Optics of the Visual System Flashcards
Describe the phenomenon of refraction
When light travels through one medium to another it changes velocity causing the ray to refract, this makes it appear to bend
Where is the angle of incidence found?
Between the normal and the ray of incidence
Where is the angle of refraction found?
Between the normal and the ray of refraction
What is the equation for calculating index of refraction?
Speed of light in a vacuum/speed of light in a medium
What should the index of refraction always be?
Greater than 1 because the denominator is always smaller than the numerator
When the light goes from less dense to more dense where does it bend?
Towards the normal
How many types of lens are there? What are they called?
2 types:
Concave
Convex
Describe the properties of a convex lens
Converging lens that causes light rays to come together at a point
Describe the properties of a concave lens
A diverging lens that causes light rays to spread away from each other
What type of lens is converging?
Convex
What type of lens is diverging?
Concave
What type of lens causes light rays to come together?
Convex
What type of lens causes light rays to spread apart?
Concave
What is ametropia?
Refractive error, there is a mismatch between axial length and refractive power which means parallel rays don’t fall on the retina and theres no accomodation
What is the medical name for near sightedness?
Myopia
What is the medical name for far sightedness?
Hyperopia
What are the types of ametropia?
Myopia
Hyperopia
Astigmatism
Presbyopia
What happens to light rays in those with myopia?
Light rays converge at a point anterior to the retina
What are the types of myopia? Describe them
Axial myopia= excessively long globe, more common
Refractive myopia= excessive refractive power
What type of myopia is more common?
Axial myopia
What are symptoms of myopia?
Blurred vision, squinting to help overcome this, headache as a result
How is myopia corrected?
Diverging lens (negative power), contact lens, removal of lens to reduce refractive power
What happens to light rays in those with hyperopia?
Light rays converge at a point posterior to the retina
What are the types of hyperopia? Describe them
Axial hyperopia= excessively short globe (more common)
Refractive hyperopia= excessive refractive power
What type of hyperopia is more common?
Axial
Do those with near sightedness struggle to see near or far objects?
Far
Do those with far sightedness struggle to see near or far objects?
Near
Do those with myopia struggle to see near or far objects?
Far
Do those with hyperopia struggle to see near or far objects?
Near
What are symptoms of hyperopia?
Blurred vision when looking at things up close eg reading, worse if there is reduced light, burning in eyes, eye pain, headache in frontal region
Where do those with hyperopia commonly get a headache?
In the frontal region
How is hyperopia corrected?
Converging lens (positive power), contact lens, correction intraocular lens
What happens to light rays in astigmatism?
Parallel rays focus in 2 focal lines instead of at a singular focal point because the refractive media is not spherical
How many focal points are there in someone with asrigmatism?
2
What are symptoms of astigmatism?
Headache, eye pain, blurred or distorted vision, head tilting/turning
How is astigmatism treated?
Cylinder lens
What is the near response triad? Describe it
Its how the eye adapts to look at close objects
1) pupillary miosis to increase depth of field
2) convergence to align both eyes towards a near object
3) accomodation to increase the refractive power of the lens
In the near response triad what structure allows pupillary miosis?
Sphincter pupillae
In the near response triad what structure allows convergence?
Medial recti of both eyes
In the near response triad what structure allows accomodation?
Circular cilliary muscle
What is presbyopia?
Naturally occuring loss of accomodation
What is accomodation?
Focus on near objects
At what age is there usually onset of presbyopia?
40 years
How is presbyopia corrected?
Via reading glasses that have a convex lens so they increase refractive power or by contact lens
What are the 3 main types of optical correction?
Contact lens
Intraocular lens
Surgical correction
What are some advantages of contact lens?
Higher quality of optical image, influences the size of the image less than spectacles
What are some disadvantages of contact lens?
They need careful daily cleaning and disinfection, they’re expensive
What is the best use of intraocular lens?
Optical correction of aphakia as they avoid significant magnification and distortion via spectacles
What happens when the lens is cleared surgically?
Patients loose the ability to accomodate and require reading glasses
What happens to the zonules and lens in accomodation?
Zonules relax
Lens thickens and increase in their refractive power
