Ophthalmodynamometer

Abstract

A portable ophthalmodynamometer, which operates in the active compression de, includes a transparent plastic eyecup or speculum attached to a bellows-like bladder having glass endwalls. The eyecup fits under the eyelids and is seated against the sclera by a headstrap attached to the bladder structure and secured around the head. An integral adjustment gauge facilitates correct positioning of the ophthalmodynamometer on the eyeball. An air duct extends from the interior of the bladder structure to a hand squeeze bulb whereby manipulation of the bulb increases the internal pressure of the bladder structure. Increasing bladder pressure is transmitted to the eyeball via the eyecup to thereby raise intra-ocular pressure. Bladder pressure is related to retinal artery blood pressure. Means are provided to ascertain the bladder 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 active compression principle.

An ophthalmodynamometer is an instrument which measures retinal artery pressures 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 intracranial 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 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 a 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 discomfiting the patient. It is a further object of this invention to provide an ophthalmodynamometer which is portable, 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 portable ophthalmodynamometer, which operates in an active compression mode, is provided with a transparent plastic eyecup and a fluid impermeable bladder structure. The bladder structure is substantially cylindrical with glass endwalls and a sidewall fabricated from a pleated but distensible material. The eyecup is removably secured to the bladder structure by means of a grooved retaining clip. A fixed length attachment gauge secured to the retaining clip ensures correct seating of the eyecup on the sclera. An air duct extends from the interior of the bladder structure to a squeeze bulb and pressure indicator means. After the ophthalmodynamometer has been properly placed on the eyeball with the aid of head straps the bladder structure is pressurized by means of the squeeze bulb. As the bladder pressure increases a force is transmitted to the sclera via the eyecup and the intra-ocular pressure is thereby increased. With an ophthalmoscope, systole and diastole are observed and the corresponding bladder pressure is ascertained from the pressure indicator means. Since internal bladder pressure is related to intra-ocular pressure, a measurement of retinal artery pressure is obtained.

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 wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a shows an ophthalmodynamometer according to the invention partially in section;

FIG. 1b shows an end view of the ophthalmodynamometer of FIG. 1; and

FIG. 2 shows a modification of a portion of the ophthalmodynamometer shown in FIG. 1; and

FIG. 3 shows the ophthalmodynamometer of the present invention positioned on the eye and held in place with a head strap.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1a the ophthalmodynamometer 10 of the present invention includes a transparent plastic eyecup or speculum 12 attached to a bladder 14 having a bellows-like structure. The eyecup 12 has a flared or virtually semi-spherical portion 12a which fits under the eyelids (not shown) and rests against the sclera 31 just outside the periphery of the cornea 33. The flared portion 12a tapers to a viewing port or orifice 12b having a circumference slightly larger than a cornea. (The flared portion 12a prevents the eyelids from closing when the ophthalmodynamometer is used and also exerts pressure on the sclera as will be described more fully hereinbelow). Thereafter the eyecup 12 extends as a substantially frusto-conical portion 12c having a planar rim 12d which is removably retained within a circular groove 13a provided on a plastic retaining clip or keeper 13. (A suitable eyecup 12 that may be used in the present invention may be the eyecup employed to hold the Burian Allen ERG Electrode manufactured by the Hansen Ophthalmodynamometer Development Laboratory of Iowa City, Iowa). The sidewall 14c of the bladder structure 14 is fabricated from any suitable material which is both distensible and fluid impermeable such as silicone rubber. The bladder 14 is generally cylindrical in form and has a sidewall 14c constructed in a pleated or corrugated fashion much like a bellows. Both endwalls 14a, 14b of the bladder 14 are fabricated from anti-reflection coated glass or scratch resistant plastic formed in the shape of a disc.

One endwall 14b of the bladder structure 14 is provided with a plastic circular mounting ring 16 having head strap lugs 32, 32' as can be seen best in FIG. 1b. The circular ring 16 occupies the outer periphery of the glass endwall 14b and is attached thereto by an adhesive such as permaband 101 contact cement or any other suitable means. The circular ring 16 has a thickness sufficient to provide a secure base or support for head strap lugs 32, 32'. A head strap 38 is attached to each head strap lug 32, 32' and brought behind the patient's head where it can be incrementally tightened.

A second endwall 14a of the bladder structure 14 is provided with a grooved circular retaining clip or keeper 13 which is securely attached to the glass endwall 14a by an adhesive such a permaband 101 contact cement or any other suitable means. The plastic retaining clip or keeper 13 occupies the outer periphery of glass 14a and is used to removably secure the speculum or eye cup 12 to the bladder structure 14 by means of a groove 13a.

A fixed length plastic adjustment gauge 30 is attached to the retaining clip 13 and extends above and along the upper portion of the bladder structure 14. The gauge 30 is slightly smaller than the undistended length of the bladder structure 14; within this constraint the exact length of the adjustment gauge is not critical but its optimum length will depend on the actual dimensions of a finally and fully fabricated ophthalmodynamometer 10. The gauge 30 is used by the examiner to properly position the ophthalmodynamometer 10 on the patient's eye as will be explained more fully hereinbelow. A duct 18, of any suitable material, extends through the lower portion of ring 16 to at least the interior surface of the glass endwall 14b. The duct 18 is suitably connected to a pneumatic tube 20 which extends to a normally closed exhaust valve 24 and a squeeze-bulb 26 such as those used with a conventional cuff-type sphygmomanometer. (To those skilled in the art the exhaust valve 14 is also known as sphygmomanometer inflation bulb). The exhaust valve 24 and squeeze-bulb 26 are shunted by a conventional pressure indicator 22 which transduces applied pressures to a readable numerical value.

Referring to FIGS. 1 and 3, the operation of the ophthalmodynamometer 10 is as follows. The ophthalmodynamometer 10 is placed on the eyeball so that the eyecup 12 fits under the eyelids and rests against the sclera 31 just outside the periphery of the cornea 33. The Headstraps 38 (FIG. 3) attached to the lugs 32 and 32' on the mounting ring 16 are brought behind the patient's head and thereafter incrementally tightened. The head straps 38 are tightened only until the outer surface of the ring 16 is aligned with the distal end 30a of the adjustment gauge 30 as shown in FIG. 3. When such alignment occurs the eyecup 12 is correctly seated on the sclera 30 and presses against the sclera with enough force to minimize slippage but not enough force to introduce a significant pressure increment to the eyeball prior to pressurization of the bladder structure.

After the ophthalmodynamometer has been positioned on the eyeball, the pressure within the bladder structure 14 is increased by squeezing bulb 26. As the pressure increases, the bladder structure tends to distend and exerts a pressure against the eyeball via the eyecup 12. With an opthalmoscope 40 the examiner views the fundus 34 of the eye and continues to increase the pressure until he observes the characteristic collapse of the retinal artery. Thereafter the exhaust valve 24 is opened and the pressure decreases. As the pressure decreases the examiner observes the characteristic first blood pulse at the high point of the blood pressure cycle, i.e., systole. As the pressure continues to decrease, the examiner notes the last blood pulse at the low point of the blood pressure cycle, i.e., diastole. The corresponding readings from pressure indicator 22 represent the retinal artery blood pressure at systole and diastole respectively.

It is apparent from the description of the ophthalmodynamometer's operation set forth above, that it operates in an active compression mode as opposed to a passive compression mode. In the active mode, the bladder sructure 14 is in a semi-flaccid or substantially undistended state when the ophthalmodynamometer is initially positioned on the eyeball. Thereafter, the bladder structure 14 is pressurized by squeeze-bulb 26 and caused to expand or distend to thereby transmit an increased pressure to the eyeball via the eyecup 12. If the ophthalmodynamometer 10 were operated in a passive mode, there would be no need for the squeeze-bulb 26 and the exhaust valve 24. That is, the bladder structure 14 is pressurized before it is placed on the eyeball and the internal pressure of the bladder structure 14 is increased by exerting an internal force against an endwall of the bladder structure 14 after the ophthalmodynamometer is positioned on the eyeball. The increased internal pressure within the bladder structure 14 under the influence of the external force is registered on the pressure indicator 22.

Referring to FIG. 2, wherein like numerals refer to parts already illustrated, a modification of the bladder structure shown in FIG. 1a is portrayed. The single walled bladder structure 14 of FIG. 1 is replaced by a double walled bladder structure 14' shaped substantially in the form of a toroid having pleated or corrugated sidewalls 14a' and 14b' much like a bellows. The entire double walled bladder 14' maybe fabricated from a fluid impermeable but distensible material such as silicone rubber. The double walled bladder 14' is secured to the eyecup 12 by an adhesive such as permabond 101 contact cement or by any other suitable means at endwall 14c'. And air duct 18' extends from the interior of the double walled bladder to the parallel connected pressure indicator 22, exhaust valve 24 and squeeze bulb 26 as before. An advantage of the double walled bladder structure 14' over the single walled structure is that glass endwalls are made unnecessary since the fundus 34 may be observed through the toroid hole 14d'. Operation of an ophthalmodynamometer equipped with the double walled bladder 14' is the same as that set forth hereinabove for the single walled bladder structure 14.

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 comprsiing:

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

a bladder member attached to the other of said surfaces for transmitting a force to said speculum member, said bladder member having a transparent portion concentric with said speculum opening;

first means attached to said bladder member for securing said one surface against the sclera;

second means operatively connected to said bladder member for varying the internal pressure of said bladder member; and

third means operatively connected to said bladder member for monitoring the internal pressure of said bladder member.

2. An ophthalmodynamometer according to claim 1 wherein said bladder member includes:

a closed tube having a corrugated sidewall attached to first and second transparent endwalls.

3. An ophthalmodynamometer according to claim 2 further including:

at least one head strap;

means attached to said first endwall for securing said head strap to said bladder member;

an adjustment gage;

retaining means attached to said second endwall for securing said adjustment gage to said bladder member, said retaining means including means integral therewith for securing said speculum member to said bladder member.

4. An ophthalmodynamometer comprising:

a substantially cylindrical bladder having a pleated sidewall attached to first and second transparent disc-shaped endwalls;

a keeper attached to said first endwall;

a mounting ring attached to said second endwall;

an eyecup member attached to said keeper, said eyecup member having a viewing port concentric with said transparent disc-shaped endwalls;

an adjustment gauge attached to said keeper; and

a tube having a first end portion extending through said mounting ring and said second endwall, and a second end portion serially connected to a normally closed exhaust valve, a squeeze bulb and a pressure indicator means connected in parallel with respect to each other.

5. An ophthalmodynamometer comprising:

first means for applying force over a predetermined area of an eyeball;

a bladder member attached to said first means, said bladder member having a transparent portion through which said eyeball may be observed;

second means operatively connected to said bladder member for varying the internal pressure of said bladder member;

third means operatively connected to said bladder member for monitoring the internal pressure of said bladder member;

at least one head strap attached to said bladder member; and

an adjustment gage attached to said bladder member.

6. An ophthalmodynamometer according to claim 5 wherein said bladder member includes:

a hollow substantially cylindrical bladder having a corrugated sidewall attached to first and second transparent disc shaped endwalls;

a mounting ring attached to said first endwall and having at least one head strap lug thereon for receiving said head strap; and

a keeper attached to said endwall for supporting said adjustment gage, said keeper including attachment means integral therewith for securing said first means to said keeper.

7. An ophthalmodynamometer according to clain 6 wherein said second means comprsies:

a tube member extending from the interior of said hollow cylindrical bladder through said first transparent endwall and said mounting ring to a squeeze bulb shunted by a normally closed exhaust valve.

8. An ophthalmodynamometer according to claim 7 wherein said third means comprises:

a pressure indicator shunt connected to said tube member.

9. An ophthalmodynamometer according to claim 8 wherein said first means comprises a transparent eyecup having:

a flared portion shaped to subatantially conform to the contour of a sclera and operative to prevent eyelid closure as well as exert force against the sclera; and

a frusto-conical portion terminating in a planar rim; wherein

said fursto-conical portion and said flared portion abut at their respective smallest diameters to form a viewing port having a diameter slightly larger than a cornea.

10. An ophthalmodynamometer according to claim 9 wherein said disc shaped endwalls and said viewing port are concentric.

11. An ophthalmodynamometer according to claim 10 wherein said bladder is substantially composed of a fluid impermeable, distensible material.

12. An ophthalmodynamometer according to claim 11 wherein said material is silicone rubber.