Opt. - Lec 3b - Optical Functions Of The eye

Question 1

What makes the cornea the most powerful refractive component ?

Answer 1

The curvature of the corneal surface and the refractive index of air and cornea

Question 2

Where does one third of the eyes refractive power come from?

Answer 2

Crystalline lens - due to the smaller jump between the refractive index of lens and the surrounding aqueous humour and vitreous body

Question 3

Describe accommodation of the crystalline lens when looking in the distance

Answer 3

Ciliary muscle relaxed
Lens attachments under tension
Lens power is low but sufficient enough to focus logout on the retina

Question 4

Describe accommodation of the crystalline lens when looking at a close object

Answer 4

Ciliary muscle contracts
Tension released on lens attachments
Lens surfaces steepen
Lens power is raised enough to focus light on the retina

Question 5

What is Emmetropia

Answer 5

Cornea and relaxed lens have sufficient power to focus light from distant objects onto the retina

There is no refractive error (is this then normal vision or is it in focus when it gets to the back of the retina but is not on the right place of the back of the retina?)

Question 6

What is myopia

Answer 6

Short-sightedness

Light focused in from of the retina

Eye too long/ cornea and relaxed lens too strong

Corrected with “minus spheres”/laser eye surgery to flatten the cornea

Question 7

What is hyperopia

Answer 7

Long sightedness

Objects focused behind the retina
Eye too short/cornea and relaxed lens too weak

Corrected with “plus spheres”/laser eye surgery to steepen cornea

Question 8

What is astigmatism?

Answer 8

2 focal points

Cornea rugby ball shaped

Poor vision generally

Corrected with cylinders - lenses that have power in just one meridian to refract light into just the one focal point

Question 9

What is presbyopia

Answer 9

Near objects no longer in focus

Correction - “near addition” plus lenses for reading

Question 10

What does the first number in the visual acuity score stand for?

6/_

Answer 10

Testing distance

Question 11

What does the second number mean in the visual acuity score?

_/6

Answer 11

Distance a person with “normal” vision would see that letter

Question 12

What does putting the pinhole cover down indicate?

Answer 12

Refractive error rather than disease

Question 13

Define Trichromacy

Answer 13

Normal colour vision

Good red, green and blue cones

Question 14

Define Anomalous Trichromacy

Answer 14

Only one type of cone is affected

Protanopia = no RED cone

Deuteranopia = no GREEN cone

Tritanopia = no BLUE cone

Question 15

Which statement is false?
A. Uncorrected myopes find it easier to read than hyperopia
B. ‘Spheres’ are used to correct myopes and hyperopia
C. Hyperopia eyes tend to be shorted than myopic eyes
D. Hyperopia does not affect distance vision in old eyes
E. Both distance and near vision are affected with astigmatism

Answer 15

D - hyperopia IS distance vision

Question 16

Which describes normal colour vision? 
A. Monochromacy
B. Dichromacy 
C. Trichromacy 
D. Deuteranopia
E. Protanopia

Answer 16

C