Hering's Law Research Articles

An Individualised Homoeopathic Approach to Chronic Atopic Dermatitis: A Case Report

AbstractAtopic dermatitis is a chronic inflammatory skin disease affecting about one-fifth of all individuals during their lifetime. It has substantial impact on the quality of life of the affected individual. Not only patient is affected by the social stigma of a visible skin condition but also the characteristic itch-scratch cycle often leads to skin trauma and significant sleep disruption. Though there is multitude of treatment options in modern medicine, the recurrence, and adverse effects of medications cannot be ruled out. Therefore, an alternative approach is required. The case presented here reported with the complaint of severe generalised itching eruptions for the last 8 years with a history of atopy. After thorough evaluation from the clinical and homoeopathic standpoint, a single homoeopathic medicine Arsenicum iodatum was prescribed in different potencies at different timepoints as the symptomatology corresponds. Following the administration of individualised homoeopathic (IH) medicine, there was gradual improvement in the case with disappearance of skin lesions which was also evaluated through reduction in SCORing Atopic Dermatitis and Dermatology Life Quality Index scores. During the treatment, old symptoms also reappeared indicating improvement in accordance with Hering's law of cure and Kent's 11th observation. The modified Naranjo criteria score after the treatment course was 10 which exclusively shows positive causal attribution of the IH in this case.

A new oculomotor model demystifies "Remarkable Saccades".

Hering's Law of binocular eye movement control guides most oculomotor research and supports diagnosis and treatment of clinical eye misalignment (strabismus). The law states that all eye movements are controlled by a unitary conjugate signal and a unitary vergence signal that sum. Recent evidence of temporally asynchronous inter-eye rotations during vergence (Chandna et al., 2021) challenges the viability of a unitary vergence signal. An alternative theory that might explain these anomalous results posits that the eyes are controlled independently. Yet independent control fails to explain a phenomenon known as "Remarkable Saccades" where an inappropriate saccade occurs from an eye aligned on a target during asymmetric vergence (Enright, 1992). We introduce a new model formulated to describe the Chandna et al. (2021) midline vergence result that generates remarkable saccades as an emergent property. The Hybrid Binocular Control model incorporates independent controllers for each eye with a cortical origin that interact with a unitary conjugate controller residing in brainstem. The model also accounts for behavioral variations in remarkable saccades when observers attend to an eye. Furthermore, it suggests more generally how the eyes are controlled during vergence and other voluntary eye movements, thus challenging documented oculomotor neural circuitry and suggesting that refinements are needed for clinical oculomotor interventions.

Teaching Video NeuroImages: Useful bedside testing for myasthenia gravis

During examination of a 62-year-old woman with a diagnosis of myasthenia gravis, left eyelid manual elevation caused exacerbated ptosis on the right (enhanced ptosis) (figure). According to Hering law, there is approximately equal innervation of the levator palpebrae superioris muscles in both eyelids.1 In an asymmetric ptosis, the motor impulses increase to compensate ptosis on the more affected side but also flow to the contralateral eyelid, which mitigates ptosis on that side. With manual elevation of the more affected eyelid, the need to sustain eyelid elevation is relieved, and there is an attenuation of these motor impulses causing ptosis enhancement of the other eyelid (video 1).2

A case report of hyperuricaemia with nephrolithiasis treated with homoeopathy

Introduction: Hyperuricaemia is serum urate concentration exceeding the limit of solubility, leading to its precipitation and predisposing the affected persons to gout. The increased level of uric acid in urinary excretion can also lead to nephrolithiasis. It has also been implicated as an indicator for diseases such as metabolic syndrome, diabetes mellitus, cardiovascular disease and chronic renal disease. Whereas homoeopathic literature enlists many medicines for this condition, there is a paucity of evidence-based published studies. Case Summary: The case presented here reported with the complaint of renal stone secondary to high serum uric acid levels. A single homoeopathic medicine Lycopodium was prescribed after thorough case taking which led to improvement in subjective symptoms and objectively reflecting in gradually decreasing levels of serum uric acid after elimination of stone. During the course of treatment, old symptoms also re-appeared depicting improvement in accordance with Hering's law of cure. The Modified Naranjo Criteria score after treatment was 8, which explicitly shows the positive causal attribution of the individualised homoeopathic medicine Lycopodium in this case. Homoeopathic treatment has shown favourable results in this case and demonstrates the scope of Homoeopathy in such cases.

Hering's Law in Congenital Ptosis: Evaluation of the Contralateral Response to Unilateral Congenital Ptosis Repair.

To determine the applicability and clinical relevance of Hering's law for the eyelids in cases of congenital ptosis. A retrospective chart review and digital photograph analysis of patients who underwent unilateral congenital ptosis repair at a tertiary, university-based, Oculoplastics clinic was conducted. Pre- and postoperative eyelid height (marginal reflex distance), upper eyelid symmetry, and brow position were determined using ImageJ analysis software. Changes in these values, and the relationship between the change in ipsi- and contralateral eyelid heights and brow positions, were determined. In 51 patients, the mean change in contralateral upper eyelid position (marginal reflex distance) following unilateral repair was -0.5 mm with 29% (n = 15) demonstrating a greater than 1 mm contralateral descent. The contralateral brow position remained stable with a mean change of +0.1 mm. No significant differences were seen between the 15 patients who demonstrated a contralateral upper eyelid descent greater than 1 mm and the remainder of the cohort in terms of amblyopia rate (p = 0.71), mean preoperative marginal reflex distance (p = 0.14), mean change in ipsilateral marginal reflex distance (p = 0.32), mean change in contralateral brow position (p = 0.44), or mean postoperative upper eyelid asymmetry (1.3 mm vs. 1.2 mm). Overall, the mean upper eyelid asymmetry improved from 2.6 mm preoperatively to 1.2 mm postoperatively. None of the 51 patients underwent subsequent contralateral ptosis repair. Hering's law for the eyelids applies to cases of congenital ptosis but has little clinical significance due to improved upper eyelid asymmetry following unilateral surgery.

Application of the Hering's law in corrective surgery for asymmetric bilateral ptosis

Objective To evaluate the clinical result of Hering's law in the correction of asymmetric bilateral ptosis. Methods From January 2014 to July 2016, 165 cases divided into 2 groups with asymmetric bilateral ptosis in mild and moderate ptosis were corrected with aponeurosis advancement type correction: A group of 15 cases, in which the surgery does not consider the influence of Hering's law, the first correction of mild side, and then corrected the heavier side; B group of 150 cases, in which the Hering's law was applied, the first correction of severe side so that the margin reached the edge of the cornea is tangent or low 0.5-1.0 mm, and then corrected mild side. That the difference of symmetry between the two sides of the palpebral fissure was less than 0.5 mm, and the follow-up was more than 3 months. The Pearson chi square test was used to compare the differences between the two groups. Results In this group, 165 cases were followed up for 3-24 months, 10 cases (66.67%) was satisfactory in group A (15 cases); 145 cases (96.67%) was satisfactory in group B (150 cases); After 3 months, all the failure cases got satisfactory result by using the Hering's law in corrective surgery again. The P value of chi square test between groups was less than 0.05. Conclusions The application of Hering's law in the correction of asymmetry bilateral ptosis is more satisfactory. Key words: Hering's law; Asymmetry bilateral ptosis; Levator palpebrae superioris muscle

Retrospective Analysis of the Effect of Hering's Law on Outcomes of Surgical Correction of Ptosis.

IntroductionSeveral factors may influence aesthetic outcomes of ptosis surgery, especially in patients with asymmetrical ptosis. We retrospectively assessed the effect of Hering's law on surgical outcomes of patients with asymmetrical ptosis.MethodsPatients with mild to moderate asymmetrical ptosis (N = 300) who underwent advancement or plication of upper eyelid aponeurosis between January 2014 and July 2016 were enrolled. Fifty patients (group A) underwent surgery without taking into consideration the impact of Hering's law. Of these, 35 patients with unilateral ptosis (subgroup A1) underwent standard surgery on the contralateral side, whereas 15 patients with bilateral ptosis (subgroup A2) were first operated on the milder side followed by the more severely affected side.In 250 patients (group B), surgery was performed taking cognizance of the implications of Hering's law. These included 100 patients with unilateral ptosis (B1) and 150 with bilateral ptosis (B2). Difference in bilateral palpebral fissure symmetry by less than 0.5 mm was considered as satisfactory outcome.ResultsDuration of postoperative follow-up ranged from 3 to 24 months. Satisfactory outcomes were achieved over 60% of patients in group A (A1, 60.6%; A2, 66.67%) and in 96% of patients in group B (B1, 95%; B2, 96.67%). Patients with unsatisfactory outcomes underwent repair according to Hering's law after 3 months and obtained good results.ConclusionsApplication of Hering's law may improve outcomes of corrective surgery in patients with asymmetric ptosis.

Magnetic resonance imaging in dissociated strabismus complex demonstrates generalized hypertrophy of rectus extraocular muscles

Dissociated strabismus complex (DSC) is an enigmatic form of strabismus that includes dissociated vertical deviation (DVD) and dissociated horizontal deviation (DHD). We employed magnetic resonance imaging (MRI) to evaluate the extraocular muscles in DSC. We studied 5 patients with DSC and mean age of 25years (range, 12-42years), and 15 age-matched, orthotropic control subjects. All patients had DVD; 4 also had DHD. We employed high-resolution, surface coil MRI with thin, 2mm slices and central target fixation. Volumes of the rectus and superior oblique muscles in the region 12mm posterior to 4mm anterior to the globe-optic nerve junction were measured in quasi-coronal planes in central gaze. Patients with DSC had no structural abnormalities of rectus muscles or rectus pulleys or the superior oblique muscle but exhibited modest, statistically significant increased volume of all rectus muscles ranging from 20% for medial rectus to 9% for lateral rectus (P<0.05). DSC includes various combinations of sursumduction, excycloduction, and abduction not conforming to Hering's law. We have found modest generalized enlargement of all rectus muscles. DSC is associated with generalized rectus extraocular muscle hypertrophy in the absence of other orbital abnormalities.

The Impact of Hering's Law in Blepharoptosis: Literature Review.

The aim of this literature review is to examine Hering's law, a well-documented phenomenon in blepharoptosis patients, with 10% to 20% noted in cases of unilateral ptosis. Predominantly presenting as contralateral eyelid drop postoperatively, it poses a challenge for eyelid surgeons in the pursuit of symmetry and appropriate eyelid height. Proper preoperative evaluation is of utmost importance, consisting of one of either lifting test, covering test, or phenylephrine test. A deeper understanding of Hering's law further provides adequate information for optimal management of ptosis. In regard to ptosis etiology, congenital ptosis does not appear to have a distinct relation to positive Hering's law, commonly associated with a low incidence, when compared with acquired ptosis. Ptosis in the dominant eye seems to be related to a higher incidence of the phenomenon than ptosis in the nondominant eye, with statistical significance in studies ranging from P < 0.001 to P = 0.09. This can be explained as an innate response for increased innervation to regain the field of vision. Both ptosis severity and levator function appear to be of lesser importance than ptosis etiology, with minimal incidence of Hering's law in congenital ptosis regardless of these factors. It is, however, noted that ptosis severity has direct association with contralateral eyelid position in acquired ptosis, whereas there is a lack of studies for levator function. In the event of preoperative contralateral eyelid drop, surgeons should consider simultaneous surgery instead of delayed surgery for bilateral ptosis (P = 0.002). For unilateral ptosis, although reoperation is done per patient request, it may be more appropriate to first wait for roughly 2 weeks and reassess for self-regulation to a normal eyelid position.

Monocular microsaccades are visual-task related.

During visual fixation, we constantly move our eyes. These microscopic eye movements are composed of tremor, drift, and microsaccades. Early studies concluded that microsaccades, like larger saccades, are binocular and conjugate, as expected from Hering's law of equal innervation. Here, we document the existence of monocular microsaccades during both fixation and a discrimination task, reporting the location of the gap in a foveal, low-contrast letter C. Monocular microsaccades differ in frequency, amplitude, and peak velocity from binocular microsaccades. Our analyses show that these differences are robust to different velocity and duration criteria that have been used previously to identify microsaccades. Also, the frequency of monocular microsaccades differs systematically according to the task: monocular microsaccades occur more frequently during fixation than discrimination, the opposite of their binocular equivalents. However, during discrimination, monocular microsaccades occur more often around the discrimination threshold, particularly for each subject's dominant eye and in case of successful discrimination. We suggest that monocular microsaccades play a functional role in the production of fine corrections of eye position and vergence during demanding visual tasks.

Commentary on: The Effect of Hering's Law on Different Ptosis Repair Methods.

The author of “The Effect of Hering's Law on Different Ptosis Repair Methods” should be acknowledged for his work studying a series of patients who underwent ptosis surgery.1 Eyelid ptosis presents one of the most confounding challenges to an aesthetic surgeon because often this procedure that seems so simple can have inconsistent results. When I was a fellow years ago with Crowell Beard, he told me, “If it weren't for ptosis, oculoplastic surgeons wouldn't exist.” In our practice, we have found the levator advancement procedure to be the single most effective and consistent procedure to correct small and large amounts of ptosis from many different etiologies. In addition, most adult patients with ptosis also have dermatochalasis and thus would benefit from a blepharoplasty. An anterior approach allows the surgeon to create an eyelid crease as well as to correct the anatomic defect in the dehisced levator tendon and only adds a few minutes to the operative time in experienced hands.2,3 The author presents a creditable discussion regarding the effect of Hering's dependence on the ptosis occurring on the contralateral side after unilateral ptosis surgery. The importance of preoperative evaluation of the ptosis patient cannot be overstated. It is essential, as the author points out, to try to establish the cause of the ptosis—be it aponeurotic, congenital, traumatic, or neurogenic from a Horner's syndrome—and to perform a full exam …

The Effect of Hering's Law on Different Ptosis Repair Methods.

The Hering's law effect has significant importance in surgical planning and outcomes of eyelid surgery. The current study examined the preoperative and intraoperative effect of Hering's law in Mullerectomy and levator aponeurosis advancement. A retrospective analysis was conducted of 52 patients with unilateral ptosis who underwent surgical repair from January 2011 through June 2013. Patients underwent levator aponeurosis advancement or Mullerectomy with or without tarsectomy. Preoperative and postoperative clinical documentation and photographs were evaluated. Preoperative Hering's dependency and postoperative changes in positioning of the non-operated eyelid were measured. The decision to operate on the ptotic eye alone or on both eyelids was based on preoperative Hering's dependence and intraoperative changes in the contralateral eyelid. Fifty-two patients with unilateral ptosis were included. Average age was 63.3 ± 20.1 years (range, 22-88 years; median, 61 years); 34 (65.4%) were female. The 14 cases that were not aponeurotic (either congenital, secondary to trauma, or due to postoperative ptosis) did not need contralateral repair (p = .000). In 4 (19%) cases of Mullerectomy and in 9 (52.9%) cases of levator advancement, both eyelids required surgery (p = .029). Hering's law effect was significantly more apparent in the levator advancement approach than in Mullerectomy. Levator surgery resulted in a higher incidence of combined intraoperative and postoperative Hering's law effect than did Mullerectomy. Cases with poor levator function or congenital ptosis can be repaired unilaterally with no need for contralateral surgery. The fibrotic levator palpebrae muscle and its special innervations probably explain this phenomenon. This should be considered in surgical planning.

Hering's Law Assessment Tool revisited: introducing a modified novel version--Patients' Response Assessment Tool after Homeopathic Treatment (PRATHoT) in chronic cases.

Hering's Law Assessment Tool emerged as a systematic outcome assessment tool following homeopathic intervention. The authors intend to modify it and develop a new tool-Patient Response Assessment Tool after Homeopathic Treatment (PRATHoT)-in chronic cases through Delphi technique for systematic categorization of probable outcomes following individualized homeopathic treatment in chronic cases. The PRATHoT was drafted after literature review and iterative Delphi rounds with multidisciplinary expert panel, setting Fleiss κ of 0.41 to 1.00 a priori as the desired level of multirater agreement. Following pilot testing, the tool was implemented on 37 patients suffering from knee osteoarthritis over 6 months. Logistic regression analysis confirmed that higher PRATHoT score was significantly associated with achieving pain visual analogue scale responses from the second follow-up visit onwards (B = 0.037-0.066; SE = 0.021-0.036; P = .003-.048). The tool appeared to have acceptable psychometric properties; hence, it may be considered as a promising tool, amendable for further development.

The Role of Frontalis Orbicularis Oculi Muscle Flap for Correction of Blepharoptosis With Poor Levator Function

On the basis of the close anatomical interdigitation between the longitudinal-oriented frontalis muscle and the horizontal-oriented orbicularis oculi muscle (OOM), frontalis OOM (FOOM) flap was developed to treat blepharoptosis. Retrospective study during an 11-year period, 66 patients with 81 poor levator function ptotic eyelids accepted FOOM flap shortening (65 lids; 80.2%) or double-breasted FOOM flap advancement (16 lids; 19.8%) to correct blepharoptosis. There were 51 (77.3%) patients with unilateral ptosis and 15 (22.7%) patients with bilateral ptosis. Severity of blepharoptosis included severe type in 72 (88.9%) lids, moderate type in 5 (6.2%) lids, and mild type in 4 (4.9%) lids. The underlying etiology included congenital origin in 43 (65.1%) patients, involutional change in 19 (28.8%) patients, and neurologic origin in 4 (6.1%) patients. Marginal reflex distance 1 and lid slit distance improved from -1.6 (2.0) to 3.3 (1.2) and 3.2 (2.0) to 7.2 (1.4) mm, respectively, after operation. The postoperative outcome includes good results in 54 (81.8%) patients, fair results in 10 (15.2%) patients, and poor results in 2 (3.0%) patients. The undercorrection or recurrence rate is 14.8%, and secondary revision rate is 11.1%. Positive Hering law is 17.6% among patients with unilateral ptosis. Overall patients' satisfaction rate is 95.1%. Both FOOM flap shortening and double-breasted FOOM flap advancement are effective to treat poor levator function blepharoptosis. Double-breasted FOOM flap advancement is highly recommended because of the more natural contour and minimal lagophthalmos postoperatively, because of the maximal preservation of OOM.

Eye Dominance and Hering’s Law Effect on Bilateral Blepharotosis Repair

Eye dominance and Hering's law dependence are postulated to influence eyelid position, and thus affect surgical outcomes following blepharoptosis surgery. Pseudoretraction of the contralateral eyelid, usually observed in the nondominant eye, is a well-recognized occurrence in the ophthalmic literature. In this article, these 2 phenomena were assessed preoperatively in blepharoptosis patients to evaluate their effect on postoperative outcomes. In this retrospective cohort study, postoperative eyelid position and rates of reoperation were investigated in 38 patients with bilateral involutional ptosis, who underwent bilateral ptosis repair. Institutional Review Board approval was obtained. In addition to the standard ptosis preoperative evaluation, patients were tested for Hering's law dependence and eye dominance. None of the patients included in the study had significant postoperative eyelid asymmetry or required reoperation. Eye dominance and Hering's law dependence did not affect the surgical outcomes of the patients included in this study who had bilateral ptosis repair performed. It was postulated that this may be due to the balancing of these 2 factors intraoperatively, thus negating their effect on eyelid position postoperatively.

Is Hering's Law as Important in Congenital Blepharoptosis as in Acquired Ptosis?

Although Hering's law has significant importance in the planning and outcomes of eyelid surgery, it has not been applied in all cases of ptosis. The authors evaluate whether cases of unilateral congenital ptosis require surgery on the contralateral eyelid, in keeping with Hering's law. The records of 35 consecutive patients with unilateral congenital ptosis who had surgical repair between 2007 and 2012 were retrospectively analyzed. All patients underwent either levator resection or frontalis sling surgery. Preoperative and postoperative clinical documents and photographs were evaluated for each case, including preoperative Hering's dependence and postoperative measurements of the change in position of the nonoperated eyelid. There were 19 women and 16 men, and the average patient age was 9.7 ± 10 years. The mean preoperative levator function and marginal reflex distance were 6.7 ± 4.7 mm and 0.3 ± 0.47 mm, respectively. There were significant differences in age, preoperative levator function, and marginal reflex distance between patients who underwent levator resection and those who had frontalis sling surgery. In all patients, the preoperative Hering's dependence of eyelid position did not show any decrease, and the position of the contralateral eyelid postoperatively did not differ from the baseline position. This research shows that Hering's law does not apply to cases of congenital ptosis. This is likely due to the fibrotic levator palpebrae muscle and its special innervations. Thus, it is not necessary to perform levator resection or a frontalis sling operation on the unaffected eyelid.

Monitoring improvement in health during homeopathic intervention. Development of an assessment tool based on Hering’s Law of Cure: the Hering’s Law Assessment Tool (HELAT)

Hering's 'Law of Cure' is considered important in homeopathy and thought to predict a positive outcome to treatment. No formal outcome measures are currently available to monitor response to homeopathic treatment on the basis of these assumptions. We describe a simple assessment tool, the Hering's Law Assessment Tool (HELAT) to identify and differentiate patient responses to homeopathic treatment as corresponding to Hering's Law from other symptomatic responses. We describe the development of the tool and assess its face, content and predictive validity. The HELAT was initially developed through literature review, discussion between homeopaths and clinical experience. In phase one, the tool was reviewed by three experienced homeopaths to assess face and content validity. In phase two, we tested its predictive validity by hypothesizing that the HELAT total score may predict changes in a clinical response (using standard validated rheumatological outcome, the American College of Rheumatology (ACR)20%) in 32 patients with rheumatoid arthritis receiving homeopathic intervention over 24 weeks as part of a clinical trial. The HELAT was piloted and changed to improve face and content validity and the final version was then employed for phase two as a predictor of outcome. HELAT total score predicted patient's clinical response (ACR20) [B = 1.142, SE = 0.462, P = 0.013] which was independent of practitioner assessing the patients treatment response [B = 1.04, SE = 1.01, P = 0.302]. The initial data suggests that the HELAT may hold promise for a potential clinical and research outcome measure in homeopathy. Further work is now needed to formally assess its reliability and validity for potential use in clinical practice and trials.

Binocular coordination of eye movements – Hering’s Law of equal innervation or uniocular control?

The neurophysiological basis for binocular control of eye movements in primates has been characterized by a scientific controversy that has its origin in the historical conflict of Hering and Helmholtz in the 19th century. This review focuses on two hypotheses, linked to that conflict, that seek to account for binocular coordination - Hering's Law vs. uniocular control of each eye. In an effort to manage the length of the review, the focus is on extracellular single-unit studies of premotor eye movement cells and extraocular motoneurons. In the latter half of the 20th century, these studies provided a wealth of neurophysiological data pertaining to the control of vergence and conjugate eye movements. The data were initially supportive of Hering's Law. More recent data, however, have provided support for uniocular control of each eye consistent with Helmholtz's original idea. The controversy is far from resolved. New anatomical descriptions of the disparate inputs to multiply and singly innervated extraocular muscle fibers challenge the concept of a 'final common pathway' as they suggest there may be separate groups of motoneurons involved in vergence and conjugate control of eye position. These data provide a new challenge for interpretation of uniocular premotor control networks and how they cooperate to produce coordinated eye movements.

Japanese street performer mimes violation of Hering's Law

Mime artists often use movement to imply the breaking of physical laws: suitcases levitate, air becomes as impermeable as glass. We present the simulated (and actual) violation of a physiologic principle, Hering's Law of Equal Innervation. To provide stereopsis while avoiding double vision, the movements of forward-facing primate eyes must be closely coordinated. In a 19th-century debate, Helmholtz contended that this coordination is a learned process, taming naturally independent eyes. Hering, meanwhile, believed the eyes to be inherently reined to each other and driven by a single control signal.1 Hering's view predominated and this final common pathway for horizontal eye movement came to be accepted as a unilateral signal to the abducens nucleus. This directly controls the lateral rectus of the ipsilateral, abducting, eye but also necessarily adducts the other eye, via interneurons to the contralateral oculomotor nucleus. More recent neurophysiologic evidence, however, indicates that primate saccadic commands can be encoded monocularly,2 in common with the laterally mounted, independently moving eyes of our distant evolutionary forebears. Binocular coordination might therefore not arise as a necessary consequence of neuroanatomic connectivity. If so, it might be possible to execute voluntary monocular saccades. We present a case of a …

Disorders of vergence eye movements

The aim is to re-interpret disorders of vergence in the light of recent studies that view disjunctive eye movements as but one component of three-dimensional gaze control. Most natural eye movements combine vergence with saccades, pursuit and vestibular eye movements. Electrophysiological studies in epileptic patients, as well as evidence from monkeys, indicate that frontal and parietal cortex govern vergence as a component of three-dimensional gaze. Clinicians apply Hering's law of equal innervation to interpret disjunctive movements as the superposition of conjugate and vergence commands. However, electrophysiological studies indicate that disjunctive saccades are achieved by programming each eye's movement independently. Patients with internuclear ophthalmoplegia (INO) may have preserved vergence, which can be recruited to compensate for loss of conjugacy. Vergence may also enable gaze shifts in saccadic palsy. Some forms of nystagmus suppress or change with convergence; co-contraction of the horizontal rectus muscles does not appear to be the explanation. Rather, effects of near viewing on central vestibular mechanisms or differential activation of specific types of extra-ocular muscle fiber may be responsible. Interpretation of disorders of vergence is aided by applying a scheme in which their contributions to three-dimensional gaze control is considered.