Comments on Disorders of the Fourth Cranial Nerve: Response

The chief relevance of Dr. Rutstein's communication is his as- sertion that comparison of objective and subjective torsional findings can help determine the probable age of onset of superior oblique palsy (SOP) because Dr. Rutstein believes that the absence of subjective cyclotorsion is more likely in congenital than acquired SOP. This has indeed been conventional teaching, as indicated by several textbook references and older articles cited by Rutstein, including his article in 1995 that considered durations of SO palsy in durations of 5 years, 6-15 years, and greater than 15 years.

Letters to the Editor Comments on Disorders of the Fourth Cranial Nerve: Response W e thank Dr. Rutstein for his interest in our review of “Disorders of the Fourth Cranial Nerve (1).” The chief relevance of Dr. Rutstein's communication is his assertion that comparison of objective and subjective torsional findings can help determine the probable age of onset of superior oblique palsy (SOP) because Dr. Rutstein believes that the absence of subjective cyclotorsion is more likely in congenital than acquired SOP (2). This has indeed been conventional teaching, as indicated by several textbook references and older articles cited by Rutstein, including his article in 1995 that considered durations of SO palsy in durations of 5 years, 6–15 years, and greater than 15 years (3). Although Dr. Rutstein appropriately avoided stating that the absence of subjective cyclotorsion is not an absolute discriminator of acquired SOP, we urge a stronger caveat. Many of the historically diagnosed cases of SOP were probably misdiagnosed. The three-step test, on which most clinicians (4) have relied, is subject to numerous errors (5), making it only 70% sensitive (6) and 50% specific for SOP as confirmed by orbital maging (7). The diagnosis of SO palsy has historically been the presumption in cyclovertical strabismus, applied to most cases of hypertropia for which no other clinical diagnosis could be established (8). We now know that half the cases captured in a strabismus clinic by such an approach are probably not related to a lesion of the fourth nerve or superior oblique muscle (7). A study of patients with hypertropia, in which SOP was categorized by MRI of superior oblique muscle size and function during head tilting, found not only that other conditions can mimic the findings of SOP but also that many cases of acquired SOP have a prolonged, insidious progression without identifiable etiology (7). Moreover, the claim has been refuted by an MRI-validated study that hypertropia greater in upward gaze is a characteristic of congenital and not present in acquired SOP (9). Clinicians should thus maintain some skepticism about their ability to accurately diagnose SOP and certainly their ability to ascertain its duration. There also is evidence that subjective and objective measures of cyclotorsion fail to correspond in common conditions besides SOP. Comparison of objective with subjective measures of cyclotorsion in patients with a wide variety of causes of cyclovertical strabismus suggests that patients perceive only about a third of objective cyclotorsion even when the strabismus is acquired (10). Patients with (always acquired) sagging eye syndrome nearly always exhibit objective excyclotropia, but only rarely complain of torsional diplopia (11). In addition, patients with unilateral SOP may exhibit bilateral objective excyclotorsion (12). e824 As Dr. Rutstein has emphasized, cyclotorsion may change during binocular fusion, which has implications for the correction of astigmatism. This is but a small aspect of the intrinsic role of cyclotorsion in vergence (13–15), the vestibulo-ocular reflex (16), and in ocular kinematics generally (17). Ocular torsion is a very complex matter. Clinicians ought to be cautious in interpreting its meaning. Joseph L. Demer, MD The Jules Stein Eye Institute, University of California, Los Angeles, Los Angeles, California Lanning B. Kline, MD Department of Ophthalmology, University of Alabama School of Medicine, Birmingham, Alabama The Shiley Eye Institute, University of California, San Diego, California Michael S. Vaphiades, MD Mehdi Tavakoli, MD Department of Ophthalmology, University of Alabama School of Medicine, Birmingham, Alabama The authors report no conflicts of interest. REFERENCES 1. Kline LB, Demer JL, Vaphiades MS, Tavakoli M. Disorders of the fourth cranial nerve. J Neuroophthalmol. 2021;41:176– 193. 2. Rutstein RP. Letters to the editor—disorders of the fourth cranial nerve. N Neuroophthalmol. 2021 (epub ahead of print). 3. Rutstein RP, Corliss DA. The relationship between duration of superior oblique palsy and vertical fusional vergence, cyclodeviation, and diplopia. J Am Optom Assoc. 1995;66:442–448. 4. Dosunmu EO, Hatt SR, Leske DA, Hodge DO, Holmes JM. Incidence and etiology of presumed fourth cranial nerve palsy: a population-based study. Am J Ophthalmol. 2018;185:110–114. 5. Kushner BJ. Errors in the three-step test in the diagnosis of vertical strabismus. Ophthalmology. 1987;96:127–132. 6. Manchandia A, Demer JL. Sensitivity of the three-step test in diagnosis of superior oblique palsy. J AAPOS. 2014;18:567– 571. 7. Demer JL, Clark RA, Kung J. Functional imaging of human extraocular muscles in head tilt dependent hypertropia. 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