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Keywords:

  • Bothnia dystrophy;
  • retinitis pigmentosa;
  • tinted contact lenses;
  • visual function

Abstract.

  1. Top of page
  2. Abstract.
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Purpose:  To determine whether tinted contact lenses can improve visual function in patients with Bothnia dystrophy (BD), a genetically defined retinal dystrophy with prolonged dark adaptation.

Methods:  Twelve patients with BD were fitted with the same type of soft contact lenses tinted dark brown. Visual acuity (VA), contrast vision, near vision and visual fields were tested before and 1 month after contact lens fitting. The patients completed a visual function questionnaire. The physical properties of the contact lenses were tested using spectrophotometry.

Results:  The patients with the lowest VA described the most obvious improvement in visual function. This group of patients preferred darker contact lenses and continued wearing their contact lenses after the study ended. The patients with the best VA preferred lighter contact lenses and a few patients in this group discontinued contact lens wear upon completion of the study.

Conclusions:  Visual function in BD patients was improved by dark tinted contact lenses. The optimal colour for lenses varies, depending on the season and the individual. Other patient groups with retinal dystrophies associated with prolonged dark adaptation or dysfunction of the cone system, such as cone dystrophies or achromatopsia, may also benefit from this type of contact lens.


Introduction

  1. Top of page
  2. Abstract.
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

In the rehabilitation of visually disabled persons, including individuals with hereditary retinal dystrophies, tinted lenses and spectacles with filters are currently used to maximize residual vision, improve contrast sensitivity (CS), control glare, and improve orientation and mobility skills (Eperjesi et al. 2002). Tinted contact lenses have been evaluated for the same purpose in achromatopsia and cone-rod dystrophies; however, only single cases have been studied, without regard to recent developments in knowledge of the underlying genetic defects (Schiefer et al. 1995; Park & Sunness 2004).

Bothnia dystrophy (BD) is a unique variant of retinitis pigmentosa (RP), which affects the visual cycle. A high prevalence (1 : 3600) is found in Västerbotten County in northern Sweden (Burstedt et al. 2001). A missense mutation, resulting in an amino acid substitution (R234W) of cellular retinaldehyde-binding protein (CRALBP), is present in a homozygous state (Burstedt et al. 1999). Cellular retinaldehyde-binding protein is known to function as a carrier protein of retinoids in the retinal pigment epithelium (RPE) and plays a crucial role in the visual cycle and the regeneration of rod visual pigment (Bok 1990; Saari et al. 1994). The BD phenotype is characterized by night blindness from early childhood. Progressive symptoms of impaired macular function with decreased visual acuity (VA) appear in early adulthood, leading to legal blindness in middle-aged patients. Whitish, fleck-like lesions in the fundus, similar to those observed in retinitis punctata albescens (RPA), are observed in most cases. Electrophysiological studies have shown a progressive degeneration of the rods and cones, and signs of defects in RPE functioning (Burstedt et al. 2003). Standard dark adaptometry (tested for 45 mins) was grossly affected, showing abnormal recovery of both rod and cone functions in all stages of the disease (Burstedt et al. 2001). Final thresholds of the visual sensitivity were found to be extremely prolonged in these patients, and, usually, 10 hours were required to reach a steady state (Burstedt et al. 2003).

Single patients with BD not included in this study were fitted with tinted contact lenses and experienced a positive effect. The patients seemed to benefit most from very dark tinted contact lenses. The relatively large number of BD patients in the area, knowledge of the genetic defect, and the finding of the extremely prolonged dark adaptation provided a unique opportunity to evaluate the benefit of tinted contact lenses in persons with low vision due to a defined retinal dysfunction.

Materials and Methods

  1. Top of page
  2. Abstract.
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Patients

Twelve patients with BD were included in the study (eight women, four men; age range 20–64 years). All were homozygous for the R234W mutation in CRALBP, tested using a polymerase chain reaction (PCR)-based method (Burstedt et al. 2001). All patients originated from Västerbotten County in northern Sweden. The patients were selected to represent different stages of retinal disease. Visual acuity and the remaining visual field area were taken into consideration in the selection process (Table 1). Visual acuity varied from 1.0 to 0.05 decimal VA (− 0.02 to ≥ 1.40 logMAR [logarithm of the minimum angle of resolution]). Visual field measurements from a previous study showed that half of the patients had absolute central scotomas, tested with Goldmann perimetry (object II-4-e) (Burstedt et al. 2005). Two patients were contact lens wearers before the study; both of them used clear lenses. Before the study, all patients had one or several pairs of spectacles with different tinted filter lenses and side shields.

Table 1.   Clinical data and results of visual function tests with and without tinted contact lenses in 12 patients with Bothnia dystrophy.
No. Sex/ age (yrs) Refractive error R/L VA best eye no CL* VA best eye CL*Diff CS best eye no CL* CS best eye CL*DiffNear binoc vision no CLNear binoc vision CLDiff VF area (cm2)VF best eye no CL (MD) VF best eye CL (MD)DiffVFQ-25 comp score, startVFQ -25 comp score, endDiffCL grade of tint
  • *  

    Measured in logMAR (logarithm of the minimum angle of resolution).

  • †  

    Binocular vision, decimal value.

  • ‡  

    Binocular visual field area, tested with II-4-e.

  • VA = visual acuity; CL = contact lens; CS = contrast sensitivity; Diff = difference; L = left; R = right; binoc = binocular; VF = visual field; MD = mean deviation, threshold perimetry (SITA fast); VFQ-25 = Visual Functioning Questionnaire.

  • Figures in bold indicate an improvement.

204:1M/22 −3.25/−4.00 −0.02 (L)0.020.040.020.220.200.800.80220 −14.65 −17.47 −2.8279.272.1 −7.1 (−9%)Medium
025:2F/40+0.75/−0.750.02 (L) −0.08 −0.100.200.18 −0.021.001.250.25200 −17.13 −21.18 −4.0581.971.9 −10.0 (−12%)Medium
065:2F/57+5.00/+5.500.12 (L)0.200.080.300.340.040.800.50 −0.3013 −28.26 −27.081.1876.278.82.6 (3%)Medium
217:1F/32+0.25/+0.750.36 (L)0.420.06 ≥1.401.32 ≥ −0.080.500.32 −0.1814 −31.81 −29.742.0725.133.38.2 (33%)Medium
011:3M/38 ±0.00/±0.000.52 (L)0.940.420.901.340.440.160.12 −0.04127 −27.69 −20.217.4874.379.14.8 (6%)Dark
004:5F/24+0.75/+0.750.60 (R)0.720.12 ≥1.40 ≥1.400.320.24 −0.08230 −17.28 −18.88 −1.6066.166.20.1 (0%)Medium
013:5F/31+1.00/+1.250.62 (R)0.640.02 ≥1.40 ≥1.400.250.20 −0.05114 −16.56 −23.86 −7.3046.139.9 −6.2 (−13%)Medium
011:2M/41 −6.25/−6.501.00 (R)0.94 −0.06 ≥1.401.32 ≥ −0.080.120.1211 −26.63 −25.960.6744.049.05.0 (11%)Dark
013:4F/50+0.75/+0.751.04 (R)0.90 −0.14 ≥1.401.32 ≥ −0.080.120.160.0425 −29.00 −18.2110.7949.855.86.0 (12%)Dark
005:3F/45 −10.00/−9.001.28 (L)1.26 −0.02 ≥1.40 ≥1.400.050.080.030 −29.50 −28.001.5063.073.910.9 (17%)Medium
065:1M/63+2.25/+1.251.32 (R)1.22 −0.10 ≥1.40 ≥1.400.050.060.0148 −22.32 −20.471.8564.358.8 −5.5 (−9%)Medium
013:3F/60+2.00/+3.00 ≥1.401.00 ≥ −0.40 ≥1.40 ≥1.400.050.080.0317 −31.73 −27.324.4134.547.513.0 (38%)Dark

To evaluate the effect of dark tinted contact lenses on VA, CS and threshold perimetry in healthy individuals, two persons were examined as controls (Table 2). Informed consent was obtained from all subjects. The study followed the tenets of the Declaration of Helsinki, and was approved by the Ethics Committee of Umeå University.

Table 2.   Effect of dark tinted contact lenses on visual acuity, contrast sensitivity and threshold perimetry in two healthy control subjects.
No. Sex/ age (yrs)Eye VA no CL (logMAR)VA difference CL medium (logMAR)VA difference CL dark (logMAR) CS no CL (logMAR)CS difference CL medium (logMAR)CS difference CL dark (logMAR) VF no CL (MD)VF difference CL medium (MD)VF difference CL dark (MD
  1. VA = visual acuity; CL = contact lens; CS = contrast sensitivity; VF = visual field; MD = mean deviation, threshold perimetry (SITA fast); L = left; R = right; CL dark = contact lenses tinted dark brown; CL medium = contact lenses tinted medium brown.

1F/30R −  0.14 −  0.060.160.020.040.30+ 0.24 −  1.34 −  2.20
L −  0.06 ±  0.00 −  0.060.24 −  0.08 −  0.02 −  0.23 −  2.03 −  3.37
2M/59R −  0.08 −  0.020.100.14 −  0.040.16+ 0.13 −  3.12 −  3.16
L −  0.10 ±  0.00 ±  0.000.160.040.14 −  0.15 −  3.05 −  3.79

Methods

The study started in March and was completed in May 2004. Before lens fitting, a routine slit-lamp examination was performed. The contact lenses were manufactured by Nordiska Lins AB (Gothenburg, Sweden). All patients were fitted with the same lens type, NL 72, a soft contact lens with 74% water content and a diameter of 14 mm. The contact lenses were tinted brown at a diameter of approximately 11 mm, to cover the whole cornea. The contact lens manufacturer used a tint grading based on the darkness of the dye, without regard to light transmitting properties. The same brown dye was used for all contact lenses, but the amount of time in the dye bath varied in order to obtain different tint grades.

In order to specify the physical properties of the lenses, the light transmittance of the different tinted contact lenses was examined using a spectrophotometer (Beckman DK 640; Beckman Instruments, Inc., Fullerton, CA, USA). The lenses were cut in 10-mm wide strips to fit in the cuvette holder. The first measurement was made with an empty cuvette to calibrate the equipment. Saline and a clear contact lens in saline were used as controls. Spectra were registered in the wavelength interval between 250 nm and 750 nm. The tinted contact lenses, in saline, were then examined in the following order: light, medium and dark brown (Fig. 1). To obtain the darkest tinted lenses, the manufacturer dyed the lenses twice in maximum dark brown dye following our suggestion. A red contact lens was evaluated for comparison.

image

Figure 1.  Contact lenses: clear lenses and lenses with different tint grades.

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All patients started with the darkest contact lenses as a consequence of previous experiences. Lighter lenses were fitted if, in the patient's opinion, the initial lenses were too dark. The patients were instructed to wear the contact lenses during the daytime throughout the month of the study. They were asked to insert the contact lenses early in the morning, before they were exposed to daylight.

Patients were tested without contact lenses at the beginning of the study. Patients were retested wearing the preferred type of tinted contact lenses after 4 weeks' wear. All patients were tested using their habitual distance refractive correction. Monocular VA was tested using an ETDRS (Early Treatment Diabetic Retinopathy Study) chart at a distance of 4 m. Patients who failed to read the largest letters at 4 m were tested at 2 m. Lighting conditions were standardized, using an ETDRS chart illuminator cabinet, no. 2425 (Precision Vision®, La Salle, IL, USA). Visual acuity was scored as the total number of letters read correctly, and expressed in logMAR units.

Monocular low-contrast VA was tested using letter logarithmic translucent contrast (Sloan) charts (10%) under standardized lighting conditions (Precision Vision®) at a distance of 4 m. Participants who failed to read the largest letters at 4 m were tested at 2 m. Low-contrast VA is denoted as CS. Contrast sensitivity was scored as the total number of letters read correctly, and expressed as logMAR. Near vision was tested binocularly with the new ETDRS chart ‘1’ (Precision Vision®) at 40 cm and expressed in decimal values. Participants who failed to read the largest letters at 40 cm were tested at 20 cm. The same light standard was used as above.

Goldmann perimetry with the dark contact lenses was performed only in four patients (case nos. 004:5, 005:3, 013:3, and 013:4). When comparing the Goldmann visual fields tested with and without the contact lenses, we found few or no changes regarding the isoptres representing peripheral retina, but indications of improvement in the central visual fields. In order to quantify the difference, we tested the central visual field using threshold perimetry, despite fixation difficulties in patients with central scotoma. The central visual fields were examined with threshold perimetry and the central 24–2 (24-degrees) threshold test using the Swedish Interactive Threshold Algorithm (SITA) fast method (Humphrey Field Analyzer II; Zeiss, Dublin, CA, USA), in all cases with and without the contact lenses.

The National Eye Institute Visual Functioning Questionnaire (NEI VFQ-25) was chosen to evaluate patients' subjective visual ability. The 25-item NEI VFQ-25 contains 12 subscales on general health, general vision, near vision, distance vision, peripheral vision, colour vision, ocular pain, vision-specific social functioning, vision-specific role limitations, vision-specific driving difficulties, dependency, and vision-specific mental health, respectively. The 1–5 scale ratings of the questionnaire were transformed to a 0–100 scale (Burstedt et al. 2005). For each patient, an overall composite NEI VFQ-25 score was calculated as the arithmetic mean, which is an unweighted average of the responses to all 12 subscale items except the general health-related question (Mangione et al. 2001).

Results

  1. Top of page
  2. Abstract.
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

The brown tinted contact lenses were graded according to their transmittance at 550 nm. We chose this wavelength because the retina has the highest level of sensitivity in this area. The most efficient wavelength in the light-adapted eye is 555 nm (Hart 1992). Light brown lenses had a transmittance of approximately 50%, whereas medium and dark brown lenses had transmittance rates of about 30% and 10%, respectively (Fig. 2). The red contact lens had low transmittance, but showed a shift in transmittance at this wavelength.

image

Figure 2.  Physical properties of contact lenses examined with spectrophotometry.

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All patients completed the study, four of the 12 patients wearing the darkest lenses and the other eight selecting the lens with 30% transmittance. Darker lenses were preferred by the patients with lower VA. Most patients experienced an obvious improvement in visual function with the contact lenses. The results of the VA and CS testing with and without contact lenses are presented in Table 1. The patients are listed according to central VA in the better eye. In all patients with distance VA ≤ 1.0 logMAR (0.1 decimal VA), there was an indication of better VA, at distance and at near, with tinted contact lenses. No patient in this group discontinued wearing the lenses at the end of the study. Contrast sensitivity was difficult to evaluate as most patients failed to read the test charts. However, more eyes were able to see the charts with lenses than without. Among the patients with lowest VA and the smallest remaining central visual field, the mean deviation (MD) score of threshold perimetry measurements tended to improve with tinted contact lenses.

An improvement in subjective visual function (NEI VFQ-25) was noted in the majority of patients. The two individuals with the best VA experienced a marked decline in visual function. The most obvious improvement in subjective visual function was observed among individuals with the lowest VA and individuals with a small remaining central visual field.

In the control subjects examined, there seems to have been little or no difference in the test situation regarding VA and CS with and without the dark tinted contact lenses. The threshold visual fields showed a decrease in MD for the controls when tested with dark contact lenses (Table 2).

Discussion

  1. Top of page
  2. Abstract.
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

The aim of the present study was to evaluate dark contact lenses in the visual rehabilitation of patients with BD. Bothnia dystrophy is found almost exclusively in Västerbotten County. Västerbotten is situated in sub-Arctic northern Sweden, just 200 km south of the Arctic Circle. The geographic localization implies particular conditions for individuals affected by retinal dystrophies associated with symptoms such as night blindness and extreme light sensitivity, including RP, achromatopsia and cone dystrophies. In summer, the area enjoys daylight for 24 hours a day. Late in autumn, it becomes very dark. When the snow appears, the days brighten a little. Nevertheless, for several months in the winter, there are only a few hours of daylight, causing great contrast between indoor and outdoor conditions. In early spring when snow still covers the ground, the sun is low over the horizon, reflecting off the snow and giving extremely bright light. The night blindness and daylight visual abilities of patients with BD differ from those experienced by individuals with classic RP. A patient with classic RP benefits from daylight. In BD patients, especially those in whom the remaining visual field is mainly peripheral, bright daylight will, besides causing problems with light sensitivity, also bleach the photoreceptors and cause a general reduction in visual function. The high frequency of BD, a disorder with a known genetic background in a restricted geographical area, gave us a unique opportunity to evaluate specific rehabilitation in a specific group of visually disabled patients.

We treated an otherwise untreatable group of patients by providing them with tinted contact lenses; however, the evaluation of our patients, which was generally positive, must be considered as subjective. In addition, the results of objective visual tests, such as VA, CS and central visual fields, should be evaluated with caution as most of these patients were severely visually disabled and the observed differences were often small. A similar, earlier study also found it difficult to quantify the benefit of low-vision intervention with contact lenses (Park & Sunness 2004).

This study illustrates the difficulties of evaluating a group of patients with a progressive retinal dystrophy. Genetically this material is homogenous. However, clinically the patients studied constitute a small heterogeneous group in different stages of the disease. Quantitative data in this study include testing with two different lenses, giving groups too small to evaluate statistically. Despite these limitations, some conclusions can be made.

There seemed to be a correlation between the improvement experienced in subjective visual function, tested with the NEI VFQ-25 questionnaire, and the improvement observed in the objective visual tests, with and without contact lenses. However, in our clinical contact with the patients, it was obvious that our objective visual tests and the questionnaire did not fully reflect the patients' different needs and experiences in daily life activities.

Despite their poor vision, the patients were easily able to detect the contact lenses because of their dark colour and there were no major problems in the daily care of lenses. All the patients accepted responsibility for learning lens care and most used their lenses daily, even after the study. In fact, the contact lenses were still in use by most patients about 18 months after the study concluded. Three patients discontinued wearing their contact lenses after the study. In case 217:1, the patient found no advantage in wearing lenses and also experienced discomfort caused by dry eye. Cases 025:2 and 013:5 stopped using their contact lenses due to reduced colour vision and reduced visual function in low light conditions. These three patients had the best VA (0.5–1.0 decimal acuity) in the study group.

The majority of patients described a visual improvement with tinted contact lenses compared with tinted spectacles, which did not simply refer to the cosmetic advantage of lenses over dark spectacles that hide the wearer's eyes. The advantage of contact lenses is that they stop stray light from reaching the eye. The grade of the lens tint must be individually chosen when the lenses are manufactured. Patients with very low VA generally prefer a darker tint. The patient's profession may also dictate certain requirements. Case 011:3, a farmer, would have preferred even darker lenses than those provided, despite fairly well preserved VA.

Some patients spontaneously reported a decrease in their already impaired colour vision with the tinted contact lenses. These patients, however, said that the advantages of wearing the contact lenses far outweighed this disadvantage. The grade of darkness of the contact lenses must be adjusted to the light conditions in different seasons, which makes it necessary for the patient maintain continuous contact with the clinic. The lens with 50% transmittance (light brown) was not evaluated in this study, but was later used by some patients. One year after the study, most of the patients were using two different grades of tint: a darker tint during spring and summer, and a lighter tint in late autumn and winter. Some of the patients said that their vision with the tinted lenses was comparable with their vision 10–20 years previously.

A gradual increase in retinal sensitivity to light and an improvement in electroretinogram (ERG) components have been reported in BD with prolonged dark adaptation (20–24 hours) (Gränse et al. 2001; Burstedt et al. 2003). The general benefits of tinted contact lenses for the BD patient may be explained by the fact that wearing the lenses provides the subject with constant dark adaptation, which has an effect on the retinal metabolism. This should be possible to test with ERG after wearing tinted contact lenses with different grades of tint. A separate study on full-field ERG and tinted contact lenses in BD is in progress. It is hoped that the results of this study will explain and definitively demonstrate the benefit of tinted contact lenses in BD.

Bothnia dystrophy patients with remaining central visual function and problems with light sensitivity in certain light conditions benefit from contact lenses with a more moderate dark tint. In these cases, dark lenses appear to diminish symptoms of light sensitivity via to the photopic response in the retina.

Other patient groups with retinal dystrophies associated with prolonged dark adaptation or dysfunction of the cone system, including cone dystrophies or achromatopsia, may also benefit from this type of contact lens. By contrast with red-tinted contact lenses, which have been tested previously (Park & Sunness 2004) and found to have a filtering effect mostly in the short wavelength area (Fig. 2), the dark brown lenses also have a filtering effect on longer wavelength light. A review of the spectral system sensitivity functions of the rod and cone systems carried out by Berson (1992) revealed that rods are more sensitive than cones across almost the entire visible spectrum. We tested the dark contact lenses on single patients with disorders primarily affecting the cone function, including cone-rod dystrophy (Peripherin/RDS Arg-172-Trp) and achromatopsia, with promising results.

Acknowledgements

  1. Top of page
  2. Abstract.
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

This study was presented in part at the European Association for Vision and Eye Research (EVER) Meeting, Vilamoura, Portugal, October 5–8th, 2005.

This work was supported by the Swedish Medical Research Council, Stockholm (project nos. 09745, 10866, and 13513), and by grants from the County Council of Västerbotten, Umeå, the Crown Princess Margaretha's Foundation for Vision Research, Stockholm, and the Swedish Contact Lens Foundation, Stockholm. The contact lenses were kindly provided, according to our suggestions, by Nordiska Lins, Gothenburg.

References

  1. Top of page
  2. Abstract.
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
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