Structure & Function of the Eye - Part 3

Question 1

Which lens converges light rays?

Answer 1

Convex lens (converging lens)

Question 2

Which lens sprays out light rays?

Answer 2

Concave lens (diverging lens)

Question 3

What do you call eyes which have perfect refractory power?

Answer 3

Emmetropia (light rays converge exactly on the back of the retina)

Question 4

What do you call short sightedness?

Answer 4

Myopia

Question 5

What do you call far sightedness?

Answer 5

Hyperopia

Question 6

Compare what happens to the light rays in hypermetropia vs myopia

Answer 6

Hypermetropia - light rays converge behind retinal surface

Myopia - light rays converge in front of retinal surface

Question 7

State which type of lenses can correct hypermetropic eyes and how this occurs

Answer 7

Convex lenses - provide additional converging power

Question 8

Give two causes of hypermetropia

Answer 8

Axial hypermetropia (short globe)
Refractive hyperopia (flat corneal surface)
Can be inherited, but not clear

Question 9

State two causes of myopia

Answer 9

Axial myopia (long globe)
Refractive myopia (high corneal curvature)

Question 10

Which type of lenses can correct myopic eyes, and how?

Answer 10

Convex lenses - spray light rays out a little further until they reach the back of the eyes

Question 11

What is astigmatism?

Answer 11

When each eye has different light refraction powers at different orientations, therefore the parallel rays come to focus in two different lines

Question 12

How does a patient with astigmatic eyes see distant objects?

Answer 12

As blurred ellipses

Question 13

How can you correct regular astigmatism?

Answer 13

Cylinder lenses

Question 14

Give three symptoms of myopia

Answer 14

Blurred distant vision
Headache
Squinting

Question 15

Give symptoms of hyperopia

Answer 15

Visual acuity - can vary from inability to read fine print to near vision is clear but suddenly intermittently blurry 
Asthenopic symptoms: 
-Eye pain 
-Headache 
-Burning sensation in eyes 
-Eye strain
-Blepharoconjunctivitis

Question 16

When are the symptoms of hyperopia more noticeable?

Answer 16

When patient is tired,
Lighting is weak
Printing is inadequate

Question 17

What is blepharoconjunctivitis?

Answer 17

Blepharitis - inflammation of eyelids + conjunctivitis

Question 18

What is the technical term for eye strain due to weak eyes?

Answer 18

Asthenopia

Question 19

What can result from uncorrected hyperopia?

Answer 19

Ambylopia - when the eyes cannot be corrected (lazy eye)

Question 20

What are the causes of astigmatism?

Answer 20

Hereditary

Question 21

What are the symptoms of astigmatism?

Answer 21

Asthenopic symptoms
Blurred vision
Distortion of vision
Head tilting and tuning

Question 22

How can you correct irregular astigmatism?

Answer 22

Rigid contact lenses

Surgery

Question 23

Describe the near response triad of adaptation for near vision

Answer 23

Pupillary miosis via sphincter pupilae to increase depth of field
Convergence to align eyes to a near object
Accommodation via circular ciliary muscle to increase refractive power

Question 24

What do you call age related vision loss of accommodation?

Answer 24

Presbyopia

Question 25

Describe the vision in presbyopia and what kind of lenses are needed to correct it

Answer 25

``` Distant vision is intact Convex lenses to increase refractive power of eye Bifocal Trifocal Progressive power glasses ```

Question 26

Describe the types of spectacle lenses

Answer 26

Monofocal lenses | Multifocal lenses

Question 27

What type of monofocal lenses are there?

Answer 27

Spherical lenses | Cylindrical lenses

Question 28

Give some advantages of using contact lenses

Answer 28

Higher quality of optical image Less influence on the size of retinal image than spectacle lenses Cosmetic Useful for athletic, occupational, activities

Question 29

Give indications for contact lenses

Answer 29

``` Cosmetics Athletics Occupation Irregular corneal astigmatism High anisometropia Corneal disease ```

Question 30

What is anisometropia?

Answer 30

When two eyes have different refractive powers

Question 31

Give disadvantages for contact lenses

Answer 31

Requires careful daily cleaning to avoid infections

Question 32

State some complications of contact lenses

Answer 32

Infectious keratitis Giant papillary conjunctivitis Corneal vascularisation Severe chronic conjunctivitis

Question 33

State four types of optical correction

Answer 33

Spectacles Contacts Intraocular lenses Surgical correction

Question 34

Give indications of intraocular lenses

Answer 34

Replacement of cataract crystalline lenses | Best correction for aphakia (lack of lens due to surgical removal - spectacles would be too distorting)

Question 35

State some types of surgical corrections for eye conditions

Answer 35

``` Thermokeratoplasty Keratorefractive surgery Photorefractive keratectomy (PRK) Astigmatic keratotomy LASIK (laser) Intracorneal ring (ICR) ``` ``` Intraocular surgery (lens extraction) Phakic IOL (implantable lens) ```

Question 36

What happens in clear lens extraction surgery

Answer 36

Lens extracted e.g. in cataract | Implantation of artificial lens

Question 37

What is the consequence of cataract extraction?

Answer 37

Loss of accommodation (patient will need reading glasses)

Question 38

Explain the mechanism of accommodation

Answer 38

Ciliary muscle contracts Relaxation of zonules (note these are NOT active contractile bands, they're passive elastic bands between the lens and the ciliary body) Lens becomes convex Increased refractive power of the lens

Question 39

Which nerve mediates accommodation?

Answer 39

Third cranial nerve