scholarly journals Variety of genotypes in males diagnosed as dichromatic on a conventional clinical anomaloscope

2004 ◽  
Vol 21 (3) ◽  
pp. 205-216 ◽  
Author(s):  
MAUREEN NEITZ ◽  
JOSEPH CARROLL ◽  
AGNES RENNER ◽  
HOLGER KNAU ◽  
JOHN S. WERNER ◽  
...  
Keyword(s):  
Color Vision ◽  
X Chromosome ◽  
Full Range ◽  
Gene Array ◽  
Spectral Difference ◽  
Vision Defect ◽  
Spectral Peaks ◽  
Pigment Type ◽  
Pigment Genes ◽  
Two Populations

The hypothesis that dichromatic behavior on a clinical anomaloscope can be explained by the complement and arrangement of the long- (L) and middle-wavelength (M) pigment genes was tested. It was predicted that dichromacy is associated with an X-chromosome pigment gene array capable of producing only a single functional pigment type. The simplest case of this is when deletion has left only a single X-chromosome pigment gene. The production of a single L or M pigment type can also result from rearrangements in which multiple genes remain. Often, only the two genes at the 5′ end of the array are expressed; thus, dichromacy is also predicted to occur if one of these is defective or encodes a defective pigment, or if both of them encode pigments with identical spectral sensitivities. Subjects were 128 males who accepted the full range of admixtures of the two primary lights as matching the comparison light on a Neitz or Nagel anomaloscope. Strikingly, examination of the L and M pigment genes revealed a potential cause for a color-vision defect in all 128 dichromats. This indicates that the major component of color-vision deficiency could be attributed to alterations of the pigment genes or their regulatory regions in all cases, and the variety of gene arrangements associated with dichromacy is cataloged here. However, a fraction of the dichromats (17 out of 128; 13%) had genes predicted to encode pigments that would result in two populations of cones with different spectral sensitivities. Nine of the 17 were predicted to have two pigments with slightly different spectral peaks (usually ≤ 2.5 nm) and eight had genes which specified pigments identical in peak absorption, but different in amino acid positions previously associated with optical density differences. In other subjects, reported previously, the same small spectral differences were associated with anomalous trichromacy rather than dichromacy. It appears that when the spectral difference specified by the genes is very small, the amount of residual red–green color vision measured varies; some individuals test as dichromats, others test as anomalous trichromats. The discrepancy is probably partly attributable to testing method differences and partly to a difference in performance not perception, but it seems there must also be cases in which other factors, for example, cone ratio, contribute to a person's ability to extract a color signal from a small spectral difference.

Novel form of a single X-linked visual pigment gene in a unique dichromatic color-vision defect

2006 ◽  
Vol 23 (3-4) ◽  
pp. 411-417 ◽  
Author(s):  
TAKAAKI HAYASHI ◽  
AKIKO KUBO ◽  
TOMOKAZU TAKEUCHI ◽  
TAMAKI GEKKA ◽  
SATOSHI GOTO-OMOTO ◽  
...  
Keyword(s):  
Color Vision ◽  
Crossing Over ◽  
M Gene ◽  
Spectral Difference ◽  
Unequal Crossing Over ◽  
Scale Range ◽  
Pigment Genes ◽  
The Subject ◽  
Color Vision Deficiencies ◽  
Yellow Scale

In normal trichromats, the long- (L) and middle-wavelength-sensitive (M) pigment genes are arranged in a head-to-tandem array on the X chromosome. Two amino acids at positions 277 and 285, encoded by exon 5 of the L and M genes, respectively, are essential for the spectral difference between L and M pigments whose spectral peaks are at approximately 560 and 530 nm. Intragenic or intergenic unequal crossing-over commonly occurs between the highly homologous L and M genes, resulting in red-green color vision deficiencies. The dichromacy is usually associated with a single L gene for deuteranopia or a single 5′ L-M 3′ hybrid gene with M-gene exon 5 for protanopia. We clinically diagnosed a total of 88 male dichromats using a Nagel model I anomaloscope, which included one unclassified subject in addition to 31 protanopes and 56 deuteranopes. The objective of this study was to characterize the phenotype of the subject and to determine the genotype of his X-linked pigment genes. The subject accepted not only any red-green mixture but also an extended yellow-scale range at each matching point (i.e. 20 to 32 scale units at the green primary and 3.5 to 6 scale units at the red primary). The slopes of regression lines were in the range of −0.34 to −0.23, while the mean slopes for the protanopes and deuteranopes were −0.38 and −0.01, respectively. Spectral sensitivity tests showed that the subject's curve was shifted between the protanope and deuteranope curves. Molecular analysis revealed a novel form of a single pigment gene with a unique arrangement of exon 5 (Y277 from the L gene and A285 from the M gene). The predicted λmax(541 to 546 nm) of the unique pigment was closer to the M than to the L pigment. Our outcome suggests that intragenic unequal crossing-over may have occurred between amino acid positions 279 and 283.

Molecular genetics of color-vision deficiencies

2004 ◽  
Vol 21 (3) ◽  
pp. 191-196 ◽  
Author(s):  
SAMIR S. DEEB
Keyword(s):  
Color Vision ◽  
Gene Array ◽  
Proximal Promoter ◽  
Single Amino Acid ◽  
Α Subunit ◽  
Green Color ◽  
Cone Function ◽  
Pigment Genes ◽  
Color Vision Deficiencies ◽  
Hybrid Genes

The normal X-chromosome-linked color-vision gene array is composed of a single long-wave-sensitive (L-) pigment gene followed by one or more middle-wave-sensitive (M-) pigment genes. The expression of these genes to form L- or M-cones is controlled by the proximal promoter and by the locus control region. The high degree of homology between the L- and M-pigment genes predisposed them to unequal recombination, leading to gene deletion or the formation of L/M hybrid genes that explain the majority of the common red–green color-vision deficiencies. Hybrid genes encode a variety of L-like or M-like pigments. Analysis of the gene order in arrays of normal and deutan subjects indicates that only the two most proximal genes of the array contribute to the color-vision phenotype. This is supported by the observation that only the first two genes of the array are expressed in the human retina. The severity of the color-vision defect is roughly related to the difference in absorption maxima (λmax) between the photopigments encoded by the first two genes of the array. A single amino acid polymorphism (Ser180Ala) in the L pigment accounts for the subtle difference in normal color vision and influences the severity of red–green color-vision deficiency.Blue-cone monochromacy is a rare disorder that involves absence of L- and M-cone function. It is caused either by deletion of a critical region that regulates expression of the L/M gene array, or by mutations that inactivate the L- and M-pigment genes. Total color blindness is another rare disease that involves complete absence of all cone function. A number of mutants in the genes encoding the cone-specific α- and β-subunits of the cGMP-gated cation channel as well as in the α-subunit of transducin have been implicated in this disorder.

Novel mutations in the L visual pigment gene found in Japanese men with protan color-vision defect having a normal order L/M gene array

2016 ◽  
Vol 37 (4) ◽  
pp. 471-472
Author(s):  
Sanae Muraki ◽  
Hisao Ueyama ◽  
Shoko Tanabe ◽  
Shinichi Yamade ◽  
Hisakazu Ogita ◽  
...  
Keyword(s):  
Color Vision ◽  
Visual Pigment ◽  
Gene Array ◽  
M Gene ◽  
Normal Order ◽  
Novel Mutations ◽  
Japanese Men ◽  
Color Vision Defect ◽  
Vision Defect

Testing Color Vision in Children

2022 ◽  
pp. 21-31
Author(s):  
Kristen L. Kerber
Keyword(s):  
Color Vision ◽  
Pediatric Population ◽  
Learning Experience ◽  
Color Naming ◽  
Screening Tests ◽  
Career Interests ◽  
Older Children ◽  
Vision Defect ◽  
Color Vision Defects ◽  
Vision Defects

It is important to screen for acquired or hereditary color vision defects as early as possible. Color vision is a critical part of the early learning experience, and children who have color deficiencies may have difficulties compared to their peers if there is color-based schoolwork. It becomes important for career interests/goals for older children as some jobs may require normal color vision. Hereditary red-green deficiencies are X-linked and therefore affect approximately 8% of males and less than 1% of females. Acquired color vision defects and blue-yellow defects are rare in the pediatric population; therefore, these conditions will be discussed minimally in this chapter. Infants are able to discern color by 2-3 months of age, but accurate color naming may not develop until 4-6 years of age. Screening tests are sensitive, fast, and easy to administer. If a deficiency is suspected through screening, further testing must be evaluated in order to determine the type and severity of the color vision defect. Color vision is typically tested starting at age 3 years and up.

scholarly journals Analysis of introns and promoters of L/M visual pigment genes in relation to deutan color-vision deficiency with an array of normal gene orders

2009 ◽  
Vol 54 (9) ◽  
pp. 525-530 ◽  
Author(s):  
Hisao Ueyama ◽  
Shoko Tanabe ◽  
Sanae Muraki-Oda ◽  
Shinichi Yamade ◽  
Masahito Ohji ◽  
...  
Keyword(s):  
Color Vision ◽  
Visual Pigment ◽  
Color Vision Deficiency ◽  
Normal Gene ◽  
Pigment Genes

scholarly journals A Clinical Study of Optic Disc Edema in a Tertiary Eye Center of Nepal

2019 ◽  
Vol 11 (2) ◽  
pp. 122-129
Author(s):  
Anil Parajuli ◽  
Ananda Kumar Sharma ◽  
Sanjeeta Sitaula
Keyword(s):  
Visual Acuity ◽  
Contrast Sensitivity ◽  
Color Vision ◽  
Optic Disc ◽  
Blind Spot ◽  
Optic Disc Edema ◽  
Disc Edema ◽  
Vision Defect ◽  
Common Causes ◽  
Life Threatening

Purpose: To evaluate the etiology and clinical presentation of cases with optic disc edema presenting to a tertiary eye center of Nepal. Background: The etiology of optic disc edema ranges from relatively benign to potentially sight and life threatening conditions. Till date very few studies have been done on disc edema in Nepal. Method: The authors conducted a prospective, descriptive study at B.P. Koirala Lions Center for Ophthalmic Studies (BPKLCOS), Nepal. All cases with disc edema presenting to the out patient department (OPD) from January 1, 2014 to June 30, 2015 were included in the study. Results: Total 112 patients were included in the study, out of which diagnosis could be established in 99. The mean age of the patients was 32.54 ± 13.97 years with the majority being female. The most common cause of disc edema was idiopathic intracranial hypertension (IIH) (37.5%,). Majority of the patients complained of isolated diminution of vision (38.4%). Among the eyes affected, 78.3% had best corrected visual acuity (BCVA) 6/6-6/18, 36.6% had color vision defect and 31.4% had reduced contrast sensitivity. The most common visual field defect was isolated enlarged blind spot (39.7 %). Conclusion: IIH followed by optic neuritis (ON) are the most common causes of disc edema. Conditions with disc edema mainly affect the age group 21-40 years with females affected 2.5 times more than males. Visual acuity, color vision and contrast sensitivity are deranged in majority of cases of ON and normal in majority of cases of IIH.

scholarly journals The burden of color vision defect in Nepal – an iceberg phenomenon

2019 ◽  
Vol 9 (4) ◽  
pp. 69-71
Author(s):  
Anadi Khatri ◽  
Bal Kumar K.C ◽  
Sudhir Gautam ◽  
Muna Kharel
Keyword(s):  
Color Vision ◽  
Early Stage ◽  
Descriptive Analysis ◽  
School Level ◽  
Color Vision Defect ◽  
Vision Defect ◽  
Color Vision Defects ◽  
Color Vision Test ◽  
Sequential Group ◽  
Vision Defects

Background: Color vision tests are routinely performed and are mandatory in most part of the world. However, in Nepal and many other developing countries, color vision may often be overlooked. We evaluated a possible burden of color vision in a group of patients who were specifically evaluated for a color vision defects. This study evalutes the awareness of color vision defect among the patients evaluated and highlights the importance of the color vision evaluation. Methods: A sequential group of 73 people from August to September 2017 specifically evalu­ated for color vision defect for recruitment of government employment were evaluated. Ishi­harapseudo-isochromatic plates and Farnsworth-Munsell Dichotomous D-15 test were used for screening. Mean and Standard deviation were used for descriptive analysis of the data. Results: Fifty-seven were male and sixteen were female. The mean age was 23 years (SD ± 3.7). On evaluation of the color vision defect, 9 (12.3%) were found to have total color vision defect (achromatopsia), 3 (4%)-red-green defect and 1(1%) with blue red defect. None of the patients had undergone color vision test at eye hospital previously. There were 4 patients who were registered drivers who had color vision defect. Conclusions: Color vision is an important part of the vision. It should not be ignored.All of the patients evaluated were found to be unware of their condition. Early detection of color vision defects in individuals, if possible, at school level can help them to determine their careers and future endeavors at early stage.

Sign in / Sign up

Export Citation Format

Share Document