meridional amblyopia
Also called astigmatic amblyopia, orientation-specific amblyopia
Reduced resolution for lines of one orientation, caused by uncorrected astigmatism during the years of visual development and persisting after the astigmatism is corrected1. Uncorrected astigmatism focuses one principal meridian nearer the retina than the other; the sharper meridian wins the competition for cortical cells and the blurred meridian ends up driving too few2.
It differs from an uncorrected astigmatism in an adult, which clears as soon as the cylinder is right; meridional amblyopia is what remains after the correction3. The usual cause is more than one diopter of astigmatism persisting beyond the age at which refractive error normally settles, and acuity with the first correction usually improves over months of wear1,2.
More detail
With-the-rule astigmatism blurs horizontal lines, so letters with horizontal strokes such as E and F suffer most2. It differs from isoametropic amblyopia, in which the whole image is blurred and every orientation suffers. The condition can affect one eye or both1.
Sources (3)
- Kanski, Clinical Ophthalmology (2024), ch. 18
- Steinman, Visual Perception: A Clinical Orientation, ch. 17
- von Noorden and Campos, Binocular Vision and Ocular Motility, ch. 14
Reviewed October 2026