Introduction to Cataracts

A cataract is “a clouding of the lens of the eye or of its surrounding transparent membrane that obstructs the passage of light”. Cataracts cause 50% of blindness and 33% of visual impairment around the world (Wale et al). Luckily, cataract surgery is one of the most common surgical procedures performed around the world and has a very high success rate.

The Lens

To understand cataracts, we need to begin with the lens. The crystalline lens is a transparent structure in the eye that helps to refract light on the retina. It can focus on objects at different distances by changing shape to allow a sharp image to be formed on the retina. This is known as accommodation and is an ability that is gradually lost as we age. It is made up of a lens capsule, epithelium, cortex, and nucleus. When any of these parts are opacified, that can cause a cataract. There are many classification systems of cataracts which include being classified based on the location of the opacification in relation to the lens.  

image
https://veteriankey.com/lens-introduction/ The anatomy of the lens.

Aetiology

The most common cause of cataracts is age-related due to changes in the physiology and the content of the lens. However, there are other causes and risk factors such as UV exposure, systemic (such as diabetes), ocular (such as uveitis) traumatic, congenital, and drug-related (oral and ocular steroid use).

Types

There are 3 main types of age-related cataracts, they are classified based on where the cataract is located: 

Nuclear Sclerotic: Yellowing and hardening of the nucleus of the lens. It happens gradually over time

image 1
https://eyewiki.aao.org/File:Nuclear_Sclerosis.jpg#filelinks

Cortical: Occurs when the portion of lens fibres of the cortex surrounding the nucleus becomes opacified. Most commonly presents with glare, i.e., from car headlights while driving at night

image 3
https://eyewiki.aao.org/File:Retroillumination_of_cortical_cataract.jpg

Posterior Subcapsular Cataracts: opacification of the most posterior layer, directly under the lens capsule. Tends to affect younger patients, diabetics, steroid users (oral and topical) and patients with ocular inflammation

image 4
https://eyewiki.aao.org/File:Psc.jpg

Other types of primary cataracts include Anterior subcapsular, Diabetic snowflake and membranous. 

Investigations

Visual function is determined by obtaining a history of visual disturbances and by measuring visual acuity. A thorough dilated eye examination using a slit lamp should also be performed to rule out active causes of cataracts (such as uveitis) which need addressing first before opting for surgery.

Some factors that may affect surgical planning include the severity of the cataract, the size of the dilated pupil, corneal clarity, lens stability, anterior chamber depth, optic nerve and retinal function. Some patient factors include cardio-respiratory compromise, ability to comply with laying flat, cognitive status and medications use such as alpha antagonists.

Management

The management of Cataracts is mainly split into 3 categories. All patients should be educated on how to prevent it in the first instance. If preventative measures fail, the treatment is then offered using medical or surgical methods. 

Preventative
  • Balanced diet
  • Use of Ultraviolet light (UV) blocking sunglasses
  • Use of protective eyewear to prevent injuries
  • control of blood sugar levels
Medical
  • Up to date pair of refractive glasses might suffice for patients not keen on cataract surgery
  • Avoidance of nighttime driving to prevent glare
Surgery
  • The commonest type of cataract surgery in the developed world uses ultrasound energy to break the cataract into small particles that are then aspirated through a handpiece. This is called phacoemulsification. 
  • Other methods exist which are less reliant on the expensive machines used in phacoemulsification including extracapsular cataract extraction (ECCE) where the whole nucleus-cortex complex of the cataract is removed after extracting it from the capsular bag. These can be useful techniques to use in resource-poor settings to deal with the global burden of cataract-related blindness. 

References

  1. Wale M, Derbew M, Tilahun M, Terefe M. Cataract and associated factors among adults visiting ophthalmic clinic at Debre Markos comprehensive specialized hospital, northwest Ethiopia, 2020. SAGE Open Medicine. 2021;9:205031212198963.
  2. Cataracts | National Eye Institute [Internet]. Nei.nih.gov. 2022 [cited 22 September 2022]. Available from: https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/cataracts
  3. Cataract – EyeWiki [Internet]. Eyewiki.aao.org. 2022 [cited 22 September 2022]. Available from: https://eyewiki.aao.org/Cataract
  4. Yanoff M, Duker J. Ophthalmology. [Edinburgh]: Mosby; 2008.
  5. File:Nuclear Sclerosis.jpg – EyeWiki [Internet]. Eyewiki.aao.org. 2022 [cited 22 September 2022]. Available from: https://eyewiki.aao.org/File:Nuclear_Sclerosis.jpg
  6. File:Retroillumination of cortical cataract.jpg – EyeWiki [Internet]. Eyewiki.aao.org. 2022 [cited 22 September 2022]. Available from: https://eyewiki.aao.org/File:Retroillumination_of_cortical_cataract.jpg
  7. File:Psc.jpg – EyeWiki [Internet]. Eyewiki.aao.org. 2022 [cited 22 September 2022]. Available from: https://eyewiki.aao.org/File:Psc.jpg
  8. [Internet]. Cataractcourse.com. 2022 [cited 22 September 2022]. Available from: http://cataractcourse.com/wp-content/uploads/2016/08/Anterior-segment-AA0_55107-768×639.jpg

Written by Dr Kareem Alsaffarini (FY2) & reviewed by Mr Zeyad Al-Moasseb (ST4)

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