Neuro - Visual System pt. 2 Flashcards
What is refraction?
when light passes through one medium to another, its velocity changes
How is the index of refraction calculated?
index of refraction (n) = speed of light in a vacuum / speed of light in a more dense medium = c/v
What are the basic types of lenses?
→ convex
→ concave
What is a convex lens?
→ almond shaped
→ converging lens
→ bring light rays to a point
What is a concave lens?
→ diverging lens
→ spreads light rays away
What are some applications of lenses?
cameras, etc.
What is emmetropia?
→ adequate correlation between axial length + refractive power
→ parallel light rays fall on the retina without accommodation
What is ametropia?
→ refractive error
→ mismatch between axial length + refractive power
→ parallel light rays don’t fall on the retina (no accommodation)
What are some examples of ametropia?
→ myopia (near-sightedness)
→ hyperopia (far-sightedness)
→ astigmatism
→ presbyopia
What is myopia?
→ short-sightedness
→ parallel rays converge at a focal point anterior to the retina
What are symptoms of myopia?
→ blurred distance vision
→ squint in an attempt to improve uncorrected visual acuity when gazing into distance
→ headache
What are causes of myopia?
→ not clear, possible genetic factors
→ excessive long globe (axial myopia)
→ excessive refractive power (refractive myopia)
What is myopia treatment?
→ correction with diverging lenses
→ correction with contact lens
→ correction by removing the lens to reduce refractive power of the eye
What is hyperopia?
→ long-sightedness
→ parallel rays converge at focal point posterior to the retina
What are causes of hyperopia?
→ not clear, possible genetic factors
→ excessive short globe (axial hyperopia)
→ insufficient refractive power (refractive hyperopia)
What are symptoms of hyperopia?
→ visual acuity at near tends to blur relatively early
→ nature of blur varies from inability to read fine print, to near vision is clear but suddenly and intermittently blurred
→ blurred vision is more noticeable if person is tired, printing is weak or light inadequate
→ eyepain, headache in frontal region, burning sensation in the eyes, blepharoconjunctivitis
What is amblyopia?
uncorrected hyperopia > 5D
How is hyperopia treated?
→ correction with converging lenses (positive lenses)
→ correction with positive lens + cataract extraction
→ correction with contact lenses
→ correction with intraocular lenses
What is astigmatism?
parallel rays come to focus in 2 focal lines rather than a single focal point
What are causes of astigmatism?
→ hereditary
→ refractive media is not spherical –> refract differently along one meridian than along meridian
→ perpendicular to it –> 2 focal points (punctiform object is represent as 2 sharply defined lines)
What are asthenopic symptoms?
→ fatigue → pain in or around the eyes → blurred vision → headache → occasional double vision
What is asthenopia?
→ eye strain
→ non-specific disorder
What are symptoms of astigmatism?
→ asthenopic symptoms
→ blurred vision
→ distortion of vision
→ head tilting + turning
How do you treat regular astigmatism?
cylinder lenses with or without spherical lenses
