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Optics 2 > Lecture 5: Aniseikonia & Spectacle Magnification > Flashcards

Lecture 5: Aniseikonia & Spectacle Magnification Flashcards

1
Q

Define Aniseikonia

A

BINOCULAR CONDITION. Image in 1 eye is perceived as different in size vs. other eye.

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2
Q

2 Types of Aniseikonia: What are they?

A
  1. Static: In 1 position of gaze

2. Dynamic: (Anisophoria): Optically INDUCED. ESP SIGNIFICANT in VERTICAL CONDITION esp when looking DOWN!

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3
Q

Etiology of Aniseikonia: 3 types

*Which is the most common?

A
  1. Optically Induced
  2. Retinally Induced
  3. Cortically Induced
    * Optically Induced!!
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4
Q

Optically Induced Aniseikonia

  1. What is it?
    a. 3 Causes?
A
  1. Due to DIFFERENCE in optical Mag Properties of the Eye + Auxillary Optics
    a. ANISOMETROPIA (most common), Pseudophakia, and Refractive Surgery Patients
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5
Q

Anisometropia: Review

  1. What is it? (textbook definition)
  2. Clinical Definition?
  3. Type?
  4. Prevalence?
A
  • It’s a Condition of UNEQUAL refractive state for the 2 eyes.
    1. Greater than 1 Diopter in one meridian.
    2. 2 Diopters difference (pt symptomatic around 1.5, but 2 Diopters is when we are really concerned about it.
    3. Antimetropia
    4. 5-10% of population > 20 yo.
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6
Q

Retinal Induced Aniseikonia

  1. AKA?
  2. Define
  3. Causes
  4. Other Sx?
A
  1. FIELD DEPENDENT ANISEIKONIA
  2. Aniseikonia varies w/Field Angles (angle b/w gaze direction and direction of the peripheral point)
  3. a. Compressed or stretched retina
    b. ERM, Macular Hole, Macular Edema, Retinoschisis, RD w/scleral Buckle
  4. METMORPHOPSIA
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7
Q

Retinally Induced Aniseikonia

  1. Epiretinal Membrane
  2. MAcular Edema
  3. Macular Hole
  4. Retinal Detachment
  5. Retinoschisis
A
  1. Tissue contraction causes MONOCULAR MACROPSIA
  2. Swelling of tissue causes MONOCULAR MACROPSIA
  3. Hole can cause MICROPSIA
  4. After repair, you can get MICROPSIA
  5. Retina split can cause FIELD DEPENDENT MACROPSIA in 1 direction and MICROPSIA in the other.
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8
Q

Cortically-Induced Aniseikonia (Theoretical at this point)

  1. What is it?
A
  1. Aniseikonia 2ndary to UNEQUAL division of the Primary Visual Cortex….No pts found yet in literature.
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9
Q

Whose at Risk?

  1. What signs to look for to suspect possible Aniseikonia? (6)
A
  1. Amblyopia
  2. Anisometropia
  3. Aphakia and Pseudophakia
  4. Astigmatism (greater than 2 diopters)
  5. Low Stereopsis
  6. Strabismus
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10
Q

Symptoms of Aniseikonia

  1. 2 Main things to ask about?
A
  1. Asthenopia and Diplopia or Poor Stereopsis!
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11
Q

Clinically Significant Aniseikonia

  1. Clinically Significant %?
  2. Anisometropia: How much?
A
  1. 3-5%
  2. Greater than or equal to 2.00D
    and Symptomatic at 1.50D difference
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12
Q

Spectacle Magnification

  1. 2 definitions
    a. Ratio b/w what?

b. or Change in what?

A
  1. a. RATIO b/w size of retinal image in an AMETROPIC eye BEFORE and AFTER Correction
    b. Change in RETINAL IMAGE SIZE due to CORRECTING LENS
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13
Q

When can Spectacle Mag can be a Problem?

  1. On when there’s significant changes in Rx: 3 things?
  2. Or Vertex Distance
A
  1. Aging, Systemic Disease, and Surgical

2. Going from Spectacles to Contacts

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14
Q

2 Components of Spectacle
Magnification

  1. Power Factor
    a. Power Magnification (Mp) is a FUNCTION of what 2 things?

b. What is the Eqn?

A
  1. a. Lens back vertex power (Fv) and Vertex Distance (h)

b. Mp = 1/(1-h(Fv))

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15
Q

2 Components of Spectacle
Magnification

  1. Shape Factor
    a. Shape Magnification is a function of what 3 things?

b. Ms = ?

A
  1. a. Front surface power of Lens (F1), Center Thickness (tc) in meters, and Lens Index (n)
    b. 1/(1-F1(tc/n))
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16
Q

Spectacle Magnification is equal to what?

Most pts have a hard time with a 3-5% difference in image size

A

Mspec = Mp x Ms

%Mspec = (Mspec - 1) x 100%

17
Q

Relative Spectacle Magnification

  1. What is it?
A
  1. Comparing what patient is seeing on retina w/correcting lens vs what they should be seeing if they were emmetropic.
    * or

The size of retinal image w/correction compared to the STANDARD EMMETROPIC EYE

18
Q

Testing for Aniseikonia

  1. Knapp’s Law: 2 parts
  2. DIRECT Measurement of Aniseikonia: 4 things
A
  1. a. Axial Ametropia
    b. Refractive Ametropia
  2. a. Aniseikonic Inspector
    b. Awaya Test
    c. Leaf Room Effects
    d. Space Eikonometer
19
Q

Knapp’s Law

  1. Axial Anisometrope
    a. Difference is due to a difference in what?
    b. It’s better to correct them with what?
  2. Refractive Anisometrope
    a. Difference b/w what?
    b. Better to correct them with what?
A
  1. a. in Length of the eye
    b. SPECTACLES to get same image size on retina
  2. a. due to REFRACTIVE POWER of cornea/lens
    b. Contact Lenses
20
Q

Retinal Image Size

  1. UNCORRECTED ANISOMETROPIA Caused by AXIAL AMETROPIA
    a. The Ocular components are what?
    b. The Axial Lengths are what?

c. Retinal Image size difference due to what? This is induced by what?

A
  1. a. relatively equal
    b. Unequal

c. due to UNEQUAL Axial Lengths are offset by the Unequal Spectacle Magnification, induced from the Spectacle Lenses
* She gave analogy of 2 projectors at same distance but different magnifications (it works here)
* Correct with GLASSES

21
Q

Retinal Image Size

  1. Uncorrected Anisometropia caused by Refractive Ametropia
    a. Axial Lengths are what?
    b. If Glasses are prescribed, what will happen?
A
  1. EQUAL. Resulting retinal image size in each eye to be EQUAL to the Emmetropic Eye.
    b. The Unequal Spectacle mag induced from the Glasses may Create UNEQUAL RETINAL IMAGE SIZES, causing symptoms (ANISEIKONIA)
22
Q

Relative Spectacle Mag. and Anisometropia

  1. How to tell the difference?
    a. If they’re relatively equal?
    b. If they’re
A
  1. Do Keratometry
    a. K’s relatively equal = AXIAL
    b. If they’re not…and they’re equal to the amt of ANISO error, then it’s REFRACTIVE!!
23
Q

Ametropia types

  1. Axial Myopia
    a. No Rx
    b. SRx
    c. CLRx
  2. Axial Hyperopia
    a. No Rx
    b. SRx
    c. CLRx
A
  1. a. Larger (+ Lens System)
    b. EQUAL (Glasses offset)
    c. LARGER
  2. a. Smaller (- lens system)
    b. Equal (Glasses offset)
    c. Smaller
24
Q

Ametropia Types

  1. Refractive Myopia
    a. No Rx
    b. SRx
    c. CLRx
  2. Refractive Hyperopia
    a. No Rx
    b. SRx
    c. CLRx
A
  1. a. Equal (axial Length)
    b. Small (spec mag/min from glasses)
    c. Equal
  2. a. Equal (axial Lengths)
    b. Larger (Spec mag/min from glasses)

c. Equal

25
Q

Direct Measurement of Aniseikonia

  1. What 5 tests are there? (be aware of them)
A
  1. Aniseikonic Inspector
  2. Awaya Test
  3. Brecher Test & Size Lenses
  4. Leaf Room Effects
  5. Space Eikonometer
26
Q

Solutions

  1. Contact Lenses Only
    a. Works best if Axial Lengths are what?
    b. Cosmetically?
    c. Anisophoria?
A
  1. a. Relatively Equal
    b. Cosmetically Acceptable
    c. None
27
Q

Solutions

  1. Glasses Only w/a Good VA (more axial issue)
    a. Optical Magnification Changes are Induced by Changing what?
    b. May introduce what?
A
  1. a. Shape of the Spectacle Lenses (Curvature, Thickness and VD)
    b. Anisophoria
28
Q

Solutions

  1. Glasses only w/a Poor VA
    a. Refractive Power is altered where?

b. What happens?

A
  1. a. in 1 eye to reduce magnification effects

b. Blurred vision in one eye but okay Binocular vision overall

29
Q

Solutions

  1. Combo of Glasses & CL’s
    a. Same as what?
A
  1. The Glasses only w/a poor VA but a CL corrects the Blurred eye
30
Q

How to Alter Mspec w/Glasses

  1. Plus Lenses: to DECREASE Spectacle Magnification by doing what 4 things?
A
  1. INCREASE INDEX and/or DECREASE Vertex, Base Curve, or Center Thickness
    * Opposite for Minus Lenses!
31
Q

Spectacle Magnification & VD

  1. If the Lens Vertex distance is changed, there is a change in what?
    a. This holds true for what 2 things?
A
  1. In the Retinal Image Size

a. For BOTH CONTACTS and GLASSES

32
Q

Bevel Placement to reduce Magnification differences in Power Combinations

  1. High Plus w/Lower Plus
  2. High Minus w/Lower Minus
  3. Plus one 1, minus other eye
A
  1. High Plus: Bevel toward front of Lens Edge
    lower-Plus: Bevel toward rear of lens edge
  2. High-minus: Bevel toward front of lens edge
    Lower-minus: Bevel Toward rear of lens edge
  3. Both: Bevel as far to the FRONT of LENS EDGE as possible for BOTH LENSES

Optics 2 (6 decks)

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