Refractive Error

Question 1

What 3 structures are important in focusing light onto the retina

• what is emmetropia
• what is ametropia

Answer 1

Cornea => most refraction
Lens
Axial length - length of the eyeball

Emmetropia - normal sight => object focused on retina and seen clearly

Ametropia - refractive error present

Question 2

Describe accommodation

• near objects
• far objects

Answer 2

When light rays approach from nearby objects
-ciliary body contracts => suspensary ligaments relax => lens more convex

Small and round lens => focus on near objects

When light rays approach from faraway objects
-ciliary body relaxes => sus ligaments contract => lens less convex

Tall and thin lens => fovus on far objects

Question 3

What is presbyopia

-management

Answer 3

With age, lens loses ability to change shape => reduced accommodation => difficulty seeing near objects

Managed with adding convex lens in reading glasses

Question 4

What is hypermetropia

• presentation
• management

Answer 4

Longsighted - refractive power too weak => image focused behind retina
-young patients can compensate for this by accommodating => eyestrain, headache

Managed with adding convex lens in glasses (+ve)

Question 5

What is myopia

• presentation
• management

Answer 5

Shortsighted - refractive power too strong => image focused in front of retina

Managed with adding concave lens in glasses (-ve)

Question 6

What is astigmatism

-management

Answer 6

Many foci of light on the retina
-cornea is rugbyball like => light refracts differently at different angles

Corrected with lens with different powers at different areas => focus light onto 1 part of the retina

Question 7

What is keratoconus

Answer 7

Most commonly - acquired bilateral corneal collagen disorder in 10-20s => cornea thins and distorts

Associations with Downs, EDS, Marfans

Increased astigmatism and myopia
Retinoscope - scissor, oil droplet-like
Cornea looks like cone
Vertical line in corneal stroma
Bulging of lower lid on downgaze

Contacts better than glasses => improve VA
CI for laser eye surgery
Monitor for progression
Corneal graft if scarring present

Question 8

Ways to correct refractive errors

Answer 8

Glasses - correct ametropia

• single vision - correct either myopia or hypermetropia
• bifocal - distance and near corrected in 1 lens with distinct line in between the 2 lens types (top half - distance, bottom half - near)
• varifocal - gradually increases from distance to near correction

Contacts

• rigid/hard
• soft - can be disposable on daily, monthly, annual

Laser eye surgery

• correct myopia => slice ant cornea/flatten cornea
• correct hypermetropia, astigmatism