PubMed · 4905908
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M J White. 1969. Laterality differences in perception: a review.. https://doi.org/10.1037/h0028343
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The microscopic anatomy of the eye of the Weddell seal was studied with various light and electron microscopic methods with a view to correlating morphological findings with the biology of this seal which is adapted to the extremes of the Antarctic environment and to extreme diving excursions into the lightless depths of the sea. In the retina an area centralis was found but no fovea centralis. The densely packed photoreceptors consist exclusively of highly differentiated rods, which in primates detect light at low intensity but have rather poor image discrimination. The ganglion cells are relatively scarce, suggesting a high degree of convergence of the light-sensitive cells on the ganglion cells. The pigment epithelium is almost devoid of pigment granules. The extensive tapetum lucidum is about 400-500 microm thick and is composed of about 30 layers of specialized cells. The cornea is 650 (center) to 800-900 (periphery) microm thick. Its structure and glycosaminoglycan histochemistry correspond to that of other mammals. The iridocorneal angle is unusually deep and pervaded by an elaborate trabecular meshwork, which together with a complex canal of Schlemm can be correlated with the ability to absorb large amounts of fluid. The ciliary muscle and its antagonist, the membrane of Bruch, are poorly developed, suggesting relatively poor abilities of accommodation. The combination of a well-developed tapetum lucidum, an unpigmented pigment epithelium, well-developed rods, and a high number of rods converging on only few ganglion cells is obviously an adaptation to an extreme light sensitivity, enabling the animals to make use of the little light available in the deep sea.
PROBLEM: To date, approaches to restore accommodation following cataract surgery have been based on the principle of a liquid or solid implant that moves within the capsular bag and thereby changes the optical characteristics of the eye. However, these implants have been associated with shrinking and fibrosis of the capsular bag, a problem that will not be solved in the foreseeable future. APPROACH: If accommodation is effected by shifting the whole capsule including its contents on the optical axis, capsular fibrosis will virtually no longer play a role. In order to execute this shift via the neuronal feedback mechanisms of the ciliary muscle in a controlled way, radial zonular forces or movements must be transformed into axial ones, which is possible by means of tiny permanent magnets. This paper describes the basic aspects of such an implant. The dependence of accommodation on all relevant parameters is quantified in a computer simulation. CONCLUSION: The implant described appears to be practicable with justifiable technical and surgical efforts.
A new technique, the scleral expansion band procedure, has been developed for the surgical reversal of presbyopia. An understanding of demonstrable clinical effects of the scleral expansion band procedure, based on Schachar's theory, requires a revision of historically held views concerning the mechanism of accommodation.