Las reglas oftálmicas

[nicolamarras]

Muy bien, ahora hay que buscar esta regla:



Fue ideada en el 1875 por el oftalmólogo Emile Javal (1839-1907) y sirve para el cálculo de la prescripción de lentes. Fue realizada por A. Cretes, 66 rue des Rennes, París, en madera, bronce y vidrio.

Javal es considerado el padre de ortóptica y, aunque se formó como ingeniero, más tarde se convirtió en el director del Laboratorio Oftálmico de la Sorbona. Había muchos alumnos famosos como el Dr. George Joseph Bull (1848-1911) que desarrolló, en 1887, un oftalmómetro que se basa en este instrumento. Entre otras aplicaciones la regla de Dr. Bull permite de deducir aproximadamente la edad de una persona: las diversas partes del ojo, más particularmente el cristalino, sufren modificaciones en estructura y hay una relación entre la edad de una persona y la condicion de sus ojos.

La regla de Bull:





El ocular opcional:



Las reglas oftálmicas son bien raras, pero siguen construidas: el ultimo modelo es la AIT P 40 Digital Slide Rule. Muy diferente cierto, pero siguen llamandola "Slide Rule"!

Duros a morir, estos inventos ...

Oftálmicos saludos,



Nicolas

Una de las ultimas reglas oftálmicas tradicionales:





Y la moderna digital:




PD: descripción de la regla de Bull, sorry, no puedo traducir!

It consists of a light wooden rule about 24 inches long by 1¼ inch wide that can easily be held in the hand by means of a handle fixed at right angles with the flat part. At one extremity there is a square thin piece of metal of the width of the rule, and at right angles with the latter, but on the side opposite the handle. This piece of metal contains a circular aperture a few hundredths of an inch in diameter. Toward this aperture there may be moved either a converging lens of five dioptries or a diverging lens of the same diameter, but of six dioptries.

On holding the apparatus by the handle and putting the eye to the aperture, provided or not with a lens, we see a series of dominoes extending along the rule, from the double ace, which occupies the extremity most distant from the eye, to the double six, which is very near the eye. The numbers from two to twelve, simply, are indicated, but this original means of representing them has been chosen in order to call attention to them better.

Figures are characters without physiognomy, if we may so express ourselves, while the spots on the dominoes take particular arrangements according to the number represented, and differentiate themselves more clearly from each other than figures do. They are at the same time more easily read than figures or regularly spaced dots. Now, it is very important to fix the attention upon the numbers, since they are arranged at distances expressed in dioptries and indicated by the number of the spots. On looking through the aperture, we see in the first place one of the dominoes more distinctly than the rest. Then, on endeavoring to see those that are nearer or farther off, we succeed in accommodating the eye and in seeing the numbers that express the extreme terms of the accommodation, and consequently the amplitude.

Let us now take some examples: If we wish to express in dioptries the myopia of a person, we put the apparatus in his hand, and ask him to place his eye very near the aperture and note the number of spots on the most distant domino that he sees distinctly. This is the number sought. If the observation be made through the upper lens, it will be necessary to subtract five from the number obtained; if, on the contrary, the other lens is used, it will be necessary to add six.

If it is a question of a presbyope, let him look with his spectacles, and note the nearest domino seen distinctly. This will be the number of dioptries expressing the nearest point at which he can read. This number permits us to know whether it is necessary to add or subtract dioptries in order to allow him to read nearer by or farther off. If, for example, he sees the deuce and the ace distinctly, say 3 dioptries or 0.33 meter, and we want to allow him to read at 0.25 meter, corresponding to four dioptries, it will be necessary to increase the power of his spectacles by one dioptrie.


El Distometro, todavia en uso:

[MAAG57]

El cartelito de Ulloa Óptico con el agujerito es lo que se denomina lente estenopeica, esto es, un agujero de alfiler realizado en una superficie negra y que actúa en la práctica como una lente que permite enfocar a distancias mínimas.  Un buen truco para leer la carta del restaurante si te has olvidado las gafas.   

En Urgencias se utilizan en caso de disminución de agudeza visual: si el paciente es capaz de leer un texto que antes veía borroso, el problema es de acomodación de su sistema de lentes; si la alteración no se corrigiese así, hay que empezar a pensar en cosas más serias. 

Ojoavizores saludos,

[nicolamarras]

Un buen truco para leer la carta del restaurante si te has olvidado las gafas.

Esto me occurre, siempre, que la gafas para leer no las qiero. Hay que picanearme antes que me las voy a poner!

Presbiciosos saludos,

Nicolas

Bondwell Optician Slide Rule: