Sharp cutoff filters in intraocular lenses optimize the balance between light reception and light protection

Effect of Violet Light-Filtering and Manufacturing Improvements in an Extended Depth-of-Focus Intraocular Lens on Visual Performance

Purpose

To assess the experimental visual performance and dysphotopsia characteristics of the new Tecnis Symfony OptiBlue extended-depth-of-focus with violet light-filtering (ZXR00V) intraocular lens (IOL) compared with the colorless Tecnis Symfony (ZXR00) IOL.

Methods

Range of vision was assessed with simulated visual acuity defocus curves, predicted by white light through focus modulation transfer function (MTF) measurements. The clinical visual acuity defocus curve of the ZXR00 IOL was used to validate the predicted range of vision. Image quality was compared by measuring white light MTF at a spatial frequency of 15 cycles per degree (c/deg) for 3 mm and 5 mm pupil diameters with optical powers of 5 D, 20 D, and 34 D using the average corneal eye (ACE) model with the average spherical and chromatic aberration of the cataract population. Effects on dysphotopsias were predicted by measurement and computer simulation of light scatter (straylight parameter) and subsequent determination of retinal veiling luminance (RVL) in vitro. Contrast enhancement under challenging light conditions was calculated based on the effects in RVL.

Results

The simulated visual acuity defocus curves and image quality outcomes were comparable between the ZXR00V and ZXR00 IOLs. The area under the straylight curve for the straylight parameter showed a 19% improvement in halo performance with ZXR00V versus ZXR00. A 12% to 17% reduction in RVL was achieved in favor of ZXR00V over ZXR00, which enhanced contrast vision by 9% to 13% under challenging light conditions.

Conclusion

The violet light-filtering technology and improved manufacturing of ZXR00V delivers a comparable range of vision and tolerance to refractive error to ZXR00 while mitigating dysphotopsias and enhancing contrast vision.

Comparison of the Ultraviolet Light Filtering across Different Intraocular Lenses

SIGNIFICANCE

We have analyzed the ultraviolet transmittance of some commercial intraocular lenses (IOLs). The results show differences of wavelength cutoff among them.

PURPOSE

The purpose of this study was to measure and compare the ultraviolet light transmittance of different IOLs made out of acrylic hydrophobic, hydrophilic, and hydrophilic with hydrophobic surface materials from different manufacturers.

METHODS

The spectral transmission curves of eight monofocal IOLs with the same dioptric power of +20.0 diopters were measured using a PerkinElmer Lambda 35 ultraviolet/visible spectrometer. Two IOLs of each type were tested three times. The ultraviolet cutoff wavelength at 10% transmission and the mean values were calculated.

RESULTS

All lenses prevented transmission of ultraviolet C (200 to 280 nm) and B radiation (280 to 315 nm). However, not all IOLs provided the same filtering properties in ultraviolet A (315 to 380 nm). Within the ultraviolet A range, the ultraviolet radiation cutoff wavelength of 10% ranges from approximately 360 to 400 nm. HOYA iSert 250 provided a cutoff wavelength of 398.4 nm; AcrySof SA60AT, 396.2 nm; AcrySof SA60WF, 395.7 nm; CT Asphina 404, 378.34 nm; Tecnis ZCB00, 377.70 nm; CT Lucia 607P, 379 nm; C-Flex 570C, 377 nm; and enVista MX60, 360 nm.

CONCLUSIONS

Intraocular lenses of different materials and manufacturers have different ultraviolet transmission characteristics. AcrySof (SA60AT and SA60WF) and HOYA iSert 250 provided the highest ultraviolet radiation transmission; the cutoff wavelength of 10% is close to 400 nm. In contrast, enVista IOL showed the lowest ultraviolet radiation cutoff.

Acquired color vision deficiency

Acquired color vision deficiency occurs as the result of ocular, neurologic, or systemic disease. A wide array of conditions may affect color vision, ranging from diseases of the ocular media through to pathology of the visual cortex. Traditionally, acquired color vision deficiency is considered a separate entity from congenital color vision deficiency, although emerging clinical and molecular genetic data would suggest a degree of overlap. We review the pathophysiology of acquired color vision deficiency, the data on its prevalence, theories for the preponderance of acquired S-mechanism (or tritan) deficiency, and discuss tests of color vision. We also briefly review the types of color vision deficiencies encountered in ocular disease, with an emphasis placed on larger or more detailed clinical investigations.

Effect on contrast sensitivity after clear, yellow and orange intraocular lens implantation

The objective of this study is to evaluate contrast sensitivity function (CSF) after clear, yellow- and orange-tinted intraocular lens (IOL) implantation. This was a prospective randomized study of 98 patients with senile cataract for a period of 6 months from day 1 of August 2014 to day 31 of January 2015. After phacoemulsification, 33 patients were implanted with clear IOLs (AcrySof UV-filtering IOL, SA60AT), 32 patients were implanted with yellow coloured IOLs (AcrySof Natural blue-light-attenuating and UV-filtering IOL, SN60AT with IMPRUV(®) filter) and 33 patients were implanted with orange-tinted blue-filtering IOLs (PC440Y Optech). After 1 month, monocular CSF was done under photopic (85 cd/m(2)) and mesopic (3 cd/m(2)) illumination condition with CSV-1000 test. The best corrected visual acuity (BCVA) after 1 month was 0.021 ± 0.058 logMAR for clear lens, 0.022 ± 0.059 logMAR for yellow lens and 0.019 ± 0.065 logMAR for orange lens (p = 0.989). Uniocular average photopic contrast sensitivity was 1.36 ± 0.19, 1.43 ± 0.18 and 1.46 ± 0.15 log units for clear lens, yellow lens and orange lens, respectively (statistically not significant; p = 0.076). Average mesopic contrast sensitivity was 1.02 ± 0.21 log units for clear lens, 1.00 ± 0.17 log units for yellow lens and 0.99 ± 0.15 log units for orange lens (statistically not significant; p = 0.771). Yellow or orange coloured blue-filtering IOLs are comparable to clear IOLs in terms of photopic and mesopic contrast sensitivity.

[Effect of transparent yellow and orange colored contact lenses on color discrimination in the yellow color range]

BACKGROUND

Colored transparent filters cause a change in color perception and have an impact on the perceptible amount of different colors and especially on the ability to discriminate between them. Yellow or orange tinted contact lenses worn to enhance contrast vision by reducing or blocking short wavelengths also have an effect on color perception.

METHODS

The impact of the yellow and orange tinted contact lenses Wöhlk SPORT CONTRAST on color discrimination was investigated with the Erlangen colour measurement system in a study with 14 and 16 subjects, respectively. In relation to a yellow reference color located at u' = 0.2487/v' = 0.5433, measurements of color discrimination thresholds were taken in up to 6 different color coordinate axes. Based on these thresholds, color discrimination ellipses were calculated. These results are given in the Derrington, Krauskopf and Lennie (DKL) color system.

RESULTS

Both contact lenses caused a shift of the reference color towards higher saturated colors. Color discrimination ability with the yellow and orange colored lenses was significantly enhanced along the blue-yellow axis in comparison to the reference measurements without a tinted filter. Along the red-green axis only the orange lens caused a significant reduction of color discrimination threshold distance to the reference color.

CONCLUSION

Yellow and orange tinted contact lenses enhance the ability of color discrimination. If the transmission spectra and the induced changes are taken into account, these results can also be applied to other filter media, such as blue filter intraocular lenses.

Oxidative photodegradation of ocular tissues: beneficial effects of filtering and exogenous antioxidants

The fact that light is necessary for life is generally accepted as an axiom. The extent to which light interacts and influences human biology, however, is often not fully appreciated. Exposure to sunlight, for instance, can both promote and degrade human health. There is now general scientific consensus that, although the eye evolved to respond to light, it is also damaged by excessive exposure. Light-mediated ocular damage is involved in the pathophysiology of many common forms of blindness. The type of ocular tissue damage induced by light exposure depends on the extent of exposure and wavelength. The tissues of the lens, cornea, and retina contain specific chemical moieties that have been proven to exhibit light-mediated oxidative degradation. Proteins and lipids present in the cornea, lens, and retina, meet all of the physical requirements known to initiate the process of oxidative photodegradation upon exposure to solar radiation. As such, different mechanisms have evolved in the lens, cornea, and retina to ameliorate such light-mediated oxidative damage. It appears, however, that such mechanisms are ill-matched to handle modern conditions: namely, poor diet and longer life-spans (and the degenerative diseases that accompany them). Hence, steps must be taken to protect the eye from the damaging effects of light. Preventative measures include minimizing actinic light exposure, providing exogenous filtering (e.g., through the use of protective lenses), and enhancing antioxidant defenses (e.g., through increased dietary intake of antioxidants). These strategies may yield long-term benefits in terms of reducing oxidative photodegradation of the ocular tissues.

Blue light-filtering intraocular lenses and post-operative mood: a pilot clinical study

The purpose of the study was to determine if implantation of blue-filtering intraocular lenses (IOLs) affects post-operative mood, inducing more depression, compared to patients undergoing implantation with conventional IOLs. The study was conducted at the Angers University Hospital, France. This was a prospective with a lowercase pilot study, including consecutive patients planned to undergo cataract surgery in both eyes within 1 week. The same type of IOL was used in both eyes of each patient. The choice of IOL was not randomized but driven by the habits and experience of each participating surgeon. Cognitively healthy patients (an MMSE score higher than 25) were assessed before and after surgery, using the 30-item geriatric depression scale (GDS) to seek symptoms of depression. Univariate and multiple logistic regressions were used to examine the association between the type of IOL and the 30-item GDS score improvement during the 3 months after lens implantation, while adjusting for participants' characteristics (age, visual acuity). Blue-filtering IOLs were used in 16 patients (mean ± standard deviation, 75.6 ± 7.5 years; 75 % female), and untinted IOLs in 18 patients (77.3 ± 6.9 years; 77.8 %female). Pre-operatively visual acuity and GDS scores were comparable in the two groups. The post-operative GDS score was improved by 1.91 ± 3.10 points in the whole sample (P = 0.002), as well as in each subgroup of patients. Three months after surgery, the mean change in GDS score did not differ between groups (P = 0.365), nor did the mean visual acuity (P = 0.198).

Effect of the color of the intraocular lens on optical and visual quality

Purpose: To analyze the optical quality of intraocular lenses (IOL) with an orange (PC440Y) and a yellow (SN60AT) filter, and correlate these results with the visual quality of patients with these implants. Setting: Fisabio Oftalmologνa Mιdica, Valencia, Spain. Design: Randomized prospective study. Materials and Methods: The IOL optical quality was determined using the modulation transfer function (MTF) and the spectral transmission. The visual quality of 87 eyes with cataract (51 with orange filter and 36 with yellow filter) was determined by best corrected visual acuity (BCVA) and contrast sensitivity function (CSF) under photopic and mesopic conditions. To analyze the results, we use a Student's t-test. Results: Orange lens filtered more of the blue spectrum (cut-off wavelength of 370 nm) than the yellow lens (390 nm). The MTF of the yellow lens was better than the orange lens (average modulation of 0.676 for natural and 0.672 for orange). The patients' BCVA was 0.02 + 0.10 logMAR for both lenses. The CSF obtained with the yellow lens was slightly better, although without statistically significant differences (P > 0.05). Conclusions: Both lenses are of good optical quality. The patients' visual quality was similar with both lenses, and optical quality was also similar. The color of the lens does not affect the visual quality of the patient.

Ultraviolet radiation at Mediterranean latitudes and protection efficacy of intraocular lenses

PURPOSE

After determining the mean intensity of ultraviolet radiation to which the human eye is exposed at Mediterranean latitudes, this data is used to evaluate the efficacy of the ultraviolet filters incorporated into various intraocular lenses.

METHODS

Ultraviolet radiation measured at Mediterranean latitudes was used as a reference for the theoretical calculation of the amount of radiation to which the human eye is exposed. The spectral transmission curve from 290 to 380 nm was measured for 10 IOLs using a UV/VIS Perkins-Elmer Lambda 800 spectrometer.

RESULTS

At Mediterranean latitudes, at sea level, with a mean annual solar irradiation of 50 j/cm(2), the human eye receives a quantity of UVA and UVB that is lower than the threshold toxic dose for the rabbit crystalline lens (93 j/cm(2) for UVA and 6.45 j/cm(2) for UVB). However, at higher altitudes and with albedo approaching 0.9 (fresh snow), the amount of radiation increases, with duration of exposure potentially playing a significant role. The UV filters incorporated into the IOLs studied are, in general, protective against such levels of radiation.

CONCLUSION

At Mediterranean latitudes, at sea level, the amount of UV radiation to which our eyes are exposed is insufficient to damage the crystalline lens; however, at higher altitudes, the risk of such damage exists. UV filters incorporated into intraocular lenses are generally effective, since they filter all radiation with wavelengths under 380 nm.

Comparison of visual performance with blue light-filtering and ultraviolet light-filtering intraocular lenses

PURPOSE

To compare the contrast sensitivity, glare, color perception, and visual acuity at different light intensities with yellow-tinted and clear intraocular lenses (IOLs) by different manufacturers.

SETTING

Ludwig Boltzmann Institute of Retinology and Biomicroscopic Laser-Surgery, Department of Ophthalmology, Rudolf Foundation Clinic, Vienna, Austria.

DESIGN

Comparative case series.

METHODS

Eyes were randomized to 1 of the following IOLs: AF-1 (UY) (yellow tinted), AcrySof SN60AT (yellow tinted), AF-1 (UV) (clear), or AcrySof SA60AT (clear). One week and 2 months postoperatively, monocular contrast sensitivity function and color discrimination were tested and the corrected distance and near visual acuities were evaluated. All tests were performed under different light intensities (10 to 1000 lux).

RESULTS

Of the 80 patients enrolled, 76 completed the study; there were 37 eyes in the yellow-tinted IOL group and 39 in the clear IOL group. There were no significant differences between yellow-tinted IOLs and clear IOLs except in color vision under mesopic conditions (10 lux). Patients with a yellow-tinted IOL made significantly more mistakes in the blue-light spectrum than patients with clear IOLs (P = .00015). There was no significant difference under photopic conditions (1000 lux).

CONCLUSIONS

The yellow-tinted IOLs were equivalent to the clear IOLs in postoperative contrast sensitivity, visual acuity, and color perception under photopic conditions. Patients with yellow-tinted IOLs made statistically significantly more mistakes in the blue range under dim light than patients with clear IOLs.

Spectral transmittance of intraocular lenses under natural and artificial illumination: criteria analysis for choosing a suitable filter

PURPOSE

To compare the spectral transmission of different intraocular lenses (IOLs) with either ultraviolet (UV) or blue-light filters, and to analyze the performance of these filters with artificial light sources as well as sunlight.

DESIGN

Experimental study.

METHODS

The spectral transmission curve of 10 IOLs was measured using a PerkinElmer Lambda 800 UV/VIS spectrometer (Waltham, MA). Different filtering simulations were performed using the D65 standard illuminant as daylight and standard incandescent lamp and fluorescent bulb illuminants.

MAIN OUTCOMES MEASURES

Spectral transmittance of the IOLs.

RESULTS

All the IOLs studied provide good UVC (200-280 nm) and UVB (280-315 nm) protection, except for one that presented an appreciable window at 270 nm. Nevertheless, both natural and artificial sources have practically no emission under 300 nm. In the UVA (315-380 nm) range the curves of the different IOLs manifested different degrees of absorption.

CONCLUSIONS

Not all the UV filters incorporated in different IOLs protect equally. The filters that provide greater photoprotection against UV radiation, even blue light, are yellow and orange. Then, yellow and orange IOL filters may be best suited for cases requiring special retinal protection. The filters that favor better photoreception of visible light (380-780 nm) are those that transmit this radiation close to 100%. Artificial illumination practically does not emit in the UV range, but its levels of illumination are very low when compared with solar light. A possible balance between photoprotection and photoreception could be a sharp cutoff filter with the cutoff wavelength near 400 nm and a maximum transmittance around 100%.

In vivo quantification of the retinal reflectance spectral composition in elderly subjects before and after cataract surgery: Implications for the non-visual effects of light

Light is the signal that entrains the biological clock in humans to the 24-hour external time. Recently, it has been shown that short wavelengths play a key role in this process. In the present study, we describe a procedure to measure, objectively and in a quick way, the spectral composition of the light reaching the retina in vivo. The instruments involved are the foveal reflection analyzer (FRA) and the macular pigment reflectometer (MPR). By making use of these reflectometers, we show quantitatively that in subjects with cataracts, the light input is especially reduced in the short wavelength range. After cataract surgery during which the crystalline lens is replaced by a transparent artificial lens, the transmittance of the short wavelengths (between 420-500 nm) improved on average by a factor of 4. We conclude that this technique holds great promises for the chronobiological field because it allows for quantification of the spectral composition and light levels reaching the retina in vivo.

Blue-blocking IOLs: a complete review of the literature

Intraocular lenses (IOLs) that block both ultraviolet and blue wavelength light (<500 nm)were introduced in the 1990s. Since then, the potential benefits and harm from blocking blue light has been debated. We report the results of a complete review of all peer-reviewed published studies regarding the impact of blocking the transmission of blue light. Fifty-six published reports on subjects related to blue-blocking lenses including sleep disturbance, visual outcomes, cataract surgery, lens transmittance, sunlight exposure, and macular disease were found in peer reviewed journals from 1962 to 2009. Eleven reports specifically compared visual outcomes between blue-blocking IOLs and nonblue-locking IOLs. Of these, 10 independent studies (10/11, 91%) concluded that there are no significant effects of blue-blocking IOLs on various meters of visual performance including visual acuity, contrast sensitivity, color perception, and photopic, mesopic, and scotopic sensitivities. Only one group of authors reported that the use of blue-blocking IOLs may have detrimental effects on scotopic vision and circadian rhythms. However, the actual clinical significance of these potential negative effects on scotopic vision and on sleep patterns is uncertain. The benefits of blocking the transmission of blue light to the macula and the relationship between progression of age-related macular degeneration remain unclear. However, the published studies clearly state that the use of blue-blocking IOLs is not detrimental in visual acuity, color perception, and contrast sensitivity. The reported potential negative effects on scotopic vision and sleep disturbance appear to be minimal and may not be clinically relevant. (Surv Ophthalmol 55:284--289, 2010. 2010 Elsevier Inc. All rights reserved.)

Color discrimination by patients with different types of light-filtering intraocular lenses

PURPOSE

To evaluate photopic and mesopic color discrimination in patients with different types of light-filtering intraocular lenses (IOLs).

SETTING

Peking University Third Hospital, Peking University Eye Center, Beijing, China.

METHODS

Cataract patients with different types of IOLs were enrolled 3 months postoperatively. Overall and partial color discrimination under photopic (1000 lux) and mesopic (40 lux) conditions were evaluated with the Farnsworth-Munsell (FM) 100-hue test. Corrected distance visual acuity (CDVA) was tested under both conditions. Subjective visual quality was assessed with the 25-item National Eye Institute Visual Functioning Questionnaire (NEI VFQ-25).

RESULTS

The study evaluated 43 patients with a blue light-filtering IOL (15 photochromic, 13 yellow tinted) or an IOL filtering ultraviolet light only (n = 15). The difference in the FM 100-hue total error scores under photopic or mesopic conditions was not statistically significant between groups. There were no statistically significant differences in partial error scores in the 10 bands of the FM 100-hue color circle under photopic conditions. Under mesopic condition, there were statistically significant differences in partial error scores in the green to blue-green band (color caps 36 to 46) and the blue-green to blue band (color caps 46 to 54) (P = .005 and P = .030, respectively). There were no statistically significant differences in mean overall or subheading NEI VFQ-25 scores.

CONCLUSIONS

Filtering blue lights under mesopic conditions seemed to modify color discrimination in the green-to-blue bands postoperatively. The modification did not disturb overall color discrimination or cause subjective discomfort.

Blue-blocking IOLs decrease photoreception without providing significant photoprotection

Violet and blue light are responsible for 45% of scotopic, 67% of melanopsin, 83% of human circadian (melatonin suppression) and 94% of S-cone photoreception in pseudophakic eyes (isoilluminance source). Yellow chromophores in blue-blocking intraocular lenses (IOLs) eliminate between 43 and 57% of violet and blue light between 400 and 500 nm, depending on their dioptric power. This restriction adversely affects pseudophakic photopic luminance contrast, photopic S-cone foveal threshold, mesopic contrast acuity, scotopic short-wavelength sensitivity and circadian photoreception. Yellow IOL chromophores provide no tangible clinical benefits in exchange for the photoreception losses they cause. They fail to decrease disability glare or improve contrast sensitivity. Most epidemiological evidence shows that environmental light exposure and cataract surgery are not significant risk factors for the progression of age-related macular degeneration (AMD). Thus, the use of blue-blocking IOLs is not evidence-based medicine. Most AMD occurs in phakic adults over 60 years of age, despite crystalline lens photoprotection far greater than that of blue-blocking IOLs. Therefore, if light does play some role in the pathogenesis of AMD, then 1) senescent crystalline lenses do not prevent it, so neither can blue-blocking IOLs that offer far less photoprotection, and 2) all pseudophakes should wear sunglasses in bright environments. Pseudophakes have the freedom to remove their sunglasses for optimal photoreception whenever they choose to do so, provided that they are not encumbered permanently by yellow IOL chromophores. In essence, yellow chromophores are placebos for prevention of AMD that permanently restrict a pseudophake's dim light and circadian photoreception at ages when they are needed most. If yellow IOLs had been the standard of care, then colorless UV-blocking IOLs could be advocated now as "premium" IOLs because they offer dim light and circadian photoreception roughly 15-20 years more youthful than blue-blocking IOLs.

New approach to evaluate retinal protection by intraocular lenses against age-related lipofuscin accumulation-mediated retinal phototoxicity

PURPOSE

To present a new approach for evaluating intraocular lenses (IOLs) for retinal protection from age-related lipofuscin accumulation-mediated phototoxicity.

SETTING

Alcon Laboratories Inc., Fort Worth, Texas, USA, and Cardiff University, Cardiff, United Kingdom.

METHODS

Age-related lipofuscin accumulation-mediated action spectra for retinal phototoxicity in an aphakic eye were created for this evaluation. Transmission curves for 6 IOLs and for cornea and spectral radiant power distribution for sunlight and 2 lamps were used. Pseudophakic action spectra and retinal phototoxicity for 3 wavelength ranges and 3 ages were computed. The percentage protection of each IOL was computed as the reduction in phototoxicity relative to the aphakic eye.

RESULTS

Retinal phototoxicity increased 3.66 times from the third to ninth decade of age. The comparative retinal phototoxicity and retinal protection provided by IOLs were dependent on the light source and range of wavelength; however, unlike phototoxicity, retinal protection was independent of age. The 420 to 480 nm range was the most useful for discriminating protection by IOLs.

CONCLUSIONS

Retinal phototoxicity significantly increased with age; however, the retinal protection by IOLs was independent of age. The interaction between the transmission curve of IOLs and light sources required inclusion of widely used lamps besides sunlight for evaluation of IOLs. For the 420 to 480 nm wavelength range, the 3 light sources clearly discriminated the protection provided by IOLs. The AcrySof Natural IOL (Alcon) provided the highest protection consistently for the tested light sources.

Spectral transmission of intraocular lenses expressed as a virtual age

AIM

Currently available intraocular lenses (IOL) have widely different spectral filters. This study aimed to calculate the virtual age of IOL with regard to photoprotection and photoreception, i.e. the age of the natural lens that has similar effects on these aspects.

METHODS

With diffuse solar radiation as a light source blue light damage was calculated for natural lenses at all ages, commercially available IOL and Schott steep cut-off filters in the wavelength range 300-600 nm. Similarly, the input to the short wavelength sensitive cone system was calculated for the range 380-600 nm.

RESULTS

The virtual age for photoprotection of IOL and steep cut-off filters varied from under 0 to 66 years. Most IOL had similar ages for photoreception, and thus show a reasonable resemblance to the spectral properties of the natural lens. Two IOL and all steep cut-off filters had a lower age for photoreception than for photoprotection, and thus outperformed the natural lens.

CONCLUSION

The virtual age of an IOL relates its spectral filtering properties to what happens in the healthy crystalline lens. Many older IOL types offer less protection than the lens of a newborn. Middle age seems a reasonable choice for an IOL.

Optical density of the aging human ocular media in the visible and the UV

We analyzed the literature on the absorption in the young and aging human eye media. Five templates were derived to provide an adequate description of the spectra from 300 to 700 nm for the lens, cornea, aqueous, and vitreous. Two templates were found in all media. They stand for Rayleigh scatter and the absorbance of tryptophan. Three additional templates for the lens represent absorbance in kynurenine derivatives, such as 3-hydroxykynurenine glucoside (3HKG), and absorbance in two substances found at older age. Except for Rayleigh scatter, all templates have a Gaussian shape. Aging-trend functions were derived that show a linear slope on an age-squared scale. The result can be used to correct for media losses in visual perception tasks, in fundus reflectometry, and in studies on light damage.