meridional amblyopia
Also called astigmatic amblyopia, orientation-specific amblyopia
Meridional amblyopia is a lasting reduction in the ability to resolve lines of a particular orientation. It develops when astigmatism remains uncorrected during the years of visual development, and the deficit persists even after the astigmatism is corrected.1
Astigmatism brings the eye's two principal meridians into focus at different distances from the retina, making some line orientations clearer than others. During visual development, the clearer orientations receive stronger cortical representation, while the consistently blurred orientations receive less.2
This distinguishes meridional amblyopia from the optical blur of uncorrected astigmatism in an adult: the appropriate cylinder correction clears the optical blur, but a developmental deficit may remain.3 It is typically associated with more than 1 diopter of astigmatism that persists beyond the age when refractive error normally stabilizes.1,2 Acuity often improves over several months of wearing the first correction, although an orientation-specific deficit may persist.1,2
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