Warren Hill, M.D. is medical director, East Valley Ophthalmology, Mesa, Ariz.
“The AcrySofIQ IOL is a solid choice to lessen the amount of positive spherical aberration in the pseudophakic eye.”
Warren Hill, M.D.
Surgeons currently debate how much positive spherical aberration should be corrected with IOL implantation. Data from recent studies suggest that leaving a small amount of positive spherical aberration in the eye may be beneficial.
In eyes that have visual acuity better than 20/15, the spherical aberration of the eyes is, on average, about positive 0.10 µm with a 6-mm pupil size.1 These clinical observations suggest that preserving some positive spherical aberration may enhance overall image quality.
The AcrySofIQ (SN60WF) IOL (Alcon, Fort Worth, Texas) is a solid choice to lessen the amount of positive spherical aberration in the pseudophakic eye. The AcrySofIQ lens is aspheric and duplicates the typical aberrations of the youthful eye. Most youthful eyes have a median value of positive aberration.
On average, a 20-year-old human crystalline lens produces roughly 0.20 microns of negative spherical aberration to counteract the positive spherical aberration of the cornea. If a surgeon would like to maintain a small amount of positive aberration in a patient, the AcrySofIQ seems to straddle what is found in the average population.
The three currently available aspheric IOLs have distinctly different compensation strategies: the AcrySofIQ provides 0.20 µm of negative spherical aberration for a 6mm pupil; the Tecnis Z9001 (silicone) and Z9003 (acrylic) provide 0.27 µm of negative spherical aberration (for a 6-mm pupil); and the SofPort LI61AO does not add any spherical aberration.
Because the AcrySofIQ lens is aspheric, it has a slightly higher A-Constant than the normal SA60 or SN60 AcrySof Single-Piece, and Natural series, respectively. There are some clinical data that suggest that because of improved contrast sensitivity, patients with the IQ IOL may drive better and have improved visual quality in dim light conditions.
This becomes especially important when you have patients with large pupils. When a pupil is larger than 4 mm under mesopic conditions, improvements in contrast sensitivity have been reported recently in patient studies,2 and suggest you get a clearer image with the AcrySof IQ IOL.
Compared with a spherical lens, the amount of spherical aberration with the IQ IOL is much less as the pupil size becomes larger3 (Figure 1). The more spherical aberration there is, the lower the quality of the image.
This lens performs better than a spherical lens under almost all conditions. It straddles the population nicely, and if you believe some spherical aberration can match that which is found in the youthful human eye and in people with high visual performance, the AcrySof IQ IOL is an excellent choice.
1. Levy Y, Segal O, Avni I, Zadok D. Ocular higher-order aberrations in eyes with supernormal vision. American Journal of Ophthalmology 2005; 139: 225-228
2. Beiko G. Personalized correction of spherical aberration in cataract surgery. AAO Meeting, Chicago, October 2005.
3. Braunstein R. Reduced Spherical Aberration in Cataract Patients with an Aspheric Optic IOL. Alcon Speaker Forum, ASCRS•ASOA Symposium & Congress, 2006, San Francisco.