Retinal micromovements, the visual line, and Donders' law.

PURPOSE: To report the relationship of the retinal micromovements to the visual line and to confirm the validity of Donders' Law. METHODS: Two video cameras suspended from a headband were used to record eye (video-oculography) and head movements. Eye positions in held gaze and following various trajectories to a target were recorded in five normal, young subjects. The videotapes were analyzed off-line using a computer algorithm. RESULTS: Retinal micromovements cause the visual line to trace a zigzag pathway across the foveola, which has an approximate diameter of 350 microm (about 2 degrees). The mean micromovement was about 10 microm in 33.3 msec. The cumulative effect of successive micromovements may move the visual line across the foveola from edge to edge depending on the elapsed time. When the visual line reaches the edge of the foveola it changes its direction. When the eye resets to the same target by different trajectories, the visual line may alight up to about 350 microm from its original location anywhere within the foveola. CONCLUSIONS: Donders' Law is upheld because for each direction of gaze, and regardless of the trajectory used to reach that direction of gaze, the retina has a constant orientation to an index head plane at any given moment in time. Failure to consider that the micromovements cause a shift in the position of the visual line within the foveola may account for the exceptions to Donders' Law found by contemporary researchers using invasive recording techniques.

The effect of technology on the indications for cataract surgery.

Before the introduction of modern ophthalmic surgical technology following World War II, cataract extraction was easier and safer to perform if the cataract was far advanced (mature) and both eyes were involved. The surgeon was constrained from early surgery by the frequency of severe complications, the long convalescent period, and the distortions of aphakic glasses. Now it is easier to perform phacoemulsification and implant lenses in the early stages of cataract formation when the nucleus is soft and the posterior lens capsule has not been weakened with age. Also, modern small-incision extracapsular cataract extraction has a low rate of complications and a short convalescent period. It is feasible to extract a clear lens or one with minimal opacifications and have a grateful patient. The surgeon is capable of improving the refractive state of the eye by selecting the power of the intraocular lens. These facts have led to instances where cataracts have been extracted that were responsible for minimal or no symptoms.

The construction of the new Kresge Eye Institute.

The present Kresge Eye Institute building, the site of the Department of Ophthalmology of the Wayne State University School of Medicine, opened in 1989. The new building was the culmination of a decade of planning, persuasion, perseverance, and compromise. The previous facility was physically connected to the Harper Hospital in the Detroit Medical Center and began operation in 1974. A campaign to expand the Kresge Eye Institute started in 1979 when the dean of the medical school and the majority of the administrators and trustees agreed that expansion was justified, but there were many political and economic obstacles. After ten years of negotiation, when the situation seemed hopeless, fiscal problems threatened to close the Hutzel Hospital, a component of the Detroit Medical Center. The Medical Center Board agreed with the Hutzel Hospital trustees to sustain the Hutzel Hospital by transforming the hospital into a specialty hospital containing only three services: ophthalmology, orthopedics, and obstetrics. A new Kresge Eye Institute was approved on the condition that it be moved from the Harper Hospital to the Hutzel Hospital. By 1989, a four-story building connected to the Hutzel Hospital was completed. Although economic and political factors were more important than medical needs in obtaining the new building, the result was an institution of the appropriate size and scope to serve the ophthalmic needs of metropolitan Detroit and the Wayne State University School of Medicine.

The primary position of the eyes, the resetting saccade, and the transverse visual head plane. Head movements around the cervical joints.

Photographic and video analyses show that the primary position of the eyes is a natural constant position in alert normal humans, and the eyes are automatically saccadically reset to this position from any displacement of the visual line. The primary position is not dependent on fixation, the fusion reflex, gravity, or the head position. The primary position is defined anatomically by head and eye planes and lines that are localized by photography, magnetic resonance imaging, and x-rays of the head and neck. The eyes are in the primary position when the principal (horizontal) retinal plane is coplanar with the transverse visual head (brain) plane (TVHP), and the equatorial plane of the eye is coplanar with a fixed orbital plane (Listing's plane). Evidence is presented to indicate an active neurologic basis for the primary position instead of passive mechanical forces. A different understanding of the primary position and the conception of the TVHP may be valuable in analyzing oculomotor defects.

Elemental and structural studies of the rat galactose cataract.

A series of rat galactose lenses, from 1 to 20 days on the 50% galactose diet, were frozen in the whole eye, and fractured from pole to pole in the frozen state. Lyophilized half-lenses were prepared for analysis by energy dispersive spectrometry (EDS). Following elemental analysis, some specimens were embedded and sectioned for histological studies. Elemental X-ray maps, and/or profiles, were made for K, Na, Cl, Ca, P, and S. As early as two days on the galactose diet, a crescent-shaped region ("streak") of Cl, Na, and Ca gain, and K loss develops near the equatorial surface. Between this region and the equatorial surface are the nucleated differentiating fiber cells which maintain low Cl, Na, and Ca, and high K (viable equatorial zone, VEZ). With time the "streak" expands anteriorly, centrally and posteriorly, eventually (by 20 days) including most of the lens. The VEZ, including the epithelium, however, is non-reactive to the galactose diet, which is deleterious to the fully differentiated fiber cells. Eventually, the VEZ undergoes a characteristic morphological change, apparently due in part to changes in its physical environment.

Ocular torsion and primary retinal meridians.

I measured ocular torsion during and after head- and body-tilt, ocular convergence, and conjugate gaze. Extensive examination on 15 normal human subjects and additional observations on 400 consecutive patients without extraocular motor defects failed to show static ocular tension. During dynamic head-tilt, intermittent, small-amplitude, saccadic, wheel-like torsional eye movements were recorded as moving faster than the head so that the eyes preceded the head. Between these intermittent saccades, and at the end of the head-tilt, there was no residual ocular torsion. The absence of static ocular torsion allows for formulation of a generalization linking the oculomotor to the visual sensory system. The primary retinal meridians become aligned with each other in the normal individual during binocular fixation, regardless of the position of the head in space or the point of ocular fixation. The vestibular and oculomotor systems function to inhibit rather than produce ocular torsion; the eyes are oriented to a plane in the brain rather than to the horizon. In particular, the oblique muscles function mainly to maintain the alignment of the primary retinal meridians and, therefore, to inhibit torsion in the normal state.

Computer assisted tomography in experimentally induced orbital pseudotumor.

Induction of an entity that is comparable to pseudotumor of the orbit in humans has been performed successfully in the rabbit. Injection of a retrobulbar antigen in a previously sensitized rabbit produced a profound inflammatory mass. Proptosis, soft tissue swelling, and an orbital mass effect were grossly visible after a short interval. Computer assisted tomography disclosed dense orbital mass and uveoscleral thickening. Exenteration specimens confirmed as inflammatory cell mass similar to the histology associated with pseudotumor of the human orbit.

Square wave jerks in Friedreich's ataxia.

We observed a brother and sister with Friedreich's ataxia during steady fixation. They both had abnormal eye movements consisting of randomly occurring, small amplitude, conjugate horizontal saccades away from the fixation target. The saccades were followed by maintenance of this eccentric position for a brief period, and finally, a corrective saccade back to the original position. Electro-oculographic recordings showed these eye movements to be square wave jerks. They had an amplitude ranging from 1.5 to 10.7 degrees and a duration averaging less than 200 msec. Square wave jerks were also superimposed on pursuit movements in both patients. Square wave jerks are an additional ocular finding that may signify chronic cerebellar dysfunction. More specifically, they are an additional neuro-ophthalmological finding that may be observed in Friedreich's ataxia.

Ocular torsion and the function of the vertical extraocular muscles.

The vertical corneal meridia are not kept perpendicular to the horizon in human and nonhuman primates when the head or body is tilted, i.e., compensatory counter-rolling of the eyes does not occur. The slight torsional displacement of the vertical corneal meridia noted by many observers may be the result of rotation around an axis or to translation of the globe. The neurologic and structural systems that control the actions of the vertical muscles in human and nonhuman primates do not appear to provide a mechanism for wheel-rotation of the eyes around the pupillary axis. Ocular torsion is not a normal function of the vertical extraocular muscles. Their function is probably the reverse, i.e., the inhibition or prevention of ocular torsion and the stabilization of the eyes when the head or body inclines. Torsional displacement of a vertical corneal meridian occurs only when there is an abnormal muscle imbalance. Wheel-like movements (cycloduction) around the pupillary axis or visual line do not occur. Torsional displacement of a vertical corneal meridian occurs only with a simultaneous vertical movement. The vertical rectus and the oblique muscles in man work together to produce vertical ocular movements regardless of head position of body posture while maintaining the vertical corneal meridia parallel to the sagittal plane of the head. The vestibular apparatus may be responsible for distributing innervation among these muscles, enabling them to function in this manner.