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Biomedical subjects

E Zrenner

Publications and source records attributed to E Zrenner.

At least 19 recordsLinked to original sources
PubMed1999

Selective loss of cone function in mice lacking the cyclic nucleotide-gated channel CNG3.

Two types of photoreceptors, rods and cones, coexist in the vertebrate retina. An in-depth analysis of the retinal circuitry that transmits rod and cone signals has been hampered by the presence of intimate physical and functional connections between rod and cone pathways. By deleting the cyclic nucleotide-gated channel CNG3 we have generated a mouse lacking any cone-mediated photoresponse. In contrast, the rod pathway is completely intact in CNG3-deficient mice. The functional loss of cone function correlates with a progressive degeneration of cone photoreceptors but not of other retinal cell types. CNG3-deficient mice provide an animal model to dissect unequivocally the contribution of rod and cone pathways for normal retinal function.

Animals↗
PubMed1999

Twelve novel myosin VIIA mutations in 34 patients with Usher syndrome type I: confirmation of genetic heterogeneity.

Usher syndrome is a heterogeneous autosomal recessive trait and the most common cause of hereditary deaf-blindness. Usher syndrome type I (USH1) is characterised by profound congenital sensorineural hearing loss, vestibular dysfunction, and prepubertal onset of retinitis pigmentosa. Of the at least six different loci for USH1, USH1B maps on chromosome 11q13, and the MYO7A gene has been shown to be defective in USH1B. MYO7A encodes myosin VIIA, an unconventional myosin, and it consists of 48 coding exons. In this study, MYO7A was analysed in 34 unrelated Usher type I patients by single-strand conformation polymorphism analysis and direct sequencing. We identified a total of 12 novel and unique mutations, all single base changes. In addition, we found a previously reported nonsense mutation (C31X) on nine alleles of a total of six patients from Denmark.

Chromosome Mapping↗
PubMed1999

[White-noise field campimetry in HIV+ patients].

PURPOSE: The first morphological changes in eyes with HIV infection are microvascular disease of the retina with cotton-wool spots and microaneurysms. The study was performed to find out if evidence of disturbances of ocular microcirculation can be established by non-invasive methods. PATIENTS AND METHODS: Twenty-seven patients with HIV infection and without opportunistic infections underwent thorough ophthalmologic examination with threshold-oriented, suprathreshold perimetry (TAP 2000 ct, Oculus) and white-noise field campimetry (TEC, Oculus). RESULTS: Visual field examination was normal in 23 out of 27 patients (85%), whereas 4 patients showed relative field defects in at least one eye. In white-noise field campimetry 13 out of 23 perimetrically unaffected patients (56%) perceived scotomas in one or both eyes. These scotomas were not stable. Three of 4 patients with relative scotomas in the visual field had cotton-wool spots in the retina and showed a stable scotoma in campimetry. Visual acuity, IOP, and cup/disc ratio were within normal ranges. CONCLUSION: White-noise field campimetry complements the standard examination of patients with HIV and might be capable of indicating disturbances of ocular microcirculation by a non-invasive method before morphological changes in the retina can be seen.

Adult↗
PubMed1999

Evaluation of the Night Vision Spectacles on patients with impaired night vision.

BACKGROUND: The Night Vision Spectacles (NiViS) were developed by a consortium of European companies to assist individuals who suffer from impaired night vision. They consist of a head-mounted video camera (input) and binocular displays (output) connected to a portable computer processor, which uses an algorithm to enhance the luminance and contrast of the video image. METHODS: Eighteen patients with impaired night vision were tested, including those with retinitis pigmentosa (7), Usher syndrome (2), fundus albipunctatus (1) and complete (4) and incomplete (4) congenital stationary night blindness. Normal trichromats (3) and typical, complete achromats (2) acted as controls. A battery of tests assessed: visual acuity at 5 m (projection unit) and 1 m (chart) and at high and low contrasts; contrast sensitivity; absolute and increment threshold; the influence of glare; contrast motion detection; and hand-eye performance. The tests were performed, with and without the NiViS, at three adaptation levels: low scotopic (10(-3) cd/m2), high scotopic (10(-2) cd/m2) and mesopic (10(-1) cd/m2). RESULTS: At the low and high scotopic levels, the majority of patients showed improved performance on the visual acuity, contrast sensitivity and motion contrast tests with the NiViS. At the mesopic level, the advantage with the NiViS was greatly reduced, but still present for contrast sensitivity. CONCLUSION: Patients with impaired night vision can benefit from the NiViS when performing tasks involving contrast and motion perception. Those with normal visual fields and retaining good photopic vision will benefit more than those with constricted visual fields and impaired cone vision. Recommendations regarding desirable improvements of the NiViS and suitability for the individual patient are given.

Adolescent↗
PubMed1999

Comparative study of visual, auditory, and olfactory function in Usher syndrome.

BACKGROUND: Usher syndrome is a genotypically and phenotypically heterogeneous group of autosomal recessive diseases featuring retinitis pigmentosa (RP) and sensorineural hearing loss. A general ciliary dysfunction has been suspected following reports of a mutated cytoskeletal protein (myosin VIIA) in type IB, and preliminary data has suggested an olfactory deficit. The purpose of this study was to quantitatively assess olfactory function in Usher syndrome patients and to search for a correlation between the degree of impairment of the three sensory systems as indication of an underlying ciliary defect. METHODS: 39 patients with Usher syndrome (8 type I, 31 type II) were examined. The ophthalmologic protocol included patient history, visual acuity, eye morphology, Goldmann perimetry, and electroretinography. The ENT protocol included a thorough examination, speech-recognition test, pure-tone audiometry and an olfactory function test. RESULTS: In both groups, visual acuity was typically 20/40, the remaining visual field area was small, and the ERG responses were low to non-detectable. Average hearing loss was 100% in type I and 40% in type II. Olfactory thresholds were normal [median 9.7 (I) and 8.5 (II) vs. 8.5 in the control group]. There were multiple significant correlations between parameters of the same organ, but no relationship between parameters of different sensory systems. CONCLUSION: Almost all Usher syndrome patients in this study had an advanced form of RP. In contrast, auditory function differed considerably between type I and type II. An impairment of the olfactory system could not be detected, and there was no correlation between parameters representing visual function, hearing ability, and olfactory sense.

Adult↗
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

[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↗