System for measuring distances in the anterior chamber of the eye

#N/A

#Glaucoma is one of the leading causes of irreversible blindness worldwide. With early detection, accurate diagnosis and appropriate therapy, the visual loss of glaucoma is largely preventable. Glaucoma is not a single disease, but a large group of disorders sharing optic nerve damage as a common feature. The optic nerve damage is related to the intraocular pressure in most cases and to visual field loss in all cases.

#Determination of the anatomic type of glaucoma, namely, “open angle” or “narrow or closed angle,” is essential for effective treatment. Differentiation between open and narrow or closed angles must be made before a therapeutic strategy may be devised. Historically, the depth of the anterior chamber has been evaluated by the technique of gonioscopy, in which a lens is coupled to or contacts the cornea, which is uncomfortable for the patient. Direct (Koeppe) gonioscopy also requires the patient to be in a recumbent position. Gonioscopy also requires dexterity to coordinate the patient, lens, microscope and illumination source and experience to-interpret anatomic landmarks. The ancillary technique of B-scan ultrasonography has been used in recent years, but also requires contact with the corneal surface.

#The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:

#FIG. 1A is a schematic front view of an anterior chamber measurement system in conjunction with a slit lamp ophthalmology examination table according to the present invention;

#FIG. 1B is a schematic view of the slit lamp ophthalmology examination table of FIG. 1A with the anterior chamber measurement system removed;

#The anterior chamber measurement system of the present invention allows a user to readily make multiple distance measurements in the anterior chamber of the eye for purposes such as the detection and diagnosis of scleric angle closure, a process that may lead to glaucoma in a more advanced state. A first embodiment of an anterior chamber measurement system 10 is shown generally in FIGS. 1A and 2A. In this embodiment, the measurement system interfaces with an existing slit lamp ophthalmology examination table 12. (See FIG. 1B.) A slip lamp 14, a device that is commonly used in eye examinations, typically includes a stereo optical microscope 16 mounted on a movable stage 18 for motion in the X and Y directions in a horizontal plane and vertically in the Z direction. The stage is typically permanently mounted on a stable table 20 or other surface and includes a joystick 22 that is movable by the user, for example, an ophthalmologist, to move the microscope. For movement in the horizontal plane, the stage includes a horizontal drive shaft 24 along which the microscope is movable in the X direction. Typically, the drive shaft is 16 or 18 mm in diameter, but the shaft is not limited to these diameters. The shaft is further mounted for movement in the Y direction along the optical axis of a patient's eye, typically over a range of 76 mm or other distances determined by the specific slit lamp. Typically, a set of rack and pinion mechanisms 28, enclosed within separate housings 29, is provided for the Y-direction motion. In the illustrated slit lamp configuration, the shaft rotates as the motion is advanced, although other slit lamp configurations are possible.

#Referring to FIGS. 2A-7, the measurement system includes a base 30 that mounts securely and firmly to the slit lamp table 20 in any suitable manner and to also prevent vibrations. In the embodiment illustrated, an extension 32 of the base is provided to depend downwardly along the side of the slit lamp table and a clamp plate 34 extends beneath the table. One or more adjustable clamping elements 36, such as set screws, pass through corresponding threaded holes in the clamp plate to abut against the underside of the table. Preferably, a clamp sheet 38 is provided between the clamping elements and the underside of the table to distribute the clamping pressure from the clamping elements and to protect the underside of the table against marks from the clamping elements. Any other suitable clamping mechanism, as would be known in the art, may be provided. The clamping mechanism may be readily removable if desired, for example, if the measurement system is to be used with more than one slit lamp table. Alternatively, the measurement system may be permanently affixed to the slit lamp table in any suitable manner.

#The measurement system includes an interface 40 to the slit lamp horizontal drive shaft to travel with the drive shaft in the Y direction orthogonal to the axial length of the drive shaft. The drive shaft interface includes a forked shaft pick-up 42 that fits snugly over the slit lamp drive shaft 24. The shaft pick-up 42 is mounted to a linearly translatable slide mechanism 44, discussed further below, which overlays the rack and pinion mechanism 28 in its housing 29 and yields a precise motion following the shaft 24 in the Y direction. Thus, as the microscope is moved in the Y direction along the optical axis of the patient's eye, the shaft pick-up and the slide mechanism move the same distance.