How We See 1 Flashcards
What is refraction?
Bending of light when it passes rom one optical medium to another.
When light rays pass through a biconvex or biconcave lens, they all converge at a point.
What is this point known as?
Focal point
In the focal point in front or behind the lens in-
1. Biconcave
2. Biconvex
- Behind
- In front
List the parts of the eye which are refractive media.
(all the structures in the pathway of light).
Aqueous humor, the lens, vitreous humor,
In the fibrous coat of the eye, which element is the refractive media?
The lens
In the vascular coat of the eye, which element is the refractive media?
Aqueous humor
In the sensory coat of the eye, which element is the refractive media?
Vitreous humor
Which two parts of the eye are responsible for bending the light?
Cornea
Lens
Out of the cornea and lens, which media is the more powerful bender of light?
Cornea
What is the refractive index of the cornea compared to the lens?
Measured in D
Cornea=45D
Lens= 15D
Which can change it’s shapes- the lens or the cornea
The lens
When objects are distant, >6m away, which type of rays from the object reach the eye>
Parallel rays
When objects are closer, which type of rays from the object reach the eye?
Divergent rays
What happens to the divergent rays coming from closer objects?
They need to be refracted in order to form an image on the retina.
->maybe think of how when you’re using a camera, it takes a little more time to focus on something up close than further away
Describe the changes seen in the lens when the object comes closer and divergent rays start to hit the eye.
Lens becomes thicker and more powerful so a clear image is formed on the retina.
What is meant by accommodation?
The capacity of the eye to change focus on distant and close objects.
Which three things happen simultaneously to enable accommodation?
Lens change shape
Pupil constricts
Eyes converge
What happens to the lens during accommodation?
Lens becomes thicker and more spherical.
Which type of innervation does to the oculomotor nerve supply the ciliary body with?
Parasympathetic innervation.
What happens to the ciliary body when it contracts due to parasympathetic innervation?
Ciliary body bulges
->think about how if you contract biceps, the muscle flexes and bulges.
What is more powerful: a thicker or thinner lens?
Thicker -> has more refractive power
What causes pupil to constrict?
Constrictor pupillae
Does contristor pupillae get parasympathetic or sympathetic innervation?
Parasympathetic
What happens to focus when the pupil constricts?
Focus sharpens allowing only a few rays from the object to pass into eye
What is convergenace?
The eyes looking inwards to focus on an object much closer
Which muscle allows convergence to take place?
Medial rectus
->this is why the medial rectus is a lot thicker than lateral rectus as nowadays, people looking more at phones and computers, things a lot closer to the eye so it must converge.
Emmetrope?
Perfect, 20/20 vision
Myopa?
Short sighted
Hyperopia?
Long sighted
Astigmatism?
Non-spherical curvature of the cornea or lens
Presbyopia?
Long-sightedness of old age
If a person over the age of 40 required glasses for reading, which refractive error would they have?
Presbyopia
What is the most common cause of myopia?
(myopia=short sighted)
Eyeball too long
->wow girl, the rest of you wasn’t long enough???
Therefore, is a person with myopia has a longer eyeball, what happens when the lens bends rays of light?
They form the image in front of the retina so far off objects are not seen as clearly
What are some symptoms of myopia?
Headaches
Complaining of not being able to see distant objects
What might be seen in infants/preverbal children with myopia?
Divergent squint
->aww throwback x
What might be observed in toddlers with myopia?
Loss of interest in sports/people and more interest in books and pictures.
What can a divergent squint lead to if not treated?
A lazy eye- amblyopia
What is the corrective treatment for myopia?
Bending power needs to be decreased either by:
-spectacles
-contact lenses
-laser eye surgery
In those with myopia, do they need biconcave or biconvex lenses?
Biconcave
->maybe remember this because you always think of biconcave first rather than biconvex and you have myopia?
When is laser eye surgery more effective?
When there is greater vision loss.
For example, if vision is -1.25, there probably won’t be much benefit in laser eye surgery.
Where in the eye are objects focused in someone with hyperopia?
Behind the retina
->compared to myopia where the object focuses in front of the retina
What is the most common cause of hyperopia?
Eyeball too short
or
Cornea and lens too flat
How can a person with hyperopia see things that are further away?
Uses accommodative power to makes lens thicker to image forms on retina rather than behind it.
However, this uses up lens power to see objects further away which should be seen without any power, meaning there is none left to focus on closer objects.
What are symptoms of hyperopia in young indiviuals?
Eyestrain after reading or working on a computer
What would be seen in a child or toddler with hyperopia?
Convergent squint
What could a convergent squint progress to?
A lazy eye so needs immediate correction with glasses or lenses
Which type of lens in used for those with hyperopia?
Biconvex
What are some corrective treatment options for those with hyperopia?
Lenses/glasses
Laser eye surgery
Okay….
you see a patient in the hospital and they have a pair of contact lenses on their bedside table. The prescription reads +2.5. Which type of visual impairment do they have?
Hyperopia
->myopia prescriptions are negative
What happens to the images formed by the eye in someone with astigmatism?
More than one image formed, either on, in front or behind the retina.
This means close and distant objects may appear hazy at all times.
Why is all vision blurry in those with astigmatism?
Surface has different curvatures in different meridians
->e.g. a football is spherical so will have equal curvatures, think of those with astigmatism as having` a rugby ball shaped eye to understand this
How can astigmatism be corrected?
Special glasses
Special contact lenses
Laser eye treatment
Which type of glasses can be used to correct astigmatism?
Cylindrical glasses- these are only curved on one axis
Which type of contact lenses can be used to correct astigmatism?
Toric lenses
What will be seen when looking at a prescription for someone with astigmatism?
The power of the lens e.g. positive or negative
The meridian on which the lens needs to act e.g. 90 degrees etc.
At what age can presbyopia occur?
Fifth decade- 40 and above
What causes presbyopia?
Older age means lens gets less mobile/elastic so when the ciliary body contracts, it doesn’t move as much
What is the corrective treatment for presbyopia?
Biconvex reading glasses
