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The Three-step Test
LEITERS
incidence of cytomegalovirus (CMV) retinitis may also be related to CMV-HIV interaction.' We hope that additional studies will clarify the nature of HIV retinopathy and better define its relationship to ocular HIV infection. HERBERT L. CANTRILL, MD Minneapolis, Minnesota References 1. Pomerantz RJ, Kuritzkes DR, de la Monte SM, et al. Infection of the retina by human immunodeficiency virus Type I. N Engl J Med 1987; 317:1643-7. 2. Kestelyn P, Van de Perre P, Sprecher-Goldberger S. Isolation of the human t-ceilleukemia/lymphotropic virus type IIIfrom aqueous humor in two patients with perivasculitis of the retinal vessels. Int Ophthalmol 1986; 9:247-51. 3. Skolnik PR, Kosloff BR, Hirsch MS. Bidirectional interactions between human immunodeficiency virus type I and cytomegalovirus. J Infect Dis 1988; 157:508-14.
The Three-step Test
Dear Editor: The errors in diagnosis of vertical strabismus using Park's three-step test, as discussed by Kushner in his article, "Errors in the Three-step Test in the Diagnosis of Vertical Strabismus" (Ophthalmology 1989; 96:127-132) were found in his several cases because the test was misapplied, and therefore the article was misleading. The test is not intended to be an isolated diagnostic procedure and does not take into account, for example, restrictive disease. It is used after first eliciting a thoughtful, detailed history with particular reference to the neurologic system and performing a careful eye examination with testing of extraocular motility (ductions and versions). If restrictive disorders are found, forced ductions are performed, not Park's three-step. If there is an obvious neurologic dysfunction as the cause of the squint, the test may be superfluous. Comments on each of his cases illustrate how the reader may be misled. Case 1. Sudden diplopia after trauma suggests cranial nerve injury or restriction from orbital fracture. Testing of versions in up and downgaze and measurements of the hyperdeviation in these same directions would have been sufficient to make a presumptive diagnosis leading one to investigative efforts other than Park's three-step. Case 2. Again, conclusions based on the isolated threestep test are specious and double maddox rod testing is needed to elaborate on appropriate findings from the test, especially in regard to bilaterality. Case 3. The diagnosis of dissociated hyperdeviations can be properly made by measuring the hyper in the primary position and observing the movement of the eye at the expected prism end point. It is well known that this disorder is variable in different gaze positions. To evaluate this disorder by Park's three-step test is not helpful.
Case 4. The patient's history and clinical course would be more instructive than the three-step test. Versions should have been adequate to recognize the surgical failure. Case 5. The three-step test in this case shows a right inferior rectus rather than a left inferior oblique palsy as stated in the article. The small degree of incomitancy of the hyper should have indicated to the examiner that it was related to the dissociation of the eyes rather than an isolated cyclovertical muscle palsy. Case 6. The history of posterior fossa signs are important here and direct one to examinations other than the three-step test. Skew deviations rarely show significant incomitancy of the hyper. Case 7. Variability of measurements of strabismus in myasthenia is diagnostic. An appropriate diagnosis of superior oblique palsy on one occasion may be absent on a later examination, confirming the suspected cause as being myasthenia. In conclusion, the author has misapplied and misconstrued the three-step test in a successful effort to demonstrate that it, by itself alone, does not enable the examiner to diagnose all disorders causing vertical strabismus. The reader should not be misled into discarding or demeaning this test because of its misapplication. It must be used in the context of appropriate ocular motility evaluation and logical use of a careful history. MONT JAY CARTWRIGHT, MD DAVIS B. WYATT, MD Richmond, Virginia
Author's reply
Dear Editor: Cartwright and Wyatt point out that it is inappropriate to use the three-step test in many of the clinical entities described in my series. They further point out that the three-step test is not intended to be an isolated diagnostic procedure. I fully agree with them. In fact, the purpose of my article was to point out those very facts. The only thing with which I disagree in the thoughtful letter from Cartwright and Wyatt is their statement that my article is misleading. The three-step test is only valid if one knows one is dealing with an isolated palsy of a cyclovertical muscle. In 14 years of practice, I have never had a patient present to me with the chief complaint, "I have a palsy of one of my cyclovertical muscles," followed by a plea for me to isolate the affected one. Instead, patients present with the symptom of either diplopia or asthenopia. Although in his original description of the three-step test, Parks did not imply that the test should be used in cases of nonparalytic strabismus, I am unaware of any articles describing this test, nor textbook chapters on vertical strabismus which specifically outline clinical conditions which
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incidence of cytomegalovirus (CMV) retinitis may also be related to CMV-HIV interaction.' We hope that additional studies will clarify the nature of HIV retinopathy and better define its relationship to ocular HIV infection. HERBERT L. CANTRILL, MD Minneapolis, Minnesota References 1. Pomerantz RJ, Kuritzkes DR, de la Monte SM, et al. Infection of the retina by human immunodeficiency virus Type I. N Engl J Med 1987; 317:1643-7. 2. Kestelyn P, Van de Perre P, Sprecher-Goldberger S. Isolation of the human t-ceilleukemia/lymphotropic virus type IIIfrom aqueous humor in two patients with perivasculitis of the retinal vessels. Int Ophthalmol 1986; 9:247-51. 3. Skolnik PR, Kosloff BR, Hirsch MS. Bidirectional interactions between human immunodeficiency virus type I and cytomegalovirus. J Infect Dis 1988; 157:508-14.
The Three-step Test
Dear Editor: The errors in diagnosis of vertical strabismus using Park's three-step test, as discussed by Kushner in his article, "Errors in the Three-step Test in the Diagnosis of Vertical Strabismus" (Ophthalmology 1989; 96:127-132) were found in his several cases because the test was misapplied, and therefore the article was misleading. The test is not intended to be an isolated diagnostic procedure and does not take into account, for example, restrictive disease. It is used after first eliciting a thoughtful, detailed history with particular reference to the neurologic system and performing a careful eye examination with testing of extraocular motility (ductions and versions). If restrictive disorders are found, forced ductions are performed, not Park's three-step. If there is an obvious neurologic dysfunction as the cause of the squint, the test may be superfluous. Comments on each of his cases illustrate how the reader may be misled. Case 1. Sudden diplopia after trauma suggests cranial nerve injury or restriction from orbital fracture. Testing of versions in up and downgaze and measurements of the hyperdeviation in these same directions would have been sufficient to make a presumptive diagnosis leading one to investigative efforts other than Park's three-step. Case 2. Again, conclusions based on the isolated threestep test are specious and double maddox rod testing is needed to elaborate on appropriate findings from the test, especially in regard to bilaterality. Case 3. The diagnosis of dissociated hyperdeviations can be properly made by measuring the hyper in the primary position and observing the movement of the eye at the expected prism end point. It is well known that this disorder is variable in different gaze positions. To evaluate this disorder by Park's three-step test is not helpful.
Case 4. The patient's history and clinical course would be more instructive than the three-step test. Versions should have been adequate to recognize the surgical failure. Case 5. The three-step test in this case shows a right inferior rectus rather than a left inferior oblique palsy as stated in the article. The small degree of incomitancy of the hyper should have indicated to the examiner that it was related to the dissociation of the eyes rather than an isolated cyclovertical muscle palsy. Case 6. The history of posterior fossa signs are important here and direct one to examinations other than the three-step test. Skew deviations rarely show significant incomitancy of the hyper. Case 7. Variability of measurements of strabismus in myasthenia is diagnostic. An appropriate diagnosis of superior oblique palsy on one occasion may be absent on a later examination, confirming the suspected cause as being myasthenia. In conclusion, the author has misapplied and misconstrued the three-step test in a successful effort to demonstrate that it, by itself alone, does not enable the examiner to diagnose all disorders causing vertical strabismus. The reader should not be misled into discarding or demeaning this test because of its misapplication. It must be used in the context of appropriate ocular motility evaluation and logical use of a careful history. MONT JAY CARTWRIGHT, MD DAVIS B. WYATT, MD Richmond, Virginia
Author's reply
Dear Editor: Cartwright and Wyatt point out that it is inappropriate to use the three-step test in many of the clinical entities described in my series. They further point out that the three-step test is not intended to be an isolated diagnostic procedure. I fully agree with them. In fact, the purpose of my article was to point out those very facts. The only thing with which I disagree in the thoughtful letter from Cartwright and Wyatt is their statement that my article is misleading. The three-step test is only valid if one knows one is dealing with an isolated palsy of a cyclovertical muscle. In 14 years of practice, I have never had a patient present to me with the chief complaint, "I have a palsy of one of my cyclovertical muscles," followed by a plea for me to isolate the affected one. Instead, patients present with the symptom of either diplopia or asthenopia. Although in his original description of the three-step test, Parks did not imply that the test should be used in cases of nonparalytic strabismus, I am unaware of any articles describing this test, nor textbook chapters on vertical strabismus which specifically outline clinical conditions which
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