Negative Spherical Lenses Research Articles

Catadioptric Optical System Design of 15-Magnitude Star Sensor with Large Entrance Pupil Diameter.

The optical system is one of the core components for star sensors, whose imaging quality directly influences the performance of star sensors for star detection, thereby determining the attitude control accuracy of spacecrafts. Here, we report a new type of optical system with a catadioptric structure and a large entrance pupil diameter for a 15-magnitude star sensor. It consists of an improved Cassegrain system (R-C system), an aperture correction spherical lens group and a field of view correction spherical lens group. By embedding the secondary mirror of the R-C system into the output surface of the negative spherical lens of the aperture correction spherical lens group, the blocking of incident light is eliminated from the secondary mirror holder. After the structure optimization, the catadioptric optical system (COS) had a spectral range of 450 nm–950 nm, an entrance pupil diameter of 250 mm, a half-diagonal field of view of 1.4° and a focal length of 390 mm. By using theoretical calculations and experimental measurements, it was verified that the COS, with the ability to correct astigmatism, lateral color and distortion, can fulfill the detection of 15-magnitude dark stars.

АComparative analysis of the magnitude of the distance and lens-induced objective accommodative response in patients with different refraction

To study the magnitude of objective accommodative response (OAR) with account to the method of image defocusing. The latter can be realized by bringing the object nearer to the eye or by adding a minus lens in front of the viewer. We examined 63 patients (126 eyes) with different refraction aged from 7 to 31 years. All patients underwent a series of OAR measurements on WR-5100K Grand Seiko Binocular Open-Field Autorefkeratometer under different conditions, including negative spherical lenses of -3.0 D and -5.0 D, test optotypes corresponding to visual acuity of 0.2 and 0.7 and presented at a distance of 5 m, and a set of variably sized optotypes presented at a distance of 33 cm and 20 cm. A disparity was found between the magnitude of accommodative responses evoked through different means: placing a negative lens in front of the viewer while he/she looks into the distance or bringing the object closer to the eye. In almost all cases lens-induced responses were less pronounced than distance-induced. In all myopic children, accommodative lag was longer at near than at distance. Generally, in all groups, OAR to distant objects as well as responses to a 3.0 D accommodative task at near did not depend on the size of the object. There was an insignificant and statistically unreliable difference for objects placed 20 cm away (5.0 D accommodative task): OAR to a smaller font was stronger than that to a larger one. In children and adults with emmetropia, hyperopic children, and myopic adults, longer accommodative lags were characteristic of lens-induced responses. In children with myopia, longer lags were observed at near. Moreover, at near, OAR to a smaller font was stronger than that to a larger one.

Study on accommodation by autorefraction and dynamic refraction in children

PurposeChildhood accommodation interferes with accurate diagnosis of the latent refractive errors. Dynamic retinoscopy offers accurate measurements of accommodative response, while an autorefractometer can predict the accommodative system activation in children. A correlation of the accommodative effort with the dynamic refraction has been investigated in emmetropic children, before and after cycloplegia. MethodsA prospective clinical study of accommodative effort in 149 emmetropic children, in the age group 3–16 years, has been conducted using TOPCON AR RM-8000B autorefractor. Dynamic refraction was performed by monocular estimation method before and after cycloplegia, using the retinoscope mirror light as target. Retinoscopic reflex produced ‘with the motion’ was corrected with positive spherical lenses, and that ‘against the motion’ was corrected with negative spherical lenses, to achieve neutralization. ResultsMean accommodative effort measured for 149 children included in the study was −0.63±0.69D and dynamic refraction was −0.07±0.44D before cycloplegia, while the mean was+0.52D after cycloplegia, irrespective of the method used. Autorefractor measured −0.17D of accommodative effort per unit change in dynamic refraction before cycloplegia and +0.90D after cycloplegia. ConclusionsThe performance of TOPCON AR RM-8000B autorefractor was comparable to dynamic retinoscopy. Presence of many children, and in turn, large number of accommodative response data in 11–13 and 14–15 years group is probably linked to prolonged reading/writing. The accuracy and the agreement of the actual accommodative measurements revealed after cycloplegia.

What Drives Adaptive Gait Changes to Acutely Presented Monocular Blur?

To determine whether gait alterations due to monocular spherical lens blur were a safety strategy or driven by lens magnification. Adaptive gait and visual function were measured in 10 older adults (mean age, 74.9 ± 4.8 years) with the participants' optimal refractive correction and when monocularly blurred with ±1.00 DS and ±2.00 DS lens over the dominant eye. Adaptive gait measurements for the lead and trail foot included foot position before the raised surface, toe clearance of the raised surface edge, and foot position on the raised surface. Vision measurements included binocular visual acuity, contrast sensitivity, and stereoacuity. Equal levels of monocular positive and negative spherical lens blur led to very different stepping strategies when negotiating a raised surface. Positive blur lenses led to an increased vertical toe clearance and reduced distance of the lead foot position on the raised surface. Negative lenses led to the opposite of these changes. Findings suggest that step negotiation strategies were driven by the magnification effect provided by the spherical lenses. Steps appeared closer and larger with magnification from positive lenses and further away and smaller with minification from negative lenses and gait was adjusted accordingly. These results suggest that previously reported adaptive gait changes to monocular spherical lens blur were not safety strategies as previously suggested but driven by lens magnification. The significance of these findings in terms of prescribing large refractive changes in frail older patients is discussed.

Stereoscopic acuity with induced refractive errors.

The relation between refractive error and stereoscopic acuity was investigated by measuring stereoacuity with different combinations of positive and negative spherical lenses over the usual refractive correction. A detailed study was performed on two subjects. In general, there was little change in stereoacuity when the added lenses were of equal power. On the other hand, power inequality almost invariably caused a reduction in stereoacuity. A technique is described for detecting a refractive overcorrection by means of a sequence of stereoacuity measurements.

Adaptation to optically reduced size.

Previous investigators have reported some difficulty in obtaining evidence for adaptation to optically reduced size. A study is reported in which a ballistic target-pointing task was used to examine such adaptation. In the first experiment size was reduced either by means of negative spherical lenses, or cylindrical lenses which reduced image size in only one dimension. Both lens types produced a negative aftereffect of adaptation, which increased as a function of lens strength. There was also a tendency for cylindrical lenses to give larger aftereffects. In a second experiment, in which a modified adaptation procedure was used, adaptation to cylindrical distortion was found to be significantly greater than adaptation to equivalent spherical distortion. These data are interpreted with respect to the relative amounts of distance distortion induced by viewing through the different lens types. The third experiment employed a cylindrical lens and a mental rotation procedure to determine whether adaptation in the first two experiments may have been visual or visuomotor in nature. Results indicated that adaptation was not purely visual. It is concluded that it is possible to demonstrate adaptation to size distortion by using an appropriate procedure.