Vision

Question 1

What is refraction in the eye and what two structures does it involve?

Answer 1

Refraction involves the cornea (45d) and lens (15d) bending lights from objects to form an image at the retina.

Question 2

How does the distance of an object affect refraction of the eye?

Answer 2

The closer an object is, more refraction is needed. When an object is far away only parallel rays hit the retina but when an object is closer, divergent rays also hit the retina which require more bending (refraction).

Question 3

What is accommodation and what three things happen when the eye focuses on something closer?

Answer 3

Accommodation is the changes in both eye when it goes from focusing long distance to short distance. The pupil constricts, the lens changes shape and the eyes converge.

Question 4

Name four refractive errors and what its called if there is an absence of refractive errors

Answer 4

Myopia-short sighted
Hyperopia-long sighted
Presbyopia-long sighted from old age
Astigmatism-non spherical curvature (rugby ball) of cornea or lens.
Emmetropia-perfect vision

Question 5

Describe the causes of four refractive errors

Answer 5

Myopia-eyeball is too long so light rays hit the retina in front so can’t see far away objects
Hyperopia-eyeball is too short so light rays hit behind the retina so can’t see close objects
Astigmatism-cornea and lens are misshaped so light rays might not hit retina at all so near and far objects are hazy.
Presbyopia-lens gets less elastic with age so less able to change shape.

Question 6

Describe how to treat these four refractive errors

Answer 6

Myopia-biconcave glasses, lenses or laser surgery
Hyperopia-biconvex glasses, lenses or laser surgery
Astigmatism-cylindrical glasses and toric lenses
Presbyopia-biconvex reading glasses

Question 7

What is transduction?

Answer 7

How an image formed by the retina is transformed into an action potential

Question 8

How is transduction achieved?

Answer 8

Retinal in the rods and cones (Vit A) isomerises into a straight chain when light hits it which causes bleaching of the retina. This starts off a cascade of reactions in the cytoplasm which hyperpolarises and becomes an AP in the optic nerve cells.

Question 9

How do you test the visual field?

Answer 9

Test with confrontation test or automated perimetry

Question 10

Name a cause of bitemporal hemianopia

Answer 10

Optic chiasm disruption

Question 11

Name some causes of homonymous hemianopia

Answer 11

Optic radiation disruption (contralateral)
Optic tract disruption (contralateral)
Internal capsular infarction