Colour vision and retinal nerve fibre layer photography in patients with an Acrysof® Natural intraocular lens

Authors


Marja-Liisa Vuori MD
Department of Ophthalmology
Turku University Hospital
Kiinamyllynkatu 4–8
20520 Turku
Finland
Tel: + 358 2 313 2591
Fax: + 358 2 313 2595
Email: marja-liisa.vuori@tyks.fi

Abstract.

Purpose: To study colour vision and retinal nerve fibre layer (RNFL) photographs in patients with an Acrysof® Natural intraocular lens (IOL).

Methods: We carried out a randomized double-blind study. An Acrysof® Natural IOL (model SN60AT) was implanted in 25 eyes of 19 patients and an Acrysof® IOL (model SA60AT) was implanted in 27 eyes of 18 control patients. The patients returned for colour vision tests and fundus photography 1−6 months after the surgery.

Results: Standard pseudoisochromatic plates, part 2, were correctly interpreted and the Farnsworth−Munsell 100-hue test (FM 100) total and individual box scores were normal in all IOL eyes. In the FM 100 hue test there were no significant differences in the results of the total error scores or the error scores of the individual boxes between the eyes with Acrysof® Natural and those with Acrysof® lenses. The yellow coloration of the Acrysof® Natural IOL did not affect the visibility of the RNFL in photographs.

Conclusions: The Acrysof® Natural IOL did not affect colour vision in the tested patients, even in the blue region of the spectrum, and can be implanted in patients who need to have normal colour vision for the purposes of their occupation. The Acrysof® Natural IOL does not interfere with RNFL photography and can also be used in patients with glaucoma.

Introduction

Age-related macular degeneration (AMD) is one of the leading causes of blindness worldwide. Blue light is considered to be one of the risk factors in AMD. Visible and ultraviolet (UV) radiation can produce photochemical lesions in the neural retina and retinal pigment epithelium (RPE) (Noell 1980; Weiter 1987). Retinal pigment epithelium cells are particularly susceptible to wavelengths within the blue region of the spectrum (Ham et al. 1978; Busch et al. 1999). In a normal ageing eye, the human lens becomes yellowish and absorbs more blue spectral colours than a younger lens.

Blue light enters the pseudophakic eye easily. In a previous study of the polymethylmethacrylate (PMMA) intraocular lens (IOL), the spectral transmission was found to be 80–90% at a wavelength of only about 420 nm (Mäntyjärvi et al. 1997). The commonly used UV-absorbing foldable IOLs filter less than 10% of visible blue light (Ernest 2003). In the growing group of patients who undergo cataract surgery protection of the retina from blue light seems rational. The Acrysof® Natural (Alcon, Fort Worth, TX, USA) is a new IOL with a 0.40% chromophore designed to filter UV and blue light. According to the manufacturer, the Acrysof® Natural IOL reduces transmittance of blue light wavelengths from 71% at 400 nm to 22% at 475 nm. This lens has been shown to protect RPE cells against blue light-induced death in laboratory models and it has thus been suggested to reduce the risk or progression of macular degeneration (Sparrow 2003). However, the blue light filter raises questions as to whether this new IOL might cause blue colour vision defects.

Retinal nerve fibre layer (RNFL) imaging with shorter wavelengths (i.e. blue light at 495 nm) is a widely used method of assessing glaucomatous changes in the fundus. As RNFL visibility is affected by the yellowing of the human lens (Siik et al. 1997), it might also be affected by a yellow IOL.

The purpose of the present study was to analyse colour vision in patients with Acrysof® Natural IOL implants compared to clear acrylic lens implants in otherwise healthy eyes. In addition, we also studied the visibility of the RNFL in photographs in both patient groups.

Materials and Methods

The study protocol was approved by the Ethics Committee of Turku University Hospital and the study was conducted according to the Helsinki Declaration. Written informed consent was obtained.

A total of 37 white patients scheduled for phacoemulsification and IOL implantation were included in this randomized, double-blind study. Sealed envelopes containing the code for the planned IOL type were used for randomization. Patients known to have hereditary colour vision defects were excluded. Patients using medications that might affect colour vision, such as ethambutol, any medication for epilepsy, amiodarone, digitalis and anti-inflammatory drugs, were also excluded. Patients with diabetes or any other ocular pathology except cataract were also excluded. All patients underwent an uneventful standard phacoemulsification through a temporal clear cornea wound. An Acrysof® Natural IOL (model SN60AT) was implanted in 25 eyes of 19 patients and an Acrysof® IOL (model SA60AT) was implanted in 27 eyes of 18 control patients. Only the results of the right eye were used for the analysis of colour vision in patients with bilateral implantation. At 1−6 months after surgery, the patients returned for colour vision tests and fundus photography. Best corrected visual acuity (VA) was measured with Snellen charts and biomicroscopy was performed to rule out any opacity in the ocular media. The pupils were dilated after colour vision tests for fundus photography.

Standard pseudoisochromatic plates, part 2, (SPP2) (Ichikawa et al. 1983) and the Farnsworth−Munsell 100-hue test (FM 100) (Farnsworth 1957) were used for colour vision tests. The error scores in the FM 100 hue test were calculated as square roots, the axis was established according to Smith et al. (1985), and the figure of the results was drawn according to Kinnear (1970). Illumination for the colour vision tests was provided by a Macbeth easel lamp (Macbeth Division, Kollmorgen Corp., Newburgh, New York, USA). Results were compared to age-matched normal values (Verriest et al. 1982; Mäntyjärvi 2001).

Retinal nerve fibre layer photographs were taken with a Canon 60 Z fundus camera (Canon, Tokyo, Japan) using a blue filter and contrast was enhanced to the maximum visibility using Topcon IMAGEnet 2000 software (Topcon, Tokyo, Japan). Photographs were evaluated in a masked fashion by one of the authors.

Unpaired t-test (StatView; Abacus Concepts, Inc., Berkeley, California, USA) was used in the statistical analysis and the significance limit was set at a p-value of 0.05.

Results

The mean age of the subjects was 72 ± 8 years (range 58−83 years) in the Acrysof® Natural group and 73 ± 7 years (range 60−84 years) in the Acrysof® group (p = 0.597). The mean ± SD for VA was −0.01 ± 0.05 logMAR in the Acrysof® Natural group (n = 19) and −0.01 ± 0.05 in the Acrysof® group (n = 18); there was no statistically significant difference between the groups (p = 0.999). In the biomicroscopic examination the posterior capsule appeared clear in all test eyes.

Colour vision was normal in all IOL eyes. The SPP2 plates were correctly interpreted and the FM 100 hue test total and individual box scores in all IOL eyes were normal within the values of mean + 2 × SD; 97.5% confidence in 1-tailed test (Verriest et al. 1982; Mäntyjärvi 2001). In the FM 100 hue test, there were no significant differences in the results of the total error scores or the error scores of the individual boxes between the eyes with Acrysof® Natural and those with Acrysof® lenses (Table 1).

Table 1.  FM 100 test results in eyes with Acrysof® Natural IOLs and Acrysof® IOLs.
 Acrysof®Acrysof®Unpaired
 Natural IOLIOLt-test
 (mean ± SD)(mean ± SD) 
FM 1008.56 ± 2.908.43 ± 1.680.869
Box 13.60 ± 1.443.16 ± 1.380.352
Box 23.94 ± 1.813.85 ± 0.770.841
Box 35.27 ± 1.335.16 ± 1.090.787
Box 43.63 ± 2.234.13 ± 1.400.418

In the photographic analysis, two eyes of one patient in the Acrysof® Natural group were excluded because of a very lightly pigmented fundus. In all other eyes in both groups the RNFL was clearly visible. The yellow coloration of the Acrysof® Natural IOL did not affect the visibility of the RNFL in photographs (Figs 1 and 2).

Figure 1.

Retinal nerve fibre layer photograph through the Acrysof® IOL.

Figure 2.

Retinal nerve fibre layer photograph through the Acrysof® Natural IOL.

Discussion

Colour vision has been studied previously in patients with PMMA and silicone IOLs and found to be normal (Harper et al. 1988; Marre et al. 1988; Mäntyjärvi & Tuppurainen 1996; Mäntyjärvi et al. 1997). A previous study with a different yellow IOL (Hoya IOL) found no significant differences between the yellow and the ordinary IOLs (Yuan et al. 2004). Only one study has reported Farnsworth−Munsell 100-hue test results as being worse in pseudophakic eyes than in normal control eyes (Jay et al. 1982). On the other hand, a few studies have found colour vision in eyes with IOL implants to be better than in normal age-matched control eyes, especially in the blue−purple region (Werner & Hardenbergh 1983; Mäntyjärvi et al. 1997).

In a previous study (Cionni 2003) none of the test subjects with the Acrysof® Natural IOL failed the Farnsworth D 15 colour perception test. However, the Farnsworth D 15 test reveals only strong colour vision defects, not mild ones. The present study, which used SPP2 plates and the FM 100 test, found colour vision to be normal with both the yellow Acrysof® Natural IOL and the normal Acrysof® IOL. As the Acrysof® Natural IOL does not interfere with colour perception, it can be used in patients who need normal colour vision in their occupations.

There are no previous studies on the effect of a yellow IOL on RNFL visibility in photographs. The diagnosis and detection of progression in open-angle glaucoma is based on three cornerstones: evaluation of the optic disc, RNFL and visual fields. In RNFL imaging shorter wavelengths (i.e. blue light at 495 nm) are used. A yellow Acrysof® Natural IOL might interfere with RNFL imaging by providing a yellow filter and might complicate the further evaluation of glaucoma patients after IOL implantation. In the present study, however, the RNFL was clearly visible in patients in both study groups and was readily assessed in all the photographs. The Acrysof® Natural IOL does not interfere with the analysis of the RNFL in photographs and thus can also be used in patients with glaucoma.

In conclusion, the Acrysof® Natural IOL did not affect colour vision even at the blue region of the spectrum in the tested patients and can be implanted in patients who need to maintain normal colour vision for their occupation. The Acrysof® Natural IOL does not interfere with RNFL photography and can also be used in patients with glaucoma.

Ancillary