progressive-addition lens
A progressive addition lens (PAL) is a one-piece multifocal spectacle lens whose front surface curvature increases gradually from the upper distance portion to the lower near portion.1,2 The changing curvature raises the plus power smoothly, so the wearer can see clearly at any distance by positioning the head and eyes.1
A progressive corridor joins the distance portion to the near portion, and the power changes gradually along it. The near portion, where the full near addition is found, sits down and inward.1 Because the power changes continuously, the lens has no visible segment line and none of the image jump that a segmented multifocal produces.2
The same change in curvature produces unwanted surface astigmatism, which in sufficient amounts blurs vision and limits the field of clear vision. Designs place this astigmatism in the lower quadrants, lateral to the corridor and the near zone, where the wearer notices it least.2 The change in power and magnification also causes skew distortion, so straight lines can look curved through the lower lateral areas of the lens. All progressive lenses are inherently aspheric because of their changing curvature.2
More detail
Owen Aves patented the first progressive addition lens in 1907.2 Progressive addition lenses are sometimes called invisible bifocals, a name that properly belongs to blended bifocals, whose round segment has had its dividing line polished out.1
Manufacturers use the word aspheric loosely for progressive lenses. Some apply asphericity to the distance portion to compensate for a base curve flatter than best form, and others use the word when unwanted astigmatism reaches well into the upper half of the lens.2
Sources (8)
- Brooks and Borish, System for Ophthalmic Dispensing, ch. 20
- Introduction to Ophthalmic Optics, ch. 11
- Charman, W.N. 2014. Optics of progressive addition lenses. In: Benjamin, W.J. ed. Borish's Clinical Refraction. 2nd ed. St. Louis: Butterworth-Heinemann, pp.1029-1054.
- Fowler, C.W. and Pateras, C. 1990. Progressive addition lenses–Part I. Ophthalmic and Physiological Optics, 10(2), pp.183-195.
- Grosvenor, T. 2007. Primary Care Optometry. 5th ed. St. Louis: Butterworth-Heinemann Elsevier.
- Meister, D.J. and Fisher, S.W. 2008. Progress in the spectacle correction of presbyopia. Part 2: Modern progressive lens technologies. Clinical and Experimental Optometry, 91(3), pp.251-264.
- Rutstein, R. and Daum, K. 1997. Anomalies of Binocular Vision: Diagnosis & Management. St. Louis: Mosby.
- Sheedy, J.E., Hardy, R.F. and Hayes, J.R. 2006. Progressive addition lenses—matching the specific lens to patient needs. Optometry, 77(1), pp.17-31.
Reviewed October 2026