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Biomedical subjects

E Zrenner

Publications and source records attributed to E Zrenner.

At least 73 records · Page 4Linked to original sources
PubMed1999

Colour vision disturbances in chronic smokers.

PURPOSE: The aim of the present study was to test the influence of smoking on colour perception. SUBJECTS AND METHODS: At the University Eye Hospital Tübingen, 76 generally healthy smokers with inconspicuous ophthalmological findings (visual acuity, refraction, intraocular pressure, morphology) were examined by the cap-sorting test, Roth 28-hue desaturated. Group 1 was comprised of smokers (n = 20; M 9, F 11; mean age 28.1+/-10.3 years) with a smoking consumption of less than one packet of cigarettes per day (8.4+/-5.3 cigarettes/day) for 9.1+/-8.3 years. Group 2 consisted of smokers (n = 32; M 22, F 10; mean age 28.6+/-9.7 years) with a smoking consumption of one or more than one packet per day (30+/-8.4 cigarettes/ day) for 9.5+/-8.3 years. Generally healthy and ophthalmologically normal non-smokers served as a control group (n = 76; M 41, F 35; mean age 30+/-9 years). RESULTS: The average error score of the control group was (median +/- mean absolute deviation) 42+/-18. Group 1 showed no difference to the control group (51+/-27; P = 0.42). On the other hand, group 2 had a significantly higher error score than the control group (102+/-45; P<0.0001). CONCLUSION: Otherwise healthy smokers with a cigarette consumption of less than 20 cigarettes per day do not show any disturbances in colour vision. Smokers who consume more than 20 cigarettes per day may suffer colour vision defects as a result.

Adult↗
PubMed1999

Familial macular cone dystrophy: diagnostic value of multifocal ERG and two-color threshold perimetry.

BACKGROUND: It is difficult to detect receptor dysfunction in patients with marked bilateral visual loss but only mild morphological alterations of the fundus. METHODS: Two patients, father and son, with visual acuity loss to 20/100 were examined. Using the multifocal ERG, 61 local cone ERGs from each eye were derived from the central visual field. The dark-adapted two-color threshold perimetry using stimuli of 500 nm and 656 nm for rod and cone function was investigated along the horizontal meridian of the visual field. RESULTS: In the multifocal ERG of both patients a macular response was absent. From eccentricity at and anterior to 5 degrees, good multifocal cone activity was recorded. Cone thresholds were markedly diminished in the macula. The rod thresholds were borderline in the father and normal in the son. CONCLUSIONS: Multifocal ERG is a novel technique, very well suited to reveal the topography of cone function. Using two-color threshold perimetry affords an opportunity to differentiate between rod and cone functional defects. Both together helped to establish the diagnosis of macular cone dystrophy in the present family.

Adult↗
PubMed1999

A temporal deficit in juvenile diabetics.

BACKGROUND: In this study we examined the temporal domain of visual function in diabetics without retinopathy by examining wavelength discrimination ability at two exposure durations. The results were compared to those found by heterochromatic brightness matching and anomaloscope matches. METHODS: Wavelength discrimination was performed between 440 and 540 nm at exposure times of 1 s and 0.04 s in eight juvenile diabetic patients without retinopathy. The monochromatic stimuli were presented in Maxwellian view and were set to be equally bright prior to the experiment using heterochromatic brightness matching. In addition, Rayleigh and Moreland anomaloscope matches were performed. The results of the diabetic group were compared to those of an age-matched control group of eight subjects with normal colour vision. RESULTS: Wavelength discrimination showed no difference between the groups for an exposure time of 1 s. With an exposure duration of 0.04 s, however, the diabetics show raised thresholds for the shortest wavelengths tested. In addition, brightness matches were increased at the short wavelengths, and anomaloscope matches showed a decrease in the match range for the Moreland (blue-yellow) equation. CONCLUSION: The results indicate post-receptoral alterations in diabetic patients with no visible changes in their retinae.

Adolescent↗
PubMed1999

Leber's hereditary optic neuropathy: clinical and molecular genetic findings in a patient with a new mutation in the ND6 gene.

BACKGROUND: Leber's hereditary optic neuropathy (LHON) is a maternally inherited ocular disease associated with mutations in the mitochondrial DNA (mtDNA). We describe the clinical and molecular genetic findings in a LHON patient and his family with a new mtDNA mutation at np14568 in the ND6 gene. METHODS: Ophthalmological examination was performed in one affected male and two maternal relatives. Direct sequence analysis of the complete mtDNA protein coding region was initiated in the affected patient. Four unaffected maternal relatives also underwent molecular genetic evaluation. RESULTS: Clinical examination of the affected male showed typical features of LHON. In his unaffected mother slight peripapillary microangiopathy was found. Molecular analysis did not show any of the common LHON mutations. A nucleotide exchange was detected at position 14568 replacing a glycine by serine in the ND6 gene. This mutation was the only new mutation found within the entire protein and tRNA coding region of the patient's mitochondrial genome. This novel mutation was also present in four non-affected maternal family members, but absent in 60 other LHON lineages and 175 unrelated controls. CONCLUSION: The new mutation at nucleotide position 14568 lies in the close vicinity of other LHON-related mutations (np14459, np14484, np14498, np14596) within the evolutionarily most conserved region of the ND6 gene. Since no other mutation was detected throughout the mtDNA coding region and the new alteration was excluded in controls, our clinical and molecular genetic findings suggest that the novel point mutation at np14568 is responsible for LHON in this family.

Adolescent↗
PubMed1999

Development of brightness matching and colour vision deficits in juvenile diabetics.

We studied hue discrimination and brightness matching throughout the spectrum in ten juvenile patients suffering from diabetes mellitus (Type I) with no (eight patients) or mild (two patients) retinopathy. In addition, the FM 100-Hue test was performed. The data were collected once every year over 5 years. Over the 5 years, the diabetics show a continual change in the shape of their brightness matching function. Wavelength discrimination ability remains quite stable with time at the long end of the spectrum but is variable at short wavelengths. FM-100 error scores remain similar over the period tested, at a level slightly higher than that of a control group. Additional experiments show that the sensitivity of the S-cone in the diabetic group is similar to that of controls. The results can be explained by an early relative reduction in the sensitivity of post-receptoral processes in juvenile diabetics.

Adolescent↗
PubMed1999

Can subretinal microphotodiodes successfully replace degenerated photoreceptors?

The idea of implanting microphotodiode arrays as visual prostheses has aroused controversy on its feasibility from the moment it appeared in print. We now present results which basically support the concept of replacing damaged photoreceptors with subretinally implanted stimulation devices. Network activity in degenerated rat retinae could be modulated through local electrical stimulation in vitro. We also investigated the long term stability and biocompatibility of the subretinal implants and their impact on retinal physiology in rats. Ganzfeld electroretinograms and histology showed no significant side effect of subretinal implants on retinal function or the architecture of the inner retina.

Animals↗
PubMed1999

Maturation of intrinsic membrane properties in rat retinal ganglion cells.

In view of the prominent role of voltage-activated conductances in both neuronal differentiation and signal transmission, the present study describes developmental alterations of ion channel properties during the functional maturation of rat RGCs, i.e., between embryonic day 15 when RGCs start to differentiate (E15) and postnatal day 35 (P35) when the retina is fully developed and the animals had already visual input for about 2 weeks. While the sodium system seems to reach maturity already at the end of the second postnatal week, significant alterations in the potassium system were found only from postnatal day 10 on. The functional implications of these alterations are discussed.

Action Potentials↗
PubMed1999

Scanning laser densitometry and color perimetry demonstrate reduced photopigment density and sensitivity in two patients with retinal degeneration.

PURPOSE: To test the feasibility of scanning laser densitometry with a modified Rodenstock scanning laser ophthalmoscope (SLO) to measure the rod and cone photopigment distribution in patients with retinal diseases. METHODS: Scanning laser densitometry was performed using a modified Rodenstock scanning laser ophthalmoscope. The distribution of the photopigments was calculated from dark adapted and bleached images taken with the 514 nm laser of the SLO. This wavelength is absorbed by rod and cone photopigments. Discrimination is possible due to their different spatial distribution. Additionally, to measure retinal sensitivity profiles, dark adapted two color static perimetry with a Tübinger manual perimeter was performed along the horizontal meridian with 1 degree spacing. RESULTS: A patient with retinitis pigmentosa had slightly reduced photopigment density within the central +/- 5 degrees but no detectable photopigment for eccentricities beyond 5 degrees. A patient with cone dystrophy had nearly normal pigment density beyond +/- 5 degrees, but considerably reduced photopigment density within the central +/- 5 degrees. Within the central +/- 5 degrees, the patient with retinitis pigmentosa had normal sensitivity for the red stimulus and reduced sensitivity for the green stimulus. There was no measurable function beyond 7 degrees. The patient with cone dystrophy had normal sensitivity for the green stimulus outside the foveal center and reduced sensitivity for the red stimulus at the foveal center. The results of color perimetry for this patient with a central scotoma were probably influenced by eccentric fixation. CONCLUSION: Scanning laser densitometry with a modified Rodenstock SLO is a useful method to assess the human photopigment distribution. Densitometry results were confirmed by dark adapted two color static perimetry. Photopigment distribution and retinal sensitivity profiles can be measured with high spatial resolution. This may help to measure exactly the temporal development of retinal diseases and to test the success of different therapeutic treatments. Both methods have limitations at the present state of development. However, some of these limitations can be overcome by further improving the instruments.

Adult↗
PubMed1999

Long-term survival of retinal cell cultures on retinal implant materials.

The aim of the present study was to evaluate cell adhesion and cell survival of mammalian retinal neurons on different materials used for the production of multi-photodiode arrays (MPDAs) intended for implantation in the subretinal space of patients suffering from progressive photoreceptor cell loss. The survival rates of different types of retinal neurons and glia cells were monitored by conventional histochemical techniques and immunocytochemistry up to 4 weeks. Whereas most of the materials tested showed good biocompatibility, cell survival of retinal glia and neurons was markedly reduced on titanium nitride (TiN), especially for culturing periods longer than 2 weeks. The effect was not mediated by diffusible factors released from TiN material. In conclusion, most of the materials tested in this study are suitable for the production of functional MPDAs and no complications are to be expected from long-term implantations of them in the subretinal space.

Animals↗
PubMed1999

[Clinical significance of objective vision assessment using visually evoked cortical potentials induced by rapid pattern sequences of different spatial frequency].

BACKGROUND: In patients where reliable subjective assessment of visual acuity is impossible, further diagnostics should be enhanced by an objective method. PATIENTS AND METHODS: A group of 34 patients was examined by objective assessment of visual acuity using visual evoked potentials (VEP) as described by Hajek and Zrenner in 1988. The presentation of five checkerboards with different spatial frequency in repetitive sequences on a TV-monitor elicits a series of transient visual evoked potentials. Shape and amplitude of each wavelet depends on check size and directly reflect a spatial tuning function with a low- and high-frequency cut-off. This amplitude is described by a polynomial fit (2nd order). The function's intersection with the x-axis at higher spatial frequencies leads to an estimation of the visual acuity. RESULT: This result is compared to the subjectively determined visual acuity. In the majority of the presented cases the suspected malingering was confirmed. CONCLUSION: Patients with suspected malingering represent the primary indication of the described method.

Adult↗
PubMed1999

Biochemical but not clinical vitamin A deficiency results from mutations in the gene for retinol binding protein.

BACKGROUND: Two German sisters aged 14 and 17 y were admitted to the Tübingen eye hospital with a history of night blindness. In both siblings, plasma retinol binding protein (RBP) concentrations were below the limit of detection (<0.6 micromol/L) and plasma retinol concentrations were extremely low (0.19 micromol/L). Interestingly, intestinal absorption of retinyl esters was normal. In addition, other factors associated with low retinol concentrations (eg, low plasma transthyretin or zinc concentrations or mutations in the transthyretin gene) were not present. Neither sibling had a history of systemic disease. OBJECTIVE: Our aim was to investigate the cause of the retinol deficiency in these 2 siblings. DESIGN: The 2 siblings and their mother were examined clinically, including administration of the relative-dose-response test, DNA sequencing of the RBP gene, and routine laboratory testing. RESULTS: Genomic DNA sequence analysis revealed 2 point mutations in the RBP gene: a T-to-A substitution at nucleotide 1282 of exon 3 and a G-to-A substitution at nucleotide 1549 of exon 4. These mutations resulted in amino acid substitutions of asparagine for isoleucine at position 41 (Ile41-->Asn) and of aspartate for glycine at position 74 (Gly74-->Asp). Sequence analysis of cloned polymerase chain reaction products spanning exons 3 and 4 showed that these mutations were localized on different alleles. The genetic defect induced severe biochemical vitamin A deficiency but only mild clinical symptoms (night blindness and a modest retinal dystrophy without effects on growth). CONCLUSIONS: We conclude that the cellular supply of vitamin A to target tissues might be bypassed in these siblings via circulating retinyl esters, beta-carotene, or retinoic acid, thereby maintaining the health of peripheral tissues.

Adolescent↗
PubMed1999

Preretinopic changes in the colour vision of juvenile diabetics.

AIMS: To examine the colour vision of juvenile patients suffering from diabetes mellitus without retinopathy in relation to metabolic and ophthalmic state. METHODS: Metameric matches, both Rayleigh (red/green) and Moreland (blue/green) were used to test the colour vision yearly of 10 juvenile patients. The patients were monitored over 4 years, and during the final year, their blood glucose level was determined directly after testing colour vision. An ophthalmic examination was performed on the day of colour vision testing and blood and urine were analysed regularly throughout the 4 years. Their results are compared with an aged matched control group of 20 subjects, seven of whom were retested after 9-16 months. RESULTS: After 4 years, the colour vision results show an enlarged matching range for the Moreland match, as well as a smaller increase in the matching range for the Rayleigh match. No significant correlation was found between blood glucose at the time of testing and any of the variables measured. CONCLUSION: The pattern of colour vision deficits in metameric matching shown by juvenile diabetics is consistent with postreceptoral alterations of the inner retina, at this preretinopic stage of disease. Duration of diabetes is correlated with both colour vision changes and morphological alteration of the retina.

Adolescent↗
PubMed1999

Direct visual resolution of gene copy number in the human photopigment gene array.

PURPOSE: To visualize by direct fluorescent in situ hybridization the entire human visual pigment gene array on single X-chromosome fibers and to compare the results with values obtained by other molecular techniques. METHODS: The size of the opsin gene array on the X-chromosome in eight male subjects was investigated by (i) direct visual in situ hybridization (DIRVISH) on elongated DNA fibers: (ii) quantitation of genomic restriction fragments after Southern blot hybridization; (iii) quantitation of restriction fragment length polymorphism after PCR amplification (PCR/RFLP), and (iv) sizing of NotI fragments by pulsed field gel electrophoresis and Southern blot detection. Each male subject's color vision was assessed by Rayleigh matches on a Nagel Type 1 anomaloscope. RESULTS: The number of genes resolved by the DIRVISH protocol, which ranges from 1 to 6, agrees exactly with the gene array sizes obtained in the same male subjects from pulsed field gel electrophoresis, but differs from the estimates derived from the commonly used indirect Southern blot hybridization and PCR/RFLP quantitation methods. In particular, the PCR/RFLP method overestimates the copy number in all but the smallest arrays. CONCLUSIONS: Visualization of the X-chromosome opsin gene array by DIRVISH provides a new, direct method for obtaining exact copy numbers and helps to resolve the controversy about the range and the average visual pigment gene number in the human population in favor of smaller average array sizes.

Blotting, Southern↗
PubMed1999

Phenotype in retinol deficiency due to a hereditary defect in retinol binding protein synthesis.

PURPOSE: To describe the phenotype caused by a retinol deficiency in a family with compound heterozygous missense mutations (Ile41Asn and Gly75Asp) in the gene for serum retinol binding protein (RBP). METHODS: The two affected sisters, 17 (BR) and 13 (MR) years old, were examined clinically and with perimetry, color vision tests, dark adaptometry, rod- and cone-isolated electroretinograms (ERGs), multifocal ERGs, electrooculograms (EOGs), and laboratory tests. RESULTS: There were no complaints besides night vision problems and no history of systemic disease. Visual acuity was reduced to 20/40 (BR) and 20/25 (MR). Anterior segments were normal except for a discrete iris coloboma. Both patients showed a typical "fundus xerophthalmicus," featuring a progressed atrophy of the retinal pigment epithelium. Dark adaptation thresholds were elevated. In the scotopic ERG, only reduced mixed responses were recordable. The photopic ERG was reduced in BR and normal in MR; implicit times were highly (BR) to slightly (MR) elevated. There was no (BR) to little (MR) light reaction in the EOG. All-trans retinol levels were 0.19 microM and 0.18 microM (normal range, 0.7-1.5 microM) for BR and MR, respectively, and did not increase in a dose-response test. RBP was below detection threshold, and retinyl esters were normal. CONCLUSIONS: Both affected siblings had no detectable serum RBP, one sixth of normal retinol levels, and normal retinyl esters. The retinal pigment epithelium was severely affected, but besides acne there were no changes to other organs. This gives evidence for an alternative tissue source of vitamin A, presumably retinyl esters from chylomicron remnants. The normal retinol levels in the tear fluid explain the lack of xerophthalmia. However, considering the role of RBP in the tear fluid and, during development, in the yolk sac there is also evidence that there are organ-specific RBP forms not affected by the genetic defect.

Adolescent↗
PubMed1998

Human rod monochromacy: linkage analysis and mapping of a cone photoreceptor expressed candidate gene on chromosome 2q11.

We have performed linkage analysis in eight families with rod monochromacy, an autosomal recessively inherited condition with complete color blindness. Significant linkage was found with markers located at the pericentromeric region of chromosome 2. A maximum lod score of 5.36 was obtained for marker D2S2333 at theta = 0.00. Mapping of meiotic breakpoints localized the disease gene between markers D2S2187 and D2S2229. Homozygosity for a number of subsequent markers indicating identity by descent was found in two families and provides evidence for a further refinement of the locus proximal to D2S373. This defines an interval of approximately 3 cM covering the ACHM2 locus for rod monochromacy. Radiation hybrid mapping of the CNGA3 gene encoding the alpha-subunit of the cGMP gated cation channel in human cone photoreceptors resulted in a maximum lod score of 16.1 with marker D2S2311 combined with a calculated physical distance of 6.19cR10,000. Screening of the CEPH YAC library and subsequent STS mapping indicated the physical order cen-D2S2222-D2S2175-(D2S2187/D2S2311)-qtel ofmarkers on 2q11 and showed that the CNGA3 gene maps most closely to D2S2187 and D2S2311. These data indicate that the CNGA3 gene maps within the critical interval of the ACHM2 locus for rod monochromacy and thus is a candidate gene for this disease.

Chromosome Breakage↗