Architecture of a Bench-Type Carbonate Lake Margin and Its Relation to Fluvially Dominated Deltas, Las Minas Basin, Upper Miocene, Spain

The Upper Miocene stratigraphic succession of the Las Minas Basin, located at the external zone of the Betic Chain in SE Spain, preserves several examples of lake carbonate bench deposits. Excellent exposures of the carbonate benches allow detailed observation of the architecture of these sediments and provide new insights for the ‘‘steep-gradient bench margin–low energy’’ model proposed by Platt and Wright (1991). The lake carbonate benches developed in close association with fluvially dominated shallow deltas that exhibit typical Gilbert-type profiles. The delta sequences comprise bottomset prodelta marl facies, distal to proximal foreset facies, deposited mainly in a delta-front environment, and topset facies, the latter reflecting both subaqueous delta-front and subaerial delta-plain environments. The development of the carbonate benches was constrained by the convexupward morphology of the deltaic deposits, which led to the available accommodation space for the growth of the steep-gradient platforms. The benches display a progradational pattern characterized by sigmoid-oblique internal geometries and offlap upper boundary relationships, which suggests that the carbonate benches developed under slow though continuous lake-level rise. Both the dimensions of the benches and the dominant carbonate components (i.e., encrusted charophyte stems and calcified cyanobaterial remains), allow comparisons with the progradational marl benches recognized in modern temperate hardwater lakes. Accordingly, the case study presented here provides a good ancient sedimentary analog for low-energy lake carbonate benches. Moreover, the evolutionary trend inferred from the fossil example offers new insights into the depositional conditions of this type of sediment and allows recognition of the transitional pattern from bench to ramp carbonate lake margins.

Phenomenological model of visual acuity

We propose in this work a model for describing visual acuity (VV) as a function of defocus and pupil diameter. Although the model is mainly based on geometrical optics, it also incorporates nongeometrical effects phenomenologically. Compared to similar visual acuity models, the proposed one considers the effect of astigmatism and the variability of best corrected VV among individuals; it also takes into account the accommodation and the “tolerance to defocus,” the latter through a phenomenological parameter. We have fitted the model to the VV data provided in the works of Holladay et al. and Peters, showing the ability of this model to accurately describe the variation of VV against blur and pupil diameter. We have also performed a comparison between the proposed model and others previously published in the literature. The model is mainly intended for use in the design of ophthalmic compensations, but it can also be useful in other fields such as visual ergonomics, design of visual tests, and optical instrumentation.

Accommodative changes produced in response to overnight orthokeratology

Background To evaluate short-term (3 months) and long-term (3 years) accommodative changes produced by overnight orthokeratology (OK). Methods A prospective, longitudinal study on young adult subjects with low to moderate myopia was carried out. A total of 93 patients took part in the study. Out of these, 72 were enrolled into the short-term follow-up: 21 were on a control group, 26 on a Paragon CRT contact lenses group, and 25 on a Seefree contact lenses group. The other 21 patients were old CRT wearers on long-term follow-up. Accommodative function was assessed by means of negative and positive relative accommodation (NRA / PRA), monocular accommodative amplitude (MAA), accommodative lag, and monocular accommodative facility (MAF). These values were compared among the three short-term groups at the follow-up visit. The long- and short-term follow-up data was compared among the CRT groups. Results Subjective accommodative results did not suffer any statistically significant changes in any of the accommodative tests for any of the short-term groups when compared to baseline. There were no statistically significant differences between the three short-term groups at the follow-up visit. When comparing the short- and long-term groups, only the NRA showed a significant difference (p = 0.0006) among all the accommodation tests. Conclusions OK does not induce changes in the ocular accommodative function for either short-term or long-term periods.