Non-contact type tonometer

Surgery – Diagnostic testing – Testing aqueous humor pressure or related condition

Reexamination Certificate

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Reexamination Certificate

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06190317

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a non-contact type tonometer for obtaining the eye pressure of an eye to be examined.
2. Description of the Related Art
Conventionally, a non-contact type tonometer is known in which a stream of air is blown onto an eye to be examined to deform the cornea, and the degree of the deformation thereof is optically detected to measure the eye pressure of the examined eye without contact.
In a non-contact type tonometer of this kind, its optical system is readily stained with tears, dusts, and the like, because the stream of air is blown via a nozzle to the examined eye. The stained optical system sometimes precludes the alignment thereof, or produces errors in the measurements. In order to solve this problem, Japanese Patent Gazette No. Hei 2-12086 (Prior Art 1) and Japanese Patent Laid-Open Publication No. Hei 7-171110 (Prior Art 2) disclose a non-contact type tonometer comprising a mechanism for detecting stains in the optical system and alerting thereon an examiner.
In Prior Art 1, a lens cap is mounted in front of an objective lens when the detection of the stains is performed. The stain can be detected by measuring the quantity of the reflected light from the lens cap.
However, it is very bothersome for the operator to mount the lens cap in front of the objective lens every time he or she begins detecting the stain.
Meanwhile, in Prior Art 2, a stain-detecting system detects the stain based on the quantity of the alignment detection light reflected at the cornea. The operator does not have to do anything particular in order to detect the stain, such as mounting a lens cap in front of the objective lens.
However, in the apparatus disclosed in Prior Art 2, another problem occurs when the operation check of the instrument is carried out by using a model eye. If the reflectance of the model eye is much smaller than average ones of human eyes, the stain-detecting system may judge that the stain exists, even though the optical system is not stained.
The reason is explained below.
The apparatus disclosed in Prior Art 2 judges that the stain exists, when the quantity of the cornea-reflected light of the alignment detection light becomes equal to or smaller than the prescribed value. And this “prescribed value” is determined based on the average reflectance of human eyes.
On the other hand, the reflectance of a model eye depends on its material and structure. Some model eyes have reflectance closer to the average reflectance of human eyes while others have reflectance much smaller than the average reflectance of human eyes.
Thus, when a model eye having extremely small reflectance is used, the stain alert is issued even in unstained optical systems, because the “prescribed value” is determined based on the average reflectance of human eyes.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a non-contact type tonometer which can avoid issuing the stain alert in case of measuring a model eye having smaller reflectance.
To accomplish the foregoing object, the non-contact type tonometer according to a first aspect of the present invention comprises air stream blowing means for blowing a stream of air onto an eye to be examined, cornea deformation detecting means for optically detecting a deformation of a cornea caused by said air stream blowing means, a calculation unit for calculating an eye pressure of said eye to be examined on the basis of a result of the detection by said cornea deformation detecting means, light quantity measuring means for detecting a quantity of reflected light of a light beam projected onto said eye to be examined, and judging means for judging whether said eye to be examined is a human eye or a model eye by comparing with one another a plurality of light quantity data obtained by said light quantity measuring means.
This provides an advantage that a judgement can be automatically made on whether the subject is a human eye or a model eye to prevent a stain alert displaying function from operating incorrectly.
The non-contact type tonometer according to a second aspect of the present invention is further characterized in that in the cases where the measurement on said eye pressure of said eye to be examined is conducted a plurality of times said light quantity measuring means detects the quantity of said reflected light at each measurement.
The non-contact type tonometer according to a third aspect of the present invention is further characterized in that in the cases where a difference between the plurality of light quantity data is equal to or greater than a prescribed value, the judging means makes a judgement that the eye to be examined is a human eye.
The non-contact type tonometer according to a third aspect of the present invention is further characterized in that said light quantity measuring means also serve as an alignment detecting system for detecting a state of alignment between said eye to be examined and the apparatus itself.


REFERENCES:
patent: 4665923 (1987-05-01), Kobayashi
patent: 4995393 (1991-02-01), Katsurgi et al.
patent: 5002056 (1991-03-01), Takaheshi et al.
patent: 2-12086 (1990-03-01), None
patent: 7-171110 (1995-07-01), None

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