referring to fig1 apparatus 10 includes scleral cup 11 that communicates with negative pressure source 12 via conduit or confined flow passageway 13 . negative pressure source 12 can be a pump such as a syringe having barrel 14 within which is received a reciprocating plunger 15 actuated by means of plunger rod 23 . alternatively , negative pressure source 12 can be a power - driven vacuum pump or a similar device . three - way valve 16 is provided in conduit 13 between scleral cup 11 and negative pressure source 12 , as well as check valve 17 which permits the maintaining of a predetermined negative pressure within conduit 13 and scleral cup 11 when the latter is applied to the eye of a patient . negative pressure indicator 18 , such as a vacuum gauge or the like , is operably associated with conduit 13 so as to give an indication of negative pressure within scleral cup 11 . alternatively , indicator 18 can be a pressure transducer associated with a transcriber . pressure release valve 19 is provided in auxiliary conduit 20 which permits communication between conduit 13 and ambient atmosphere . in this manner , when valve 19 is opened , negative pressure within conduit 13 and within scleral cup 11 applied to the eye of a patient can be vented to the atmosphere , i . e ., released . preferably pressure release valve 19 is a needle valve or the like that permits a controlled release of the negative pressure at a desired rate over an extended period of time . three - way valve 16 is optional but desirable in that additional flexibility is imparted to the present apparatus . for instance , valve 16 can be used to hold negative pressure within scleral cup 11 after the latter has been applied to the eye of a patient by closing off communication with main conduit 13 . also , with valve 16 closed , negative pressure can be built up within that portion of conduit 13 defined by valve 16 and check valve 17 to a desired value before any negative pressure is applied to the eye through scleral cup 11 . three - way valve 16 additionally can serve as a rapid pressure release valve , if desired . check valve 17 facilitates the maintenance of negative pressure within conduit 13 and also permits the build - up of greater negative pressure within conduit 13 by moving plunger or piston 15 through a plurality of reciprocating strokes . in order to release the positive pressure generated by plunger 15 within barrel or bore 14 and against check valve 17 during a compression stroke , pressure relief valve 21 is provided in conduit 13 between check valve 17 and plunger or piston 15 . pressure relief valve 21 can be a conventional flapper valve or reed valve , or can be associated with plunger 15 in any other operable manner to provide pressure relief during the compression stroke , e . g ., by being built into plunger 15 instead of being mounted on end segment 22 of conduit 13 . to facilitate manipulation and use of scleral cup 11 , distal end segment 24 of conduit 13 preferably is flexible , for example , a piece of flexible tubing . the preferred configuration of scleral cup 11 is illustrated in fig2 . scleral cup 11 preferably is a hollow housing or member including conical head portion 25 with rim 29 formed in an edge of the wall defining the head portion , defining a circular opening or mouth of cup 11 that is adapted to be placed on the sclera of an eye and hollow stem portion 26 unitary with hed portion 25 . usually stem portion 26 is cylindrical and distal end 28 thereof is adapted for connection to flexible end segment 24 of conduit 13 . head portion 25 at the apex merges into stem portion 26 and portions 25 and 26 together define central through passageway 27 by means of which the negative pressure generated within conduit 13 is transmitted to the eye that is being studied . rim 29 is rounded and has peripheral surface 30 beveled inwardly for optimum contact with but minimal contact on the eye when scleral cup 11 is in use . preferably the height of the conical head portion is about the same as the diameter of central through passageway 27 at the base of conical head portion 25 . the shape and size of scleral cup 11 is selected on the basis of its efficacy to efficiently increase intraocular pressure while minimizing the potential for damage to the sclera , patient discomfort , and the effects of spurious forces , as well as for its ease of application . in this regard , it is desirable to maximize the force that can be applied to the eye by a given , preferably relatively soft partial vacuum ( relatively low negative relative pressure ), in order to avoid damage to the portion of the eye experiencing the vacuum . to this end , it is preferable to maximize the ratio of the area enclosed by rim 29 over which the negative pressure can be applied to the area of contact between the rim and the sclera . at the same time , it is desirable to minimize the contact pressure between rim 29 and the sclera produced by this force , in order to avoid damage to the conjunctiva and sclera contacted by the rim . further , to aid in ease of attachment , increase patient comfort , minimize spurious effects arising from interaction of the cup with the eyelids , and permit forward fixation , the cup should have an outside diameter at the base of conical head section 25 corresponding to the spherical segment of the sclera of the forward fixated in vivo human eye which is readily accessable . inasmuch as there is variation in the dimensions of eyes , it will be readily understood by persons skilled in the art that as a practical matter these conditions cannot be met exactly using a singlesized eye cup . these competing requirements can be substantially met in the case of the human eye with a cup having a diameter of between 9 and 10 millimeters as the inside dimension at the base of conical head section 25 and a diameter of about 13 millimeters as the outside dimension ( i . e ., a cup having an outside diameter of about 13 millimeters and a wall thickness on the order of 1 . 5 to 2 . 0 millimeters ). for such a cup , the scleral contact surface , rim 29 , should be beveled inwards to have a concave radius of curvature of about 13 millimeters in order to optimally minimize contact pressure . the material of construction for scleral cup 11 is not overly critical and can be metal or plastic . a particularly preferred material of construction is a transparent acrylic resin such as those commercially available from e . i . dupont de nemours & amp ; co . of wilmington , del ., under the designation &# 34 ; lucite &# 34 ;. use of the apparatus of the present invention is illustrated in fig3 where scleral cup 11 is shown applied to sclera 31 . initially , valves 16 and 19 ( fig1 ) are closed and negative pressure within conduit 13 is built up to an intermediate value of the order of about 50 to 75 mm hg . cup 11 is then applied to sclera 31 and valve 16 is opened to transmit the negative pressure to the eye . as a result , cup 11 is held in place by the negative pressure which can then be adjusted to the desired value while other measurements , e . g ., intraocular pressure and pulse , are being made . after the desired measurements have been completed , the negative pressure within cup 11 and conduit 13 is vented to ambient atmosphere by opening needle valve 19 ( and / or valve 16 ). when the pressure within cup 11 reaches about atmospheric , cup 11 is removed from sclera 31 by simply lifting cup 11 off the eye . the foregoing specification and accompanying drawings are intended as illustrative and are not to be taken as limiting . still other variations , modifications , and rearrangements of parts within the spirit and scope of this invention are possible and will readily present themselves to those skilled in the art .
a cup for use with a vacuum apparatus to modify intraocular pressure by applying a distorting force to the sclera is in the form of a rigid thick - walled hollow cone with beveled base edges dimensioned to fit the curvature of the scleral surface . the inside and outside dimensions of the base are chosen to minimize patient discomfort and the potential for damage to the eye and to promote ease of application .