Accommodation

Question 1

What is accommodation?

Answer 1

The ability of the eye to increase dioptric power to get a clear image of a near object (closer = ciliary body contracts, zonules relax, lens thickens)

Question 2

What is accommodation driven by?

Answer 2

Blur
Convergence
Proximal Cues
Tonic Convergence

Question 3

What is the role of the lens?

Answer 3

Adjust focal length to focus image on retina

Question 4

Whats the refractive media number for air, cornea, aqueous humour, lens and vitreous humour?

Answer 4

Air = 1.0
Cornea = 1.376
Lens = 1.42
Aqueous & Vitreous Humour = 1.336

Question 5

How do we work out the power of a lens?

Answer 5

1 / focal length

Question 6

What is power of lens the same as?

Answer 6

Accommodation as it’s the additional power of lens needed

Question 7

What is the same as focal length?

Answer 7

Same as fixation distance

Question 8

How do we work out accommodation (in dioptres)?

Answer 8

1 / fixation distance (meters)

Question 9

If focal length of a lens is 2m, what’s its power?

Answer 9

1 / 2 = 0.5D

Question 10

How do we work out focal length (in meters)?

Answer 10

1 / power of lens (accommodation)

Question 11

What’s accommodation like in a 0-8wk old?

Answer 11

Sporadic, intermittent and inaccurate

Question 12

What’s accommodation like in a 8-9wk old?

Answer 12

Adult-like

Question 13

What’s accommodation like in a 3mo?

Answer 13

Fully developed

Question 14

What’s presbyopia?

Answer 14

An age-related inability to accommodate that begins 40-45yo due to sclerosis of the crystalline lens

Question 15

How do we calculate approximate accommodation expected for someone’s age?

Answer 15

4squared - (age/4)

Question 16

What is Hofstetter’s formula for calculating a person’s age?

Answer 16

18.5 - (0.3 x age in years)

Question 17

How do we calculate amplitude of accommodation (D)?

Answer 17

1 / Near Point (meters)
so 10D at 24yo = 0.1m or 10cm

Question 18

How do we calculate near point?

Answer 18

1 / amplitude of accommodation

Question 19

How do we measure accommodation at near?

Answer 19

Using the RAF rule N-Series drum

Question 20

How long is RAF rule and what is around the rule?

Answer 20

52cm.
Cm
Dioptre Spheres
Age
Whether defective, reduced or normal (convergence only)

Question 21

What does a patient tell you when using the RAF rule for accommodation?

Answer 21

When the text becomes blurred

Question 22

What’s the conventional method for accommodation using the RAF rule?

Answer 22

Conventional Method: Clear to blur

Question 23

What’s the modified push-up method for accommodation using the RAF rule?

Answer 23

Modified push-up method: blur to clear

Question 24

When is the modified push-up method for accommodation used?

Answer 24

Modified only really used when thinking that the patient isn’t trying hard enough to accommodate BUT there is evidence it is easier to judge with the modified method (so able to reach a further away point)

Question 25

How do you use the RAF rule (method) for accommodation?

Answer 25

- Observe patients as they should show miosis at near - 3x repeat for fatigue - Test BEO, RE & LE - With glasses - Compare with age norms

Question 26

Wat are the symptoms of impaired accommodation

Answer 26

- Accommodation insufficiency - Accommodation fatigue - Accommodation Inertia - Accommodation Paralysis - Accommodation Spasm

Question 27

What's hypermyopia?

Answer 27

Long-Sightedness Refractive power too little for the eye so light falls behind the retina or axial length too short

Question 28

What's myopia?

Answer 28

Short-Sightedness Refractive power too much for the eye so light falls in front of the retina or axial length is too long

Question 29

What's anisometropia?

Answer 29

1 Dioptre of power difference between the eyes

Question 30

How do we correct hypermetropia?

Answer 30

Convex lens (+ve) Gives further convergence of light rays = lens relaxes (Without glasses) They need to accommodate to see distance objects clearly but MORE accommodation is needed to see near objects clearly more so than an emmetrope

Question 31

If someone has +4DS at near as a hypermetrope, what would their vision be like without glasses if: Dist: 0D Near: 3D

Answer 31

Without glasses: Dist: 0D + 4D = 4D Near: 3D + 4D = 7D

Question 32

What's myopia's accommodation like?

Answer 32

As refractive power is too much, accommodation cannot help but, at near, will be seen clearly without needing as much accommodation effort

Question 33

What lens do we use to correct myopia?

Answer 33

Concave (-ve) which diverges light rays, they induce accommodation as it causes rays to diverge when entering the eyes

Question 34

If someone with -2DS is looking at near with glasses, what is their -ve without glasses if: Dist: 0D Near: 3D

Answer 34

Without Glasses: Dist: 0D Near: 3D - 2D = 1D (as without glasses they accommodate -2D less than an emmetrope as they over accommodate in general)

Question 35

What are the effects of lenses on ET & XT?+

Answer 35

+ve in Eso = Eso will reduce +ve in Exo = Exo will increase -ve in Eso = Eso will increase -ve in Exo = Exo will decrease