errors.

Age-related eye conditions

Cataracts

Cataracts are implicated as one of the leading causes of vision impairment and blindness worldwide and increase in prevalence with age. In fact, over 50% of Americans over age 80 have cataracts.⁵ Cataracts refer to the clouding of the eye's natural lens, which is normally clear. This clouding occurs gradually and can lead to blurred vision, faded colours, increased sensitivity to glare, and even difficulty seeing at night. The clouding is a result of the breakdown and clumping of proteins within the lens as we age, resulting in the formation of a cloudy region on the lens, which over time leads to vision loss. 

The most effective treatment for cataracts is surgery, a common and relatively safe procedure that involves removing the cloudy lens and replacing it with an artificial one, restoring clear vision for many individuals. However, pending surgery, there are other methods for managing life with cataracts. At-home management involves simple adjustments such as using brighter lighting, wearing UV-protected sunglasses, and using a magnifying glass for tasks like reading. Additionally, updating prescriptions for glasses or contact lenses can improve vision in the early stages of cataract development.

Age-related macular degeneration (AMD)

AMD is a prevalent eye disease that affects central vision clarity, resulting from damage to the macula over time, the area of the eye responsible for sharp and straight-ahead vision control. Situated within the retina, the macula's deterioration gradually impairs central visual clarity that is essential for activities like reading, driving, and recognising faces. While AMD stands as a leading cause of vision loss among older adults, it typically does not lead to complete blindness. 

There are 2 types of AMD:

• Dry AMD (atrophic AMD): This form is more common, accounting for about 80-90% of all AMD cases. It occurs when small yellow deposits called drusen accumulate under the retina, gradually thinning and drying out the macula. It occurs in 3 stages: early, intermediate and late. Unfortunately, there is no treatment for dry AMD.
• Wet AMD (advanced neovascular AMD): Although less common, wet AMD is more severe and typically progresses more rapidly. It occurs when abnormal blood vessels grow beneath the macula and leak blood and fluid, damaging the macula. Wet AMD can lead to sudden and significant changes in vision, including the appearance of straight lines appearing wavy or distorted.

While there is currently no cure for AMD, early detection and treatment can help slow disease progression and preserve remaining vision. Treatment options for wet AMD may include anti-VEGF injections, which help prevent the growth of abnormal blood vessels, and photodynamic therapy (PDT). Lifestyle changes such as quitting smoking, maintaining a healthy diet rich in antioxidants and omega-3 fatty acids, and protecting the eyes from UV light with sunglasses. In addition, regular eye exams are crucial in managing AMD and reducing the risk of vision loss.

Glaucoma

Glaucoma is a group of eye conditions that damage the optic nerve, which is crucial for transmitting visual information from the eye to the brain. The precise cause is unknown but the damage results from elevated pressure within the eye, leading to gradual vision loss and potentially irreversible blindness if left untreated. Glaucoma is commonly referred to as the "silent thief of sight" because it usually advances slowly and without obvious signs until substantial vision loss occurs, which is why regular eye exams are crucial for early detection.⁶ 

There are several types of glaucoma but the 2 most common are:

• Open-angle glaucoma: The most common form of glaucoma. It develops gradually, as the drainage angle within the eye becomes less efficient at draining the fluid in the front part of the eye. As a result, eye pressure gradually increases, leading to optic nerve damage and peripheral vision loss.
• Angle-closure glaucoma: This type of glaucoma occurs when the drainage angle within the eye becomes blocked, leading to a sudden increase in intraocular pressure (IOP). This can result in severe symptoms such as eye pain, headaches, nausea, and blurred vision. Angle-closure glaucoma is considered an emergency medical condition and requires urgent care to avoid permanent visual loss.

Treatment won’t reverse any vision loss but it can prevent it from worsening. Treatment options typically include; prescription eye drops to lower the IOP, laser therapy to improve drainage, and in more advanced cases surgical procedures to drain fluid.

Glaucoma is a very serious condition, so it is important to be able to identify the risk factors which include age, family history, ethnicity (African, Hispanic, or Asian), elevated IOP, thin corneas, and certain medical conditions like diabetes and high blood pressure.⁶ 

Diabetic retinopathy

Diabetes retinopathy is a vision-related consequence of diabetes. High blood sugar levels damage the blood vessels in the retina. Over time, these damaged blood vessels can leak fluid or bleed, leading to vision problems. Diabetic retinopathy can cause symptoms such as blurred or distorted vision, floaters, and difficulty seeing at night. Without timely treatment, it can progress to more severe stages and result in permanent vision loss or blindness. This condition often leads to the development of other visual diseases such as diabetic macular oedema (DME), neovascular glaucoma and retinal detachment.⁷

While treatment cannot reverse vision damage, it can halt further deterioration. Controlling diabetes, blood pressure and cholesterol is also important. Treatment options include anti-VEGF injections and corticosteroids to slow or reverse diabetic retinopathy, laser treatment to reduce retinal swelling and stop leakage, and, in severe cases, vitrectomy surgery to address significant bleeding or scarring in the retina.^7,8

Summary 

Understanding common eye diseases and their implications is vital for proactive eye health management. With over 2.2 billion individuals globally affected by vision impairment, prevention and timely intervention are crucial. From refractive errors to age-related conditions like cataracts, AMD, glaucoma, and diabetic retinopathy, each condition underscores the importance of regular eye check-ups and early detection. By prioritising healthy lifestyle choices and seeking timely treatment, individuals can mitigate the risk of vision loss and preserve their quality of life. Through collective efforts in education, awareness, and accessible eye care, we can strive towards a future where vision impairment is minimised, and better eye health is within reach for all.