What Is A Cataract In The Eye?

Cataracts are a clouding of the lens inside the eye.  A cataract is what eye doctors call the lens of the eye when it becomes cloudy and difficult to see through. Each eye can develop a cataract at the same time or at different times. Cataracts cannot spread from one eye to the other eye.

What Causes Cataract?

In most cases, a cataract is caused by simply getting older. It is usually an age-related disease, and it will happen to every single person if they live long enough. There are some other causes of cataracts, such as trauma to the eye and diabetes, but these are not as common as cataracts that are caused by aging. The lens of the eye is responsible for focusing the light which enters the eye onto the retina. That information is then sent via the optic nerve to the brain for processing.  When the eye’s natural lens develops a cataract, it obscures the light and makes vision blurry. Left untreated, cataracts may progress and lead to decreased vision or even blindness. As expected, the most common complaint when a person has a cataract is blurry vision.

Depending on the cause and type of cataract, the progression and severity of cataracts can vary. Around age 40, the proteins that make up the lens in the eye start to break down, leading to the formation of cataracts. Although age is the most common risk factor for cataracts, some other common risk factors are exposure to ultraviolet light, radiation exposure or radiation treatment, smoking, excessive alcohol consumption, diabetes, previous invasive eye surgery, traumatic eye injury, genetics, and taking steroid medications. 

How Common Are Cataracts?

It is estimated that about 95 million people are affected by cataracts (1). 36 million people are blind worldwide, and 13.5 million are blind due to cataracts (2,3). It is the leading cause of preventable blindness in low and middle income countries. Around age 50, about 5.22% of people have cataracts. As people continue to age, that number increases to about 15.45% at age 60, and 36.49% at age 70. By the time people are 80, around 68.30% of people have cataracts(4).

Related: Sleeping Position After Cataract Surgery

What Are Cataract Symptoms?

Cataracts will begin as cloudy or blurry vision and with time, vision will continue to decrease. Some types of cataracts will also develop a yellow or brown tint which may distort color vision. People also may experience difficulty seeing at night, and may have increasing trouble with nighttime driving due to glare or seeing halos around headlights or stop lights. Sometimes people may experience frequent changes in their glasses prescription and may also experience a phenomenon known as myopic shift due to cataracts. With myopic shift, or “second sight of the elderly”, people may start to realize they no longer need their reading glasses. However, this is not due to an improvement in their sight, but rather a progression of their cataracts which changes the way the light focuses in the eye.

Cataract Treatment

Some cataracts may progress very slowly and cause little to no decrease in vision. In these cases, it is acceptable to delay invasive treatment and continue to monitor the progression of the cataract with yearly eye exams until it becomes visually significant. Waiting too long, however, may lead to complications like lens-induced glaucoma and a more difficult cataract extraction surgery. Therefore, when a cataract has matured to the point where decreased vision causes difficulty with daily activities, it may be advised to undergo surgery by an Ophthalmologist. In this surgery, the cloudy lens is taken out and replaced with a new artificial lens.  Thankfully with technological developments and advances in surgical techniques, cataract surgery has become one of the most common surgeries performed worldwide with good outcomes with low rates of complications.

1. Liu YC, Wilkins M, Kim T, Malyugin B, Mehta JS. Cataracts. Lancet. 2017 Aug 5;390(10094):600-612. doi: 10.1016/S0140-6736(17)30544-5. Epub 2017 Feb 25. PMID: 28242111.
2. Flaxman SR, Bourne RRA, Resnikoff S, Ackland P, Braithwaite T, Cicinelli MV, Das A, Jonas JB, Keeffe J, Kempen JH, Leasher J, Limburg H, Naidoo K, Pesudovs K, Silvester A, Stevens GA, Tahhan N, Wong TY, Taylor HR; Vision Loss Expert Group of the Global Burden of Disease Study. Global causes of blindness and distance vision impairment 1990-2020: a systematic review and meta-analysis. Lancet Glob Health. 2017 Dec;5(12):e1221-e1234. doi: 10.1016/S2214-109X(17)30393-5. Epub 2017 Oct 11. PMID: 29032195.
3. Hashemi, H., Pakzad, R., Yekta, A. et al. Global and regional prevalence of age-related cataract: a comprehensive systematic review and meta-analysis. Eye 34, 1357–1370 (2020). https://doi.org/10.1038/s41433-020-0806-3
4. Cataract Tables | National Eye Institute. Nei.nih.gov. https://www.nei.nih.gov/learn-about-eye-health/outreach-campaigns-and-resources/eye-health-data-and-statistics/cataract-data-and-statistics/cataract-tables. Published 2022.