Furthermore, it should be noted that where the Ski-optometer is used in skioscopy, it is not necessary to remove the retinoscope from the eye or to constantly locate a new reflex with each lens change. This permits a direct comparison of the final lens and eliminates the usual difficulty in mastering skioscopy. The chief cause of this difficulty is due to the fact that the transferring of the trial-case lenses makes it practically impossible for the student to determine whether the previous lens caused more “with” or “against” motion.
Fig. 9—The Woolf ophthalmic bracket. A convenient and portable accessory in skioscopy and muscle testing; can be used with or without Greek cross.
Where the indirect method is employed in skioscopy, best results are secured through the use of the Woolf ophthalmic bracket and concentrated filament lamp, together with an iris diaphragm chimney. The latter permits the reduction or increase of the amount of light entering the eye, as it is agreed that a large pupil requires less light, a small pupil requiring more light. The bracket referred to permits the operator to swing the light into any desired position ([Fig. 9]), while the iris diaphragm chimney serves as a shutter. This apparatus may also be employed for muscle testing, as described in a subsequent paragraph.
A Simplified Skioscopic Method
In using the Ski-optometer, instead of working forty inches away from the patient in skioscopy and deducting 1.D., the refractionist will find it more convenient to work at a twenty inch distance, deducting 2.D. This working distance may be accurately measured and maintained by using the reading rod accompanying the instrument. Instead of deducting 2.D. from the total findings, however, it is preferable to insert a +2.D. trial-case lens in the rear cell of the instrument directly next to the patient’s eye. After determining the weakest lens required to neutralize the shadow in both meridians, the additional +2.D. lens should be removed and the total result of the examination read from the instrument’s register.
To illustrate a case in skioscopy where spherical lenses are employed to correct both meridians, assume that the vertical shadow requires a +1.25D lens to cause its reversal, while the horizontal requires +2.00D. Employment of the customary diagram, illustrated in [Fig. 10], would show the patient required +1.25 sph. = +.75 cyl. axis 90°, which when transposed is equivalent to +2.00 sph. = -.75 cyl. axis 180°.
Fig. 10—Where spherical lenses are employed in skioscopy, above indicates patient requires
+1.25 Sph. = +.75 Cyl. Axis 90°
or +2 Sph. = -.75 Cyl. Axis 180°