Biomedical subjects

M P Simunovic

Publications and source records attributed to M P Simunovic.

5 recordsLinked to original sources

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

Is color vision deficiency an advantage under scotopic conditions?

PURPOSE: To examine experimentally whether color vision deficiency confers a selective advantage under scotopic conditions. METHODS: Red-green color-deficient subjects, monochromats, and age-matched color-normal control subjects were examined. In each subject the time course of dark adaptation, scotopic visual field sensitivity, and performance on a scotopic perceptual task were measured. RESULTS: No significant differences were found between red-green color-deficient subjects and control subjects on any of the three tests. Our small sample of monochromats had higher absolute thresholds than the corresponding control subjects, but their performance at the scotopic visual field test and perceptual task did not differ significantly from that of color-normal subjects. CONCLUSIONS: No evidence was found that red-green color deficiency or monochromatism confers a selective advantage under scotopic conditions.

Adolescent↗

PubMed1998

Colour discrimination ellipses in patients with dominant optic atrophy.

Many colour tests require a visual acuity of at least 0.1, making them unsuitable for low vision patients. To assess colour vision in patients with sub-normal acuity, we re-designed a previously described test so that its spatial details would be coarse enough to be resolvable by subjects with severe visual impairment. The test measures chromatic discrimination along 20 axes evenly spaced in CIE 1976 L*u*v* colour space. We detail the results for this test in a group of patients with dominant optic atrophy. Despite the lack of evidence for genetic heterogeneity in dominant optic atrophy, we observed phenotypic variation both between and within families.

Adult↗

PubMed1998

The cone dystrophies.

The cone dystrophies are a heterogeneous group of inherited disorders that result in dysfunction of the cone photoreceptors and sometimes their post-receptoral pathways. The major clinical features of cone dystrophy are photophobia, reduced visual acuity and abnormal colour vision. Ganzfeld electroretinography shows reduced or absent cone responses. On the basis of their natural history, the cone dystrophies may be broadly divided into two groups: stationary and progressive cone dystrophies. The stationary cone dystrophies have received more attention, and subsequently our knowledge of their molecular genetic, psychophysical and clinical characteristics is better developed. Various methods of classification have been proposed for the progressive cone dystrophies, but none is entirely satisfactory, largely because the underlying disease mechanisms are poorly understood. Multidisciplinary studies involving clinical assessment, molecular genetics, electrophysiology and psychophysics should lead to an improved understanding of the pathogenesis of these disorders.

Color Vision Defects↗

PubMed1997

Post radial keratotomy RGP fitting--a case study.

The procedure of radial keratotomy produces an abnormal corneal topography, with the central cornea being flatter than the periphery. As a result, fitting the post-radial keratotomy (RK) patient with rigid gas permeable (RGP) lenses can be an enormously difficult task. Unlike standard lens designs, the Ortho-K series of lenses, originally designed for use in orthokeratology, possess a back peripheral radius (BPR) which is steeper than the back optic zone radius (BOZR). It is proposed that these lenses may provide a more acceptable fit than conventional RGPs for the post-RK patient.

Journal Article↗