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We analyzed the structural and functional relationship between lens sutures and lens optical quality (focal length variability) by correlative scanning electron microscopy (SEM) and laser scan analysis. Twenty-two rabbit lenses (8 pigmented and 14 albino) were used in this study. Lenses were initially scanned by a low-power helium-neon laser beam that was passed either at an acute angle to a lens suture or along a lens suture. The results of laser scan analysis with the incident beam passed at an acute angle to a lens suture showed that generally, rabbit lenses were well corrected for spherical aberration. Subsequent SEM analysis showed that areas of lenses scanned that produced the least amount of focal variability were characterized by uniform fiber cells arranged in parallel, radial cell columns. In contrast, the results of laser scan analysis with the incident beam passed along a lens suture showed that there was significant focal length variability, i.e., spherical aberration at the lens sutures. Subsequent SEM analysis showed that the areas of lenses scanned that produced the greatest amounts of focal variability (lens sutures) were characterized by nonuniform fiber cell ends arranged as erratic suture branches in single growth shells and collectively as erratic suture planes formed between growth shells extending from the embryonic nucleus to the lens periphery. Furthermore, the amount of focal variability was directly proportional to the degree of structural disorder at the lens sutures. This is the first study to unequivocally show that the relationship between lens optical quality and specific parameters of lens morphology (lens sutures) can be quantified. These findings may help to elucidate the pathologic changes that lead to presbyopia and cortical cataractogenesis because these lenses are characterized by asymmetrical suture patterns and planes.
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PMID:Lens optical quality is a direct function of lens sutural architecture. 205 2

Horizontal binocular eye movements of three subjects were recorded with the scleral sensor coil--revolving magnetic field technique during voluntary shifts of gaze between pairs of stationary, real, continuously visible targets. The target pairs were located either along the median plane (requiring symmetrical vergence), or on either side of the median plane (requiring asymmetrical vergence). Symmetrical vergence was primarily smooth, but it was often assisted by small, disjunctive saccades. Peak vergence speeds were very high; they increased from about 50 degrees s-1 for vergence changes of 5 degrees to between 150 and 200 degrees s-1 for vergence changes of 34 degrees. Differences between convergence and divergence were idiosyncratic. Asymmetrical vergence, requiring a vergence of 11 degrees combined with a version of 45 degrees, was largely saccadic. Unequal saccades mediated virtually all (95%) of the vergence required in the divergent direction, whereas 75% of the vergence required in the convergent direction was mediated by unequal saccades, with the remaining convergence mediated by smooth vergence, following completion of the saccades. Peak divergence speeds during these saccades were very high (180 degrees s-1 for a change of vergence of 11 degrees); much faster than the smooth, symmetrical vergence change of comparable size (14 degrees). Peak convergent saccadic speeds were about 20% lower. This difference in peak speed was caused by an initial, transient divergence, observed at the beginning of all horizontal saccades. The waveform of disjunctive saccades did not have the same shape as the waveform of conjugate saccades of similar size. The smaller saccade of the disjunctive pair was stretched out in time so as to have the same duration as its larger, companion saccade. These results permitted the conclusion that the subsystems controlling saccades and vergence are not independent. Vergence responses were relatively slow and incomplete with monocular viewing, which excluded disparity as a cue. Monocularly stimulated vergence decreased as a function of the increasing presbyopia of our three subjects. Subjects were able to generate some vergence in darkness towards previously seen and remembered targets. Such responses, however, were slow, irregular and evanescent. In conclusion, vergence shifts between targets, which provided all natural cues to distance, were fast and accurate; they appeared adequate to provide effective binocular vision under natural conditions. This result could not have been expected on the basis of previous observations, all of which had been made with severely reduced cues to depth.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Ocular vergence under natural conditions. II. Gaze shifts between real targets differing in distance and direction. 256 20