Optics (Visual-System 2) Flashcards
What is refraction?
The change in the direction of a wave passing from one medium to another caused by its change in velocity.
The frequency of the wave remains the same.
V = f x wavelength
Given frequency is constant, , V is directly proportional to wavelength.
What is the refractive index?
N= speed of light in a vacuum/ speed of light in a medium
c/v
What is the refractive index of air?
1
What happens to light at the boundary at two media?
There is partial reflection and refraction (Depending on the angle of incidence and the critical angle of the medium).
Incidence > critical angle, there is refraction
Incidence = Critical angle, the angle of refraction is 90 degrees.
What are the two types of lenses?
Convex and concave
What does a converging lens do?
A converging lens takes light rays and brings them to a focal point.
What is a diverging lens?
Takes light rays and spreads them outward.
What is emmetropia?
Parallel light rays fall on the retina (there is no accommodation) .
Adequate correlation between axial length and refractive power.
-Does not require correction
What is ametropia?
Refractive error
Mismatch between axial length and refractive power.
The parallel light rays don’t fall on the retina (no accommodation).
What is myopia?
Near-sightedness
Converge at focal point anterior to the retina.
Why is hyperopia?
Farsightedness
What are the common causes of myopia?
Excessive long globe (axial myopia)
Excessive refractive power (refractive myopia)
What are the common symptoms of myopia?
Blurred distance vision
Squint in an attempt to improve uncorrected visual acuity when gazing into the distance
Headache
How can myopia be treated?
1) Correcting with diverging lens (negative lens)
2) Correction with contact lens
3) Correction 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 is the main cause of hyperopia?
Excessive short globe (axial hyperopia)
Insufficient refractive power (refractive hyperopia)
What are the main symptoms of hyperopia?
Visual acuity at near tends to blur relatively early.
Nature of blue is vary from inability to read fine print to near vision is clear by suddenly and intermittently blur.
Blurred vision is more noticeable if person is tired, printing is weak or light inadequate.
Asthenopic symptoms: eyepain, headache in frontal regions, burning sensation in eyes, blepharoconjunctivitis
At what distance does visual acuity diminish in patients with hyperopia?
Near distanced
Where is the headache pain located with hyperopia asthenopic symptoms?
Frontal region
What is abmlyopia?
Uncorrected hyperopia > 5D.
What is hyperopia?
Farsightedness (hyperopia) is a common vision condition in which you can see distant objects clearly, but objects nearby may be blurry.
Which lens should be prescribed in patients with hyperopia?
Correction with converging (Positive lens)
Correction with positive lens + cataract extraction
Correction with contact lens
Correction with intraocular lens
What is astigmatism?
A defect in the eye or in a lens caused by a deviation from spherical curvature, which results in distorted images, as light rays are prevented from meeting at a common focus.
Parallel rays come to focus in 2 focal lines rather than a single focal point.
What is the cause if astigmatism?
Refractive media is not spherical, refract differently along one meridian than along meridian perpendicular to it– Focal points (Punctiform object is is represent as 2 sharply defined lines)
