Color blindness

Color blindness or color vision deficiency (CVD) is the decreased ability to see color or differences in color. It can impair tasks such as selecting ripe fruit, choosing clothing, and reading traffic lights. Color blindness may make some academic activities more difficult. However, issues are generally minor, and people with colorblindness automatically develop adaptations and coping mechanisms. People with total color blindness (achromatopsia) may also be uncomfortable in bright environments and have decreased visual acuity. The most common cause of color blindness is an inherited problem or variation in the functionality of one or more of the three classes of cone cells in the retina, which mediate color vision. The most common form is caused by a genetic disorder called congenital red–green color blindness. Males are more likely to be color blind than females, becaus

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Optische Augenlängenmessung für klinische Anwendungen

Beate Möller

Cataract is the leading cause of blindness worldwide. The clouding of the human eye lens is called "Grauer Star" in German. In the industrialized countries this process of increased blindness is corrected by the surgical removal of the clouded lens and its replacement by a plastic lens (intraocular lens, IOL). Cataract surgery is the most frequent surgery worldwide. In Europe more than two million operations are performed annually. For the selection of an optimum replacement the refractive power of the lens is calculated from the radius of curvature of the cornea, the length of the eye and the anterior chamber depth. Therefore these data have to be measured before every surgery. Until now the length of the eye was measured exclusively by ultrasound in the clinical praxis. For this procedure the sound transducer has to be placed directly or via a water funnel onto the cornea. It was the aim of the work presented in this thesis to lay the framework for introducing into the clinical praxis a contact free optical length measurement of the eye. The basic parameters for the measurement were determined. Starting from the state of the art new solutions were found, implemented in a laboratory device, and tested clinically. A two-beam interferometer with light of short coherence length that had been developed at the University Vienna was analyzed and compared with the one-beam technique. Neglecting practical limitations due to the optical arrangement and assuming shot-noise limited detection the one-beam technique allows the measurement of reflected light that is a factor of two lower compared to the two-beam technique. From the point of view of detection both techniques are therefore equivalent. The advantage of the two-beam technique is its independence from the eye movement. Until now the two-beam technique utilizes for detection only 1 over 400 of the light reflected from the retina and 1 over 2500 to 1 over 4000 of the light reflected from the cornea. This causes the dynamic range to drop by 26 dB. Furthermore the noise of the electronics (excess noise) comes into play. In this work a novel concept for the optical configuration in the two-beam interferometer is presented. By using a diffractive lens cornea and retina are imaged simultaneously onto the detector and the losses of the light from the retina are minimized. The cornea is imaged with an efficiency of 5.6 per cent. In order to minimize the requirements on the patient the measuring time was shortened to 1 s. Therefore the scan speed was increased by a factor of four compared to the state of the art. In the laboratory device it fluctuated by 20 per cent. To keep the detection narrow band it was necessary to implement a signal processing that is largely independent of the scan speed. By using a synchronous demodulation of two 90 degrees phase-shifted channels that are added as vector quantities a filter with self-adjusting center frequency was created. Its bandwidth is 4 kHz with signal frequencies between 30 kHz and 90 kHz. This concept was realized as a compact slit-lamp head and tested clinically. A shot-noise limited detection with a dynamic range of 105 dB was achieved (input power 200 µW). On the healthy eye the signal-to-noise ratio was limited by the digitization range of 8 bit. On the eye with cataract the measuring was not limited by the degree of clouding any more. The optical lengths were determined along the line of sight. They agreed with the post operative results. In some cases refractive errors of more than 2 dpt would have been avoidable by determining the IOL from the measurement of the optical length of the eye. This technique allows a comfortable, contact free optical eye length measurement that works correctly in 95 per cent of all eyes with cataract. Additionally smaller post operative refractive errors can be achieved as compared with traditional techniques. These results were the basis for the development of the IOL-Master – a novel device for the cataract treatment – at the Carl Zeiss Jena GmbH. With this device all biometric data can be measured in a non-contact fashion and intraocular lenses can be calculated and selected.

EPFL2001

Clinical and genetic investigation of a large Tunisian family with complete achromatopsia: identification of a new nonsense mutation in GNAT2 gene

Farah Ouechtati

Complete achromatopsia is a rare autosomal recessive disease associated with CNGA3, CNGB3, GNAT2 and PDE6C mutations. This retinal disorder is characterized by complete loss of color discrimination due to the absence or alteration of the cones function. The purpose of the present study was the clinical and the genetic characterization of achromatopsia in a large consanguineous Tunisian family. Ophthalmic evaluation included a full clinical examination, color vision testing and electroretinography. Linkage analysis using microsatellite markers flanking CNGA3, CNGB3, GNAT2 and PDE6C genes was performed. Mutations were screened by direct sequencing. A total of 12 individuals were diagnosed with congenital complete achromatopsia. They are members of six nuclear consanguineous families belonging to the same large consanguineous family. Linkage analysis revealed linkage to GNAT2. Mutational screening of GNAT2 revealed three intronic variations c.119-69G > C, c.161+66A > T and c.875 31G > C that co-segregated with a novel mutation p.R313X. An identical GNAT2 haplotype segregating with this mutation was identified, indicating a founder mutation. All patients were homozygous for the p.R313X mutation. This is the first report of the clinical and genetic investigation of complete achromatopsia in North Africa and the largest family with recessive achromatopsia involving GNAT2; thus, providing a unique opportunity for genotype-phenotype correlation for this extremely rare condition. Journal of Human Genetics (2011) 56, 22-28; doi:10.1038/jhg.2010.128; published online 25 November 2010

2011

Development of Visual Memory Capacity Following Early-Onset and Extended Blindness

Marin Vogelsang, Lukas Vogelsang

It is unknown whether visual memory capacity can develop if onset of pattern vision is delayed for several years following birth. We had an opportunity to address this question through our work with an unusual population of 12 congenitally blind individuals ranging in age from 8 to 22 years. After providing them with sight surgery, we longitudinally evaluated their visual memory capacity using an image-memorization task. Our findings revealed poor visual memory capacity soon after surgery but significant improvement in subsequent months. Although there may be limits to this improvement, performance 1 year after surgery was found to be comparable with that of control participants with matched visual acuity. These findings provide evidence for plasticity of visual memory mechanisms into late childhood but do not rule out vulnerability to early deprivation. Our computational simulations suggest that a potential mechanism to account for changes in memory performance may be progressive representational elaboration in image encoding.

SAGE PUBLICATIONS INC2022

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Color

Color (American English) or colour (Commonwealth English) is the visual perception based on the electromagnetic spectrum. Though color is not an inherent property of matter, color perception is rela

Cone cell

Cone cells, or cones, are photoreceptor cells in the retinas of vertebrates' eyes, including the human eye. They respond differently to light of different wavelengths, and the combination of their res

Primary color

A set of primary colors or primary colours (see spelling differences) consists of colorants or colored lights that can be mixed in varying amounts to produce a gamut of colors. This is the essential