1. Field of the Invention
The present invention is generally concerned with fitting ophthalmic lenses into the rings or surrounds that an eyeglass frame comprises for this purpose and it is more particularly but not exclusively directed to the case of corrective ophthalmic lenses.
2. Description of the Prior Art
As is known, unprocessed ophthalmic lenses as supplied to optometrists by the manufacturers have a circular contour at the periphery and, for obvious economic reasons, for a given type of ophthalmic lens optometrists are offered a plurality of unprocessed ophthalmic lenses of different peripheral diameters, the cost of unprocessed ophthalmic lenses being proportional to the diameter.
Thus for each eyeglass frame to be fitted with lenses the optometrist has to determine which of the available unprocessed ophthalmic lenses is the most economical to use, given the particular shape of the rings or surrounds of the eyeglass frame; in other words, he has to determine the lens within the contour of which the contour of the ring or surround will fit most closely.
As it happens, the problem is that more often than not the optometrist does not actually have the corresponding unprocessed ophthalmic lenses available to him, but only cards carrying diagrams of the ophthalmic lenses, and that in the case of corrective ophthalmic lenses he must take into account, conjointly, the physiological characteristics of the patient concerned and the optical characteristics of the corrective ophthalmic lenses.
In practice, the principal factor that the optometrist has to take into account is the horizontal distance between the pupils of the patient concerned, more precisely half the patient's interpupillary distance, for proper alignment of the optical center of the corresponding ophthalmic lens relative to the normal axis of vision of each eye of the patient.
In the case of progressive ophthalmic lenses, that is to say ophthalmic lenses of which the lower part, used for close vision, features progressively varying optical power along one meridian at least, unlike the upper part which is reserved for far vision and is usually of constant refractive power, the optometrist also has to take into account the vertical distance between the horizontal line passing through the pupil of the patient concerned for far vision and the bottom of the ring or surround of the eyeglass frame to be fitted with lenses.
Various instruments and apparatus have already been proposed to facilitate the task of the optometrist in determining the diameter of the unprocessed ophthalmic lenses to fit a particular eyeglass frame.
In one relatively simple formula, as described in the French patent filed Feb. 2, 1970 under application No. 70 03453 and published under number 2.307.340, this is a simple rule which, carrying diagrams of the available unprocessed ophthalmic lenses, may be equipped with a cursor movable along its length on which the eyeglass frame to be fitted with lenses may be placed.
As no support specifically for holding the eyeglass frame is provided, the operation to be undertaken is relatively clumsy and imprecise, and there may result some uncertainty as to the determined diameter.
Also, it is not possible with an instrument like this to take into account the aforementioned vertical distance.
In a more sophisticated formula, as described for example in the European patent application filed June 19, 1980 under the number 80400903.3 and published under the number 0 021 998, the apparatus proposed for determining the diameter of an unprocessed ophthalmic lens to fit a particular eyeglass frame comprises, on a base, a guide on said base adapted to receive a card carrying diagrams of available unprocessed ophthalmic lenses and a support on said base adapted to receive the eyeglass frame to be fitted with lenses.
In this way, and advantageously, the frame may be more firmly held.
In practice, however, this apparatus is relatively complex, expensive and bulky, in particular because the guide adapted to receive a card is mobile relative to the base whereas the support adapted to receive the eyeglass frame to be fitted with lenses is fixed relative to the base and, as these components are spaced from each other, to achieve virtual superposition of the corresponding images it is necessary to employ an optical system with light source and mirror.
Furthermore, using an apparatus like this is also relatively complicated; for example, two separate operations are necessary just to allow for the interpupillary distance, or rather half the interpupillary distance, of the patient concerned.
An object of the present invention is an apparatus for determining the diameter of an unprocessed ophthalmic lens to fit a particular eyeglass frame advantageously free of these disadvantages.