Amblyopia and Binocular Vision Disparity in Eye Exams

Amblyopic disparity

I would like to ask...
I have congenital amblyopia in my left eye, approximately 250 degrees, while my right eye has myopia, around 150 degrees.
I want to know if the calculation of the visual disparity between both eyes during an eye exam involves adding the degrees of both eyes, and what does refractive power mean? I hope the doctor can clarify this for me, and how is the calculation of astigmatism done?

yaimingwai, 20~29 year old female. Ask Date: 2004/06/03

Dr. Lin Zhengyi reply Ophthalmology

Do you know if your left eye is hyperopic or myopic? If it is hyperopic, it should be written as +250 diopters; if it is myopic, it should be written as -250 diopters.
The right eye, which is "myopic 150 degrees," should be written as -150 diopters.
If one eye is hyperopic and the other is myopic, the calculation for the difference in refraction is +250 - (-150) = 400 diopters.
If both eyes are myopic, the calculation for the difference in refraction is -250 - (-150) = -100 diopters, but we take the absolute value, so the difference in refraction is 100 diopters.

Diopter is a measure of the lens (or eye) ability to refract light.
Convex lenses have a positive diopter value, while concave lenses have a negative diopter value.
The value of diopters is the reciprocal of the focal length (measured in meters).
For example, a convex lens with a focal length of 1 meter is referred to as a +1 diopter lens, while a -2 diopter lens has a focal length of -50 centimeters (-0.5 meters).
When people say "myopia 100 degrees," it should actually be written as -1 diopter, while hyperopia of 250 degrees should be written as +2.5 diopters, meaning the "degree" divided by 100 equals the "diopter."
When calculating the difference in refraction, if astigmatism is to be included (note that it is not "flash" light), the value of astigmatism should be divided by 2 and then added to the spherical power.
However, it is important to note that most astigmatism values are expressed as negative numbers.

Reply Date: 2004/06/03

More Info

Amblyopia, commonly known as "lazy eye," is a condition where one eye does not develop proper vision during childhood. It often occurs when there is a significant difference in the refractive error between the two eyes, leading to binocular vision disparity. In your case, with your left eye having a refractive error of approximately -250 degrees (indicating moderate myopia) and your right eye at -150 degrees (indicating mild myopia), this difference can contribute to the development of amblyopia if not addressed early on.

In terms of calculating the disparity between your two eyes during an eye exam, it is not simply a matter of adding the refractive errors together. Instead, the concept of "binocular vision disparity" refers to how the brain processes the images from both eyes. The brain typically prefers to use the eye with better vision, which can lead to the underdevelopment of the visual pathways from the weaker eye.
Refractive error is measured in diopters (D), which quantifies how much the eye deviates from normal vision. A negative value indicates myopia (nearsightedness), while a positive value indicates hyperopia (farsightedness). The greater the absolute value of the refractive error, the more significant the vision correction needed. In your case, the left eye has a higher degree of myopia compared to the right eye, which can lead to a visual imbalance.

Regarding the calculation of "flash" or "glare" sensitivity, this typically refers to how well your eyes can handle bright lights or sudden changes in light intensity. It is not calculated in the same way as refractive errors but is assessed through various tests during an eye exam. These tests may involve exposing your eyes to bright lights and observing how your pupils react, as well as how quickly your vision adjusts back to normal after the exposure.

In managing amblyopia, treatment options may include corrective lenses, patching the stronger eye to force the weaker eye to work harder, or vision therapy exercises. The goal is to improve the visual acuity of the amblyopic eye and enhance binocular vision.
It is crucial to have regular eye exams, especially since you have a significant difference in the refractive errors of your eyes. An eye care professional can provide tailored advice and treatment options based on your specific condition. If you have concerns about your vision or the effectiveness of your current treatment, do not hesitate to seek further evaluation from an eye specialist. Early intervention can significantly improve outcomes in amblyopia and help in achieving better binocular vision.

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