Carter C. Collins

Miniature Passive Pressure Transensor for Implanting in the Eye

A newly developed method for measurement of intraocular and other physiological pressures consists of a novel displacement transducer contained in a distensible pillbox small enough (3 to 60 ?l) to be implanted in the eye of a small laboratory animal. Nothing pierces or even touches the globe. This passive resonant transensor absorbs energy from an oscillating detector coil outside of the animal at a frequency dependent upon the pressure in the eye. Passive operation provides extended life, but limits useful range to less than 10 transducer diameters, which has proved sufficient for intraocular pressure measurement.

Seeing with the skin

A system for converting an optical image into a tactile display has been evaluated to see what promise it has as a visual substitution system. After surprisingly little training, Ss are able to recognize common objects and to describe their arrangement in three-dimensional space. When given control of the sensing and imaging device, a television camera, Ss quickly achieve external subjective localization of the percepts. Limitations of the system thus far appear to be more a function of display resolution than limitations of the skin as a receptor surface. The acquisition of skill with the device has been remarkably similar for blind and sighted Ss.

Tactile Television - Mechanical and Electrical Image Projection

The feasibility of communicating pictorial information through the skin has been demonstrated. A tactile television system has permitted blind subjects to determine the position, size, shape, and orientation of visible objects and to track moving targets. The system comprises 1) a vidicon camera utilizing a zoom lens, 2) a digital switching matrix to sequentially connect each element of the photocathode surface through a single video amplifier and signal conditioner to each of the 3) 400 tactile stimulators in a 20 × 20 matrix in contact with a 10-inch square of skin. This image-projector matrix impresses on the skin a two-dimensional vibrating facsimile of either the silhouette or the outline of a visible object. The single-channel swept system exhibits inherent economies when a great number of picture elements is to be processed. Since the fovea of the human eye subserving the central two degrees of detailed vision is comprised of cone cells in a matrix about 200 receptors across, the present 20-line system permits picture transmission with a linear resolution about one-tenth that of the fovea, and has proved adequate for the recognition of human faces. Calculations indicate that the input capacity of the skin of the trunk should compare favorably with that of the fovea. We have determined the electrical-stimulus parameters for painless stimulation of the sensation of mechanical vibration with small electrodes in a closely spaced matrix.

On Mobility Aids for the Blind

I will briefly summarize the results of some 20 years of research at the Smith-Kettlewell Institute of Visual Sciences which I have directed toward the development of mobility aids for the blind. I will attempt to point out what we can learn from these investigations that may prove valuable in directing the thrust of future developments.

Elements of the peripheral oculomotor apparatus.

ABSTRACT In awake patients the rectus muscles exert about 15 grams force on the globe. Stiffness of orbital tissues to rotation is nearly linear and is about 0.5 gm/degree. Stiffness of rectus muscles to rotation is about 1.0 gm/degree, and is the same from 30° of abduction to 30° of adduction. These values can be separately determined. The balance between them should help predict the type and amount of surgery required to correct an imbalance.

Simultaneous and successive cutaneous two-point thresholds for vibration

An array of factors, of a type used in a video-tactile visual substitution system, was used to determine two-point thresholds for vibration on the skin of the back. In the first study simultaneous stimulus presentations using the constant stimulus method resulted in a median threshold of 17.8 mm. In the second study, both simultaneous and successive thresholds were near 11 mm. These results differ from classical studies using touch calipers which give simultaneous thresholds Of 68 mm and successive thresholds of 17 mm.

Eye Muscle Prosthesis

We inserted a silicone rubber elastic band along the course of a paralyzed lateral rectus and of a paralyzed superior oblique to restore alignment and to provide a spring against which the antagonist could pull. The lateral rectus band has been in place for 7 years. It provides alignment and a field of single binocular vision of 20 degrees. The superior oblique band has been in place for 17 months. It provides alignment and single vision over 30 degrees from the primary position except for a restriction in upgaze-adduction to 25 degrees (Brown syndrome) and in downgaze-adduction to 20 degrees. Such engineered elastic bands are a useful addition to current surgical techniques for management of cases of paralysis and restriction.

A tactile vision substitution system.

ABSTRACT A prototype of a tactile television system has been developed, in which a television camera image is projected onto the skin of the back by means of vibrating electromechanical stimulators. Blind subjects, within a few hours of training, have learned to identify geometric forms, movement in depth, environmental objects, photographs of faces, and block letter words.

Length-tension recording system for strabismus surgery

Described is a technique for quickly assessing and graphically displaying the mechanical length-tension (L-T) characteristics of the passive tissues restraining eye movement and for measuring the patterns and magnitudes of active forces developed by the individual oculorotary muscles. Semiconductor strain gages mounted on the shanks of a custom-machined eye forceps and an ultrasonic method of making continuous duction measurements of the eye are proved feasible. When the forceps are interfaced with a dedicated microcomputer, the system provides a permanent. quantitative, L-T record displayed in real time. The instrumented L-T forceps system has provided a noninvasive means for quickly and simply assessing the mechanical underlying determinants of strabismus pathology in the office, the laboratory, and the operating room and can aid in the planning and immediate intraoperative alteration of strabismus surgery. A brief description of actual use and a few examples of clinical results are included from over 200 human records.<<ETX>>