Common conditions of the eye Flashcards
What is nuclear sclerosis?
Age-related lens opacification. Makes objects appear less clear and patients see more of the red spectrum. Can get a nuclear-sclerotic type cataract in which the lens becomes cloudy and yellow before eventually hardening.
Which eye condition causes the highest % of blindness?
Cataracts.
Why do cataracts develop?
Affect the lens.
Lens fibres are never shed, they just become compacted in the middle. The lens has no blood supply and it relies on diffusion for nutrition. It absorbs harmful UV rays to protect them from damaging the retina –> this can cause opacity in the lens –> cataract.
So, 3 reasons why a cataract develops -
1) Fibres never shed
2) Avascular lens
3) Absorbs UV rays
What is an immature cortical cataract?
Seen as spoke-like opacities. Patient will be fine during the day if the cataract is on the periphery and the pupil is constricted, but as light decreases and pupil dilates they will complain of haziness in their vision.
Which drugs will dilate the pupil?
Anti-cholinergic drugs like atropine (eye drops). Usually, the pupillary sphincter muscle contracts in response to release of ACh - this interaction is blocked which allows the dilator muscle to dilate the pupil.
What are sutural and zonular cataracts?
Types of childhood cataracts formed due to opacification of certain zones in-utero. Need to be treated aggressively or the brain will start to suppress the image from these zones.
How are cataracts treated?
NOT BY EYEDROPS.
Day surgery in which the lens with the cataract is removed by phacoemulsification and a plastic lens is placed in the capsular bag.
Lens implant after cataract surgery - posterior chamber intra ocular lens (PCIOL).
Lanosterol may be used in the future.
Describe the normal circulation of AH.
AH is produced by the ciliary body in the posterior chamber. It flows out through the pupil to the anterior chamber. It then reaches the angle of the AC and gets filtered out via the trabecular meshwork. It then goes through Schlemm’s canal where it is taken to the normal venous network.
What is glaucoma?
Raised IOP due to the AH pathway being blocked.
2nd most common cause of global blindness.
Most common cause is primary open angle glaucoma (POAG), which is bilateral.
What are the consequences of raised IOP?
Raised IOP puts pressure on the nerve fibres on the surface of the retina. They die out which causes visual field defects.
This results in an altered field of vision.
Ultimately, all nerve fibres are lost which leads to blindness.
What can be seen on fundoscopy in someone with POAG?
The pressure on the optic nerve head can be seen on fundoscopy - disc appears pale, unhealthy and cupped.
What are the triad of signs of glaucoma?
1) Raised IOP
2) Visual field defects
3) Optic disc changes on fundoscopy
How is POAG treated?
1) Eyedrops to decrease IOP: prostaglandin analogues enhance outflow of AH; beta-blockers which decrease the production of fluid; and carbonic anhydrase inhibitors which decrease the production of intraocular fluid.
2) Laser trabeculoplasty: laser eye surgery which results in better drainage of the eye; results may take 3 months to appear.
3) Trabeculectomy surgery: removal of the trabecular network.
What is angle closure glaucoma (ACG)?
Rapid or sudden increase in IOP due to peripheral iris blocking the angle. The angle can close for many reasons:
1) Functional block in a small eye with a large lens
2) Mid-dilated pupil: periphery of iris crowds around the angle and outflow is obstructed
3) Iris sticks to pupillary border which prevents reaching AC - this leads to balooning of the iris anteriorly which obstructs the angle.
What are the symptoms of ACG?
- Sudden onset
- Pain
- Loss/blurry vision (can be confused with migraine)
- O/E: red eyes and often opaque cornea (as raised IOP is driving fluid into the cornea)
- Shallow AC with closed angle
- Mid-dilated pupil
- Severely raised IOP
How is an acute episode of ACG treated?
1) Need to reduce IOP:
- IV infusion of carbonic anhydrase inhibitors
- Analgesics, antiemetics
- Constrictor eye drops like pilocarpine (cholinergic agonist)
- Beta-blocker eye drops like timolol
- Steroid eye drops like dexamethosone
2) Iridotomy: laser on both eyes to bypass the blockage (on the unaffected eye to prevent the condition from occurring)
Why might keratoplasty be needed after treatment of a corneal pathology?
Some treatments cause opacification.
What is the inflammatory pathology of the cornea?
Corneal ulcers. These can be infectious (viral, bacterial or fungal infection of the cornea) or non-infectious (trauma, degeneration or dystrophy/wasting).
What is the non-inflammatory pathology of the cornea?
Corneal dystrophies.
These are bilateral, opacifying and usually genetically determined. Sometimes due to accumulation of lipids in the cornea.
Describe the clinical presentation of corneal dystrophies.
1) 1st to 4th decade
2) Usually present with decreased vision
3) Start in 1 of the layers of the cornea and spread to the others
What is lattice dystrophy?
Autosomal dominant deposition of amyloid material in the corneal stroma.
Presents with eye irritation, photo sensitivity, pain and blurred vision. O/E criss-crossing opacities in the stroma.
Treatment is to manage symptoms, may require corneal transplant.
What is Fuch’s endothelial dystrophy?
Asymmetrical bilateral progressive oedema of the cornea in the elderly (60-70). Caused by destruction and death of endothelial cells - if these fall below a critical level that is needed to keep the cornea clear which causes oedema and opacification of the cornea.
Symptomatic treatment then transplant.
What is the uvea?
The vascular layer of the eyeball: iris, ciliary body and choroid.
What does the iris do?
Controls the diameter of the pupil and therefore controls the amount of light entering the eyeball.
