Method and apparatus for monitoring the arteriovenous oxygen difference from the ocular fundus

• US 5,308,919 A
• Filed: 04/27/1992
• Issued: 05/03/1994
• Est. Priority Date: 04/27/1992
• Status: Expired due to Term

• Current Assignee: Thomas E. Minnich
• Original Assignee: Thomas E. Minnich
• Inventors: Minnich, Thomas E.
• Primary Examiner(s): Sykes, Angela D.
• Application Number:
  US07/874,022
• Time in Patent Office: 736 Days
• Field of Search: 128/633, 128/664, 128/665-666, 128/676, 128/691, 356/41, 356/319, 356/320, 351/205.6, 351/221
• US Class Current: 600/320
• CPC Class Codes: A61B 5/14555 specially adapted for the eye fundus

Abstract

A non-invasive eye oximeter which monitors the arteriovenous oxygen difference. The optic disc region of the ocular fundus is illuminated with three or more wavelengths of light focused in approximately the same area. One of the light sources serves as a tracking beam which, through reflectance spectrophotometry, is used to determine when the tracking light beam is focused upon the optic disc. The scanning light beams are primarily focused within the boundary of the tracking beam. The intensity of light reflected from retinal venules and arterioles is detected, and the arteriovenous oxygen difference is determined.

Claims

1. An ocular fundus scanning system comprising:

targeting light beam generator means for emitting a targeting light beam having light of at least a first wavelength, said emitted light beam illuminating a portion of a fundus region of an eye including an optic disc, wherein said first wavelength reflects from said optic disc with greater intensity than from fundus tissue surrounding said optic disc;

targeting light beam focusing means for focusing said targeting light beam as a spot of illumination on said fundus region, said targeting light beam, reflecting from said fundus region thereby forming a reflected targeting beam, and for focusing said reflected targeting light beam;

targeting light beam detector means for detecting said reflected targeting light beam, said targeting light beam being associated with said targeting light beam focusing means;

eye scanner means for illuminating a plurality of points within said spot of illumination and for producing a signal proportional to the value of oxygen saturation of oxyhemoglobin in arterioles and venules of said optic disc;

signal processing means for detecting increased intensity of said reflected targeting light beam as said targeting light beam reflects from said optic disc, said signal processing means activating said eye scanner means when said increased intensity of said reflected targeting beam is detected, analyzing said signals proportional to oxygen saturation of oxyhemoglobin and determining a value of arteriovenous oxygen difference; and

display means for displaying information concerning said arteriovenous oxygen difference.

2. The ocular fundus scanning system of claim 1 wherein said fundus scanning system further comprises a targeting light beam spectral isolator means for passing light of said first wavelength in cooperation with said targeting light beam generator means.

3. The ocular fundus scanning system of claim 1 wherein said targeting light beam has a wavelength not substantially longer than 589 nm.

4. The ocular fundus scanning system of claim 1 wherein said scanning system further comprises an optic disc scanner housing means for containing said targeting light beam generator means, said targeting light beam focusing means, and said eye scanner means, and light shielding means for blocking out extraneous light in cooperation with said optic disc scanner housing means.

5. The ocular fundus scanning system of claim 1 wherein said eye scanner means comprises:

primary light beam generator means for generating a primary light beam of a second wavelength, wherein said second wavelength is selected so as to have a low value of absorbance by oxyhemoglobin;

secondary light beam generator means for generating a secondary light beam of an isobestic wavelength;

first scanning beam focusing means for focusing said primary light beam and said secondary light beam within said targeting beam spot of illumination;

means for altering a light path of said primary and secondary light beams, said altering means allowing said beams to inscribe a path on said optic disc;

second scanning beam focusing means for focusing said primary and secondary light beams reflected from said optic disc;

scanning beam detector means for detecting said reflected primary and secondary light beams said scanning beam detector means producing signals proportional to oxygen saturation of oxyhemoglobin in said arterioles and venules of said optic disc; and

light source control means for activating and controlling said targeting light beam and said primary and secondary light beams, said light source control means being associated with and activated by said signal processing means.

6. The ocular fundus scanning system of claim 5 wherein said light source control means simultaneously deactivates said targeting light beam and activates said primary and secondary light beams, said light source control means activating said primary and secondary light beams in a pulsatile, alternating fashion.

7. The ocular fundus scanning system of claim 5 wherein said light path altering means is in association with said first scanning beam focusing means.

8. The ocular fundus scanning system of claim 5 wherein said scanning beam detector means is in association with said second scanning beam focusing means.

9. An ocular fundus scanning system comprising:

targeting light beam generator means for emitting a targeting light beam having light of a first wavelength, said emitted light beam illuminating a portion of a fundus region of an eye, said fundus region including an optic disc, wherein said targeting light beam has a wavelength not substantially longer than 589 nm, said targeting light beam reflecting from said optic disc with greater intensity than from fundus tissue surrounding said optic disc;

first targeting light beam focusing means for focusing said targeting light beam as a spot of illumination on said fundus region, said targeting light beam reflecting from said fundus region thereby forming a reflected targeting beam;

second targeting light beam focusing means for focusing said reflected targeting light beam;

targeting light beam photodetector means for detecting said reflected targeting light beam, said targeting light beam photodetector means being associated with said second targeting light beam focusing means;

primary light beam generator means for generating a primary light beam of a second wavelength, wherein said second wavelength is selected so as to have a low value of absorbance by oxyhemoglobin;

secondary light beam generator means for generating a secondary light beam of an isobestic wavelength;

first scanning beam focusing means for focusing said primary light beam and said secondary light beam within said targeting beam spot of illumination;

galvanometer means for slightly altering a light path of said primary and secondary light beams, said galvanometer means causing said primary and secondary light beams to inscribe a curvilinear path across arterioles and venules of said optic disc, said galvanometer means being associated with said first scanning beam focusing means;

second scanning beam focusing means for focusing said primary and secondary light beams as said primary and secondary light beams reflect from said arterioles and venules of said optic disc;

scanning beam photodetector means for detecting said reflected primary and secondary light beams said scanning beam photodetector means producing signals proportional to oxygen saturation of oxyhemoglobin in said arterioles and venules of said optic disc, said scanning beam photodetector means being associated with said second scanning beam focusing means;

signal processing means for detecting increased intensity of said reflected targeting light beam as said targeting light beam reflects from said optic disc, for analyzing said signals proportional to oxygen saturation of oxyhemoglobin and for determining a value of arteriovenous oxygen difference;

light source control means for simultaneously deactivating said targeting light beam and activating said primary and secondary light beams in a pulsatile alternating fashion said light source control means being associated with said signal processing means, said light source control means being activated by said signal processing means;

display means for displaying said determined value of arteriovenous oxygen difference; and

optic disc scanner housing means for containing said first targeting light beam generator means, said targeting light beam focusing means, said primary and secondary light beam generator means and said first and second scanning beam focusing means, and a light shield means for blocking extraneous light in cooperation with said optic disc scanner housing means.

10. The ocular fundus scanning system of claim 9 wherein said first targeting light beam focusing means also collimates said targeting light beam.

11. The ocular fundus scanning system of claim 9 wherein said first targeting light beam focusing means forces said targeting light beam to form a spot of illumination having a diameter large enough to substantially envelop said optic disc.

12. The ocular fundus scanning system of claim 9 wherein said primary and said secondary light beam to generator means generates said primary and secondary each form a spot of illumination, of said fundus region, having a diameter in a range of approximately 50 to 100 microns.

13. A method of determining arteriovenous oxygen difference which comprises the steps of:

illuminating a fundus region of an eye, said fundus region including an optic disc, with light of a wavelength that is reflected by said optic disc with greater intensity than by tissue surrounding said optic disc;

detecting said greater intensity of said light when said light is reflected by said optic disc;

focusing a primary wavelength of light that has a low value of absorbance by oxyhemoglobin and a substantially isobestic wavelength of light on said optic disc region and illuminating a plurality of points in a curvilinear path on said optic disc region by alternating activation of said primary wavelength of light and said substantially isobestic wavelength of light in a pulsatile fashion, when said greater intensity of said light, reflected by said optic disc, is detected, causing said primary wavelength of light and said substantially isobestic wavelength of light to reflect from vasculature of said optic disc region of said fundus;

detecting said reflected primary and isobestic wavelengths of light, thereby producing signals proportional to values of oxygen saturation of oxyhemoglobin in arterioles and venules of said optic disc; and

calculating said arteriovenous oxygen difference by reflectance spectrophotometry means using said signals proportional to values of oxygen saturation.

14. The ocular fundus scanning system comprising:

targeting light beam generator means for emitting a targeting light beam having light of at least a first wavelength, said targeting light beam generator means illuminating a portion of a fundus region of an eye including an optic disc, wherein said first wavelength reflects from said optic disc with greater intensity than from fundus tissue surrounding said optic disc;

targeting light beam focusing means for focusing said targeting light beam as a spot of illumination on said fundus region, said targeting light beam reflecting from said fundus region thereby forming a reflected targeting beam, and for focusing said reflected targeting light beam;

targeting light beam detector means for detecting said reflected targeting light beam, said targeting light beam detector means being inserted with said targeting light beam focusing means;

primary light beam generator means for generating a primary light beam of a second wavelength, wherein said second wavelength is selected so as to have a low value of absorbance by oxyhemoglobin;

secondary light beam generator means for generating a secondary light beam of an isobestic wavelength;

first scanning beam focusing means for focusing said primary light beam and said secondary light beam within said targeting beam spot of illumination;

means for altering a light path of said primary and secondary light beams, said altering means causing said primary and secondary light beams to inscribe a path across arterioles and venules of said optic disc, said altering means being associated with said first scanning beam focusing means;

second scanning beam focusing means for focusing said primary and secondary light beams as said primary and secondary light beams reflect from said arterioles and venules of said optic disc;

scanning beam detector means for detecting said reflected primary and secondary light beams, said scanning beam detector means producing signals proportional to oxygen saturation of oxyhemoglobin in said arterioles and venules of said optic disc, said scanning beam detector means being associated with said second scanning beam focusing means;

light source control means for activating and controlling said targeting light beam and said primary and secondary light beams, said light source control means simultaneously deactivating said targeting light beam and activating said primary and secondary light beams, said light source control means activating said primary and secondary light beams in a pulsatile, alternating fashion,

signal processing means for detecting increased intensity of said reflected targeting light beam as said targeting light beam reflects from said optic disc, for activating said scanning beam detector means when said increased intensity of said reflected targeting beam is detected and for analyzing said signals proportional to oxygen saturation of oxyhemoglobin and for determining a value of arteriovenous oxygen difference, said light source control means being activated by said signal processing means; and

display means for displaying information concerning said arteriovenous oxygen difference.

15. The ocular fundus scanning system of claim 14 wherein said light path altering means is associated with said first scanning beam focusing means.

16. The ocular fundus scanning system of claim 14 wherein said scanning beam detector means is associated with said second scanning beam focusing means.