Hering's Law Research Articles

Mathematical Certainty of Homeopathy

HAHNEMANN wanted us to treat patients with a science that is as perfect as mathematics. To practise this science is an art. Art that involves no mathematics! PRAFULL VIJAYAKAR has tactfully combined these two into one by introducing - for a change not a “path-breaking” but rather a path-making concept. He has combined Embryology and Miasms to better understand ORGANON and HERING's law of cure. This article shares his views on this topic.

Evaluation and Management of Unilateral Ptosis and Avoiding Contralateral Ptosis

Treating unilateral ptosis can be challenging and a proper preoperative evaluation may help prevent unexpected outcomes on the contralateral lid. Preoperative evaluation should include testing for Hering's law, which remains useful in understanding the phenomenon of induced contralateral eyelid retraction in the context of ptosis. Approximately 10% to 20% of patients with unilateral ptosis have some degree of induced retraction on clinical evaluation in the contralateral lid. When there is a positive Hering's test on preoperative examination, the surgeon should consider a bilateral ptosis procedure. The surgical approach to unilateral ptosis depends on the severity of the ptosis and its etiology, and the surgeon should be aware of which procedure is most likely to provide the best outcome in selected instances.

Hering's law tested with the pursuit theory of motion parallax

Hering's law tested with the pursuit theory of motion parallax

Pioneers of eye movement research.

Recent advances in the technology affording eye movement recordings carry the risk of neglecting past achievements. Without the assistance of this modern armoury, great strides were made in describing the ways the eyes move. For Aristotle the fundamental features of eye movements were binocular, and he described the combined functions of the eyes. This was later given support using simple procedures like placing a finger over the eyelid of the closed eye and culminated in Hering's law of equal innervation. However, the overriding concern in the 19th century was with eye position rather than eye movements. Appreciating discontinuities of eye movements arose from studies of vertigo. The characteristics of nystagmus were recorded before those of saccades and fixations. Eye movements during reading were described by Hering and by Lamare in 1879; both used similar techniques of listening to sounds made during contractions of the extraocular muscles. Photographic records of eye movements during reading were made by Dodge early in the 20th century, and this stimulated research using a wider array of patterns. In the mid-20th century attention shifted to the stability of the eyes during fixation, with the emphasis on involuntary movements. The contributions of pioneers from Aristotle to Yarbus are outlined.

Unilateral INO is associated with ocular tilt reaction in pontomesencephalic lesions

Correlation of internuclear ophthalmoplegia (INO) with components of the ocular tilt reaction (OTR) in order to localize graviceptive (specifically otolithic) pathways in the brainstem. We retrospectively analyzed data of 120 patients with INO (87 unilateral [9 of whom had one-and-a-half syndrome], 33 bilateral) for OTR (subjective visual vertical [SVV], ocular torsion, skew deviation) to localize causative brainstem lesions in MRI. Unilateral INO was accompanied by at least one component of OTR: SVV tilt in 96%, ocular torsion in 79%, and skew deviation in 50%. All components were directed to the contralesional side. Contralateral OTR occurred in 89% of patients with one-and-a-half syndrome. Only 9% of patients with bilateral INO exhibited OTR. MRI showed distinct lesions in 68%, which almost exclusively projected onto the pontomesencephalic medial longitudinal fascicle (96%). Follow-up measurements revealed SVV and ocular torsion normalized faster than the adduction deficit in INO. First, unilateral internuclear ophthalmoplegia (INO) is regularly associated with contraversive ocular tilt reaction (OTR): INO plus. Thus, graviceptive pathways join the medial longitudinal fascicle after crossing between the vestibular and abducens nuclei. Second, the different time course and degree of recovery of OTR components and INO signs can be explained by the hypothesis that vestibular tone imbalance is compensated by central vestibular adaptation mechanisms (probably driven mainly by cerebellar-vestibular projections), whereas impaired adduction is less susceptible to compensation according to Hering's law and can only be overcome by lesion repair. Third, bilateral INO is seldom associated with OTR, confirming that bilateral impairment of graviceptive pathways does not cause imbalance in roll plane.

The Art of Prescribing

This case was an eye opener, a learning experience for me. Most of us know that homeopathic drugs are “safe and harmless”. But this case illustrates a plain truth that homeopathic drugs can also suppress and that the concept of disease progression as explained by Hahnemann must be clearly understood. The case shows how important being aware of “Hering's law of the direction of cure” is in a correct understanding of the follow-up and that the fact that symptoms have disappeared does not necessarily indicate the patient has been cured.

Effect of Unilateral Blepharoptosis Repair on Contralateral Eyelid Position

This study evaluates the effect of unilateral blepharoptosis repair on contralateral eyelid position and assesses the relation between preoperative eyelid height interdependence, consistent with Hering law, and surgical outcome. The medical records of 54 patients (21 men, 33 women; mean age, 65 years) who underwent external levator advancement for unilateral aponeurotic blepharoptosis were reviewed for preoperative and postoperative margin reflex distance (MRD) of the nonoperated eye. To assess the relation between preoperative Hering dependence (mechanical elevation of the ptotic eyelid causing a decrease in contralateral eyelid height) and postoperative eyelid position, the change in MRD of the nonoperated eye was compared between subjects who on preoperative evaluation did (n=18) and did not (n=36) demonstrate eyelid height interdependence, using the 2-sample t test. After unilateral blepharoptosis repair, the mean (+/- SD) change in contralateral MRD was -0.2 +/- 0.8 mm. There was no significant difference in contralateral MRD change in subjects with and without preoperative Hering dependence (-0.3 +/- 0.8 mm versus -0.2 +/- 0.9 mm, respectively, p=0.78). Seventeen percent (9 of 54) of patients had a contralateral MRD decrease of more than 1 mm. Three patients (5.6%) required contralateral blepharoptosis repair within 1 year of initial surgery. After levator advancement for unilateral blepharoptosis, roughly 17% of patients will have a decrease in contralateral eyelid height of more than 1 mm, with 5% of patients requiring surgical repair during the first postoperative year. The degree of change in contralateral eyelid height cannot be reliably predicted by preoperative assessment of Hering dependence.

Small incision transcutaneous levator aponeurotic repair for blepharoptosis.

Patients presenting with blepharoptosis due to disinsertion or thinning of the levator aponeurosis require surgical repair. A minimally invasive approach directed specifically at the levator aponeurotic anatomic defect may provide benefits to the patient. Proposed advantages of a small eyelid incision (8-13 mm) include less local anesthetic and tissue distortion, less ecchymosis and edema, decreased operative times, a shortened recovery period, and improved surgical results. We describe our results with the use of a small incision ptosis repair in select patients. A retrospective chart review between January 2000 and September 2001 included 91 patients and 118 eyelids with blepharoptosis due to aponeurotic disinsertion, corrected by a minimally invasive approach. The small incision technique comprised levator aponeurotic resection and advancement. Pre- and postoperative upper eyelid marginal reflex distances (MRD1), eyelid contour, need for reoperation, and complications (overcorrection, undercorrection, hematoma, and infection) were recorded. The average preoperative MRD1 measured 0.5 +/- 1.1 mm, with a range of -2.0 to 2.5 mm. The average postoperative MRD1 measured 2.6 +/- 0.8 mm, with a range of 1 to 5.5 mm (P < 0.0001). Of the 118 eyelids corrected by a small incision technique, there were 4 overcorrections, 3 undercorrections, 1 failure, 1 postoperative ptosis procedure of the contralateral upper eyelid secondary to Hering's law ptosis, and 4 patients requesting surgical treatment of dermatochalasis. No symptomatic dry eye, exposure keratopathy, or other complication resulted in association with the overcorrections. No contour abnormalities, infections, hematomas, or other complications were noted. Our experience suggests that utilization of a small skin incision is safe, precise, and efficient and allows for more rapid recovery from surgery. The authors note a decreased incidence of reoperation and postoperative complaints compared with historical larger-incision cases.

Ocular rotation axes during dynamic Bielschowsky head-tilt testing in unilateral trochlear nerve palsy.

To explain the positive Bielschowsky head-tilt (BHT) sign in unilateral trochlear nerve palsy (uTNP) by the kinematics of three-dimensional eye rotations. Twelve patients with uTNP monocularly fixed on targets on a Hess screen were oscillated (+/- 35 degrees, 0.3 Hz) about the roll axis on a motorized turntable (dynamic BHT). Three-dimensional eye movements were recorded with dual search coils. Normal data were collected from 11 healthy subjects. The rotation axis of the viewing paretic or unaffected eye was nearly parallel to the line of sight. The rotation axis of the covered fellow eye, however, was tilted inward relative to the other axis. This convergence of axes increased with gaze toward the unaffected side. Over entire cycles of head roll, the rotation axis of either eye remained relatively stable in both the viewing and covered conditions. In patients with uTNP, circular gaze trajectories of the covered paretic or unaffected eye during dynamic BHT are a direct consequence of the nasal deviation of the rotation axis from the line of sight. This, in turn, is a geometrical result of decreased force by the superior oblique muscle (SO) of the covered paretic eye or, according to Hering's law, increased force parallel to the paretic SO in the covered unaffected eye. The horizontal incomitance of rotation axes along horizontal eye positions can be explained by the same mechanism.

Oculomotricidade e seus fundamentos

Partindo-se de um circuito esquemático relacionando os sistemas sensorial (visual binocular) e oculomotor, cujos defeitos em vias aferentes ou eferentes, ou de suas interações, explicam o aparecimento dos estrabismos e suas conseqüências, são examinados os fundamentos e referenciais da movimentação ocular. Apresentam-se os conceitos de eixos e planos, centro de massa e de rotação, definem-se os movimentos monoculares de translação e de rotação e os binoculares de versões e vergências. É também referida a função dos centros de comando para movimentos voluntários e reflexos, a dos núcleos oculomotores e a respectiva inervação aos músculos oculares externos. Numa segunda parte (fisiologia da musculatura ocular extrínseca) são comentadas as atividades de contração e relaxamento e a importância da lei de Sherrington. Voltando-se ao conceito de posição primária do olhar e dos referenciais das rotações, menciona-se a diversidade de vários sistemas de medidas. Em seguida, são analisadas as ações musculares rotacionais com bases no plano de ação muscular e na distribuição anatômica dos músculos, levando a resultados em posição primária do olhar e nas outras. Os efeitos de fáscias e membranas intermusculares são também comentados, terminando-se com a concepção moderna sobre as ações musculares (ação simultânea de todos os músculos em quaisquer das posições oculares). Com os condicionantes da lei de Hering, desenvolve-se o conceito de posições diagnósticas (das disfunções oculomotoras), diferentemente do clássico: os músculos são considerados em pares, de acordo às suas ações predominantes ___ horizontais (retos horizontais), verticais (retos verticais) ou torcionais (oblíquos). Em cada qual devem ser comparadas as ações em condições diametralmente opostas de fixação ocular e posições do olhar (por exemplo, supradextroversão na fixação com o olho direito e infralevoversão na fixação com o olho esquerdo, para comparação de ações dos músculos retos superior direito e inferior esquerdo, respectivamente). Também é analisada a influência das inclinações de cabeça sobre essas ações. O artigo termina examinando a relação sincinética entre a acomodação e convergência, a convergência proximal e as unidades dessas funções.

Incomitance of ocular rotation axes in trochlear nerve palsy.

Strabismus due to palsy of a single muscle in one eye is always incomitant, which is a consequence of Hering's law of equal innervation. We asked whether this law had similar consequences on the orientation of ocular rotation axes. Patients with unilateral trochlear nerve palsy were oscillated about the nasooccipital (= roll) axis (+/-35 degrees, 0.3 Hz), and monocularly fixed on targets on a head-fixed Hess screen. Both the covered and uncovered eyes were measured with dual search coils. The rotation axis of the covered eye (paretic or healthy) tilted more nasally from the line of sight when gaze was directed toward the side of the healthy eye. The rotation axis of the viewing eye (paretic or healthy), however, remained roughly aligned with the line of sight. We conclude that incomitance due to eye muscle palsy extends to ocular rotation axes during vestibular stimulation.

Neural basis of disjunctive eye movements.

New evidence has challenged a widely accepted interpretation of Hering's law of equal innervation, which states that disjunctive saccades are produced by the linear addition of conjugate and vergence innervation commands produced by independent oculomotor subsystems. We hypothesize, instead, that saccades are produced by a monocular premotor control network. A model, based on this hypothesis and consistent with known brain-stem anatomy, simulates realistic disjunctive saccades including initial and late slow vergence movements.

Determination of resting upper eyelid position in patients with ptosis

Many patients with blepharoptosis have increased innervational tone to both levator palpebrae superioris muscles, subject to the Hering law. Other patients may habitually contract the frontalis muscles to clear the visual axes. Determination of the resting eyelid position is helpful in planning surgical correction. A technique for simultaneously relaxing the frontalis muscles and eliminating excess levator innervation employs interruption of fixation of the eye with ptosis and manual elevation of the contralateral upper eyelid.

Transformation of the visual-line value in binocular vision: stimuli on corresponding points can be seen in two different directions.

We examined Wheatstone's (1838 Philosophical Transactions of the Royal Society of London 128 371-394) claim that images falling on retinally corresponding points can be seen in two different directions, in violation of Hering's law of identical visual direction. Our analyses showed that random-dot stereograms contain stimulus elements that are conceptually equivalent to the line stimuli in the stereogram from which Wheatstone made his claim. Our experiment demonstrated that two lines embedded in a random-dot stereogram appeared in two different directions when they stimulated retinally corresponding points, if the disparity gradient value of the lines was infinity relative to adjacent elements. To ensure that the two lines stimulated corresponding points, observers made vergence eye movements while maintaining the perception of the two lines in two different directions.

Tests of two hypotheses to account for different-sized saccades during disjunctive gaze shifts.

Rapid shifts of the point of visual fixation between objects that lie in different directions and at different depths require disjunctive eye movements. We tested whether the saccadic component of such movements is equal for both eyes (Hering's law) or is unequal. We compared the saccadic pulses of abducting and adducting movements when horizontal gaze was shifted from a distant to a near target aligned on the visual axis of one eye (Müller paradigm) in ten normal subjects. We similarly compared horizontal saccades made between two distant targets lying in the same field of movement as during the Müller paradigm tests, and between targets lying symmetrically on either side of the midline, at near side of the midline, at near or far. We measured the ratio of the amplitude of the movements of each eye in corresponding directions due to the saccadic component, as well as corresponding ratios of peak velocity and peak acceleration. In response to a Müller test paradigm requiring about 17 degrees of vergence, the change in position of the unaligned eye was typically twice the size of the corresponding movement of the aligned eye. The ratio of peak velocities for the unaligned/aligned eyes was about 1.5, which was greater than for saccades made between distant targets. The ratio of peak acceleration for unaligned/aligned eyes was about 1.0 during shifts from near to far and about 1.3 for shifts from far to near, these values being similar to corresponding ratios for saccades between distant targets. These measurements of peak acceleration indicate that the saccadic pulses sent to each eye during the Müller paradigm are more equal than would be deduced by comparing the changes in eye position. We retested five subjects to compare directly the peak acceleration of saccades made during the Müller paradigm with similar-sized "conjugate" saccades made between targets at optical infinity. Saccades made during the Müller paradigm were significant slower (P < 0.005) than similar-sized conjugate saccades; this indicated that the different-sized movements during Müller paradigm are not simply due differences in saccadic pulse size but are also influenced by the concurrent vergence movement. A model for saccade-vergence interactions, which incorporates equal saccadic pulses for each eye, and differing contributions from convergence and divergence, accounts for many of these findings.

Premotor commands encode monocular eye movements.

Binocular coordination of eye movements is essential for stereopsis (depth perception) and to prevent double vision. More than a century ago, Hering and Helmholtz debated the neural basis of binocular coordination. Helmholtz believed that each eye is controlled independently and that binocular coordination is learned. Hering believed that both eyes are innervated by common command signals that yoke the eye movements (Hering's law of equal innervation). Here we provide evidence that Hering's law is unlikely to be correct. We show that premotor neurons in the paramedian pontine reticular formation that were thought to encode conjugate velocity commands for saccades (rapid eye movements) actually encode monocular commands for either right or left eye saccades. However, 66% of the abducens motor neurons, which innervate the ipsilateral lateral rectus muscle, fire as a result of movements of either eye. The distribution of sensitivity to ipsilateral and contralateral eye movements across the abducens motor neuron pool may provide a basis for learning binocular coordination in infancy and adapting it throughout life.

Is there a primary and secondary torsion deviation in paralysis of the grand oblique muscle?

An extraocular muscle palsy is conventionally characterized by a deviation of the visual axes, this being greater when measured with the affected eye fixing. By definition and illustrating Hering's law, this secondary angle of deviation is greater than the primary one, measured with the sound eye fixing. We present here a comparative study of the amount of subjective excyclodeviation measured in patients suffering from IVth nerve palsy, with the sound or affected eye fixing. Two groups of patients were entered into the study: Group 1 (N = 54) for superior oblique palsies studied retrospectively and Group 2 (N = 14), for a prospective study of those recently acquired (post-traumatic) and followed over 6 months. In both groups, measurements were made at two stages, early (1 to 7 weeks after onset) and late (4 to 6 months later). In both groups, the majority of cases showed a greater secondary torsional deviation, the difference between this and the primary deviation lessening on late stage measurements. In both groups, the difference between primary and secondary torsional deviation was not statistically significant.

Evidence for separate control of slow version and vergence eye movements: support for Hering's Law.

When a visual stimulus changes direction and distance simultaneously, Hering's Law argues that the resulting eye movements are the result of combined version and vergence control processes. Recently, it has been suggested that slow asymmetrical eye movements might be guided by monocular control processes wherein each eye is driven by its own retinal image. Experimental results presented here show behavioral differences between slow version and slow vergence eye movements, indicating that different control processes drive the two "pure" responses. Specifically, version tracking of constant velocity stimuli (i.e., smooth pursuit) is more precise, showing less variation in tracking velocity than movements of equal velocity produced by vergence stimuli. When the two stimuli are combined, the variability in tracking is consistent with the addition of the two components in proportion to their respective stimuli. These results provide support for Hering's Law, at least for low velocity, smooth tracking movements (i.e., slow version and slow vergence.

Hering's law and eyebrow position.

A patient with bilateral but asymmetrical brow ptosis is presented in whom the frontalis action on the relative position of the eyebrows could be demonstrated to obey Hering's law of equal innervation. The neurological basis for this finding is discussed, along with the implications for the surgical management of brow ptosis.

Binocular eye movements not coordinated during REM sleep.

Rapid eye movements (REMs) are a defining characteristic of REM sleep during which vivid dreams occur. It has been suggested that REMs may be binocularly coordinated and related to "watching" dream images. For the first time, binocular eye movements were recorded during natural REM sleep in monkeys to test the conjugate nature of the oculomotor system and the "scanning hypothesis" of REMs during sleep. During REM sleep, the lines of sight of the two eyes are frequently misaligned up to 30 degrees horizontally and/or vertically. Since the lines of sight usually don't intersect, there is no fixation point. Instead, each eye is aimed at a different part of the visual field during REM sleep. Furthermore, REMs are not usually conjugate, but are disjunctive or even monocular in horizontal or vertical directions. These data argue against the idea that REMs actually "track" dream images, unless each eye is watching its own dream! Binocular misalignment and disjunctive (even monocular) REMs during sleep suggest that separate left eye and right eye pathways generate saccades in each eye and control the position of each eye. Binocular coordination cannot be the passive result of anatomical connectivity as has been argued previously, but instead must result from a high-level process associated with the awake state that coordinates activity in left-eye and right-eye pathways. Hering's law of equal innervation is not consistent with these data.