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A Further, Very Delicate Test for Astigmatic Axis, Using the Cross Cylinder by an Astigmatic Dial and without use of Letter Charts*
A FURTHER, VERY DELICATE TEST FOR ASTIGMATIC AXIS, USING THE CROSS CYLINDER WITH AN ASTIGMATIC DIAL AND WITHOUT USE OF LETTER CHARTS* WILLIAM H. CRISP, M.D. Denver, Colorado AND GEORGE H .
STINE,
M.D.
Colorado Springs, Colorado
the light of any evidence which may be furnished by ophthalmology, skiascopy, or an astigmatic dial. In the larger astigmatic errors it may not have to be resorted to at all, although even here it may sometimes clear up doubts. In the small astigmatic errors (to which some workers pay little or no attention, but which may be quite important) it is most valuable. The rotating cross is most conveniently and expeditiously used with a pulley mechanism for remote control from the examiner's chair near the patient, although some refractionists will rely (less conveniently) upon the services of an office helper for changing the position of the lines of the cross. Ophthalmologists who refract with a mirror and laterally inverted charts will, of course, have their charts within arm's length. The only disadvantage of the test as compared with the combined use of cross cylinder and letter charts or wagon-wheel chart is that, for absolute accuracy, the position of the rotating cross should be changed with each change of axis of the cylinder in the trial frame, although a discrepancy of a few degrees in the placing of the cross lines is usually of little practical importance. At each step of the procedure, the lines of the rotating cross are made to straddle exactly the axis of the correcting cylinder in the trial frame. That is to say, the two lines of the dial should stand at 45 degrees to either side of the axis of the trial cylinder. The cross cylinder, usually the 0.12D. or the 0.25D., is held so that its axes correspond with the two axes of the rotating cross (that * Presented before the Section on Ophthalmology, is at 45 degrees with the axis of the trial American Medical Association, Chicago, June, 1948. cylinder), and the cross cylinder is turned
The purpose of the procedure as to astigmatic axis proposed in the paper presented by Crisp1 at the meeting of the American Ophthalmological Society in 1942 was to afford a delicate control test for axis in astigmatic errors, especially of low amount, in which the test for axis with cross cylinder and test letters seemed insufficiently definite and reliable. That test utilized the wagonwheel type of astigmatic dialj more particularly the axis chart either of Lancaster and Regan or of Verhoeff. In the course of the preliminary clinical and photographic studies in relation to that test for axis, it became obvious that several other astigmatic dials might yield", interesting results along the same lines, and brief consideration was given to the use of a rotating single cross for the purpose. Stine proceeded to devote further attention to these possibilities, and later reported to Crisp his studies and observations. From these Stine had evolved the new test, which Crisp now proposes shall be known as the "Stine test for astigmatic axis." Both of the present writers have continued to employ this new test during the past 2 or 3 years, and have found it more definite and freer from complications than any other test known to them. The new test is of surprising delicacy and simplicity, although like other subjective tests it demands full Understanding and cooperation on the part of the patient. Like Crisp's test it is generally used as a control after preliminary testing for axis with the cross cylinder and the letter chart, and in
1065
1066
WILLIAM H. CRISP AND GEORGE H. STINE
or "flipped" in the same manner as in testing for axis with the letter chart. T h e patient is asked to say with which position of the cross cylinder the two lines of the rotating dial appear more nearly matched as to blackness or sharpness, or with which position of the cross cylinder there is the lesser amount of contrast between the two lines. T h e cylinder in the trial
m
If the choice has been made, and the position of the lens in the trial frame is changed, the position of the rotating cross must also be changed so as to straddle exactly (or at least approximately) the new position of the axis of the trial cylinder. T h e final stage of the test is reached when the patient insists that the variation of emphasis, or the reversal of sharpness or
ø
A
^-
ß
Fig. 1* (Crisp and Stine). Basic error of camera lens, rendered astigmatic, represents a final need for correction with +1.0D. cylinder axis 90°. For these two photographs the correcting +1.0D. cylinder had been placed inaccurately with its axis at 80 degrees. The two lines of the rotating cross were set respectively at 35 and 125 degrees. The cross cylinder was first placed with its plus axis at 35 degrees, and then with its plus axis at 125 degrees. The choice as to relative uniformity is obviously for the second of the two positions, indicating that the correcting plus cylinder should be turned toward 90 degrees. Astigmatic difference between the two lines in A is 0.59D., and in B, 0.09D. frame is then moved toward the corresponding axis of the cross cylinder (plus toward plus, minus toward minus) in the position which gives greater uniformity of the lines or the lesser contrast between them. * Note as to illustrations. For definiteness of illustration the basic error of the camera lens was that of mixed astigmatism, requiring a final correction with —0.25D. sph. Z +1.0D. cyl. ax. 90°, and the 0.12D., cross cylinder (—0.12D. sph. _ +0.25D. cyl.) was used. In actual practice it will be found that similar sharp differentiation by the patient is usually obtainable with such a weak cross cylinder and when dealing with a correcting cylinder as low as 0.25D. The astigmatic differences between the two lines of the dial in the meridians shown in the illustrations were determined by the use of Percival's* equation for obliquely crossed cylinders and the law as to square of the cosine.
blackness from one line to the other, is equal in both positions of the cross cylinder ; and, as under the test with cross cylinder and letters, the patient's accuracy may be crossexamined by turning the trial cylinder to each side of the selected position and repeating the test. T h e patient may occasionally misunderstand the test and may answer paradoxically. Like other tests, this one is usually more reliable in the absence of active accommodation, although sometimes less accurate if the patient's vision is appreciably fogged. T h e use of a slightly over- or under-correcting trial cylinder affects the accuracy of the test practically not at all, although a slight over~ correction may often increase its sensitivity.
1067
TEST FOR ASTIGMATIC AXIS Very occasionally, determination must be made between conflicting results as to the use of this test and the use of letters with
It seems worth while to point out that, subject to spherical measurements, it is possible to accomplish all the measurements
X 'X
m
Fig. 2 (Crisp and Stine). For this pair of photographs the correcting +1.0D. cylinder had been inaccurately placed with its axis at 100 degrees, the cross was set with its lines at 55 and 145 degrees respectively, and the cross cylinder was held with its plus axis first at 55 degrees and then at 145 degrees. The choice is obviously for the former position, indicating that the axis of the correcting plus cylinder should be turned toward 90 degrees. Astigmatic difference between the two lines is 0.09D. in C, and 0.59D., in D.
X XE
·
F
Fig. 3 (Crisp and Stine). For these two photographs the correcting plus cylinder was — at 90 degrees. The rotating cross was placed with its axis in the proper position, namely placed with its lines respectively at 45 and 135 degrees, and the cross cylinder was held with its; plus axis first at 45 and then at 135 degrees. There is obviously no choice as to the "equal inequality" of sharpness of the two lines on the rotating cross, indicating that the correcting cylinder is now at the proper axis. Astigmatic difference between the two lines is 0.25D. in both E and F. the cross cylinder. But, generally speaking, the test with cross cylinder a n d rotating cross is as delicate a n d reliable a s any p r o cedure in refractive work, or more so.
(axis and strength) for astigmatism by means of the rotating cross, without resort to t h e letter chart. A s demonstrated by Crisp in 1917, 2 the rotating cross m a y be
1068
WILLIAM H. CRISP AND GEORGE H. STINE
conveniently used in combination with a low cross cylinder for extreme refinement as to the exact fraction of astigmatism. For this purpose, the axis having been determined, and the cross having been rotated so that one of its lines coincides with the axis of the trial cylinder, the cross cylinder (usually the 0.12D.) is held with the plus or minus axis alternately parallel with the axis of the trial cylinder. If both lines of the cross are actually equal, each position of the cross cylinder will slightly sharpen one of the lines of the cross and will slightly blur the other. Thus, the patient's selection may be made to discriminate as to the error being slightly above or slightly below an exact eighth of a diopter of astigmatic difference. If the patient's response is paradoxical, all that is necessary is to inquire which position makes the two cross lines more equal in sharpness. The definiteness of this test may, of course,
be vitiated by the presence of irregular astigmatism. As to the axis test which is the main topic of this paper, a further application of the same principle may be made during determination of the axis by cylinder skiascopy. In this application, a cross cylinder of proper strength (as demonstrated by experience in the individual case) is held with its axes at 45 degrees with the axis of the cylinder before the patient's eye, and the examiner decides which way there is less suggestion of uncorrected astigmatism. But, as stated in regard to use of the test at the trial case (subjective test), in most patients, except those with larger errors or amblyopic eyes, such doubts may be settled more expeditiously and more conclusively along subjective lines. 1276 Emerson Street (3). 23 East Pikes Peak Avenue.
REFERENCES
1. Crisp, W. H. : A new cross-cylinder test for astigmatic axis, without use of test type. Tr. Am. Ophth. Soc, 40:54,1942; also Am. J. Ophth., 26 :S71,1943. 2. — ; — : Combined use of cross cylinder and astigmatic dial. Ann. Ophth., 26:42, 1917. 3. Percival, A. S. : Decentration and oblique cylinders. Brit. J. Ophth., 5:4S3 (Oct.) 1921.
OPHTHALMIC MINIATURE
To evert the upper lid grasp the eyelashes between the thumb and index finger of the left hand and draw the lid down towards you, pressing the center of it back with the handle of your sound before the eye is opened and the lid released. It will then be everted so that its inner surface is fully exposed for accurate, deliberate and complete treatment. The everted lid should be gradually returned to its proper place; do not allow it to snap back suddenly—a bad practice Memorandum Book of a Tenth-Century Oculist Translated by Casey A. Wood.
STINE,
M.D.
Colorado Springs, Colorado
the light of any evidence which may be furnished by ophthalmology, skiascopy, or an astigmatic dial. In the larger astigmatic errors it may not have to be resorted to at all, although even here it may sometimes clear up doubts. In the small astigmatic errors (to which some workers pay little or no attention, but which may be quite important) it is most valuable. The rotating cross is most conveniently and expeditiously used with a pulley mechanism for remote control from the examiner's chair near the patient, although some refractionists will rely (less conveniently) upon the services of an office helper for changing the position of the lines of the cross. Ophthalmologists who refract with a mirror and laterally inverted charts will, of course, have their charts within arm's length. The only disadvantage of the test as compared with the combined use of cross cylinder and letter charts or wagon-wheel chart is that, for absolute accuracy, the position of the rotating cross should be changed with each change of axis of the cylinder in the trial frame, although a discrepancy of a few degrees in the placing of the cross lines is usually of little practical importance. At each step of the procedure, the lines of the rotating cross are made to straddle exactly the axis of the correcting cylinder in the trial frame. That is to say, the two lines of the dial should stand at 45 degrees to either side of the axis of the trial cylinder. The cross cylinder, usually the 0.12D. or the 0.25D., is held so that its axes correspond with the two axes of the rotating cross (that * Presented before the Section on Ophthalmology, is at 45 degrees with the axis of the trial American Medical Association, Chicago, June, 1948. cylinder), and the cross cylinder is turned
The purpose of the procedure as to astigmatic axis proposed in the paper presented by Crisp1 at the meeting of the American Ophthalmological Society in 1942 was to afford a delicate control test for axis in astigmatic errors, especially of low amount, in which the test for axis with cross cylinder and test letters seemed insufficiently definite and reliable. That test utilized the wagonwheel type of astigmatic dialj more particularly the axis chart either of Lancaster and Regan or of Verhoeff. In the course of the preliminary clinical and photographic studies in relation to that test for axis, it became obvious that several other astigmatic dials might yield", interesting results along the same lines, and brief consideration was given to the use of a rotating single cross for the purpose. Stine proceeded to devote further attention to these possibilities, and later reported to Crisp his studies and observations. From these Stine had evolved the new test, which Crisp now proposes shall be known as the "Stine test for astigmatic axis." Both of the present writers have continued to employ this new test during the past 2 or 3 years, and have found it more definite and freer from complications than any other test known to them. The new test is of surprising delicacy and simplicity, although like other subjective tests it demands full Understanding and cooperation on the part of the patient. Like Crisp's test it is generally used as a control after preliminary testing for axis with the cross cylinder and the letter chart, and in
1065
1066
WILLIAM H. CRISP AND GEORGE H. STINE
or "flipped" in the same manner as in testing for axis with the letter chart. T h e patient is asked to say with which position of the cross cylinder the two lines of the rotating dial appear more nearly matched as to blackness or sharpness, or with which position of the cross cylinder there is the lesser amount of contrast between the two lines. T h e cylinder in the trial
m
If the choice has been made, and the position of the lens in the trial frame is changed, the position of the rotating cross must also be changed so as to straddle exactly (or at least approximately) the new position of the axis of the trial cylinder. T h e final stage of the test is reached when the patient insists that the variation of emphasis, or the reversal of sharpness or
ø
A
^-
ß
Fig. 1* (Crisp and Stine). Basic error of camera lens, rendered astigmatic, represents a final need for correction with +1.0D. cylinder axis 90°. For these two photographs the correcting +1.0D. cylinder had been placed inaccurately with its axis at 80 degrees. The two lines of the rotating cross were set respectively at 35 and 125 degrees. The cross cylinder was first placed with its plus axis at 35 degrees, and then with its plus axis at 125 degrees. The choice as to relative uniformity is obviously for the second of the two positions, indicating that the correcting plus cylinder should be turned toward 90 degrees. Astigmatic difference between the two lines in A is 0.59D., and in B, 0.09D. frame is then moved toward the corresponding axis of the cross cylinder (plus toward plus, minus toward minus) in the position which gives greater uniformity of the lines or the lesser contrast between them. * Note as to illustrations. For definiteness of illustration the basic error of the camera lens was that of mixed astigmatism, requiring a final correction with —0.25D. sph. Z +1.0D. cyl. ax. 90°, and the 0.12D., cross cylinder (—0.12D. sph. _ +0.25D. cyl.) was used. In actual practice it will be found that similar sharp differentiation by the patient is usually obtainable with such a weak cross cylinder and when dealing with a correcting cylinder as low as 0.25D. The astigmatic differences between the two lines of the dial in the meridians shown in the illustrations were determined by the use of Percival's* equation for obliquely crossed cylinders and the law as to square of the cosine.
blackness from one line to the other, is equal in both positions of the cross cylinder ; and, as under the test with cross cylinder and letters, the patient's accuracy may be crossexamined by turning the trial cylinder to each side of the selected position and repeating the test. T h e patient may occasionally misunderstand the test and may answer paradoxically. Like other tests, this one is usually more reliable in the absence of active accommodation, although sometimes less accurate if the patient's vision is appreciably fogged. T h e use of a slightly over- or under-correcting trial cylinder affects the accuracy of the test practically not at all, although a slight over~ correction may often increase its sensitivity.
1067
TEST FOR ASTIGMATIC AXIS Very occasionally, determination must be made between conflicting results as to the use of this test and the use of letters with
It seems worth while to point out that, subject to spherical measurements, it is possible to accomplish all the measurements
X 'X
m
Fig. 2 (Crisp and Stine). For this pair of photographs the correcting +1.0D. cylinder had been inaccurately placed with its axis at 100 degrees, the cross was set with its lines at 55 and 145 degrees respectively, and the cross cylinder was held with its plus axis first at 55 degrees and then at 145 degrees. The choice is obviously for the former position, indicating that the axis of the correcting plus cylinder should be turned toward 90 degrees. Astigmatic difference between the two lines is 0.09D. in C, and 0.59D., in D.
X XE
·
F
Fig. 3 (Crisp and Stine). For these two photographs the correcting plus cylinder was — at 90 degrees. The rotating cross was placed with its axis in the proper position, namely placed with its lines respectively at 45 and 135 degrees, and the cross cylinder was held with its; plus axis first at 45 and then at 135 degrees. There is obviously no choice as to the "equal inequality" of sharpness of the two lines on the rotating cross, indicating that the correcting cylinder is now at the proper axis. Astigmatic difference between the two lines is 0.25D. in both E and F. the cross cylinder. But, generally speaking, the test with cross cylinder a n d rotating cross is as delicate a n d reliable a s any p r o cedure in refractive work, or more so.
(axis and strength) for astigmatism by means of the rotating cross, without resort to t h e letter chart. A s demonstrated by Crisp in 1917, 2 the rotating cross m a y be
1068
WILLIAM H. CRISP AND GEORGE H. STINE
conveniently used in combination with a low cross cylinder for extreme refinement as to the exact fraction of astigmatism. For this purpose, the axis having been determined, and the cross having been rotated so that one of its lines coincides with the axis of the trial cylinder, the cross cylinder (usually the 0.12D.) is held with the plus or minus axis alternately parallel with the axis of the trial cylinder. If both lines of the cross are actually equal, each position of the cross cylinder will slightly sharpen one of the lines of the cross and will slightly blur the other. Thus, the patient's selection may be made to discriminate as to the error being slightly above or slightly below an exact eighth of a diopter of astigmatic difference. If the patient's response is paradoxical, all that is necessary is to inquire which position makes the two cross lines more equal in sharpness. The definiteness of this test may, of course,
be vitiated by the presence of irregular astigmatism. As to the axis test which is the main topic of this paper, a further application of the same principle may be made during determination of the axis by cylinder skiascopy. In this application, a cross cylinder of proper strength (as demonstrated by experience in the individual case) is held with its axes at 45 degrees with the axis of the cylinder before the patient's eye, and the examiner decides which way there is less suggestion of uncorrected astigmatism. But, as stated in regard to use of the test at the trial case (subjective test), in most patients, except those with larger errors or amblyopic eyes, such doubts may be settled more expeditiously and more conclusively along subjective lines. 1276 Emerson Street (3). 23 East Pikes Peak Avenue.
REFERENCES
1. Crisp, W. H. : A new cross-cylinder test for astigmatic axis, without use of test type. Tr. Am. Ophth. Soc, 40:54,1942; also Am. J. Ophth., 26 :S71,1943. 2. — ; — : Combined use of cross cylinder and astigmatic dial. Ann. Ophth., 26:42, 1917. 3. Percival, A. S. : Decentration and oblique cylinders. Brit. J. Ophth., 5:4S3 (Oct.) 1921.
OPHTHALMIC MINIATURE
To evert the upper lid grasp the eyelashes between the thumb and index finger of the left hand and draw the lid down towards you, pressing the center of it back with the handle of your sound before the eye is opened and the lid released. It will then be everted so that its inner surface is fully exposed for accurate, deliberate and complete treatment. The everted lid should be gradually returned to its proper place; do not allow it to snap back suddenly—a bad practice Memorandum Book of a Tenth-Century Oculist Translated by Casey A. Wood.