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Corneal onlays and inlays
Published in Pablo Artal, Handbook of Visual Optics, 2017
Hyperopia is a condition where the optics of the eye are not strong enough or the axial length of the eye is too short for images to come into focus on the retina without additional power. This additional power is either provided by positive (plus) powered lenses or contact lenses or may be achieved by strong accommodative effort. If a patient has had their natural crystalline lens removed and not had an IOL implanted, a condition known as “aphakia,” the eye is left with a significant amount of hyperopia, or undercorrection. Positive spectacle lenses are also used to correct aphakia; however, they are extremely thick. Positive contact lenses are an option for aphakia; however, most patients who are aphakic are older and are less able to handle contact lenses or tolerate contact lens wear. For both hyperopia and aphakia, a change in the power of the eye can be achieved by either increasing the curvature of the cornea or introducing a positive powered implant.
Evaluating the blue-light hazard from solid state lighting
Published in International Journal of Occupational Safety and Ergonomics, 2019
John D. Bullough, Andrew Bierman, Mark S. Rea
Aphakic eyes are very rare. When the crystalline lens is removed during cataract surgery or other corrective procedures, it is generally replaced with an IOL designed to make up for the absence of refractive power provided by the original lens. Some IOLs transmit substantial optical radiation in both the UV (300--400 nm [33]) and visible (400--700 nm) bands, while others are designed as so-called UV-blocking, violet-blocking or blue-blocking lenses with varying degrees of short-wavelength cutoff filtering (an example of each type is shown in Figure 2 [45]). Depending upon the type of IOL, these lenses will confer varying degrees of protection against the blue-light hazard in comparison with the eye’s natural crystalline lens [46], which is characterized by the blue-light hazard function B(λ). As a comparison, the aphakic hazard function A(λ) was point-by-point multiplied by each of the spectral transmittance curves in Figure 2, and the resulting values are shown in Figure 3 together with B(λ). These curves show that, depending upon the wavelength band and the type of IOL, the blue-light hazard from very short-wavelength light (400–440 nm) and from near-UV radiation (300–400 nm) [33] could be higher, similar or lower than the risk to an individual with a natural crystalline lens. Of interest, the IOL labeled UV-blocking results in very similar blue-light hazard protection as the crystalline lens assumed to underlie the B(λ) function. It has been argued [45,47,48] that IOLs which block transmission into the visible wavelength region (>400 nm) are undesirable because of their negative impacts on color vision and circadian photoreception.