Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

H+N - C > Vision 1 > Flashcards

Vision 1 Flashcards

1
Q

What is refraction?

A

Bending of light when it passes from one optical medium to another

Light rays bending to form a sharp image on the retina

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are refractive errors?

A

Mismatch between how much we bend light rays

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What parts of the eye does light pass through and therefore contribute to refraction

A

Cornea
Aqueous humor
Lens
Vitreous humor

All these transparent to allow light to fall on retina

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How does a share image form on the retina?

A

Light waves from an object bend at the cornea, bend some more at the lens to form a clear image on the retina.
This bending of light waves is called Refraction.

When an object comes closer, the eye needs more bending power to focus on an object (the lens becomes thicker and hence more powerful, and a clear image is formed on the retina again)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is better at refraction cornea or lens?

A

Cornea is the most powerful “bender” of light (45D) but lens (15D) has the capacity to change its “bending power”

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Explain accommodation

A

Our eyes have the capacity to change the focus from distant objects (infinity) to close objects (20cm)

The changes occurring in both eyes as it changes focus from a distant to a close object is called accommodation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What 3 things happen simultaneously and comprise accommodation?

A
  • LENS CHANGES SHAPE (becomes thicker & more spherical)
  • Pupil constricts
  • Eyes converge
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Describe the process of lens thickening

A
  • Ciliary muscle contracts making the ciliary body bulge (parasympathetic).
  • Space in the middle decreases
  • Suspensory ligaments become lax
  • Lens is no longer under stretch
  • LENS BECOMES THICKER
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Describe the process of pupil constriction

A
  • When we are looking at an object up close, we need a sharp focus.
  • To sharpen focus the pupil constricts to allow only a few rays (those from the object) to pass through.
  • Pupillary constrictor (sphincter pupillae) is a concentric muscle around the border of the pupil which gets parasympathetic innervation IIIn.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Describe the process of eye convergence

A

When focusing on an object up close, our eyes have to turn in to look at the object (convergence)

We use our medial rectus muscles of both eyes to converge (IIIn)

Humans spend a lot of time doing “close” work, so our Medial recti muscles are thicker than our lateral recti muscles.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the 4 refractive errors?

A
  • Myopia: short sightedness
  • Hyperopia: long sightedness
  • Astigmatism: non-spherical curvature of cornea (or lens)
  • Presbyopia: long-sightedness of old age

If you are lucky enough to have perfect vision you are an emmetrope (i.e. you have emmetropia)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is myopia?

A

Shortsightedness: Close objects look clear, distant objects appear hazy.

Picture focuses in front of retina

Basically the bending power of cornea + lens are too much for that eyeball

When the object is brought closer the rays coming from it are divergent; and then this “bending power” comes to use. The image is formed on the retina without needing to increase curvature of lens.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the most common cause of Myopia?

A

Eyeball too long

So the cornea and lens, when the bend rays of light, make the image to form IN FRONT of the retina. So far off objects not seen clearly.

When the object is brought closer the rays coming from it are divergent; and then this “bending power” comes to use. The image is formed on the retina without needing to increase curvature of lens.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are the symptoms of myopia?

A

Headaches, Complain of not being able to see blackboard/ distant objectsInfants & preverbal children divergent squint

Infants and preverbal children -> divergent squint

Toddlers -> loss of interest in sports/people. More interest in books, pictures.

Teachers may notice child losing interest in class

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How to correct myopia

A

Bending power needs to be decreased.

Biconcave lenses

  • Spectacles
  • Contact lenses
  • Laser eye surgery
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is hyperopia?

A

Farsightedness

Image focuses behind the retina

Close objects look hazy, distant objects appear clear.

17
Q

What causes hyperopia?

A

Eyeball too short or cornea + lens too flat

So when an image of a distant object is formed on the retina it lies BEHIND THE RETINA.

The person then automatically starts to use his accommodative power and makes the lens thicker.
This causes the image to form on the retina.

So he is using the lens power to see far off thing (that he should normally be seeing without using any power).

When seeing closer objects, he uses more and more power until ultimately, his power is all used up.

18
Q

What are the symptoms of hyperopia?

A

Eyestrain after reading/ working on the computer in a young individual.

Convergent squint in children/ toddlers - needs immediate correction with glasses/lenses to preserve vision in both eyes and prevent lazy eye

19
Q

What is the correction of hyperopia?

A

Biconvex glasses alleviates use of glasses for focusing distant objects and “restS” the accommodative power

Contact lenses
Laser eye surgery

20
Q

What is astigmatism?

A

Both close and distant objects appear hazy

Multiple images are formed

21
Q

What causes astigmatism?

A

Surface of the lens has different curvatures in different meridians

So the bending of light rays along one axis will never be the same as that of the other axis.

So image formed is always hazy, whatever the distance of the object

22
Q

How do you correct astigmatism?

A

Special glasses - called cylindrical glasses (which are curved in only one axis)

Laser eye surgery can also be used to correct the defect.

Need special contact lenses called topic lenses

23
Q

Explain presbyopia

A

Longsightedness of old age.

With age the lens gets less mobile/elastic.
So when the ciliary muscle contracts, it is not as capable as before to change shape.
So seeing near objects/ reading the newspaper starts to become difficult -> needs glasses to read

Usually starts in 50s

24
Q

How do you correct presbyopia?

A

Biconvex “reading glasses”

25
Q

What is the process of us actually seeing called?

A

Phototransduction

26
Q

What is phototransduction?

A

Visible light is an electromagnetic wave.

The energy in light waves need to stimulate photoreceptor cells on the retina (phototransduction)

Phototransduction is defined as the conversion of light energy to an electrochemical response by the photoreceptors (rods and cones)

The phototransduced rods and cones need to activate optic nerve neurones (generate an action potential)

27
Q

Explain the structure of rods and cones

A

Outer segment contains stacks of discs/laminae which have photoreceptors

  • Cones this is like an ice-cream cone shape
  • Rods this is rod shaped

Inner segment just behind with cell organelles

Outer limiting membrane divides cell. Just inside this is nucleus connected to axon and synaptic terminal.
-This area is the muller cell

28
Q

Explain the visual pigment in photoreceptor outer segments

A

Each lamellae is made up of cell membrane.
Integrated into this cell membrane is the visual pigment rhodopsin in rods and small, medium and large wave cone-opsins .
These molecules differ in their spectral sensitivity

29
Q

What are the different visual pigments and what do they correspond to on the spectrum?

A

Small wave cone-opsin = blue cone

Rodopsin

Medium wave cone-opsin = green cone

Large wave cone-opsin = red cone

30
Q

Explain the visual pigment Rhodopsin

A

Opsin + 11-cis Retinal

Integral transmembrane helical protein in the lamellae.
Chromophore nests in the opsin of this protein (11-cis retinal).

When light falls on 11-cis retinal, it isomerism to all- trans retinal

All-trans retinal cannot fit into the opsin. So rhodopsin splits.
this results in BLEACHING of the visual pigment

31
Q

What is 11-cis retinal formed from?

A

Dietary Vitamin A
Involved in visual pigment regeneration

“Carrots help see in the dark”

32
Q

How does bleaching of the visual pigment of cones and rods result in phototransduction?

A

Phototransduction cascade

33
Q

Why are photoreceptor cells unique in terms of charge?

A

Unlike other cells in the body, the photoreceptor cells are, at rest (in the dark), kept in a depolarised state by open Na+/Ca+ channels

34
Q

Explain the phototransduction cascade

A

Na channels open in cell resting state.
Photon of light activates Rhodopsin.
This causes the phototransduction cascade.
Na CHANNEL CLOSES.
Relative hyper polarisation of photoreceptor cell.
Hyperpolarisation transmitted by a flux of Ca ions to the synapse with bipolar cell.
Stimulates ultimately the retinal cell

35
Q

Explain briefly visual pigment regeneration

A

Inside photoreceptor:
-Rhodopsin activated (breaks from opsin, All-trans retinol formed)

Inside pigment epithelial cell

  • All-trans retinol converted to 11-cis retinol then 11-cis retinal
  • Retinyl esters are given off
  • Dietary vitamin A required

11-cis retinal combines with opsin to form rhodopsin again in photoreceptor

36
Q

Describe vitamin A deficiency

A

since vitamin A is supplied through the diet, any condition that affects vitamin a absorption will affect vision-(night)blindness.

Vitamin A is also essential for healthy epithelium.

So conjunctiva and corneal epithelium are also abnormal.

Vitamin A deficiency can occur in conditions such as malnutrition, malabsorption syndromes such as coeliac disease, sprue

37
Q

What is a clinical sign of vitamin A deficiency?

A

Bitot’s spots in conjunctiva

Corneal melting which leads to future opacification of the cornea

H+N - C (17 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions