Opthalmodynamometer

Abstract

An opthalmodynamometer includes an inflated toroid member attached to an speculum having a viewing port. The eye of the toroid and the viewing port are axially aligned to permit the fundus of the eye to be illuminated and viewed. Pressure applied to the toroid member is transmitted to the eyeball to thereby raise intra-ocular pressure. Internal toroid member pressure is related to retinal artery blood pressure. Means are provided to ascertain the toroid member pressure so that retinal artery blood pressure may be determined.

Government Interests

STATEMENT OF GOVERNMENT INTEREST

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

Description

BACKGROUND OF THE INVENTION

This invention relates to ophthalmodynamometers and in particular to ophthalmodynamometers which employ the compression principle.

An ophthalmodynamometer is an instrument which measures retinal artery pressure by applying a variable but calibrated force over a known area of the eye to induce systole, i.e., pulsations at the peak of the blood pressure cycle, and diastole, i.e., pulsations at the minimum of the blood pressure cycle, of the central retinal artery. With the ophthalmodynamometer the intra-ocular pressure is artificially elevated by means of mechanically applied pressure or suction. A separate apparatus, e.g., a hand held ophthalmoscope, is then employed to observe or detect the pulsations. (The essential function of the ophthalmoscope is to provide illumination through the pupil of the eye so that the examiner may view the fundus of the eye.) Measurement of retinal artery pressure can be used to detect several important body conditions, e.g., increased intra-cranial pressure, partial or complete carotid artery blockage, and carotid vascular blockage.

Present day ophthalmodynamometers increase intra-ocular pressure by using either a suction device or a compression device. The compression device employs a small flat disc which is pressed against the sclera of the eye with a calibrated force applicator. The suction device employs a small cup and a calibrated vacuum device to apply suction to a portion of the sclera. The compression and suction ophthalmodynamometer devices both distort the globe of the eye. This distortion tends to raise the pressure of the relatively incompressible vitreous fluid within the eye. The increased pressure of the vitreous fluid is then exerted against the central retinal area of the eye.

Conventional ophthalmodynamometers have several drawbacks. In both the compression type and the suction type, the actual increase in intra-ocular pressure is nonlinearly related to the external force applied to the sclera. Hence it is difficult to establish an exact relationship between the force applied to the sclera and the actual retinal artery pressure. In the compression type, the axis of pressure application is sometimes non-normal to the sclera giving rise to lateral forces which can cause slippage of the disc on the sclera. In the suction type measurement errors are sometimes introduced when there is a partial loss of vacuum around the periphery of the suction cup or the pneumatic tube providing the vacuum partially collapses. Both types of conventional ophthalmodynamometers are uncomfortable for the patient, difficult to properly and conveniently employ and generally give uncertain results. In addition, conventional ophthalmodynamometers cannot be used under field or combat conditions since they employ cumbersome equipment and normally require the patient to be in an upright position.

SUMMARY OF THE INVENTION

Accordingly, it is an object of this invention to provide a compression ophthalmodynamometer which is convenient to employ and which reliably determines retinal artery pressure without unduly discomforting the patient. It is a further object of this invention to provide an ophthalmodynamometer which is atraumatic to the eye and which can be used under field or combat conditions even where the patient is in a prone position. These and other objects of the invention are achieved as follows:

A pressurized fluid impermeable bladder shaped in the form of a toroid or life preserver is attached to one end of an eye speculum. The second end of the speculum is inserted under the eyelids and presses against the eyeball. An external force is applied to the bladder. The external force increases the pressure within the bladder. The increased pressure within the bladder is transmitted through the speculum to the eyeball to thereby increase intra-ocular pressure. Means for measuring the internal pressure of the bladder is provided so that bladder pressure can be determined. Bladder pressure is related to intra-ocular pressure, hence retinal artery pressure can be determined.

Other objects, advantages, and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a compression ophthalmodynamometer according to the invention;

FIG. 2 shows the ophthalmodynamometer of FIG. 1 applied to the eyeball and partially in section; and

FIG. 3 shows an alternate embodiment of an ophthalmodynamometer according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 the ophthalmodynamometer of the present invention includes a transparent plastic eyecup or speculum 10 having a flared or virtually semi-spherical portion 10a which fits under the eyelids and rests against the sclera. The flared portion 10a prevents the eyelids from closing when the ophthalmodynamometer is being used and also exerts pressure on the sclera as will be more fully described hereinbelow. The flared portion 10a tapers to an orifice or viewing port 10b having a diameter slightly larger than a cornea. Thereafter the eyecup 10 extends from the viewing port 10b as a frusto-conical portion 10c terminating in a planar circular rim 10d which abuts a pressurized bladder 14. (An eyecup 10 suitable for use with the present invention may be that used to hold a Burian Allen ERG Electrode manufactured by the Hansen Ophthalmic Development Laboratory of Iowa City, Iowa.) The bladder 14 may be fixedly secured to the rim 10d of the eyecup 10 by an adhesive such as Permabond 101 contact cement or any other suitable means. Alternatively, the bladder 14 may be removably attached to the eyecup 10 by means of a grooved circular retaining clip (not shown) affixed to the periphery of the bladder 14.

The bladder 14 is fabricated from any suitable fluid impermeable, distensible material, such as silicone rubber, which is capable of being inflated or pressurized i.e., capable of holding a fluid under pressure. The bladder 14 is formed substantially in the shape of a toroid or doughnut with the eye 15 of the toroid concentric with the viewing port 10b of the speculum 10. A pressure indicator 18 is connected to the bladder 14 by a pneumatic tube 16 which extends through the wall of the bladder 14 to its interior. The pressure indicator 18 is of conventional construction and serves to transduce the internal pressure of the bladder 14 to a numerical value which can be read by the examiner.

Referring to FIG. 2, the flared portion 10a of the speculum 10 is shown inserted under the eyelids 30, 30' and resting against the sclera 32 of the eye just beyond the periphery of the cornea 31. The speculum 10 and attached bladder 14 are positioned on the sclera 32 so that the lens 34 of the eye, the speculum viewing port 10b and the eye of the toroid 15 are concentric. With the ophthalmodynamometer positioned in this manner, light from an ophthalmoscope 40 can be directed into the lens 34 of the eye so that an examiner may view the fundus 36 of the eye while an external force is applied to the bladder 14 by means of a suitable force applicator 42. The force applicator 42 may, for example, be formed as a thin plastic ring 42a having a curved depending plastic stem 42b. The ring 42a is placed against the outer periphery of the bladder so as not to interfere with the light emanating from the ophthalmoscope 40. The stem 42b of the force applicator 42 may be connected to a conventional source of calibrated forces such as a modification of the well-known Goldman applanation tonometer or any other suitable device which will cause force applicator 42 to bear against the bladder 14 with controlled force. (Alternatively the force applicator 42 may be hand held by the stem 42b and manually pressed against the bladder. In another embodiment the force applicator may be affixed to the bladder 14 by any suitable means and serve not only to increase bladder pressure but also to facilitate positioning of the ophthalmodynamometer on the eye. Other suitable means for increasing the pressure within the bladder 14 will occur to those skilled in the art. For example, the force applicator 42 may be entirely dispensed with and the ophthalmoscope 40 may be pressed against the bladder 14 as the examiner views the fundus 36 of the eye.)

Operation of the ophthalmodynamometer is as follows. The ophthalmodynamometer eyecup 10 is inserted under the eyelids 30, 30' and held in place by hand, by the force applicator, or by any other suitable means. Thereafter an external force is applied to the bladder 14. The internal pressure of the bladder 14 increases under the influence of the external force and this pressure increment is transmitted to the sclera 30 via the speculum 10 to thereby increase the intra-ocular pressure. As the pressure within the bladder 14 and the eyeball increases, the examiner notes the characteristic collapse of the retinal artery at the low point of the blood pressure cycle, i.e., diastole. As the pressure within the bladder 14 is further increased, the examiner notes the characteristic rapid pulsation of the retinal artery yielding to a sustained collapse even at the peak of the blood pressure cycle, i.e., systole. To obtain the retinal artery pressure, the readings of the pressure indicator 18 at diastole and systole are converted to blood pressure readings according to a previously determined calibration. (For example, the exact relationship between the pressure within the bladder 14 and the intra-ocular pressure can be determined experimentally by raising the pressure within the bladder to several distinct but known levels and measuring the intra-ocular tension with a Schiotz tonometer at each distinct level. This kind of experiment would result in a chart of corresponding bladder pressures and intra-ocular pressures. The chart would then serve as the previously determined calibration set forth above. Alternatively, the relationship may be established by inserting a hollow needle into the eyeball of a cadaver after the ophthalmodynamometer has been positioned over the sclera. The internal bladder pressure is then raised to several distinct but known levels and the corresponding intra-ocular pressures are determined with a second pressure indicator attached to the hollow needle.)

Many modifications of the invention will occur to those skilled in the art without departing from the spirit of the invention. One such modification is shown in FIG. 3 which shows a bladder formed as a single walled bellows 50 which can be used in lieu of the toroid shaped bladder 14 shown in FIGS. 1 and 2. The bellows 50 is substantially cylindrical in shape and is attached to the speculum 10 by an adhesive such as Permabond 101 contact cement or any other suitable means. The sidewall 50a of the bellows 50 is fabricated from distensible rubber such as silicone rubber (or any other material which is distensible and fluid impermeable) and is pleated. The endwalls 50b, 50c of the bellows 50 are fabricated from disc-shaped reflection coated glass to provide an unobstructed view through the bellows structure. The pneumatic tube 16 extends through the endwall 50c and opens into the interior of the bellows 50. Operation of the device shown in FIG. 3 is the same as that set forth for the device shown in FIGS. 1 and 2.

In addition to measuring the retinal artery pressure, the ophthalmodynamometer of the present invention can also be used to measure the effect of increased intra-ocular pressure on the electroretinogram (ERG). This can be accomplished by mounting a conventional Burian Allen ERG electrode within the viewing port of the eyecup 12. The electrode is a ring type corneal electrode which picks up the electrical response of the eye to a flash of light. As the intra-ocular pressure is varied to any desired level in the manner set forth above, the eye is stimulated with light flashes and the output of the electrode is observed on a recorder or other suitable device.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

Claims

We claim:

1. An ophthalmodynamometer comprising:

a speculum member provided with a viewing port;

a pressurized toroidal bladder attached to said speculum member with the eye of the toroidal bladder coaxial with said speculum viewing port; and

means operatively connected to said bladder for determining the internal pressure of said bladder.

2. An ophthalmodynamometer according to claim 1 wherein:

said bladder is substantially composed of an impermeable distensible material; and

the diameter of the eye of said bladder is equal to or greater than the diameter of the speculum viewing port.

3. An ophthalmodynamometer according to claim 1 wherein said pressure determining means includes:

a pneumatic tube member operatively connected to the bladder; and

a pressure indicator means connected to said pneumatic tube member for indicating the internal pressure of said bladder.

4. An ophthalmodynamometer according to claim 1 further including: force applicator means attached to said bladder for applying an external force to said bladder.

5. An ophthalmodynamometer according to claim 4 wherein said force applicator means comprises:

a ring attached to said bladder and having a curved stem depending therefrom.

6. An ophthalmodynamometer comprising:

a speculum having an opening formed by two oppositely flaring annular surfaces, one of said surfaces being formed to fit against the sclera of the eye beneath the upper and lower eyelids; and

a pressurized bladder attached to the outer periphery of the other of said surfaces, said bladder defining an opening therethrough that is coaxial with said speculum opening; and

means operatively connected to said bladder for determining the internal pressure of said bladder.