A retinal laser ellipsometer has been developed by coupling a Fourier ellipsometer to a laser scanning system. The instrument has been used to assess the origin and the amount of change in the state of polarization of a laser beam that has double passed the retina around the optic nerve head of postmortemhuman eyes. Eight eyes with no history of glaucoma were studied. At 200 points around the optic nerve head of each eye the Mueller matrices of the retina were examined for the amount of retardation, the orientation of the optic axis, and the amount of dichroism. The degree of polarization preservation of the detected light varied between 50% and 87%. Little dichroism was found, and there was no obvious correlation to the physical arrangement of any retinal structure. However, there was a substantial amount of linear uniaxial birefringence with the optic axis perpendicular to the incident laser beam. Furthermore the calculated optic axis direction showed a strong correlation with the physical orientation of the radial symmetrically arranged retinal nerve fiber axons around the optic nerve head. The local distribution of the corresponding retardation values showed two maxima that coincided with the areas of the thickest retinal nerve fiber layer. These results support the hypothesis that the thickness of the form birefringent retinal nerve fiber layer can be assessed by ellipsometric methods.
The assessment of the condition of the retinal nerve fiber layer plays an important role for the early detection of blinding eye diseases like glaucoma. We describe the application of a scanning laser polarimeter for quantitative measurements of the retinal nerve fiber layer thickness in vivo. The measuring beam of the scanning laser polarimeter is focused on the retina and penetrates the birefringent nerve fiber layer. The retardation of the light double-passing the nerve fiber layer is proportional to its thickness and is measured at 256 by 256 positions within a field of view of 15 by 15 degrees. The measurement time is less than 1 second. During the measurement, the polarization effects of the anterior segment of the human eye are canceled by a cornea polarization compensator. The retinal retardation values are displayed as a color coded map of the retinal nerve fiber layer thickness distribution.
-In order to find out whether a reduction in load-bearing on chicken legs would modify the activity and leg bone tissue, an original suspension device was developed in order to alleviate half of the weight-load on the legs. Thirty-six 5 d-old male meat-type chicks were assigned to 12 groups, each of 3 birds: a control bird (C), a bird equipped with a harness (H) and one equipped with a harness and suspended from a balance (S). The counterweights of the balance reduced the load on the legs by 50%. Behaviour in the birds was recorded twice for a 22-hour period. The birds were slaughtered at 19 d of age. Their legs were then weighed and the humeri, tibiotarsi and femurs were used for computation of length, biomechanical stiffness and composition. Tibiotarsi were also used for histomorphometry. Body weight at 19 d of age was significantly higher in the C birds (642 g vs. 586 g in the H and S groups, P < 0.05). The distance travelled as measured in the second week of the experiment was greater in S birds (338 m per 22 h vs. 246 in the C group and 252 in the H group, P < 0.05). The length of the tibiotarsi and femora was greater in the S birds when corrected for body weight (P < 0.05). Bone stiffness, composition and histological parameters were not significantly different in the 3 groups. We thus concluded that a reduction in load-bearing on the legs of young chicks enhances locomotor activity and longitudinal growth of leg bones. Bone quality was not affected, probably due to the contradictory effects of increased exercise and reduced weight.
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