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PubMed2002

A frameshift insertion in the cone cyclic nucleotide gated cation channel causes complete achromatopsia in a consanguineous family from a rural isolate.

Complete achromatopsia is genetically heterogeneous and segregates with mutations in CNGA3 or CNGB3 genes, which respectively encode for alpha- and beta-subunits of the cyclic-nucleotide-gated (CNG) cation channel expressed in cone photoreceptors. High incidence of the disease (1 in 60) was detected in a rural isolate in central Chile. We excluded previously reported mutations in a consanguineous kindred with five affected members. Genotype analysis with short tandem repeat polymorphic (STRP) markers provided evidence to search for the causative mutation in CNGB3. Two sequence variations, c.492_493insT and c.488A>G, flanking an adenosine (A(5)) repeat in exon 4 were identified. The frameshift mutation creates two consecutive stop codons in exon 5 that would induce premature translation termination. The severely truncated beta-subunit is likely to render a nonfunctional cone CNG channel and cause total colour blindness in this kindred.

Chromosomes, Human, Pair 8↗
PubMed2005

CNGB3 mutations account for 50% of all cases with autosomal recessive achromatopsia.

Achromatopsia is a congenital, autosomal recessively inherited disorder characterized by a lack of color discrimination, low visual acuity (<0.2), photophobia, and nystagmus. Mutations in the genes for CNGA3, CNGB3, and GNAT2 have been associated with this disorder. Here, we analyzed the spectrum and prevalence of CNGB3 gene mutations in a cohort of 341 independent patients with achromatopsia. In 163 patients, CNGB3 mutations could be identified. A total of 105 achromats carried apparent homozygous mutations, 44 were compound (double) heterozygotes, and 14 patients had only a single mutant allele. The derived CNGB3 mutation spectrum comprises 28 different mutations including 12 nonsense mutations, eight insertions and/or deletions, five putative splice site mutations, and three missense mutations. Thus, the majority of mutations in the CNGB3 gene result in significantly altered and/or truncated polypeptides. Several mutations were found recurrently, in particular a 1 bp deletion, c.1148delC, which accounts for over 70% of all CNGB3 mutant alleles. In conclusion, mutations in the CNGB3 gene are responsible for approximately 50% of all patients with achromatopsia. This indicates that the CNGB3/ACHM3 locus on chromosome 8q21 is the major locus for achromatopsia in patients of European origin or descent.

Alleles↗
PubMed2002

Symptomatic abnormalities of dark adaptation in patients with EFEMP1 retinal dystrophy (Malattia Leventinese/Doyne honeycomb retinal dystrophy).

PURPOSE: To investigate the nature of symptomatic visual disturbance in patients with EFEMP1 retinal dystrophy in the absence of geographic atrophy or choroidal neovascularization. METHODS: Patients presenting to a tertiary referral centre underwent clinical evaluation, fluorescein angiography, colour contrast sensitivity, focal, pattern, and standard electroretinography, electrooculography, scotopic threshold perimetry and dark adaptometry. RESULTS: Clinical features included reduced central vision, difficulty passing from light to dark, and diffuse submacular and peripapillary deposits, which were hyperfluorescent by fluorescein angiography. Colour contrast thresholds were abnormal in all six patients studied and both pattern and focal electroretinograms were abnormal in five of six patients. The scotopic and mixed rod-cone single flash ERG was normal but two patients demonstrated reduced oscillatory potentials and one had borderline delayed 30 Hz responses. Scotopic thresholds were elevated and rod-mediated dark adaptation kinetics were markedly prolonged in all six patients when measured over the central visible confluent deposits. CONCLUSIONS: In patients with EFEMP1 retinal dystrophy with confluent macular deposits, scotopic sensitivity is reduced and dark adaptation kinetics are prolonged over the macular deposits but are normal elsewhere. These results emphasize the localised nature of functional deficits in some patients with EFEMP1 retinal dystrophy and correlate well with the patient's visual symptoms. Symptomatic visual dysfunction may precede the development of clinically evident geographic atrophy or choroidal neovascularization in this disorder.

Color Vision Defects↗
PubMed2005

Blue cone monochromatism: a phenotype and genotype assessment with evidence of progressive loss of cone function in older individuals.

AIM: To perform a detailed clinical and psychophysical assessment of the members of three British families affected with blue cone monochromatism (BCM), and to determine the molecular basis of disease in these families. METHODS: Affected and unaffected members of three families with BCM were examined clinically and underwent electrophysiological and detailed psychophysical testing. Blood samples were taken for DNA extraction. The strategy for molecular analysis was to amplify the coding regions of the long wavelength-sensitive (L) and middle wavelength-sensitive (M) cone opsin genes and the upstream locus control region by polymerase chain reaction, and to examine these fragments for mutations by direct sequencing. RESULTS: We have confirmed the reported finding of protan-like D-15 arrangements of patients with BCM. In addition, we have demonstrated that the Mollon-Reffin (MR) Minimal test is a useful colour-discrimination test to aid in the diagnosis of BCM. Affected males were shown to fail the protan and deutan axes, but retained good discrimination on the tritan axis of the MR test, a compelling evidence for residual colour vision in BCM. This residual tritan discrimination was also readily detected with HRR plates. In two families, psychophysical testing demonstrated evidence for progression of disease. In two pedigrees, BCM could be linked to unequal crossovers within the opsin gene array that resulted in a single 5'-L/M-3' hybrid gene, with an inactivating Cys203Arg mutation. The causative mutations were not identified in the third family. CONCLUSIONS: The MR test is a useful method of detecting BCM across a wide range of age groups; residual tritan colour discrimination is clearly demonstrated and allows BCM to be distinguished from rod monochromatism. BCM is usually classified as a stationary cone dysfunction syndrome; however, two of our families show evidence of progression. This is the first report of progression associated with a genotype consisting of a single 5'-L/M-3' hybrid gene carrying an inactivating mutation. We have confirmed that the Cys203Arg inactivating mutation is a common sequence change in blue cone monochromats.

Adolescent↗
PubMed2001

For whales and seals the ocean is not blue: a visual pigment loss in marine mammals.

Most terrestrial mammals have colour vision based on two spectrally different visual pigments located in two types of retinal cone photoreceptors, i.e. they are cone dichromats with long-to-middle-wave-sensitive (commonly green) L-cones and short-wave-sensitive (commonly blue) S-cones. With visual pigment-specific antibodies, we here demonstrate an absence of S-cones in the retinae of all whales and seals studied. The sample includes seven species of toothed whales (Odontoceti) and five species of marine carnivores (eared and earless seals). These marine mammals have only L-cones (cone monochromacy) and hence are essentially colour-blind. For comparison, the study also includes the wolf, ferret and European river otter (Carnivora) as well as the mouflon and pygmy hippopotamus (Artiodactyla), close terrestrial relatives of the seals and whales, respectively. These have a normal complement of S-cones and L-cones. The S-cone loss in marine species from two distant mammalian orders strongly argues for convergent evolution and an adaptive advantage of that trait in the marine visual environment. To us this suggests that the S-cones may have been lost in all whales and seals. However, as the spectral composition of light in clear ocean waters is increasingly blue-shifted with depth, an S-cone loss would seem particularly disadvantageous. We discuss some hypotheses to explain this paradox.

Animals↗
PubMed2001

The regional cortical basis of achromatopsia: a study on macaque monkeys and an achromatopsic patient.

Previous experiments have revealed total loss of colour vision following removal of all inferior temporal cortex, a condition akin to complete cerebral achromatopsia in humans. Whether less extensive ablation genuinely impairs colour perception without abolishing it or retards learning involving coloured stimuli is contested. We therefore tested macaque monkeys, with total removal of temporal areas TEO and TE but sparing rostral and perirhinal temporal cortex and the upper bank of the superior temporal sulcus. Compared with three monkeys with lateral parietal ablations, the monkeys with TEO/TE lesions were impaired at learning and retention of simultaneous two-choice colour discriminations and with a nine-choice oddity discrimination whether the coloured target was embedded among grey distracters of the same luminance or among isoluminant coloured distracters. However, their performance was superior to that of an achromatopsic human subject and to that previously measured in monkeys with much larger temporal lobe ablation. They were only mildly impaired at nine-choice oddity discrimination for grey stimuli where the grey target was brighter than the grey distracters. The impairment could be exacerbated or alleviated by altering the colour of the background of the displays and by static and dynamic luminance masking of the entire display in a manner that indicates that the colour deficit reflects a change in perception rather than a disorder of learning and memory. It resembles central dyschromatopsia in human subjects but falls short of achromatopsia.

Animals↗
PubMed2002

Autoantibodies to photoreceptor membrane proteins and outer plexiform layer in patients with cancer-associated retinopathy.

Cancer-associated retinopathy (CAR) is a paraneoplastic syndrome that is characterized by degeneration of the retina as a remote effect of cancer outside the eye. The detection of autoantibodies associated with the retinopathy may precede the diagnosis of the underlying cancer. We have examined the sera of two patients with CAR by Western blot analysis. Autoantibodies to a 40kD antigen doublet and a 35 kD antigen were detected. Tissue specificity of the autoantigens was determined by testing several different tissues. The 40 kD antigen doublet was most abundant in retinal extract but was also present in lung and spleen extracts. The 35 kD antigen showed little tissue specificity and was present in all tissues tested. Fractionation of retinal proteins into water-soluble and -insoluble proteins revealed that the 40 kD antigen doublet was highly insoluble and probably represented membrane-associated proteins. Immunohistochemical analysis of the retina showed that the 40 kD antigens locate to the photoreceptors while the 35 kD antigen is located in the outer plexiform layer.

Adenocarcinoma↗
PubMed2003

Prevalence of undetected ocular conditions in a pilot sample of school children.

Parents of 134 children (age 5-18 years; 84% participation) attending a private school gave informed consent for their child's participation in a pilot study to demonstrate the feasibility and estimate sample size for a larger study of myopia prevalence, the Sydney Myopia Study. LogMAR visual acuity and other ocular assessments, including cycloplegic autorefraction (tropicamide 1%) and examination of the media and fundus, were performed. The prevalence of significant ocular conditions was 28.2%. Eleven children (8.4%) wore glasses. Five were referred for a change in their correction. Previously undetected ocular conditions (19.8%) included one child with ocular pathology and four children with strabismus. Uncorrected refractive error (16.8%) was the most common reason for referral and was more predominant in the senior students (25%), corresponding with an age-related shift in mean spherical equivalent refraction towards myopia (less than 7 years: +0.40 +/- 0.60 D; more than 15 years: -1.15 +/- 1.18 D). Three senior students were classified as having socially significant correctable vision impairment. These findings suggest that reliance on ad hoc referrals could result in delayed referral and that vision screening in both early and later school years may be desirable.

Adolescent↗
PubMed2003

Day-blindness in three dogs: clinical and electroretinographic findings.

A 6-month-old Rhodesian ridgeback-cross, a 6-year-old Chihuahua and a 12-month-old Australian cattle dog were presented to the authors with a history of colliding with obstacles in daylight. Ophthalmic examination was normal and all three dogs successfully negotiated obstacle courses in dim light. In daylight the dogs became suddenly blind and repeatedly collided with obstacles. Elecroretinography (ERG) revealed no retinal activity to high frequency (30 Hz), bright intensity blue light retinal stimulation by any dog, confirming cone dysfunction. Achromatopsia has previously been recorded in Alaskan malamutes and miniature poodles. This clinical case series illustrates the characteristic behavioral presentation and the electroretinographic findings of severe day-blindness and demonstrates that this condition may exist in other breeds of dogs.

Animals↗
PubMed1999

Colour vision abnormalities and movement time in Parkinson's disease.

Visual system dysfunction has been reported in Parkinson's disease (PD). The objective of the present study was to evaluate a putative association of distorted colour vision and delayed initiation and execution of movement in PD. We performed the Farnsworth-Munsell 100-hue test and estimated the total error score in 30 previously untreated parkinsonian patients and 30 age- and sex-matched controls. We then determined slowness in motor readiness and motor programming in the parkinsonian subjects on the same day. Subjects were asked to press a start button and release it after the randomized appearance of a visual stimulus and to move their right index finger to a reaction button as quickly as possible. Reaction time was considered as elapsed time between onset of the stimulus light and release of the start button, movement time was the time period between release of the start button and the pressing of the reaction button. Significant differences appeared between parkinsonian patients' and controls' reaction times (P = 0.007), movement time (P = 0.001) and total error score (P = 2.23E-08). A significant relation (Spearman R = 0.473, P = 0.008) was found between movement time and total error score, but not between reaction time and total error score (Spearman R = 0.259, P = 0.166). We conclude, that visual dysfunction and execution of movement are more influenced by altered dopaminergic neurotransmission in PD in comparison to the initiation of movement.

Adult↗
PubMed2001

The ChromaGen contact lens system: colour vision test results and subjective responses.

The ChromaGen lens system is designed to enhance colour perception in colour vision deficiency (CVD). To investigate its efficacy, 14 CVD subjects were prescribed ChromaGen contact lenses. Colour vision tests (Ishihara, Farnsworth Munsell D-15, Farnsworth Lantern) were administered at baseline, lens dispensing, and after a 2-week lens-wearing trial during which subjective responses were recorded daily using visual analogue scales. ChromaGen lenses significantly reduced ishihara error rates (p < 0.001; ANOVA), particularly for deutan subjects. There was also a significant reduction in errors (p < 0.005) on the D-15 test. Conversely, lens wear had no significant effect on Farnsworth Lantern test performance. Subjectively, subjects reported enhanced colour perception, but poor vision in dim light. Judgement of distance and motion were only slightly affected. We conclude that ChromaGen lenses may enhance subjective colour experience and assist in certain colour-related tasks, but are not indicated as an aid for CVD in occupations with colour vision-related restrictions.

Adolescent↗
PubMed2002

Ocular optics, electroretinography and primary open angle glaucoma.

Advancing the knowledge of ocular image quality is important in the development of new tests for the earlier detection of primary open angle glaucoma (POAG). Loss of blue sensitivity is an important feature of POAG; however, it is difficult to separate this loss from the effects of wavelength related intraocular light scatter and media absorption. A technique for recording the S-cone electroretinogram is described which may solve these problems. The effect of scattered light is avoided by a Ganzfeld stimulus and the absorption of short wavelength light is compensated by a photometric balancing of blue and green stimuli using the M-cone response. The modulation transfer function of the eye has enabled the true spatial tuning function of the retina to be determined by pattern electroretinography (PERG). This has demonstrated the role of retinal ganglion cells in the generation of the PERG. These techniques are shown to be highly sensitive tests in the early stages of POAG.

Adult↗
PubMed2001

Visual function is stable in patients who continue long-term vigabatrin therapy: implications for clinical decision making.

PURPOSE: Vigabatrin (VGB) has been shown to cause visual field constriction and other forms of mild visual dysfunction. We determined the safety of continuing VGB therapy in patients who had received prolonged treatment (>2 years) with the drug by serially monitoring changes in visual function over a 1-year period of continued therapy. We also followed up patients who discontinued VGB to see whether alternative therapies are effective. METHODS: Fifteen of 17 patients who continued VGB therapy had visual-function testing (visual acuity, color vision, kinetic and static perimetry) every 3 months for 1 year. Eighteen patients who discontinued VGB were given alternative antiepileptic drugs (AEDs); their seizure responses were measured after > or =3 months of treatment. RESULTS: Patients continuing VGB showed no worsening of visual acuity, color vision, or visual-field constriction beyond that measured in the initial test. Many patients who discontinued VGB had good seizure control with either newer or previously unsuccessful AEDs. CONCLUSIONS: For patients who have an excellent response to VGB and only mild visual changes, continued therapy may be safe with close visual monitoring. Patients who do not have a significant reduction in seizures or who experience considerable visual dysfunction with VGB may respond well to alternative therapies.

Adult↗