Bv Lec 2 Flashcards
What’s aniseikonia
A perceived relative difference in size and or shape of the ocular images
What causes aniseikonia
Anisometropia
Amblyopia
Ocular pathology of media in cornea or lens
Retinal pathology
What’s physiological aniseikonia
The normal relative difference in ocular image size due to image disparities introduced by lateral separation of eyes, assymetrical convergence, or assymetry of field of vision
What’s an iseikonic lens
Lenses that equalise magnification for patients with aniseikonia.
For axial anisometropia
What’s an isogonal lens
Lenses that produce identical spectacle magnification.
For refractive aniseikonia
What’s a size lens
Lens that changes magnification but not power. Used in diagnosis of aniseikonia
Percentage of magnification (aniseikonia) that produces symptoms
1-2%?
Moderate ~5%?
Long standing large >5%?
1-2% is symptomatic
Moderate ~5% is still symptomatic if sensory fusion mechanisms are active (not suppressed)
Long standing large >5% is a symptomatic if sensory fusion mechanisms are inactive (suppressed)
Types of corneal refractive anisometropia
Unequal corneal curvature
Corneal astigmatism
Corneal transplants
What’s meridional aniseikonia
Aniseikonia in which there’s a symmetrical meridional difference between the size of the ocular images in the 2 eyes, so that the image in one meridian is larger/smaller than corresponding meridian of the other eye
What are 3 causes aniseikonia due to the lens
Monocular intraocular implant
Monocular aphakia
Incipient cataract
What’s anatomical aniseikonia
Aniseikonia due to an anatomical cause like unequal distribution of retinal elements
Properties of retinally induced aniseikonia
Local aniseikonia
Occasional paradoxical aniseikonia
Static aniseikonia unrelated to dynamic
Need lens design for static and another for dynamic
Classic lens design often doesn’t solve problem
What’s static aniseikonia
Ocular image difference when we fixate on a point in a very brief instant of time
Methods to measure aniseikonia
1) measuring stereoscopic spatial distortion
- Static aniseikonia
- Remole Eikonometer
- Aniseikonia Inspector
- Awaya Test
2) Measuring the optically induced anisophoria
- Dynamic Aniseikonia
- Robertson Technique
What’s acquired optical aniseikonia
And what 2 factors matter
Aniseikonia due to lenses worn
High vertex distance =high mag
High centre thickness =high mag
