Questions: Which patients are ‘at risk’ for aniseikonia – axial or refractive anisometropes? Corrected or uncorrected? We only care about symptoms when people are corrected



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Questions:

  1. Which patients are ‘at risk’ for aniseikonia – axial or refractive anisometropes? Corrected or uncorrected?

We only care about symptoms when people are corrected. REFRACTIVE ametropes (hyperopes and myopes) all have the same retinal image size before correction, so they will have different retinal image sizes after correction (especially with glasses) because of the magnifying power of plus lenses and the minifying power of minus lenses.


  1. Describe the distortion of the back wall of the leaf room when the meridional magnifier was axis 090 over your right eye (geometric effect). How does this change with the meridional magnifier axis 180 over your right eye (induced effect)?

With the meridional magnifier x090 in front of the right eye the back wall of the leaf room appeared tilted so that the right side was farther away and bigger and the left side was closer and smaller (geometric effect). When the axis was switched to x180 in front of the right eye the distortion reversed direction so that now the left side appeared farther away and bigger and the right side appeared closer and smaller (induced effect).


  1. Explain how the depth impression of the geometric effect occurs.

With axis 090 over the right eye, there is no magnification in the vertical meridian, only magnification in the horizontal meridian. Consequently, the right eye sees the back wall as a rectangle while the left eye sees the back wall as a square. This difference in magnification between the 2 eyes in the horizontal meridian sets up an uncrossed disparity between the right and left eye images of the right side of the back wall which makes it appear far, and a crossed disparity between the right and left eye images of the left side of the back wall which make it appear close.


  1. Explain how the size impression of the geometric effect occurs.

The back wall of the leaf room looked like a trapezoid with a bigger farther right side and a smaller closer left side. Usually, things that are far look small. But the right side is the same size as the left side, so because it looks far, it must be bigger.


  1. Which should be the stronger effect (geometric or induced) and why? What is the implication of this for the distortion caused by overall magnifying lenses?

The geometric effect is stronger for most people, and we think that the geometric effect should be because we can explain the depth effect on the basis of binocular disparity, whereas we cannot explain why we even get a depth effect with the vertical disparities set up by x180 (induced effect) meridional magnification. An overall magnifier is a combination of axis 090 (geometric) and axis 180 (induced) effects, and because the distortions these effects cause are in opposite directions they cancel – all except for the slight axis 090 geometric effect that is stronger for most people.


  1. Do the size lenses produce similar distortions outside of the leaf room? Why or why not?

How will you advise such patients about the possibility experiencing aniseikonic distortions?

No, there is no spatial distortion outside of the leaf room because the corners and edges are not hidden, and these architectural cues over-ride distortions you might see when they are hidden, as in the leaf room.
There would be no distortion in structured environments, but your aniseikonic patients might see the distortion when in unstructured environments like the woods, beach, skiing, rock climbing (oooh no!) that you might warn them about.


  1. How would you describe the shape of your baseline horopter? At what distance is the horopter flat?

The shape of the horopter is a function of viewing distance: at this close distance the horopter should be concave towards the observer. At the ‘abathic’ distance of about 1 meter the horopter is flat, and at further viewing distances it becomes convex to the viewer.


  1. What differences do you find between your baseline horopter and the size lens plot? Can you explain your findings?

The overall magnifier over the right eye causes a slight geometric effect, where, if distortion could be perceived, it would be that the right side of the Objective Fronto-Parallel Plane appears farther on the right and closer on the left. But the mission of the observer is to align the pegs so that they appear to be in a plane parallel to their face, so they compensate for the distortion they see by pulling the pegs on the right closer, and pushing the pegs on the left further back.


  1. What differences do you find between your baseline horopter and the BO prism curve? How do you think viewing through prisms might cause this effect?

Light is deviated towards the base of a prism, and the image is projected to the apex. Following this property of prisms, a BO prism will cause the Objective Fronto-Parallel Plane to appear concave towards the viewer. But the mission of the observer is to align the pegs so that they appear to be in a plane parallel to their face, so they compensate for the distortion they see by aligning the pegs so that they are convex towards their face.


  1. Explain the results you got with the x090 meridional magnifier ofer the left eye on the tilting plane.


Remember what you saw in the leaf room with the meridional magnifier x090 in front of the RIGHT eye – the same side -> the RIGHT side appeared farther away. The question is about having the meridional magnifier x090 in front of the LEFT eye, so it would be that the LEFT side appears farther away.

Now your job is to arrange the plane so that it appears to be parallel to your face, so you compensate for the distortion you see by pulling the left side closer. This would be a counter-clockwise (positive) rotation, so all data for meridional magnifiers x090 in front of the left eye will be in the positive quadrant for the left eye. The strongest magnifier may have been difficult to fuse so the effect may have been less strong than with the medium strength magnifier. Because the geometric effect is stronger for most people this slope might be steeper that when the axis is 180.




  1. Explain the results you got with the x180 meridional magnifier over the left eye on the tilting plane.


Remember what you saw in the leaf room with the meridional magnifier x180 in front of the RIGHT eye – the opposite side -> the LEFT side appeared farther away. The question is about having the meridional magnifier x180 in front of the LEFT eye, so it would be that the RIGHT side appears farther away.

Your job is to arrange the plane so that it appears to be parallel to your face, so you compensate for the distortion you see by pulling the right side closer. This would be a clockwise (negative) rotation, so all data for meridional magnifiers x180 in front of the left eye will be in the negative quadrant for the left eye. The strongest magnifier may have been difficult to fuse so the effect may have been less strong than with the medium strength magnifier.



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