Posture and eye.
P.E. Gallenga1, C. Mincarelli2, C.E. Gallenga3 and L. Mele4
1 Clinic Ophthalmology University G. D’Annunzio, Chieti-Pescara, Chieti, Italy
2 CNO Stenella, Pescara, Italy
3 Department of Morphology, Surgery and Experimental Medicine University of Ferrara, Ferrara, Italy
4 Department of Ophthalmology, Cornea Transplant Unit, II University, Naples, Italy
vision and posture, refraction defects, low vision, anomalous head position, stabilometric platform, muscular chains
The visual telereceptor represents an important entry for postural stability understood as control and energy expenditure in space. Information for the control of the visual target involves feedback and feedforward responses from the proprioceptors of the extrinsic ocular muscles, from vestibular proprioceptors, from receptors of semicircular canals, from proprioceptors of the temporal muscle and neck muscles: system coordinated by the cerebellum. The visual apparatus is universally recognized as a postural receptor which simultaneously identifies proprioceptive components (neuromuscular spindles, Golgi tendon organs of extrinsic muscles) and exteroceptive components (cones and rods). The proprioceptive afferents, in respect to the visual, transmit information in response to the stimulus more quickly (70-100ms vs 200ms). The input discharges on the foot through the muscular chains that represent circuits in continuity of direction and of plan through which the organizational forces of the balance of the body are propagated. The problem of prescription lenses and which type of lens to recommend based on the refractive defect and personal needs, should also include patient comfort and the evaluation of how the lens and prescribed glasses interact on the patient’s well-being, which expresses itself in interference with the posture. That is, with the correction of postural abnormalities induced by the refraction defect, since emmetropia, binocular vision and stereoscopic sense do not change the posture, but their deficit does. Refraction defects and low vision therefore induce postural variations that can be evaluated with a digitalised stabilometric platform.
The tonic-postural system consists of peripheral receptors - afferent and efferent nerve pathways – and peripheral and central nervous system. The receptors, that is the "entrances", are represented by the foot receptor, the visual telereceptor, the stomatognathic apparatus (occlusal system and tongue), and the inner ear. The afferent system is represented by the articular musculotendinous proprioceptive component, cutaneous, visceral and propriospinal; the efferent system is represented by a vestibular, reticular, cerebellar component (1) (Fig. 1 a, b). 1a 1b Fig. 1. a) Muscular output control. b) Gaze movement control. In a complex and continuous Feedforward/Feedback/Feedforward circuit, the central nervous system uses the information from its receptors to become aware of the position of the body in space in the context of gravity balance and the position of the head towards the trunk (2) (head-neck axis, shoulder girdle, column-pelvis, plantar support). The control of gaze movements also occurs with complex feedback/feedforward interactions, circuits that allow for fine and constant adjustments to keep the target - even mobile - in the center of the fixation field, stimulating the macular cones for distinct vision and keeping body balance (Fig. 1b). In the nineteenth and early twentieth centuries, the roles of organs and systems in terms of postural control were gradually defined: in 1828 Flourens demonstrated the importance of the vestibule, Romberg in 1853 the role of the eyes, Longet in 1861 the proprioception of the paravertebral muscles, De Cyon in 1911 the oculomotor proprioception, and Magnus in 1926 the role of the sole of the foot, up to the 'helicoidal' theory of Paparella Treccia (3)(1978) that surpasses the theories of Root and Farabeuf (1870). Considering the elastic system of the muscle chains in agreement with Mézières - Busquet (Fig.2 a, b) we can interpret why a breech, gnathological, visual, vestibular disorder causes an imbalance that spreads over the whole muscular chain in an ascending or descending and also spiral manner. 2a 2b Fig. 2. a, b) Muscular chains. Using surface electromyography, the participation of the anterior temporal muscles to gaze movements and to the optical correction worn was highlighted by the Monaco team (4). Activation is interpreted as a way to discharge the extrinsic ocular muscles to the chains (Fig. 3). Fig. 3. EMG traces of the anterior temporal muscles, masseter, anterior digastric, sternocleidomastoid (black: right; red: left) .Above left: eyes closed, right: eyes open; below left: wrong correction, right: correction updated. Disturbing activity of the erroneous correction with excitation of the anterior temporal signal, is attenuated wearing the appropriate correction. (courtesy D'Andrea). The main reflexes that induce eye movements are:The vestibular-ocular movements keep the images on the retina stable during the phasic movements of the head;The optokinetic movements keep the images on the retina stable during the phasic movements of the head;The saccadic movements quickly bring the fovea towards a peripheral visual target;The tracking movements keep the image of a moving object fixed on the retina;The movements of vergency cause an object farther away or closer to always project onto both foveas; Using a “moving room”, a room with a stable floor and movable walls, Lee and Aronson (5) demonstrated in 1974, that the movement of the walls induced significant loss of balance, with oscillation and inclination of the body according to the direction of the movement of the wall for postural compensation in the opposite direction to the movement of the wall, for modification of the visual alignment: when the subject perceived the closest walls, with variation of the visual alignment, he compensated the sensation of falling forward, moving the body backward. Bricot (6) (1998) states: “All the right/left imbalances of the oculomotor muscles will have as a consequence a right/left imbalance of the body which in turn will generate tilting and rotations”. An exophoria due to the lack of convergence, which involves asymmetry of tension of the extraocular muscles, can cause external rotation of the femoral-tibial axis with valgus attitude of the foot (6). An oblique astigmatism can initially cause an anomalous position of the head (PAC) with torticollis, for research of distinct vision, then, over time, the breakup of the rachideo equilibrium, which was demonstrated in a study on the journalists of a Rome newspaper (7). The ocular torticollis is taken in the presence of refraction defects, peripheral anomalies, nystagmus, essential/ infantile esotropia, palpebral ptosis, in an attempt to obtain single binocular vision in incipient deviations, such as paralysis and acquired/congenital muscle restriction syndromes, in alphabetic syndromes and in cases where diplopia or confusion is established due to loss of alignment of the visual axes in the direction of the interested gaze, that is to cancel the diplopia or preserve the binocular collaboration. The PAC, a forced position, may also be a consequence of neurological, vestibular and orthopedic anomalies: for this reason it is fundamental to differentiate the ocular causes from extraoculars. Incorrect diagnosis can lead to treating children with PAC incorrectly using busts or corsets or insoles and orthopedic therapies, when the problem, instead, must be solved with suitable optical correction. Nucci et al. (8), in a multidisciplinary trial, documented the frequency of causes of PAC in 73 children: orthopedics 35/73, ocular 25/73, neurological 5/73, mixed 8/73 of whom 2 with concomitant paresis of the Great Oblique muscle. Even gnathological or postural disorders can induce PAC, in an attempt to keep the visual axes aligned. Cases have been described of patients with short legs with ipsilateral hyperforia and contralateral hypophoria (9) and correlation of malocclusion with convergence deficit (10-12) in addition to correlations with palatal anomalies, maxillary and zygomatic, which contribute to the skeletal orbital apparatus functional to oculomotor balance (12). The imbalance, the bascules, and the rotations are projected to the foot sole and can be recorded with electronic platform.
Fig. 4. Platform for digitalized biometry: a 3D analyzer of plantar support (Courtesy DIASU© Rome, Italy).
The measurable parameters are: X med measures the displacement of the center of gravity on the frontal plane (right-left); Y med measures the displacement of the center of gravity in the sagittal plane (forward-backward); S surface of the ellipse: contains 90% of the sampled points, expresses the precision of the postural system; L. The length of the trace: is related to the energy expended by the system; V average speed of displacement of the center of pressure; LFS length as a function of surface: energy spent depending on the accuracy of the system; IR Romberg index: ratio between surface open eyes/surface closed eyes (S O E/ S.C.E); greater or equal oscillations with open eyes indicate that the vision is disturbing on the posture; ICh index of Chieti (12): ratio between surface without glasses/surface with glasses x 100 ((S.WO.G/ S.W.G) x 100); if the oscillations are reduced it means that the refractive situation is disturbing on the posture and that the optical correction is effective.
Fig. 5. Comparison of the surface without glasses (green) and with glasses (red) significant reduction of the oscillation surface with the use of glasses appropriate in case of “compound myopic astigmatism”; Chieti index: >100, the glasses are effective in posture balancement. (Courtesy Serra Institute, Pescara, Italy).
There is abundant literature on this subject. An Italian study (12) showed that out of 361 carriers of refractive defect, latent/manifest strabismus, amblyopia, ocular torticollis, only 137 were not carriers of postural disorder modifiable with optical correction, while 224/361 presented with optical correction (sphere, cylinder, prism):
– improvement of postural overload, the surface of the ball expressing the precision of the postural system;
– improvement of the pressure center trace, related to the energy expended by the system;
Evaluation with a visually impaired patient (13) allowed us to extrapolate four rules:
– in the nystagmus we have rotation on the side of the dominant eye;
– in nystagmus the optical correction positively affects posture;
– in central defects we have hypercharging on the side of the dominant eye;
– in peripheral defects we have contralateral hyperload compared to the dominant one.
It is to be hoped that the postural assessment is completed upon completion of the ophthalmological prescription, in an interdisciplinary relationship with other professional figures interested in posturology (14) to optimize patient comfort and not only to avoid the prescription of orthopedic/physiatric insoles to correct postural disorders in astigmatic children, solvable with lenses. The problem of prescription lenses and which type of lens to recommend based on the refractive defect and personal needs, should also include patient comfort and the evaluation of how the lens and prescribed glasses interact on the patient’s well-being, which expresses itself in interference with the posture. That is, with the correction of postural abnormalities induced by the refraction defect, since emmetropia, binocular vision and stereoscopic sense do not change the posture, but their deficit does. Refraction defects and low vision therefore induce postural variations that can be evaluated with a digitalised stabilometric platform (15).
The stabilometric platform stands as a complementary tool of significant importance in the functional evaluation of the ophthalmic patient and deserves further studies that may lead to new applications and a new holistic approach (12).
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