Visual System - Optics Flashcards
What is refraction?
light passes from one medium into another (velocity and direction changes)
What is the index of refraction?
n=speed of light in a vacuum/speed of light in a medium
The angle of incidence is equal to?
angle of reflection
The angle of incidence is > or < than what?
angle of refraction depending on the direction of the light
What types of lenses are there?
convex
concave
What is an application of converging lenses?
camera uses a lens to focus an image on film
Emmetropia
adequate correlation between axial length and refractive power
parallel light rays fall on the retina
Ametropia
mismatch between axial length and refractive power
parallel light rays don’t fall on the retina (myopia, hyperopia, astigmatism, presbyopia)
What is myopia?
Parallel rays converge at a focal point anterior to the retina
What are causes of myopia?
excessive long globe (more common)
excessive refractive power
What are symptoms of myopia?
Blurred distance vision
Squint in an attempt to improve uncorrected visual acuity when gazing into the distance
Headache
List treatments of myopia.
correction with diverging lenses, with contact lens, by removing the lens to reduce refractive power of the eye
What is hyperopia?
Parallel rays converge at a focal point posterior to the retina
What are the causes of hyperopia?
excessive short globe (axial hyperopia) : more common
insufficient refractive power (refractive hyperopia)
What are symptoms of hyperopia?
visual acuity at near tends to blur relatively early
asthenopic symptoms : eyepain, headache in frontal region, burning sensation in the eyes, blepharoconjunctivitis
What is amblyopia?
eye fails to achieve normal visual acuity, even with prescription eyeglasses or contact lenses
List treatments of hyperopia.
correction with converging lenses/with` +ve lens + cataract extraction/with contact lens/with intraocular lens
What is astigmatism?
Parallel rays come to focus in 2 focal lines rather than a single focal point
Astigmatism etiology
hereditary
What is the cause of astigmatism?
refractive media is not spherical–>refract differently along one meridian than along meridian perpendicular to it–>2 focal points
What are symptoms of astigmatism?
Asthenopic symptoms (headache , eyepain)
blurred vision
distortion of vision
head tilting and turning
How to treat regular astigmatism?
Regular astigmatism : cylinder lenses with or without spherical lenses (convex or concave), Sx
How to treat irregular astigmatism?
rigid cylinder lenses, surgery
Near response triad?
Adaptation for Near Vision
Pupillary Miosis (Sphincter Pupillae) to increase depth of field
Convergence (medial recti from both eyes) to align both eyes towards a near object
Accommodation (Circular Ciliary Muscle) to increase the refractive power of lens for near vision
What is presbyopia?
Naturally occurring loss of accommodation (focus for near objects), distant vision intact
Presbyopia onset from what age?
40
Presbyopia is corrected by?
reading glasses (convex lenses) to increase refractive power of the eye
What type of convex lenses are used for treatment of presbyopia?
reading glasses
bifocals
trifocals
progressive power glasses
What type of spectacle lenses are used for treatment of presbyopia?
Monofocal lenses : spherical lenses , cylindrical lenses
Multifocal lenses
For who might contact lenses be helpful?
cosmetic , athletic activities , occupational , irregular corneal astigmatism , high anisometropia , corneal disease
What are disadvantages to contact lenses?
careful daily cleaning and disinfection , expense
What are possible complications of contact lenses?
infectious keratitis , giant papillary conjunctivitis , corneal vascularization , severe chronic conjunctivitis
Intraocular lenses
replacement of cataract crystalline lens
give best optical correction for aphakia , avoid significant magnification and distortion caused by spectacle lenses
Types of surgical correction for optical issues
Keratorefractive surgery :RK, AK, PRK, LASIK, ICR, thermokeratoplasty
Intraocular surgery : clear lens extraction (with or without IOL), phakic IOL
