To evaluate someone’s vision, the optician or optometrist will measure their visual acuity as a unit of measurement which determines their ability to identify objects located a particular distance away. We first measure the visual acuity of the right eye and then the left, finishing the test by evaluating both eyes at the same time.
- Myopia: a refractive error where images are focused in front of the retina due to the eyeball being too large or the focusing power being more than is necessary. It causes blurry vision when looking at objects at a distance but does not usually affect near vision.
- Hyperopia: a refractive defect where images are focused behind the retina due to the eyeball being too small or not having enough power to focus on nearby images. As such, it can cause both near vision and distance vision to become blurry, depending on the patient’s dioptres.
- Astigmatism: a refractive defect caused by the cornea not being spherical, with one meridian being more curved than the other. It causes visual distortion or blurry vision in both near and distant vision.
- Presbyopia: occurs mainly among 40-45 year olds and causes difficulties focusing with near vision. It is caused by a reduction in accommodative power and gets progressively worse with age.