Advances in Cataract Surgery

Majed Alkharashi; Walter J Stark; Yassine J Daoud


Expert Rev Ophthalmol. 2013;8(5):447-456. 

In This Article

Intraocular Lenses

In recent years, significant technological advances have improved our understanding of the aberrations of the normal human eye as well as the human eye that has been altered by refractive surgery. New corneal imaging techniques such as Scheimpflug imaging, placido-disk videokeratography and anterior segment optical coherence tomography have enhanced our understanding of the shape and functionality of the human cornea. These instruments have shown that the normal cornea is flatter in the central 2 mm, with steepening from 2–4 mm, and, then, flattening again beyond 4 mm. This correlates well with the fact that the spherical aberration value is not a constant throughout the cornea, but rather varies as one moves radially from the center of the cornea.[101] Further, in the young human eye, the positive spherical aberration introduced by the cornea is partially corrected by the negative spherical aberration introduced by the crystalline lens.[17] However changes that occur in the lens with age cause the positive spherical aberration of the lens to increase.[18] Thus, the aberration compensation is gradually lost, leading to an increase in total ocular aberrations. This, in turn, leads to a corresponding loss in optical and visual quality, reduction of scotopic contrast sensitivity and increase in optical side effects such as glare and haloes.[19,20]

This new understanding of ocular optics and aberrations has led to the development of new aspheric IOLs to neutralize the positive corneal spherical aberration and improve visual quality.[21] This may be due to the improvement in contrast sensitivity and improved retinal image.[22,23] However, caution must be exercised in using aspheric IOLs in patients at risk of decentration (e.g., pseudoexfoliation and trauma) as this may induce further higher order aberrations.[24] Aspheric IOL should also be avoided in eyes that had hyperopic LASIK treatment as this might increase the negative spherical aberration of the eye.