GB2405953A - Pupil distance mesuring rule - Google Patents

Abstract

A rule for use in spectacle dispensing, that incorporates a selection of the following: a varifocal chart for marking up varifocal lenses and determining an appropriate lens type; a compact library of varifocal markings for the same purpose; a chart for determining an appropriate uncut lens diameter; a system to measure head width; rules for measurement of total and monocular pupil distance; a pair of perpendicular rules for measurement of box height and width, modified to allow measurement of varifocal fitting height; charts for determination of bend angle and pantoscopic angle. The rule may be lightweight, made of laminated card or paper, or of plastic. The rule may be 100mm long and 50mm wide. A bi-directional scale is provided on one side of the rule and a seperate scale is provided on the other side of the rule. The various charts are provided using both sides of the rule.

Description

1 2405953 Multipurpose Spectacle Dispensing Rule This invention relates to

a pupil rule for use in spectacle dispensing, that may also be used to replace other resources that may be required whilst still remaining conveniently small.

Pupil rules commonly are made of a heavy, robust plastic, and contain a large number of different measuring scales for the measurement of monocular pupil distances, total pupil distances, pantoscopic angle, length to bend, and varifocal fitting heights. Individual features may vary. They are commonly 150mm long.

For a dispensing optician in a busy optical practice, these pupil rules are not always convenient, as they are often too bulky to be carried in a pocket, and will by necessity need to be complimented by a number of other tools, such as: fitting charts for individual varifocal lenses; head callipers for the measurement of patients' head widths; referees material to identify brand markings on varifocal lenses and specific features of these lenses.

The objective of this invention is to provide a small, light and convenient tool, that can be used in the place of several of the mentioned tools, accurately.

Thus the invention is a short pupil rule, made of laminated card or plastic, with two sides designated left and right, the right bearing a OlOOmm rule, the left a 0-50 bi-directional rule. Each side also carries a corresponding chart for the marking up of a general range of varifocal spectacle lenses, which also demonstrates uncut lens diameter. Each side also carries a system for the measurement of head width. Each side also carries a small library of varifocal markings for easy identification. The invention also carries the most relevant tools found on a standard pupil rule, such as charts for measuring varifocal fitting heights, frame box height and box width, pantoscopic angle, and bend angle. Each chart is clearly marked, easy to use and designed to be accurate for all spectacle dispensing.

The invention can be placed in an inside or top pocket and produced when needed to be used: as a pupil rule; as a varifocal markings library; in place of head width callipers; to estimate a required uncut diameter; for quick determination of whether or not a varifocal lens can be glazed effectively into a chosen frame.

The invention is a rectangular area of a lightweight material such as laminated paper or plastic, of mickness dependent on material, and of length at least 100mm and width at least 50mm.

At the centre of the invention is a multipurpose varifocal chart, which features on both sides, one for a left lens and one for a right. As shown in figure 1, each chart displays the position of the sharpest focus of the reading area of a standard varifocal (minimum fitting height 18-22mm) as a black circle (1), and of a compact varifocal (minimum fitting height 16-18mm) as a blue circle (2). This allows a quick and easy visual analysis of the appropriate type for a specific marked frame. The corresponding minimum fitting heights as described above are projected to the edge of the rule' as is the Horizontal Centration Line (HCL), so that the edge of the rule may be used to determine in a shop floor environment whether or not a frame selection may be suitable for one of the varifocal types. The chart also includes markings to allow fitting crosses to be aligned in the correct position for different types of vadfocal lenses, which have differing centration heights depending on manufacturer and design. Based on the popular centration height of 4mm, the chart also includes on the right side a number of concentric circles representing uncut lens diameters, and on the left side an equivalent set of concentric ovals representing uncut decentred lenses. These markings allow a quick visual guide for a dispenser, indicating which uncut lens size should be ordered: the minimum blank size is often preferred. They can also be used for single vision lenses.

Split between the two charts is a table of commonplace varifocal markings.

This compact library is a quick reference to guide dispensers when discussing lenses with patients, allowing present lens type to be identified and this information used in the recommendation. The table includes data on the vertical positioning of the distance centre in relation to the markings on the lenses, so that the lenses can be marked up.

The vertical axis of the fitting crosses is aligned with the centre of the invention, i.e. 50mm from each end. As figure 2 shows, on the right side top edge, a O-lOOmm rule is included, running from O at the left- hand end (by convention) to 100mm at the right-hand end, with the 50mm mark aligning with the vertical projection of the fitting crosses vertical axis. On the left side, a similar arrangement as described above exists, however the rule begins at O in the centre (on the central vertical axis as above), and runs to 50mm in each direction. Thus the right side can be used for measuring total pupil distance, and the left for measuring monocular pupil distance. Both rules have the numbers marking each 5mm interval upside-down in relation to the rest of the invention, as the rules are placed at the top edge and the invention must, therefore, be used upside-down for measurement.

Both sides also feature a system for the measurement of head width. As figure 3 demonstrates, the problem of head width exceeding the specified convenient length of the instrument is countered with Pythagoras' theorem.

The dispenser aligns a selected eye with the patients opposing eye as shown (i.e dispenserts left to patient's right eye, or vice versa). The patient's ear is a distance A away from a dime line through the patient's eye. A known point on the invention is aligned with the patient's eye, and from this position, wim their open eye, the dispenser observes me ear. Since me invention is closer to the dispenser than a line between the patient's ears, by a distance equivalent to the length-to-bend (LTB), the ear appears to be a distance B from the known point on the invention. LTB values of 80mm and 100mm are used to calculate two values of B for each value of A at 5mm intervals from 25-50mm. This is done by noting that, in figure 3, triangles PQR and PST are congruent; the scale factor is found and applied to A to find B. Between each interval, the midpoint of the highest B value for the lower A and the lowest B value for the higher A are calculated, and these values become the boundaries for zones representing values of A. This use of zones allows for variations due of LTB and dispenser's arms length (assumed to be 500mm).

Each zone is colour coded and marked on the invention. Thus the dispenser sees the patient's ear fall into a certain zone, which represents the actual value of A. The values are marked in each zone. The sum of A and the monocular PD for this eye is shown in figure 3 to be half the patient's head width (HW). The process may be repeated with the other eye: each side of the invention carries corresponding orientations of the head width measurement system. However, suitable accuracy is achieved by multiplying the measured half-head width by 2.

In order to include as many features as possible but maintain small, convenient size, each side then carries different features. The side designated right' on the invention carries (in addition to the above) a rule as shown in figure 4, centred in the same way as the edge rule of the left side, but positioned centrally with respect to the width of the invention. It also runs from O in the centre to 45mm at each end. Crossing it, at the zero point, is another rule running at right angles, starting from O and running to 25mm in each direction. These two rules allow for measurement of frame box height and box width, and can also be used to find the frame's centration distance.

The vertical part of this rule is modified: all points on the rule from lOmm to +12mm are denoted with elongated marks, 15mm long. This zone on the invention is used to determine the fitting height of a varifocal lens, having marked up the frame for varifocals. There is also a set of guidelines at one end of the invention for measurement of bend angle, as shown in figure 5: this is formed of 6 lines, at 30, 50 and 70 degrees above and below the box width rule axis (used as me reference O degrees). The box width rule axis is placed in line with the frame, and the guide-lines allow an analysis by eye of an appropriate bend angle, if one should be specified.

The side designated 'left, carries (in addition to the above, but excluding the features on the 'right)) a chart for measuring pantoscopic angle. As shown in figure 6, this consists of 7 lines radiating from one end of the invention, one parallel to the long edge of the invent on, and representing O degrees. The other 6 lines are 5, 10 and 15 degrees above and below this line. The confluence of thaw 7 lines is held up to the front of the frame, and the vertical edge of the invention adjusted to be parallel with the plane of the frame front. The arm should then appear parallel to one of the other 6 lines, and this line will describe the pantoscopic angle of the measured frame. The left' can also carry additional features or information, such as brief methodology for using the head width system, or formulae for calculation of lens thickness, for reference.

Claims (7)

1 A pupil distance measuring rule, with two sides designated left and right, each bearing: a corresponding chart for marking up varifocal lenses; a head width measurement system described with drawings herein; a 0- 100mm rule on one side, and a 0-50mm bi-directional rule as described on the other; a compact library of varifocal identification markings.

2. A rule as described in any preceding claim that carries a box height/box width measurement chart.

3. A rule as described in any preceding claim that carries a chart for measurement of pantoscopic angle.

4. A rule as described in any preceding claim that carries a chart for measurement of bend angle.

5. A rule as described in any preceding claim that carries a chart for determination of fitting height for a varifocal spectacle dispense.

6. A rule as described in any preceding claim that carries charts for estimation of uncut lens diameter.

7. A rule substantially as herein described above and in the accompanying illustrations.