Differences in macronutrient selections in users and nonusers of an oral contraceptive.

One of the problems inherent in using women in clinical research is the effect that oral contraceptive (OC) use might have on physical indexes. Although weight gain is frequently reported as a side effect of OC use, there is little empirical evidence that such weight gain actually occurs. The current study investigated differences in energy balance [ie, dietary intake, resting energy expenditure (REE), and physical activity] between groups of users and nonusers of OCs. Each group completed a protocol that covered one menstrual cycle and consisted of daily recording of dietary intake, measurement of REE once during each phase of the menstrual cycle, and reporting of physical activity over the entire cycle. Comparisons indicate that there was a marginal interaction (P = 0.06) of OC use with total energy intake, indicating a different pattern of intake for the two groups. There were qualitative between-group differences such that the OC group consumed a greater percentage of energy as fat (P = 0.02) and a lesser percentage of energy as carbohydrate (P = 0.008). No group differences were found in the percentage of energy consumed as protein, but both groups consumed significantly less protein during menses (P = 0.008). There were no significant differences in REE. Both groups of women reported marginally more activity (P = 0.09) during menses than during the luteal phase.

'A treatise on optics' by Giovanni Christoforo Bolantio.

Few accounts have survived detailing the techniques employed for the production of optical glass for astronomical and microscopical instruments during the seventeenth century in Italy; the period during which the art was being developed in the shops of Eustacho Divini and Giuseppe Campani, and other optical instrument-makers. Indeed, few of the tools of the lens-makers have been described in any detail, and few if any have survived. Consequently, the discovery of a hitherto apparently unknown Italian treatise, or what appears to have been notes for a shop manual of the period, is a contribution to present knowledge of lens-making technology even though the identity and region of the author remain unknown.

Improvements on Littmann's method of determining the size of retinal features by fundus photography.

Littmann's formula relating the size of a retinal feature to its measured image size on a telecentric fundus camera film is widely used. It requires only the corneal radius, ametropia, and Littmann's factor q obtained from nomograms or tables. These procedures are here computerized for practitioners' convenience. Basic optical principles are discussed, showing q to be a constant fraction of the theoretical ocular dimension k', the distance from the eye's second principal point to the retina. If the eye's axial length is known, three new methods of determining q become available: (a) simply reducing the axial length by a constant 1.82 mm; (b) constructing a personalized schematic eye, given additional data; (c) ray tracing through this eye to extend calculations to peripheral retinal areas. Results of all these evaluations for 12 subjects of known ocular dimensions are presented for comparison. Method (a), the simplest, is arguably the most reliable. It shows good agreement with Littmann's supplementary procedure when the eye's axial length is known.

Construction of a model eye and its applications.

Construction details are given of a model eye, based on the Bennett and Rabbetts schematic eye. It incorporates a cornea, lens, and spherical fundus. Distilled water filled the anterior and vitreous chambers. By means of a micrometer screw, the vitreous chamber depth can be precisely varied to produce axial ametropia from +11 to -17 D. Readings taken over the greater part of this range with a Topcon Autorefractor RM-A6500 were found to be repeatable and reproducible within +/- 0.25 D. The model eye was used to investigate the relationship between the actual size of a fundus feature and its photographic image in two different fundus cameras. With a Zeiss Oberkochen camera of telecentric design the magnification was found to remain constant whatever the degree of axial ametropia, whereas with a Carl Zeiss Jena camera the magnification varied linearly with ametropia. A technique developed by Littmann for determining the actual size of a retinal feature when using a fundus camera of telecentric design is discussed briefly.

What radius does the conventional keratometer measure?

The reflected mire images used in conventional keratometry suffer from oblique astigmatism, resulting in separated sagittal and tangential image planes. Further complications arise if the cornea is assumed to be aspherical. To investigate the consequential effects on the readings--hitherto largely neglected--ray tracing methods were applied to two hypothetical models. One was representative of modern variable-doubling constructions and the other of the Javal-Schiötz design. Both are seen to require the tangential image plane to be focused. Given a spherical cornea, the measured tangential image height can be converted into an accurate radius reading by means of a linear calibration formula. In the Javal-Schiötz design, a non-linear correction is needed for this. Appropriately calibrated in these ways, each model is shown to give readings extremely close to the sagittal radius of curvature at the point of incidence when applied to corneae of conicoidal form. Extensive numerical results are tabulated and the detailed calculating schemes illustrated by worked examples.

A method of determining the equivalent powers of the eye and its crystalline lens without resort to phakometry.

If the positions of the principal points of the crystalline lens are conjectured, its equivalent power and that of the eye can be calculated as described from ocular dioptrics. The only data required are the subject's refractive error and the results of keratometry and A-scan ultrasonography. The method assumes the profile of the lens to conform to an arbitrary norm. If the unknown lens profile of a given eye differs from this norm, errors will arise. These are shown to be relatively small, and even in extreme cases unlikely to exceed +/- 1.0 D for the lens and +/- 0.5 D for the eye.

An historical review of optometric principles and techniques.

Beginning with the seventeenth century, when the main scientific foundations were laid, an account is given of the development of various clinical techniques for the assessment of visual acuity and ametropia. Both subjective and objective methods of refraction, with associated instrumentation, are reviewed. Among the more recent techniques described are meridional refraction, astigmatic decomposition, and photorefraction. In various fields, some little known contributions of particular interest are brought to light.

Two simple calculating schemes for use in ophthalmic optics--II. Tracing axial pencils through systems including astigmatic surfaces at random axes.

A paraxial computing scheme is described for tracing an axial pencil of rays through any system containing astigmatic surfaces with their axes at random. In conjunction with a scheme for tracing oblique rays (Bennett, 1986) it is applied to a problem in visual optics posed by Keating (1982). This involves determining the spectacle magnification for a schematic eye with three strongly astigmatic surfaces, corrected by a spectacle lens of bi-toroidal form, the axes of all five surfaces being mutually oblique. It is shown that the suggested computing schemes yield very similar results to those found by the matrix methods of Keating. Although only two rays are needed to determine the principal dimensions of the basic retinal image of a circle, further insight into its true shape is obtained from a multiple trace, using a computerized version of the ray tracing scheme.

Two simple calculating schemes for use in ophthalmic optics--I. Tracing oblique rays through systems including astigmatic surfaces.

A ray tracing scheme using paraxial approximations is described to allow oblique rays to be traced through lenses or optical systems in which some or all of the surfaces may be astigmatic, even at different axes. It is based on consideration of the prismatic effects introduced at each surface. A numerical example reveals some lesser known properties of the circle of least confusion of astigmatic pencils.

Perinatal outcome. Similarity and predictive value of antepartum and intrapartum assessment scales.

This study evaluated five risk-screening scales containing antepartum and intrapartum subscales. Two issues were addressed: (1) whether one scale is as good as another in screening obstetric patients for perinatal risk, and (2) whether intrapartum scores are more important predictors of perinatal outcome than are antepartum scores. Four of the five scales produced fairly similar total scores, but the overall value of these scores in predicting perinatal outcome was not as good as that shown by scores derived from the least similar scale. The major differences between scales were due to the specific antepartum items they contained. In general, the antepartum scores were found to influence the prediction of infant outcome more strongly, and intrapartum scores were more predictive of maternal outcome.

Steiger on refraction: a reappraisal.

Seventy years ago Steiger, a Swiss ophthalmologist, found the distribution of corneal powers to follow a normal (binomial) curve. He noted a wide range of values among emmetropes, and he also knew that their axial lengths varied significantly. He expected that normal distributions would be found for other components of refraction and also for refraction as a whole, and in seeking a controlling mechanism he recalled the multifactorial pattern of inheritance of such characteristics as stature. The present study employs modern mathematical techniques to test the validity of 2 related hypotheses: that the components of refraction are correlated and that a polygenic mode of inheritance is responsible for determining the refractive power of the eye. In the light of this study and of other modern knowledge about refraction Steiger's work is reassessed. Most of his views are vindicated, although his assumption of a normal distribution for refraction as a whole could not be justified. His contribution to the understanding of refraction establishes him among the great names in ophthalmology.