Ultraviolet-absorbing pseudophakos: an efficacy study

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.

Ultraviolet Radiation and Cataract—A Review

Senile cataract has become a serious public health problem as the elderly population is increasing worldwide. As lens with dark iris is reported to have a higher prevalence of cataract, public health concern about cataract in Asia is a bigger issue. Among factors assumed to be involved in the pathogenesis of cataract, ultraviolet radiation (UV) has received much attention in accordance with the recent problem of ozone column depletion. It has been agreed that UV induces cataract in animal and biochemical experiments. However, in epidemiological studies, such agreement has not been reached. There are many factors that should be considered and controlled when investigating the association between cataract and UV.

In this review, we summarize major findings obtained so far on the relationship between UV and cataract, and we discuss important factors that may be the cause of disagreement in epidemiological studies. We also point out some of the research foci which should be clarified and propose protective measures against UV induced cataract.

Retinal safety of the irradiation delivered to light-adjustable intraocular lenses evaluated in a rabbit model

PURPOSE

To evaluate the safety to the retina of a light-delivery device used to irradiate a light-adjustable intraocular lens (IOL) after implantation in a rabbit model.

SETTING

John A. Moran Eye Center, University of Utah, Salt Lake City, Utah, USA.

METHODS

In this study, rabbits had phacoemulsification with implantation of an ultraviolet (UV)-filtering light-adjustable IOL (study IOL) in 1 eye and a custom-made silicone IOL without a UV filter (control IOL) in the opposite eye. The study IOLs were irradiated at 1.0, 2.0, 3.0, and 5.0 times the expected maximum UV irradiation doses and the control IOLs, at 0.3, 0.6, 1.0, and 2.0 times. One week after irradiation, slitlamp and fundus (indirect ophthalmoscopy) examinations were performed. The rabbits were then humanely killed and their eyes enucleated and processed for histopathology.

RESULTS

The 16 eyes with the study IOL (with UV filter) showed no signs of corneal, anterior segment, or retinal toxicity on histopathologic evaluation. The 16 eyes with the control IOL (no UV filter) also showed no signs of corneal or anterior segment toxicity; however, 3 eyes receiving the higher radiation doses had focal areas of retinal damage consistent with laser burn.

CONCLUSION

Pigmented rabbit eyes with a light-adjustable IOL with a UV filter showed no signs of retina toxicity after near-UV light exposure up to 5 times the expected maximum treatment dosage.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned. Additional disclosures are found in the footnotes.

Light-induced damage to the retina: role of rhodopsin chromophore revisited

The presence of the regenerable visual pigment rhodopsin has been shown to be primarily responsible for the acute photodamage to the retina. The photoexcitation of rhodopsin leads to isomerization of its chromophore 11-cis-retinal to all-trans-retinal (ATR). ATR is a potent photosensitizer and its role in mediating photodamage has been suspected for over two decades. However, there was lack of experimental evidence that free ATR exists in the retina in sufficient concentrations to impose a risk of photosensitized damage. Identification in the retina of a retinal dimer and a pyridinium bisretinoid, so called A2E, and determination of its biosynthetic pathway indicate that substantial amounts of ATR do accumulate in the retina. Both light damage and A2E accumulation are facilitated under conditions where efficient retinoid cycle operates. Efficient retinoid cycle leads to rapid regeneration of rhodopsin, which may result in ATR release from the opsin "exit site" before its enzymatic reduction to all-trans-retinol. Here we discuss photodamage to the retina where ATR could play a role as the main toxic and/or phototoxic agent. Moreover, we discuss secondary products of (photo)toxic properties accumulating within retinal lipofuscin as a result of ATR accumulation.

Blue light-absorbing intraocular lens and retinal pigment epithelium protection in vitro

PURPOSE

To compare the Alcon AcrySof Natural (SN60AT) and AcrySof (SA60AT), the AMO Sensar (AR40e) and ClariFlex, and the Pfizer CeeOn Edge 911A intraocular lenses (IOLs) as to their ability to protect retinal pigment epithelial (RPE) cells from light damage mediated by the lipofuscin fluorophore A2E.

SETTING

Department of Ophthalmology, Columbia University, New York, New York, USA.

METHODS

Cultured human RPE cells (ARPE-19 cell line) that had accumulated A2E were exposed to blue (430 nm +/- 30), green (550 +/- 10 nm), or white (390 to 750 nm) light with and without an IOL in the light path.

RESULTS

The blue light-absorbing AcrySof Natural IOL was associated with significant reduction (78% to 82%; P<.01) in the death of A2E-laden RPE that were exposed to blue, white, and green light. The decrease in the incidence of cell death was greater in magnitude than would be expected from the amount of light that was absorbed by the IOL. The considerably smaller declines in cell death observed with the AcrySof, Sensar, ClariFlex, and CeeOn Edge IOLs were likely due to nonspecific reductions in light transmittance.

CONCLUSIONS

By absorbing blue light, the AcrySof Natural IOL shields RPE cells that have accumulated the aging lipofuscin fluorophore A2E from the damaging effects of light. A long-term population-based clinical trial would determine whether a blue light-absorbing IOL can reduce the risk for or progression of age-related macular degeneration.

How much blue light should an IOL transmit?

Older, and even some modern, intraocular lenses (IOLs) transmit potentially hazardous ultraviolet radiation (UVR) to the retina. In addition, IOLs transmit more blue and green light to the retina for scotopic vision than the crystalline lenses they replace, light that is also potentially hazardous. The severity of UVR-blue type phototoxicity increases with decreasing wavelength, unlike the action spectrum of blue-green type retinal phototoxicity and the luminous efficiency of scotopic vision which both peak in the blue-green part of the optical spectrum around 500 nm. Theoretically, UVR+blue absorbing IOLs provide better retinal protection but worse scotopic sensitivity than UVR-only absorbing IOLs, but further study is needed to test this analysis. UVR is potentially hazardous and not useful for vision, so it is prudent to protect the retina from it with chromophores in IOLs. Determining authoritatively how much blue light an optimal IOL should block requires definitive studies to determine (1) the action spectrum of the retinal phototoxicity potentially involved in human retinal ageing, and (2) the amount of shorter wavelength blue light required for older adults to perform essential activities in dimly lit environments.

Blood-retinal barrier and autofluorescence of the posterior polar retina in long-standing pseudophakia

PURPOSE

To study the physiological state of the retina in long-standing pseudophakic eyes using blood-retinal barrier (BRB) disruption and autofluorescence as parameters.

SETTING

Miyake Eye Hospital, Nagoya, Japan.

METHOD

This retrospective, case-controlled study sought to determine whether ultraviolet (UV)-light-filtering and blue-light-filtering intraocular lenses (IOLs) had different outcomes in severity of BRB disruption and autofluorescence of the posterior polar retina than clear (untreated) IOLs.

RESULTS

Mean sodium fluorescein transmittance in eyes with untreated IOLs was 3.7 ng/mL +/- 2.2 (SD) 3 years after surgery (n = 40) and 3.5 +/- 1.8 ng/mL 8 years after surgery (n = 18). In eyes with a UV-filtering IOL, the values were 2.4 +/- 1.5 ng/mL (n = 39) and 2.6 +/- 2.0 ng/mL (n = 14), respectively. Eyes with a UV-filtering IOL had significantly lower transmittance (P < .01-< .05). Mean transmittance 5 years after surgery was 4.2 +/- 1.9 ng/mL in eyes with an untreated IOL (n = 31), 3.2 +/- 2.1 ng/mL in eyes with a UV-filtering IOL (n = 30), 2.8 +/- 1.9 ng/mL in eyes with a Menicon blue-light-filtering IOL (n = 20), and 2.6 +/- 1.8 ng/mL in eyes with a Hoya blue-light-filtering IOL (n = 21). The eyes with a UV-filtering and the blue-light-filtering IOLs had significantly lower transmittance than those with an untreated IOL (P < .01-< .05); the eyes with a Hoya IOL had a statistically lower mean than those with the UV-filtering IOL (P < .05). Mean autofluorescence was 44.9 +/- 6.8 (n = 14), 49.5 +/- 6.1 (n = 6), 53.0 +/- 11.9 (n = 15), and 64.5 +/- 13.2 (n = 7) at 1, 4, 9, and 14 years after surgery, respectively; there was a significant difference between 1 and 9 years and between 1 and 14 years (P < .05).

CONCLUSION

Eyes with a UV-filtering or blue-light-filtering IOL had a lower incidence of BRB disruption than eyes with an untreated IOL. Autofluorescence increased with age, even in eyes with UV-filtering IOLs.

Operating microscope-induced retinal phototoxicity: pathophysiology, clinical manifestations and prevention

Retinal light damage is a poorly understood phenomenon, due to its multifactorial etiology and relatively infrequent recognition. It has been increasingly identified following ocular surgery involving the intense light of the operating microscope. The authors describe the clinical entity, review salient features of its pathophysiology and provide guidelines for prevention of retinal phototoxicity.

Chemical investigations of ultraviolet-absorbing hydrogel material for soft intraocular lenses

A poly(2-hydroxyethyl methacrylate) hydrogel material exhibiting ultraviolet-absorbing properties was synthesized by simultaneous polymerization, crosslinking, and covalent bonding of an available polymerizable absorber. The two-stage leaching experiments carried out by aqueous extraction and the analysis of the concentrated extracts by high resolution capillary gas chromatography showed very low levels of additive released through leaching action. This proves that the ultraviolet absorbers can be successfully incorporated by covalent bonding in soft hydrogel intraocular lenses.

UV-absorbing intraocular lenses: safety, efficacy, and consequences for the cataract patient

The crystalline lens absorbs most of the incident UV radiation between 300 and 400 nm and thereby protects the retina from a significant, potential source of photochemical damage. This protection is lost when the lens is removed by cataract surgery, but can be restored by the implantation of an intraocular lens (IOL) that has UV-absorbing chromophores incorporated into a polymethylmethacrylate (PMMA) substrate. Spectrophotometric data show that the various, commercially available, UV-absorbing IOLs are not equally effective in absorbing UV radiation; thus, a standard, quantitative metric for comparing their performance is proposed. Cytotoxicity and biocompatibility studies have failed to demonstrate that UV-absorbing IOLs are unsafe, even when damaged by Nd:YAG lasers used for photodiscission posterior capsulotomy. There are positive consequences for the pseudophakic patient with a UV-absorbing IOL, in that it may restore normal spectral sensitivity, reduce erythropsia and cystoid macular edema, and stabilize the blood-vitreous barrier.

The spectra, classification, and rationale of ultraviolet-protective intraocular lenses

I measured the spectral transmittance of 16 implantable intraocular lenses from 12 manufacturers and examined the rationale for using ultraviolet-absorptive intraocular lenses to protect pseudophakic individuals from photic retinopathy. Each ultraviolet-protective lens was classified by the wavelength at which its spectral transmittance fell to 10% in the blue or ultraviolet region of the spectrum. Current ultraviolet-protective intraocular lenses differ in the effectiveness of their protection against photic retinopathy, and product descriptions may be misleading.

Ultraviolet light absorption in intraocular lenses

Implantation of ultraviolet (UV) light-absorbing intraocular lenses and the manufacturers developing these lenses has significantly increased over the past few years. In this paper, the need for filtration of UV light by intraocular lens implants is briefly examined and various new product development aspects of a UV-absorbing IOL are discussed. Two general approaches, additive and chemical bonding, to incorporating a UV-absorbing chromophore into polymethylmethacrylate lens material are described. Different UV-absorbing compounds that are being used in implants and the mechanism by which they absorb light and its dissipation is discussed. The extent of preclinical testing required to establish the biocompatibility, stability, and overall safety of new materials is summarized. Finally, a relative comparison of the extent of UV absorption by various commercially available UV intraocular lenses is presented.