BLOG: Can your pseudophakic patient see better than you?
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Post-cataract surgery patients are often thrilled with the quality of their vision.
At our clinic, which specializes in ophthalmic surgery, we are accustomed to having pseudophakic patients describe their new vision as a miracle — or even better, high-definition TV.
They are sometimes so ecstatic that the doctor is left wondering: Is this simply the shock of the new, or are they actually seeing better than I am?
The primary wavelength-limiting filter of the eye is the crystalline lens, which absorbs and blocks short wavelengths, at the blue end of the visible spectrum. Almost no wavelengths shorter than 375 nm make it through the lens.
Furthermore, blue light is increasingly blocked by the lens as it ages. The lens of a young child is very clear, allowing through 77% of the blue light wavelength at 475 nm, but this percentage decreases rapidly with age. By age 53, the transmittance of light at 475 nm has reduced on average to 58%, and by age 75 it has fallen to 22% (Boettner EA, et al).
The light scatter of the crystalline lens also worsens with age. The direct, or unscattered, light transmittance to the retina of a 5-year-old child is about 88%; at age 75 this number is 41%.
IOLs, by contrast, transmit 475 nm wavelength light at around 92%, have negligible light scatter and do not degrade with time. Most IOLs at least match the short wavelength cut-off of the crystalline lens, and a few IOLs have been used that allowed through light well into the ultraviolet range. The pseudo-accommodative Crystalens (Bausch + Lomb) was the most well-known of these.
In other words, unless you are younger than about 5 years, a pseudophake is enjoying a broader range of wavelengths — and less light scatter — than you are.
There are advantages to a phakic eye, of course. Pseudophakes have no accommodative ability and must rely on optical aids or multifocal IOL optics to focus over a range of distances. Roughly 20% of cataract surgeries result in a residual refractive error of more than 0.50 D, so many must wear glasses for all activities. Also, pseudophakes often suffer from peripheral aberrations stemming from the IOL optics.
Nevertheless, if you find yourself wondering if you are seeing as many colors as your awestruck cataract patient is — you aren’t.
References:
- Boettner EA, et al. Invest Ophthalmol Vis Sci. 1962;1(6):776-783.
- Tecnis monofocal 1-Piece IOL. https://www.jnjvisionpro.com/products/TECNIS-1-piece-iol.
For more information:
Oliver Kuhn-Wilken, OD, is a staff optometrist at Pacific Cataract and Laser Institute’s Tualatin Clinic in Oregon.
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