CHAPTER I. Ski-Optometer Construction

SKI-OPTOMETER CONSTRUCTION

A far better understanding of the instrument will be secured if the refractionist possessing a Ski-optometer will place it before him, working out each operation and experiment step by step in its proper routine.

The three moves as outlined in Fig. 1 should first be thoughtfully studied and the method of obtaining the spheres and cylinders carefully observed.

1—Set spherical indicator at “000” as illustrated above. 2—Set cylinder indicator to “0”. 3—Set pointer of supplementary disk at “open”.

The instrument should then be set at zero or “plano,” a position indicated by the appearance of the three “0 0 0” at the spherical register, in conjunction with one “0” or zero, for the cylinder at its register, marked “CC Cyl.”

After this move, the supplementary disk’s pointer should be set at “open” (Fig. 2).

CONVEX SPHERICAL LENSES

A careful study will show that the Ski-optometer’s spherical lenses are obtained by merely turning the smaller reel (Fig. 3). The first outward turn of this reel, toward the temporal side of the instrument, draws into position in regular order the spherical lenses +.25, +.50, +.75, and +1.D., as shown in Fig. 3a.

By means of a concealed tooth gear, an inner disk is automatically picked up, placing its first lens +1.25D in position (Fig. 3b). This +1.25D spherical lens remains stationary while the outer disk again revolves, adding to it the original +.25, +.50, +.75 and +1.D., the latter totalling +2.25D. At this point, the instrument again automatically picks up its inner disk, thereby placing its second lens, +2.50D, in position.

Instead of using intermediate strengths in making an examination, it is frequently desirable to make such extended changes as 1.25D to 2.50D. With the Ski-optometer, the refractionist will note that two white zeros appeared at the spherical register in connection with +1.25, and again with +2.50. A rapid outward turn of the spherical reel toward the temporal side to the point of the reappearance of the two zeros will show +3.75D; or, if increased power is still desired, a rapid turn will draw +5.D. into position (Fig. 4).

Turning the reel inward toward the nasal side will likewise decrease its convex power. In brief, each one of these lenses, showing their foci in conjunction with the two white zeros, are signals indicating the rapid increase or decrease of one and one-quarter diopter. After continuing to +6D., the next turn automatically shows zero (or “plano”), the original starting point, which is again indicated by the three white zeros.

Through the turn of the single reel—an exclusive Ski-optometer feature—all convex spherical lenses have now been attained in quarters up to +6.D, practically covering ninety percent of all refraction cases.

Should still greater power be desired, the small pointer at the outer edge of the instrument should be set at +6 sphere (Fig. 5). This controls a supplementary disk (Fig. 3c) which places an additional +6D. lens before the original range of lenses previously referred to, thus increasing the maximum power to +12D. If still greater strength is required, any additional trial-case lens may be added, a cell being provided for that purpose on the forward plate of the instrument.

OPERATES AND INDICATES AUTOMATICALLY

As previously explained, in using the Ski-optometer, it is only necessary to remember that each outward turn of the single reel toward the temporal side of the patient increases the plus power, while the reverse turn toward the patient’s nose decreases it. In fact, no attention need ever be given the register until the required sum-total is secured, it only being necessary to turn the single reel in order to be assured of the unvarying and accurate operation of the instrument.

For convenience, the contour or upper edge of the plate covering the spherical reel has been made to fit the index finger (Fig. 3). Hence the operator should note that it requires but one complete turn from extreme side to side, rather than a number of short turns, in order to bring each individual lens into position, thus obtaining the full advantage of the automatic spring-stop. This likewise permits the refractionist to operate the Ski-optometer even though the room is in total darkness.

CONCAVE SPHERICAL LENSES

Another simple and exclusive Ski-optometer advantage worthy of note is the method employed in obtaining concave, spherical lenses. Instead of employing a battery of concave lenses similar to the convex battery previously described, the instrument’s operation is greatly simplified through the use of a neutralizing process.

In short, the Ski-optometer only contains two concave lenses to obtain its entire series—namely, a -6.D and a -12.D sphere (Fig. 3c)—first setting the pointer of the supplementary disk at -6. sphere, then setting the indicator of the spherical battery at +6.

Thus zero (or plano) is obtained, the plus neutralizing the minus.

By merely turning the plus or convex spherical reel inward, or toward the patient’s nose, the convex power is then decreased, naturally increasing the concave value or total minus lens power. For example, if the spherical indicator shows +5.D, when the -6D. lens is placed behind it, the lens value at the sight opening will be -1D (Fig. 6). If required, the refractionist may continue on this plan until only the -6D. lens remains.

Should concave power stronger than -6D. be desired, by placing the pointer of the supplementary disk at -12D. Sph. and proceeding to neutralize as before, all the concave powers up to -12D. in quarters are similarly obtained. For the convenience of the operator, all minus or concave spherical powers are indicated in red; while plus, or convex powers, are indicated in white.

The instrument is also provided with an opaque or blank disk which is brought into position before the sight opening by setting the pointer of the supplementary disk at “shut” (Fig. 3c.)

Summing up, all plus and minus spherical powers have been attained from zero to 12D. in quarters, practically through the turn of the single reel—a simplicity of operation largely responsible for Ski-optometer supremacy.