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Blue light-filtering IOLs reduce parameters of age-related maculopathy
In pseudophakic eyes, UV light-filtering IOLs transmit short-wavelength blue light, which may cause retinal toxicity.
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IOLs with ultraviolet or blue-light filtering capability might prevent blood-retinal barrier disruption and lipofuscin accumulation in pseudophakic eyes, according to one ophthalmologist.
| Kensaku Miyake |
Compared with the normal crystalline lens, some available UV-filtering IOLs transmit more visible light of short wavelengths, particularly blue light, reported Kensaku Miyake, MD, in a presentation at this year’s World Ophthalmology Congress. Light in this part of the spectrum might possibly result in retinal toxicity, especially related to the onset of age-related maculopathy, glare and chromatopsia, he said.
Dr. Miyake explained that chronic exposure of the outer photoreceptor layer of the retina to UV or near-UV light leads to the formation of lipid peroxides and disruption of the blood-retinal barrier. Abnormality of the outer segment also reduces phagocytosis by the retinal pigment epithelium (RPE), resulting in accumulation of lipofuscin, the dominant fluorophore in RPE cells. This process, in turn, increases autofluorescence of the post-polar retina. Evaluation of blood-retinal barrier function and autofluorescence of the retina therefore can be used as parameters of maculopathy, Dr. Miyake said.
Using vitreous fluorophotometry, Dr. Miyake conducted two studies to evaluate blood-retinal barrier function and a third study to measure the level of autofluorescence of the RPE in eyes implanted with IOLs.
The results, he said, imply that IOLs that prevent not only UV light rays but also near-UV and blue light from reaching the retina are desirable to prevent pathologic retinal aging in pseudophakic eyes.
First study: blood-retinal barrier function
In the first study, blood-retinal barrier function was compared between eyes implanted with clear (untreated) IOLs and eyes implanted with UV-filtering IOLs at 3 and 8 years after phacoemulsification or extracapsular cataract extraction. The study included 79 elderly patients.
According to the study results, at both postoperative intervals, eyes with an untreated IOL had higher vitreous dye concentrations 3 mm from the retina, indicating significantly more blood-retinal barrier disruption.
At 3 years, mean fluorescein concentration in eyes implanted with untreated IOLs was 3.7 ± 2.2 ng/mL, compared to 2.4 ± 1.5 ng/mL in eyes with UV-blocking lenses. At 8 years, the concentration was 3.5 ± 1.8 ng/mL in eyes with untreated IOLs and 2.6 ± 2 ng/mL in eyes with UV-blocking lenses, Dr. Miyake said.
One case of postoperative cystoid macular edema was reported in an eye implanted with a clear IOL 3 years after surgery, he noted.
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Images: Miyake K |
Second study: comparing IOLs
In a second study, blood-retinal barrier function was similarly compared among eyes with an untreated IOL, a UV-filtering IOL, or one of two types of UV- and blue-light-filtering IOLs (Hoya Healthcare or Menicon) 5 years after surgery. Eyes with UV-filtering IOLs and blue light-filtering IOLs had significantly lower dye transmittance into the vitreous and more stable blood-retinal barrier than eyes with untreated IOLs, Dr. Miyake said.
Vitreous fluorophotometry, the measurement technique employed in the study, can produce measurement errors, he said. To minimize potential problems, such as the formation of fluorescent metabolites resulting from intravenous fluorescein injection, fluorescein concentration was rapidly evaluated in the vitreous 30 minutes after the injection. Furthermore, Dr. Miyake said, the study was limited to pseudophakic eyes.
| T-curves of the IOLs used in this study |
| Compared with the normal crystalline lens, many UV-light-filtering IOLs, as well as clear (untreated) IOL's, transmit more visible light of shorter wavelengths, particularly blue light, which might cause retinal toxicity. Source: Miyake K |
Third study: accumulating RPE lipofuscin
In another study, Dr. Miyake and colleagues measured autofluorescence of the posterior polar retina due to focal accumulation of autofluorescent materials such as lipofuscin.
Lipofuscin, which is thought to play a central role in the pathogenesis of age-related macular degeneration, was measured in vivo by confocal laser scanning ophthalmoscopy, Dr. Miyake explained.
In this technique, autofluorescence within a square area located between the optic disc and the macula was measured with a digital image analyzing system. Dr. Miyake said it is thought that the spatial distribution of autofluorescence correlates highly with hyperpigmentation at the level of the RPE.
According to this study, mean autofluorescence increased with the length of the postoperative period. Significant differences were observed between 1 and 9 years, and between 1 and 14 years postoperatively.
Dr. Miyake concluded that eyes implanted with UV-filtering or blue light-filtering IOLs exhibit less blood-retinal barrier disruption than eyes with untreated IOLs. Evidence also suggests that autofluorescence increases with age even in eyes with UV-filtering IOLs.
For more information:
- Kensaku Miyake, MD, can be reached at the Shohzankai Medical Foundation, Miyake Eye Hospital, 3-15-68 Ozone, Kita-ku, Nagoya 462-0825, Japan; e-mail: m-abe111007@hotmail.co.jp.
- Alex Kahney is an OSN correspondent based in Tokyo.