L3/4 - Ophthalmology

Question 1

What path does light take through the eye?

Answer 1

Through the cornea > iris > lens

Question 2

What is meant by power of a lens?

Answer 2

The power of a lens is its ability to bend light – the greater the power the greater the refraction of light.

Question 3

What type of lens is the cornea? What type of lens is the lens of the eye?

What does that mean for the cornea and the lens of the eye?

Answer 3

• The cornea is a fixed-power lens (performs most of the refraction of light)
• The lens is a variable-power lens (power is adjustable to yield a sharply focused image on the retina (for varying object distances)).

Question 4

What is the role of the zonular fibres and the suspensory ligaments of the lens?

Answer 4

The zonular fibres collectively form the suspensory ligament of the lens which connects the lens of the eye to the ciliary body.

Question 5

What is the lens primarily composed of?

Answer 5

Cells

Question 6

What are the two different regions within the lens?

Answer 6

Nucleus

Cortex

Question 7

When were the two different regions within the lens laid down?

Answer 7

• Nucleus > laid down in utero
• Cortex > laid down since birth > will continue to get laid down and grow/thicken through lifetime

Question 8

What is the biggest defect which affects the lens?

Answer 8

Cataract

Question 9

What is a cataract?

Answer 9

A clouding or loss of transparency of the lens in the eye as a result of tissue breakdown and protein clumping

Question 10

What are the two types of cataract?

Answer 10

Nuclear cataract

Cortical cataract

Question 11

What type of cataract would be the most visually disturbing and why?

Answer 11

The nuclear cataract. The cataract is formed where you want to get the accuracy of focussing light.

Question 12

What is the ciliary body? What is it composed of?

Answer 12

The ciliary body is a ring of tissue that encircles the lens.

The ciliary muscles and the ciliary processes. The ciliary processes attach the lens to the ciliary body via the zonular fibres which collectively form the suspensory ligament.

Question 13

What is the function of the ciliary body?

Answer 13

The ciliary body controls the shape of the lens.

Question 14

What happens when the ciliary muscles contract?

Answer 14

The diameter of the ciliary body reduces in size.

Question 15

What happens when the ciliary muscles contract?

Describe what the effect of the change in the lens is?

Answer 15

1. When the ciliary muscle contracts, the diameter of the ciliary body is decreased.
2. This causes the zonular fibres to slacken and reduce the tension applied to the outside of the lens
3. This allows the lens to become more rounded/curved (decreases diameter volume of lens, but increases front to back)
4. The increased curvature of the lens surface bends the light more (increased optical power)
5. The lens is adjusted for near vision (focus on things close up)

Question 16

What happens when the ciliary muscles relax?

Describe what the effect of the change in the lens is?

Answer 16

1. When the ciliary muscle relaxes, the diameter of the ciliary body is increased.
2. This causes the zonular fibres to tighten and increase the tension applied to the outside of the lens
3. This allows the lens to become more flat (increase diameter volume of lens, but decreases front to back)
4. The decreased curvature of the lens surface bends the light less (decreased optical power)
5. The lens is adjusted for long distance vision (focus on things far away)

Question 17

What is accommodation of the eye?

Answer 17

Accommodation, the mechanism by which the eye changes focus from distant to near images, is produced by a change in lens shape resulting from the action of the ciliary muscle on the zonular fibers.

Question 18

What structure produces the aqueous humour?

Answer 18

The ciliary epithelium of the ciliary body

Question 19

What is the flow of the aqueous humour?

Answer 19

From the ciliary epithelium > between lens and iris > through the natural hole in pupil > to the anterior chamber > towards angle of eye (between iris and cornea) > filtered by trabecular meshwork > into the Schlemm’s canal > into the venous system

Question 20

What is the function of the aqueous humour?

Answer 20

Nourishes the lens and cornea (provides nutrition) & maintains eye pressure

Question 21

What occurs if the angle of the eye or the trabecular meshwork is blocked?

Answer 21

The aqueous humour is produced all the time. If the angle of the eye or trabecular meshwork is blocked, flow is stopped and the aqueous humour will accumulate.

This causes an increase in pressure of the eye which will affect the optic nerves and other structures.

Question 22

What are the two principle focussing structures of the eye?

What is the converging power of each of these structures?

What is the significance of knowing the converging power of each of the structures?

Answer 22

• Cornea > 2/3rd > approx. 40 diopters
• Lens > 1/3rd > approx. 20 diopters

The power of the eye is about 60 diopters of convergence.

If a lens cataract is removed, the focussing power (20D) needs to be replaced. But everyone is unique:

• If myopic > long eye > require less focussing power > higher power lens
• If hyperopic > short eye > require more focussing power > higher power lens

Question 23

How is cataract diagnosed?

What signs will the patient present with?

Answer 23