Anterior Segment Cataract and Refractive
Figure 4: An AcrySof® Intraocular Lens SN60WF is Loaded into the Cartridge by Grasping the Peripheral Optic with Forceps
Almost all modern IOLs have incorporated an ultraviolet (UV) blocking agent to prevent erythropsia and suspected corollary light toxicity-mediated macular damage, which was seen in the late 1970s and early 1980s before the introduction of these filters.19–22
However, as early as 197822,23 it was shown that IOLs that block only
UV radiation still transmit abnormally high amounts of short wavelength violet and blue light compared with the natural crystalline lens. In 1987, RW Young wrote a review on the pathophysiology of age-related macular degeneration (AMD). In the following year the same author presented the hypothesis that solar radiation played an important role in the development of AMD and recommended both antioxidants and protective radiation filters to be intrinsic components of a program of preventive medicine.24,25
The excess
The trailing haptic will be tucked over the top of the left side of the optic so that the plunger can engage the rim of the edge of the optic without becoming entangled with the trailing haptic. Courtesy of JA Davison.
Figure 5: The Globe is Temporarily Stabilized by a Cyclodialysis Spatula
transmission of violet and blue light can cause color vision abnormality, cyanopsia,26–32
in some patients and has been shown to
produce macular changes that can be linked to the processes of AMD. The suspicion of eventual macular damage from excessive short-wavelength light has been supported by various laboratory and some but not all epidemiologic studies.26,33–48
Due to these substantial
complexities, a controlled prospective study of patients implanted with a UV-blocking IOL in one eye and a UV-blocking and spectrum-normalizing IOL in the other eye has yet to be performed.
Nevertheless, because of the potential significance of this ‘blue light hazard’,49,50
scientists began to recommend,23,45,46,51–60 and engineers at
various companies throughout the world including Alcon began to develop, IOL technology that filters varying amounts of violet61–71
or
violet and blue light from passing through to the retina. These IOLs appear yellow in color because of the blue light that has been filtered and have been termed yellow-tinted, blue-light filtering, and light-normalizing (see Figure 8).72
The trade name for Alcon IOLs with
The SN60WF IOL with some associated Viscoat is emerging from a C Monarch injector cartridge, which has been inserted through a 2.4mm incision, into the ProVisc filled anterior chamber. Courtesy of JA Davison. IOL = intraocular lens.
Figure 6: Higher Magnification Miyake View of Single-piece AcrySof® Intraocular Lens Demonstrating Good Centration of the Optic and Equal Flexion of Each Haptic within Capsular Bag
the feature is ‘AcrySof® IOL Natural’, aptly given because it simulates the normal amount of light transmitted by a young adult phakic patient (see Figure 8).
The commercial market effects of the proprietary spectrum- normalizing chemistry in a foldable IOL introduced by Alcon in 2003 led to scientific controversy. All of the studies that have been performed have incorporated basic scientific assumptions in their hypotheses, and most of the controversy over the study results has had to do with the validity of those assumptions themselves.73–75
One area of debate is the effect of the AcrySof® IOL Natural models on scotopic vision. Varying estimates of the reduction of scotopic vision exist. One study suggests that a serious loss (25.5% reduction) of scotopic vision function can occur when using the Natural IOL.76 However, when those computations were undertaken with different assumptions a corrected result showed a net increase of 52% in scotopic spectral sensitivity relative to a young phakic person.77
It has
The capsule has completely shrink-wrapped around the square optic and haptic edges. Courtesy of Alcon Surgical.
high index of refraction. There have been no reported cases of whitish optic calcification, which has been seen to a larger degree in some hydrophilic acrylic IOLs that have a water content of around 25%.18
32
Scotopic contrast sensitivity with and without glare has been reported to be the same with blue light-filtering IOLs and with UV-only
also been concluded that the expected reduction in scotopic sensitivity of 0.07 log units is visually insignificant in relation to the 4.0 log unit range of scotopic sensitivity and that it translates to contrast sensitivity reduction of 0.01 log units, which is a difference too small to reliably detect.78
US OPHTHALMIC REVIEW
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