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strabismus 106 > Accommodation > Flashcards

Accommodation Flashcards

1
Q

What is accommodation?

A

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)

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2
Q

What is accommodation driven by?

A

Blur
Convergence
Proximal Cues
Tonic Convergence

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3
Q

What is the role of the lens?

A

Adjust focal length to focus image on retina

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4
Q

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

A

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

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5
Q

How do we work out the power of a lens?

A

1 / focal length

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6
Q

What is power of lens the same as?

A

Accommodation as it’s the additional power of lens needed

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7
Q

What is the same as focal length?

A

Same as fixation distance

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8
Q

How do we work out accommodation (in dioptres)?

A

1 / fixation distance (meters)

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9
Q

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

A

1 / 2 = 0.5D

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10
Q

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

A

1 / power of lens (accommodation)

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11
Q

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

A

Sporadic, intermittent and inaccurate

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12
Q

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

A

Adult-like

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13
Q

What’s accommodation like in a 3mo?

A

Fully developed

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14
Q

What’s presbyopia?

A

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

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15
Q

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

A

4squared - (age/4)

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16
Q

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

A

18.5 - (0.3 x age in years)

17
Q

How do we calculate amplitude of accommodation (D)?

A

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

18
Q

How do we calculate near point?

A

1 / amplitude of accommodation

19
Q

How do we measure accommodation at near?

A

Using the RAF rule N-Series drum

20
Q

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

A

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

21
Q

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

A

When the text becomes blurred

22
Q

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

A

Conventional Method: Clear to blur

23
Q

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

A

Modified push-up method: blur to clear

24
Q

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

A

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)

25
Q

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

A
  • Observe patients as they should show miosis at near
  • 3x repeat for fatigue
  • Test BEO, RE & LE
  • With glasses
  • Compare with age norms
26
Q

Wat are the symptoms of impaired accommodation

A
  • Accommodation insufficiency
  • Accommodation fatigue
  • Accommodation Inertia
  • Accommodation Paralysis
  • Accommodation Spasm
27
Q

What’s hypermyopia?

A

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

28
Q

What’s myopia?

A

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

29
Q

What’s anisometropia?

A

1 Dioptre of power difference between the eyes

30
Q

How do we correct hypermetropia?

A

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

31
Q

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

A

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

32
Q

What’s myopia’s accommodation like?

A

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

33
Q

What lens do we use to correct myopia?

A

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

34
Q

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

A

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

35
Q

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

A

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

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

strabismus 106 (35 decks)

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