Ординатура / Офтальмология / Английские материалы / Optics Retinoscopy and Refractometry_Lens_2005

Appendix B

Abbreviations

80 Appendix B

Abbreviations 81

Appendix C

Exercises

84 Appendix C

The Case Option Exercises

by Janice K. Ledford, COMT

How to Use the Case Option Exercises

The Case Option Directory lists the various types of optical cases on which you may choose to work. Exercises in Unit One let you choose the patient’s responses and then tell you the appropriate optical action that corresponds to that response. This is the equivalent of watching a refractometrist at work and having him or her explain what he or she is doing as the test goes along.

Unit Two puts you in the examiner’s chair. This time you are given the patient’s response. You must then choose which of the options is the most correct action. If you make an incorrect choice, the text explains why. If you make a good judgment, your selection will be reinforced, and you move on through the measurement by choosing new responses.

Of course, the array of real patient responses is unlimited (and sometimes strange, misleading, or downright malingering). I have attempted to keep the choices and results within reasonable and believable limits.

The exercise pages are coded so you can “practice” in whichever cylinder you choose. A minus (–) sign denotes minus cylinder, and a plus (+) sign denotes plus cylinder.

The first frame of each case gives you the patient’s present glasses prescription (if worn), visual acuity with that prescription, and sometimes other pertinent information. You must always start at frame #1 of a case. From there, follow the frame numbers of the options you choose.

The exercises are arranged in an easily understood format (see sample frame on page 87). Each exercise is identified by a lowercase letter. The frame number and exercise letter appear in the upper-left corner of each frame. When working an exercise, be sure to follow THESE frame numbers.

Beneath the frame number and exercise letter are bold face numbers that identify the lenses in the refractor at that point. Boldface numbers within the text of a frame show the refractor readings after a change has been made. This feature ensures that you will not “get lost” as you go from frame to frame.

The numbers in the upper right of the frame show you what frame you just came from to help you keep your place. Occasionally there may be more than one possibility as the options branch and regroup, but when following the options, follow the frame numbers on the upper left.

The abbreviations appearing in the exercises were explained previously in Appendix B.

To get maximum benefit from the exercises, work them in order and go through each one more than once, choosing different options when appropriate.

Protocol for the Exercises

The Exercises are written using the following protocol for refractometry.

•Regardless of cylinder sign, when dealing with sphere power, plus is always offered first.

•If the patient accepts more minus sphere, the next step is to have him or her read again from the chart. If he or she cannot read smaller letters than before, return to the previous sphere setting. This is to avoid over minusing.

Exercises 85

•Start with the chart on a line or two larger than what the patient read when you checked visual acuity. There is no need for him or her to struggle with reading the chart at the beginning of the test. (You will push for smaller letters later.)

•Always check cylinder axis and power with the eye chart on one or two lines larger than the patient’s best vision.

•When using the astigmatic dial, fog with +0.50 more than the spherical refraction currently in the phoroptor. Ask patient if any of the lines on the “clock face” are darker, sharper, or clearer than the others. If so, ask which lines (eg, running from 12:00 to 6:00 or from 2:00 to 8:00). To find the axis in plus cylinder, multiply the smaller “clock hour” by 30 and rotate by 90 degrees. To find the axis in minus cylinder, multiply the smaller “clock hour” by 30. For either cylinder type, crank in 0.25 cyl until patient says all lines are equally dark.

•When using the astigmatic dial, after selecting the axis and adding cylinder, you must adjust the sphere. In plus cylinder, give –0.25 sphere for each +0.50 D of cylinder power you gave. In minus cylinder, give +0.25 sphere for each –0.50 D of cylinder power.

•When using the cross cylinder to refine axis and power, if the patient says that the two choices are about the same, it means that you are currently on the right setting. (This is because you are straddling the correct point, and each choice is an equal distance from that point.)

I.Gross Spheres—Offered in 0.50-D steps, starting with plus. Continue until the vision blurs, then return to the previous setting. You may offer minus only if the first +0.50 step blurs the vision. If more minus does not improve the vision by helping the patient to read smaller letters, return to the previous sphere setting.

II. Cylinder Axis—Always refine the axis before refining the power. In plus cylinder, follow the white dot. In minus cylinder, follow the red dot. Move in 15-degree steps until the patient reverses direction. (Smaller increments may be used with higher cylinder powers.) Then move in increasingly smaller steps (eg, 7 degrees, then 3 degrees) until both choices look the same.

III. Cylinder Power—Start with 0.50-D steps. In plus cylinder, if the patient chooses the white dot, add more plus cylinder. If the patient chooses the red dot, reduce plus cylinder. In minus cylinder, if the patient chooses the red dot, give more minus cylinder. If the patient chooses the white dot, reduce the amount of minus cylinder. With either cylinder power, once the patient reverses his or her choice (ie, has been asking for less but now wants more), try 0.25 steps until both choices look the same. Remove the cross cylinder and have the patient read the smallest letters that he or she is able to see.

IV. Fine Spheres—Again, always offer plus first. Work in 0.25-D steps. Give plus until the chart blurs; then return to the setting prior to where the blurring occurred. If the patient takes minus, he or she must earn it by reading smaller letters on the chart. If he or she cannot do this, return to the previous setting. Record the measurement and the vision obtained with it.