Cataract
How the lens stays transparent through the precise packing of its proteins, how age, light, glucose and steroids make those proteins clump and scatter light, and why that blurs and dims vision and causes glare.
By the end, you can
- Describe the structure of the lens and why it is transparent.
- Explain how crystallin proteins become damaged and aggregate to form an opacity.
- Distinguish nuclear, cortical and posterior subcapsular cataracts by location, cause and symptoms.
- Relate blurred vision, glare, faded colours and a myopic shift to light scattering and absorption.
- Explain why a cataract in infancy is urgent while age-related cataract is not.
- Recognise the slit-lamp appearances, stages and tests of cataract, and explain how lens replacement, laser capsulotomy and the medicines used around surgery act.
What it is
A cataract is an opacity of the lens of the eye that scatters or absorbs light enough to reduce vision. Most cataracts are age-related; others follow diabetes, steroid treatment, injury, radiation or eye inflammation, or are present from birth. Cataract is the leading cause of blindness worldwide and is reversible with surgery.
3 types to tell apart
- Nuclear
- The central lens hardens and turns yellow-brown with age; distance vision blurs and near vision may briefly improve.
- Cortical
- Wedge-shaped spokes in the outer lens; glare from bright lights is typical.
- Posterior subcapsular
- A plaque just under the back of the capsule; associated with steroids and diabetes, and troubles reading and bright light early.
US spelling: fibres → fibers.
Normal function
A transparent, adjustable lens
The sits behind the , suspended from the by . Relaxing the ciliary muscle tightens the zonules and flattens the lens for distance; contracting it lets the lens round up for near vision (accommodation).
The lens is enclosed in a capsule, with a layer of epithelium at the front. Epithelial cells at its equator elongate into lens fibres, which lose their nuclei and organelles and pack together in orderly layers. New fibres are added throughout life around the older ones, which form the dense central nucleus.
Transparency depends on uniform, very concentrated proteins called crystallins, packed so evenly that light passes without scattering. Lens fibres cannot replace their proteins, so crystallins must last a lifetime; antioxidants such as glutathione protect them.
Underlying change · Step 1 of 3
Lens proteins are damaged and clump
The full lesson is part of Student Pro
It takes you through all 3 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 2 of 3
Scattered light blurs and dims vision
The full lesson is part of Student Pro
It takes you through all 3 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Consequences · Step 3 of 3
Loss of function, and why age matters
The full lesson is part of Student Pro
It takes you through all 3 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Symptoms and signs
Symptoms, signs and findings
The full lesson is part of Student Pro
It takes you through all 3 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Exam detail
Exam detail
The full lesson is part of Student Pro
It takes you through all 3 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Treatment
How treatment works
The full lesson is part of Student Pro
It takes you through all 3 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Recap
Recap
The full lesson is part of Student Pro
It takes you through all 3 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Self-check
Check your understanding
The full lesson is part of Student Pro
It takes you through all 3 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .