Ocular Rotation Axes during Dynamic Bielschowsky Head-Tilt Testing in Unilateral Trochlear Nerve Palsy

Comparison of head tilt test between sagging eye syndrome and acquired unilateral trochlear nerve palsy

PURPOSE

To investigate the distinction between sagging eye syndrome (SES group) and acquired unilateral trochlear nerve palsy (Trochlear group) in the Bielschowsky head tilt test (BHTT).

METHODS

Fifteen patients in the SES group (mean age 74.6 ± 5.2 years) and 14 patients in the Trochlear group (55.2 ± 15.9 years) visited the Department of Ophthalmology, Hyogo Medical University Hospital between November 2016 and October 2022 for treatment of their diplopia. Eye position was measured with the alternate prism cover test, and values for fixation of the dominant eye, or unaffected eye, were used. Cyclodeviation was measured with the synoptophore and the Glaucoma Module Premium Edition of the SPECTRALIS optical coherence tomography. In the BHTT, eye position was measured in three head postures: primary position (PP), head tilt to the side with hypertropia (Hyper), and head tilt to the side with hypotropia (Hypo). The differences in vertical deviation between PP and Hyper (Hyper - PP), PP and Hypo (PP - Hypo) and Hyper - Hypo were measured and compared.

RESULTS

Vertical deviation in primary position was 7.3 ± 4.5 PD in the SES group and significantly larger (17.1 ± 8.4 PD) in the Trochlear group (p = 0.002). The vertical deviation in Hyper was significantly larger in the Trochlear group with 7.7 ± 4.7 PD and 22.1 ± 9.4 PD, respectively (p < 0.001), whereas the that in Hypo was not significantly different between the two groups with 6.5 ± 3.4 PD and 8.4 ± 6.6 PD, respectively (p = 0.725). The SES group showed no significant difference according to the 3 head postures (p = 0.311), while the Trochlear group showed a significantly different with smaller mean values in vertical deviation in Hypo (p < 0.001). The difference in the vertical deviation for the 3 head postures was the largest in Hyper - Hypo (1.7 ± 2.1 PD and 13.6 ± 7.1 PD, respectively), and the accuracy of SES was at the cutoff value of 6 PD, and it was considered not to be SES if the value was 6PD or higher. The accuracy of SES determination was 100% sensitivity and 100% specificity, and the area under the curve was 1.0.

CONCLUSION

The difference in Hyper - Hypo in the BHTT may be the most useful index in differentiating SES from acquired unilateral trochlear nerve palsy; if the difference was more than 6 PD, the probability of SES was very low.

Hess Lancaster Screen Test with Eye Tracker: An Objective Method for the Measurement of Binocular Gaze Direction

Background: To objectively measure with an eye tracker both eye movement conjugacy and gaze direction in different positions when performing the Hess Lancaster Screen Test (HLST) in a sample of control subjects without binocular dysfunction and compare the results with those of the traditional subjective HLST performance. Methods: The sample was selected avoiding subjects who suffered from suppression of one of the two eyes, visual acuity less than 20/25 on the Snellen chart in each eye, strabismus, or any symptom of binocular dysfunction that could alter the results. While performing the HLST, the examiner wrote down each of the points on a template in a traditional way while the eye tracker (Tobii Pro Fusion, Tobii AB, Danderyd, Sweden), placed in front of the subject, took objective measurements of the position of both eyes at each point. Of the 29 subjects recruited in this study, 13 subjects between 18 and 27 years old underwent the complete optometric examination and the HLST wearing anaglyph glasses; meanwhile, 16 people were excluded because of binocular or accommodative dysfunctions or because they didn’t give reliable eye-tracking results. Additionally, a specific program called Etracker Parse Video (University of Zaragoza, Zaragoza, Spain) was developed to analyse the prismatic deviation between both eyes at each evaluated point. Results: Similar horizontal prismatic deviations of visual axes were obtained in the different gaze positions with the Maddox rod, the manually annotated HLST, and the eye-tracker measurement. Variations were found in the magnitude of the deviation between methods but not in the direction. On the other hand, vertical deviations were more difficult for the examiner to detect and quantify, especially those with small magnitudes; more exact values were obtained when measuring objectively with the eye tracker. Conclusion: The HLST is very useful and allows the amount of heterophoria or heterotropia to be recorded in the patient’s medical record in all the main gaze positions. This test is complementary; by itself, it is not diagnostic and does not replace a complete examination of binocular vision. The eye tracker is an objective method with which we can evaluate the HLST in patients with no binocular problems, obtaining more accurate results than when it is performed in the traditional manner.

Ocular complications after posterior superior alveolar nerve block: a case of trochlear nerve palsy

Many intraoperative complications occurring during third molar surgery are described in the literature. Unilateral trochlear nerve palsy secondary to dental anaesthesia is a rare complication. We report the case of a 36-year-old healthy man, ASA I classification, requiring upper third molar extraction. Articaine 1:200,000 epinephrine for right posterior superior alveolar (PSA) nerve block was administered locally in the mucobuccal fold above the upper third molar. A few minutes after PSA nerve block the patient experienced double-vision. The patient was subsequently visited by an ophthalmologist and the condition was diagnosed as transient unilateral vertical diplopia due to temporary paralysis of the superior oblique muscle as a result of the anaesthetic solution involving the IV cranial nerve. The authors report this unusual case and discuss the possible anatomical pathways that might explain this rare phenomenon.

Dynamic aspects of trochlear nerve palsy

Trochlear nerve palsy leads to kinematic aberrations of both the paretic and the unaffected eye. During dynamic head roll, the rotation axis of the covered paretic or unaffected eye deviates inward, while the rotation axis of the viewing paretic or unaffected eye aligns with the line of sight; this convergence of rotation axes increases with gaze moving in the direction of the unaffected eye. During downward saccades, the trajectories of both eyes curve towards the unaffected side; these curvatures increase when the head is rolled to the affected side and gaze directed to the unaffected side. Hence, during both vestibular evoked and saccadic ocular movements, the unaffected eye shows similar kinematic aberrations as the paretic eye. While aberrations of the paretic eye can be explained by decreased force of the superior oblique (SO) muscle, aberrations of the unaffected eye may be due to increased force parallel to the paretic SO in the unaffected eye in accordance with Hering's law. This law, which forms the basis of conjugate eye movements, also seems to govern eye displacements in unilateral eye muscle palsy.

The effect of acute superior oblique palsy on torsional optokinetic nystagmus in monkeys

PURPOSE

To investigate the effects of acquired superior oblique palsy (SOP) and corrective strabismus surgery on torsional optokinetic nystagmus (tOKN) in monkeys.

METHODS

The trochlear nerve was severed intracranially in two rhesus monkeys (M1 and M2). For each monkey, more than 4 months after the SOP, the ipsilateral inferior oblique muscle was denervated and extirpated. For M2, 4 months later, the contralateral inferior rectus muscle was recessed by 2 mm. tOKN was elicited during monocular viewing of a rotating stimulus that was rear projected onto a screen 43.5 cm in front of the animal. Angular rotation of the stimulus about the center was 40 deg/s clockwise or counterclockwise.

RESULTS

The main findings after trochlear nerve sectioning were (1) the amplitude and peak velocity of torsional quick and slow phases of the paretic eye was less than that in the normal eye for both intorsion and extorsion, and (2) the vertical motion of the paretic eye increased during both torsional slow and quick phases. After corrective inferior oblique surgery, both of these effects were even greater.

CONCLUSIONS

Acquired SOP and corrective inferior oblique-weakening surgery create characteristic patterns of change in tOKN that reflect alterations in the dynamic properties of the extraocular muscles involved in eye torsion. tOKN also provides information complementary to that provided by the traditional Bielschowsky head-tilt test and potentially can help distinguish among different causes of vertical ocular misalignment.