Refractive Errors Flashcards
Main Types of Refractive Errors
- Farsighted (hyperopia)
- Nearsighted (myopia)
- Astigmatism
- Presbyopia
Affects eyes and can make objects appear blurry
Causes of Refractive Errors
- Genetic inheritance (eye muscles are too tight, eyeball is too short/long, curve of cornea/lens isn’t correct
- How we use our eyes
How to correct focusing problems
Glasses
Contact lenses
Eye exercises
Refractive surgery to reshape surface of cornea
Myopia
(see L3Ch2 for diagrams)
Nearsightedness
When eyeball is too long, light that enters focuses before hitting retina
Able to see objects up close than distant objects
Affects 30% of population
Typically evident in childhood/teen years
Symptoms:
- squinting
- frequent headaches
- holding books too close to face
- insisting on sitting very close to TV
Corrective Procedures for Myopia
MINUS powered lenses help redirect light rays to hit the back of the eye
Hyperopia
(see L3Ch2 for diagrams) Farsightedness When eyeball is too short, light that enters focuses past retina Affects 25-60% of population Able to focus on distance objects more easily than close up Symptoms: - squint when doing up close work - may experience headaches or eye strain
Astigmatism
Affects 16% of population
Vision is blurred at all distances
Corneal surface isn’t rounded like marble but curved more in one direction like grape
When light travels to eye, light rays focus on different parts of the retina instead of a single spot
Typically present at birth but may show improve or get worse over time
Many people have small amt of ~
Significant ~ causes blurry or distorted vision or ghost images around objects
Corrective Procedures for Astigmatism
If uncorrected, can cause eye strain and headaches
Glasses
Contacts
Refractive Surgery
Presbyopia
Affects ability to focus up close
Usually sets in between ages 35-45
Lens becomes less elastic and can no longer focus near objects into retina
May stem from weakening of smooth muscles that help lens change shape
Unavoidable as it’s part of aging process
Progressively greater difficulty reading fine print
Develop eyestrain
Blurring when transiting between different viewing distances
Aging is most common cause but can develop earlier in people with diabetes, multiple sclerosis, some cardiovascular diseases
Corrective Procedures for Presbyopia
-Bifocal lenses
-Reading glasses
-Contacts
About 90mil Americans wear corrective lenses for this
Emmetropia
Person who has no refractive error
(See L3Ch2 for diagram)
From Gr. root meaning ‘well-proportioned’
Eye and cornea are perfectly spherical
Anisometropia
People whose eyes have different refractive power
‘Aniso’ = unequal
Challenging for opticians since glasses will be of different thickness
Amblyopia
Falls under anisometropia
Causes lazy eye because the difference in refractive power between the two eyes is so large that they can’t work together
The brain can’t fuse two differently sized images together so it solves the problem by occasionally or continuously shutting off the image in one eye
Affects 2-3 children in 100
Without correction, it causes poor depth perception
Cosmetic problem because “lazy” eye turns inward or outward
Corrective Procedures for Amblyopia
Even with a prescription lens in affected eye, person won’t be able to see clearly
Children can wear a patch in front of good eye to train the other, but not 100% successful
Surgical techniques
Esotropia
Type of strabismus where eye turns inward
