Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Objective type
Reexamination Certificate
2000-05-10
2002-05-07
Manuel, George (Department: 3737)
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
Objective type
Reexamination Certificate
active
06382792
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the general field of ophthalmology and is particularly concerned with a device for determining pupillary response and other ophtalmologic parameters so as to act as an optical diagnostic tool.
BACKGROUND OF THE INVENTION
The prior art discloses various devices for measuring and recording the size of the pupil of the human eye as well as of laboratory animals. Measurement of the pupil size and reactions is an important indicator of autonomic nervous system activity and the general physiological state of the subject.
The visual pathways and the oculomotor system reflect much of the status of the nervous system as a whole. Approximately 35% of the sensory nervous fibers entering the brain are in the two optic nerves. It is estimated that 65% of intracranial diseases exhibit neuro-ophthalmic symptoms or signs. Routine neurovisual examination allows physicians and scientists to identify abnormalities indicating neurologic disorders. Important examples are brain tumors, multiple sclerosis, cerebrovascular decease and cerebral aneurysms.
The examination of pupils is particularly helpful for assessing the visual pregeniculate pathways and oculomotor system. Typically, the pupils are inspected while the patient or individual is looking at distance to avoid the pupillary constriction that occurs with a near target. Inspection of the pupils in patients with dark brown irides can be facilitated with a tangentially applied light.
The pupils should be round and equal in diameter, although less than 1 mm. of inequality may be a normal variation. Poor pupillary dilation in dim light may indicate dysfunction of the sympathetic nervous system, and poor pupillary constriction to bright light may indicate parasympathetic dysfunction.
During typical testing of the pupillary reactions to light, the patient is asked to look into the distance and a bright light is shined obliquely into each pupil in turn. Both the distant gaze and the oblique lighting help to prevent a near reaction. The individual performing the test notes both the direct reaction which is the pupillary constriction in the same eye, and the so called consensual reaction which is the pupillary constriction in the opposite eye. Both the afferent pathway and the efferent pathway are responsible for this dual reaction.
As is well known, light stimulation for example of the left retina will result in impulsive which travels up the left optic nerve and divides at the chiasm. Some impulses continue up to the left tract; some cross and continue up the right tract. The light impulse arrives at each pretectal nucleus and stimulate the cell which, in turn, send impulses down the third cranial nerve to the iris sphincter causing each pupil to constrict. It is because of the double decussation, the first in the chiasm and the second between the pretectal nuclei and the Edinger-Westphal nuclei, that the direct pupil response in the left eye equals the consensual response in the right eye.
Insofar, the so called swinging-flashlight test does the most valuable clinical test for optic nerve dysfunction currently available. The abnormality detected with this test is the afferent pupillary defect called, also known as the Marcus Gunn pupil.
To perform the so called swinging-flashlight test, one must dim room illumination and prepare a bright light. The patient maintains fixation on an object typically 15′ or more away. The bright light is held directly in front of one eye for 3 to 5 seconds moved rapidly across the bridge of the nose to the front of the other eye for 3 to 5 seconds and then shifted back to the first eye.
This procedure is typically repeated several times until the examiner is certain of the responses. The critical observations to be made are the behavior of the pupil when it is first illuminated. A normal response is initial pupillary constriction followed by variable amounts of redilation. An abnormal response is slow dilation without initial constriction. The relative afferent pupillary defect almost always indicates a lesion in the optic nerve on the affected side, although rarely a large retinal lesion may produce this defect.
In other words, during the swinging-flashlight test, the examiner projects the light on the right eye (e.i.), allowing the right pupil to constrict to a minimum size and subsequently escape to an intermediate size. The light is then quickly swung to the left eye, which constricts from an intermediate to a minimum size, subsequently escaping to an intermediate size. At this point the light is swung again to the right eye and a mental note is made of the intermediate (starting) pupil size and briskness of the response to light. These characteristics should be exactly the same in both eyes as the light is alternatively swung to each eye.
The swinging-flashlight test will determine if the amount of light transmitted from one eye is less than that carried via the fellow eye. When the light is swung to the defective eye, immediate dilation of the pupils occurs instead of the normal initial constriction. This characterizes an afferent pupillary defect.
A partial differential diagnosis includes a retinal detachment, occlusion of a central retinal artery or vein, optic neuritis, and optic neuropathy among others entities.
Although the swinging-flashlight test is widely known and used for evaluating neuro-ophthalmologic defects and more particularly the afferent pupillary defect, it suffers from a set of drawbacks. Indeed, the test is challenging to the observer both technically and mentally. During technical performance of the test, the examiner must swing the light quickly between each eye with substantial consistency in order to achieve relatively valuable and constant observations.
This is particularly difficult since the source of light, typically a small flashlight must be swung between the eyes across the nose bridge of the patient.
Also, during movement of the light source between the eyes, the light source must ideally remain substantially symmetrical and oblique relative to the pupils. This is particularly difficult to perform with consistency.
Also, the intensity of the light being shined through the pupils relatively to the room illumination may also vary considerably and affect interpretation of the test results.
Furthermore, one of the main drawbacks associated with the conventional method of performing the afferent pupillary defect test or the so called swinging-flashlight test involves the need for the observer to make a mental note of the intermediate (starting) pupil size and briskness of the response to light.
The problem is further compounded by the fact that such mental notes must be made serially for each eye. Needless to say, even with an experienced observer, the conventional method and devices used for performing the afferent pupillary defect test involves a considerable amount of subjectivity. This can lead to erroneous interpretation with detrimental consequences. Accordingly, there exists a need for an improved method and device for performing the afferent pupillary defect test and perform the evaluation of other ophtalmologic parameters. The human eye also provides numerous other parameters such as pupil form, corneal abnormalities and soforth that can be used by the clinician to evaluate not only the health of the observed eye but also the overall health of a given patient. Most clinicians only use a conventional pocket ophtalmoscope to assess these essential parameters at least in part because of the overall complexity of alternative ophtalmologic tools. This in turn, again leads to relatively frequent misdiagnosis that could be avoided should a simple yet efficient tool be available.
Advantages of the present invention include the fact that the proposed methods and devices allow an individual to assess pupillary reaction including detection of the afferent pupillary defect with reduced external variables and parameters that may potentially lead to an erroneous result and interpretations.
More particularly the present device
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