the treatment composition of the invention is an oil in water emulsion having an aqueous phase , an oil phase , and a surfactant combination used for the dual purpose of stabilizing the emulsion and spreading the emulsion over the ocular surface following its application to the eye . the surfactant combination comprises a primary surfactant and secondary surfactant and is one that enables formation of an emulsion that is stable in manufacture and during storage , but desirably meta stable when applied to the ocular surface — i . e ., one that rapidly differentiates when applied to the eye whereby a non blurring film of oil is rapidly formed over the ocular surface . a stable emulsion during manufacture and storage is one that may separate into separate phases during standing , but can be reconstituted by simple shaking . an unstable emulsion is one that breaks typically forming an oil film or slick that cannot be eliminated by simple shaking . a meta stable emulsion during use is desirable for purposes of this invention . though useable for alleviation of dry eye symptoms , a stable emulsion , as opposed to a meta stable emulsion , will not differentiate rapidly when applied to the ocular surface . this is undesirable for the following reasons . an emulsion is typically optically opaque due to the presence of two distinct phases . therefore , an opaque emulsion over the surface of the eye is likely to cause blurring . the duration of blur is dependent upon the time required for the emulsion to differentiate and form separate layers replicating a tear film . in addition , the emulsion is most easily added to the eye as a standard drop from an eyedropper . the eye is capable of holding a limited volume of fluid — a volume that is less than 25 μl . a volume of 25 μl is substantially less than the volume of a standard drop . therefore , if the emulsion is stable and fails to differentiate rapidly following application to the eye , excess emulsion will be discharged from the eye during blinking . discharge of the emulsion from the eye will result in discharge of efficacious components of the treatment solution from the eye before a long lasting tear film can be formed . for this reason , efficacious components may not be available in sufficient quantity to form the desired tear film . consequently , though a stable emulsion might alleviate the symptoms of dry eye for a limited period of time , it is a lesser preferred embodiment of the invention . a meta stable emulsion , as the term is used herein , is one that is either stable in storage , or differentiated into two separate layers , but is readily reconstituted by simple shaking prior to use . when a meta stable emulsion is added to the eye as a standard drop , it quickly differentiates permitting rapid formation of an oil film over the corneal surface without excessive oil discharge by blinking . preferably , the emulsion will differentiate within about 5 blinks following application to the eye , more preferably in a time of less than about 30 seconds . blurring may occur during the time required to move the bulk of the excess liquid to the canthi and discharge the same from the eye . during and following differentiation of the emulsion , the formation of the oil film is assisted by use of the surfactant combination which serves to help form the emulsion and facilitate the spread the oil over the surface of the eye as the emulsion breaks . consequently , a meta stable emulsion is the preferred embodiment of this invention . the surfactant combination used to form a meta stable emulsion must be carefully selected and must meet the following criteria : a . the surfactant combination must enable formation of an emulsion having long term stability , especially when exposed to the high temperatures of autoclaving needed to sterilize the formulation during manufacture , while permitting rapid phase differentiation when applied to the surface of the eye ; b . each component of the surfactant combination must be compatible with other components of the emulsion composition and permit formation of the emulsion at the physiological ph of between about 6 . 5 and 7 . 8 and preferably , at ph of between 7 . 2 and 7 . 5 ; and c . each component of the surfactant combination must be pharmaceutically acceptable for use on the eye and must be compatible with the eye — i . e ., each should be non - toxic and should not cause discomfort such as stinging in the concentrations used . as described above , the surfactants used to form the emulsions of the invention comprise a combination of a primary surfactant and a secondary surfactant . the primary surfactant is any one or more pharmaceutically acceptable surfactants that meets the above criteria and desirably forms a meta stable emulsion by itself or in combination with the secondary surfactant , but differs in chemical structure from the secondary surfactant . the literature is replete with thousands of surfactants having a variety of chemical structures described as useful for the formation and stabilization of an oil in water emulsion . to provide an exhaustive list of representative surfactants capable of functioning as a primary surfactant for purposes of the subject invention would be laborious and would omit many useful candidate materials . therefore , in addition to the representative examples given below , a procedure is given intended to enable one skilled in the art to determine if a given surfactant may be used as a primary surfactant in accordance with the preferred embodiment of the subject invention . this procedure involves the following steps : a . select a surfactant approved for use on the ocular surface within a useful concentration range as given below ; b . from the literature or by testing , determine if the surfactant is capable of forming an emulsion with the oil and water components at physiological ph ; c . prepare an emulsion having the concentration of emulsion components given below and determine if the emulsion is stable during storage , a minimum of three months under normal storage conditions , or capable of being reconstituted by simple shaking ; and d . apply the emulsion to the ocular surface and determine if the emulsion breaks on the ocular surface within a minute or less , preferably in less than 30 seconds or 5 blinks . representative examples of primary surfactants meeting the criteria given above include ionic and non - ionic surfactants but non - ionic surfactants are preferred as they are less prone to cause stinging when applied to the eye . specific examples of the nonionic surfactant include alkyl ethers such as polyoxyethylene octyl ether , polyoxyethylene lauryl ether , polyoxyethylene stearyl ether and polyoxyethylene oleyl ether ; alkyl phenyl ethers such as polyoxyethylene octylphenyl ether and polyoxyethylene nonylphenyl ether ; alkylesters such as polyoxyethylene laurate , polyoxyethylene stearate and polyoxyethylene oleate ; alkylamines such as polyoxyethylene laurylamino ether , polyoxyethylene stearylamino ether , polyoxyethylene oleylamino ether , polyoxyethylene soybean aminoether and polyoxyethylene beef tallow aminoether ; alkylamides such as polyoxyethylene lauric amide , polyoxyethylene stearic amide and polyoxyethyleneoleic amide ; vegetable oil ethers such as polyoxyethylene castor oil ether and polyoxyethylene rapeseed oil ether ; alkanol amides such as lauric acid diethanol amide , stearic acid diethanol amide and oleic acid diethanol amide ; and sorbitan ester ethers such as polyoxyethylene sorbitan monolaurate , polyoxyethylene sorbitan monopalmitate , polyoxyethylene sorbitan monostearate and polyoxyethylene sorbitan monooleate . of the above , polyoxyethylene stearates are preferred . additional suitable surfactants can be found by reference to a standard text on surfactants such as those described in ash and ash , encyclopedia of surfactants , chemical publishing company , new york , 1985 ; mccutcheon &# 39 ; s emulsifiers and detergents , north american edition , mccutcheon publishing company , glen rock , n . j ., 2000 ; and remington : the science and practice of pharmacy , nineteenth edition , vol . 1 at p . 251 coupled with the use of the procedures set forth above . the secondary surfactant is one or more surfactants meeting the above criteria and in addition , enables the emulsion to withstand autoclaving without significant degradation of the emulsion . the secondary surfactant desirably has a relatively small lipophilic group and a long chain hydrophilic group with a minimum of 6 repeating hydrophilic groups . more preferably , the secondary surfactant has an hlb of 9 or more , and most preferably , an hlb ranging between 12 and 20 , a hydrophilic group of at least 9 repeating hydrophilic groups , most preferably at least 9 ethylene oxide groups or isopropyl oxide groups , and a relatively small lipophilic group that is the same or similar in structure to the lipophilic group of the primary surfactant . exemplary nonionic surfactants include , but are not limited to the octoxynol - n series of the formula c 8 h 17 c 6 h 4 ( och 2 ch 2 ) n oh where n is between 5 and 70 and preferably between 30 and 50 , the nonoxynol - n series of the formula c 9 h 19 c 6 h 4 ( och 2 ch 2 ) p oh where p is between 5 and 40 and preferably between 15 and 30 , and polyoxyethylene c 12 - 22 alkyl ethers such as polyoxyethylene lauryl ether , polyoxyethylene cetyl ether , polyoxyethylene stearyl ether or polyoxyethylene oleyl ether . most preferred secondary surfactants are the octoxynol series of surfactants having between 30 and 50 ethylene oxide groups . numerous other surfactants having an hlb value of greater than about 9 and meeting the above criteria are listed in ash and ash , mccuthcheons , and remington , supra . the concentration of the surfactant combination used to form the emulsion may vary within wide limits . a treatment composition containing the surfactant combination in an amount as low as 0 . 01 weight percent of the total composition provides some benefit . a concentration of surfactant combination varying between 0 . 05 to 5 . 0 percent of the total composition is a clinically practical concentration range for purposes of the invention provided that the surfactant does not cause patient discomfort when used at the higher concentrations . most preferably , the concentration of the combination varies between about 0 . 25 and 2 . 5 percent by weight of the total composition . it should be understood that with many surfactants , as concentration increases , the likelihood of physical discomfort — i . e ., stinging , of the emulsion on the eye increases . thus , if significant stinging occurs when the emulsion is applied to the ocular surface , it is likely that the concentration of surfactant is too high . the ratio of the primary surfactant to the secondary surfactant may vary within relatively broad limits — for example , between 0 . 2 to 1 . 0 to 1 . 0 to 0 . 2 primary to secondary surfactant . a more preferred range varies between 0 . 5 to 1 . 0 and 1 . 0 to 0 . 5 . most preferably , the primary surfactant is used in slightly larger concentration than the secondary surfactant and the most preferred ratio varies between 1 . 0 to about 0 . 75 . the emulsions of the invention comprise an oil in water emulsion . the oil used to form the emulsion may be derived from animals , plants , nuts , petroleum , etc . those derived from animals , plant seeds , and nuts are similar to fats and are primarily glycerides or fatty acids and consequently , contain a significant number of acid and / or ester groups rendering the same polar and lesser preferred for purposes of the invention . alternatively , oils derived from petroleum are usually aliphatic or aromatic hydrocarbons that are essentially free of polar substitution and therefore suitable for purposes of the present invention provided the oil is refined so as to be compatible with human tissue such as the ocular surface . preferably , the oil is a linear hydrocarbon oil having from 10 to 50 carbon atoms and more preferably , the oil is a saturated n - alkane or isoalkane hydrocarbon having from 14 to 26 carbon atoms . unsaturated alkene hydrocarbons may be used but are less chemically stable . aromatic oils are lesser preferred because it is known that aromatic compounds are for the most part unsuitable for application to the ocular surface . mineral oil is the most preferred oil for purposes of this invention . the oil component within the emulsion may vary within reasonable limits provided the amount of oil retained on the eye following its application to the eye is within controlled volumes and does not exceed 25 μl , more preferably varies between about 1 and 10 μl and most preferably varies between about 1 and 5 μl . if the amount of oil added to the eye is in excess of 25 μl , the oil layer on the surface of the eye may be of excessive thickness and resulting in prolonged blurring . a treatment composition containing the oil in a concentration of at least 0 . 1 percent by weight of the total composition provides some benefits . a preferred concentration for the oil is at least 1 . 0 percent of the weight of the treatment composition . preferably , the oil content of the treatment solution varies between about 2 . 5 and 12 . 5 percent by weight of the composition . other additives may be present in the treatment composition . such materials include minor amounts of neutral lipids and oils such as one or more triglycerides , cholesterol esters , the natural waxes and cholesterol ; high molecular weight isoprenoids ; stabilizers , additional surfactants ; preservatives ; ph adjusters to provide a composition preferably having a ph between about 6 . 5 and 7 . 8 and most preferably , between about 7 . 2 and 7 . 5 ; salt , glycerol or sugar in sufficient concentration to form an isotonic or mildly hypotonic composition ; etc ., all as would be obvious to those skilled in the art . another useful class of additives comprises medications . as a consequence of the long term stability of the oil film formed over the surface of the eye using the emulsion compositions of the invention , prolonged and improved delivery of the medication to the eye results due to increased contact time of the medication on the eye . medications suitable for delivery to the eye using the film forming compositions of the invention are those soluble in either the aqueous or oil phase of the composition though it is preferable that the medication be soluble in the oil phase . illustrative medications include antibiotics , antiviral agents , anti - inflammatory agents and antiglaucoma agents such as illustrated in part in published european patent application no . 0 092 453 published oct . 26 , 1983 , sections 5 . 3 . 1 and 5 . 3 . 2 , incorporated herein by reference . any additional additives are added to the emulsion are added prior to formation of the emulsion using simple mixing techniques . the concentration of the additive is dependent upon the specific additive , and preferably , total additive content in addition to the surfactant and the oil are at a maximum concentration level whereby the total weight of the organics in the oil phase does not exceed 15 percent of the total weight of the emulsion . in accordance with the invention , the emulsions may be made in accordance with standard procedures . desirably , a commercial homogenizer is used to form the emulsion as equipment of this nature enhances the stability of the emulsion during transportation and storage . the use of commercial homogenizers for the formation of emulsions is within the skill of the art . the emulsions of the invention are also desirably used with subjects requiring ocular prostheses . in this instance , the treatment composition enhances the tear film layer and lubricates the boundary between the prosthesis and the ocular surface . when used with an ocular prosthesis , the treatment composition may be applied to the inner or both the inner and outer surfaces of the prostheses prior to insertion of the same into the eye . regardless of how added , the amount available to form the oil layer should be within the limits set forth above . the invention will be better understood by reference to the examples that follow . in the examples , the thickness of the lipid layer of a tear film formed over the ocular surface is evaluated by projecting a light source onto the ocular surface while viewing the reflected images from the light source on a video screen . the light source and its location is one that illuminates a surface area on the ocular surface of approximately 10 mm 2 . interference patterns are formed , the color ( s ) of which are indicative of the thickness of the oil layer . the color of the waves is correlated with a protocol of known film thickness . in this way , the tear film can be evaluated over a period of real time and rated in accordance with the following scale : further details pertaining to experimental procedure can be found in the above referenced u . s . pat . nos . 5 , 278 , 151 ; 5 , 294 , 607 ; and 5 , 578 , 586 . the data presented in the examples was obtained using individuals with baseline lipid layers of c rating or less . the data illustrates the resultant change in lipid layer characteristics from the baseline finding to the finding for lipid characteristics after the application of a standard eye drop of the test formulation to the eye . a desirable result is for improvement in lipid layer characteristics , evidenced by an increase in the alphabetical grade , with a being the most desirable , and f being the least desirable . the evaluations were performed 5 minutes after the instillation of the test formulations . the first two examples illustrate that emulsions may be formed using surfactants having properties and hlbs suggesting suitability for formation of stable oil in water emulsions , but illustrate that the emulsions so formed are unstable at autoclaving temperatures and therefore unsuitable for dry eye treatment . example 3 illustrates that a surfactant that might be suitable for formation of an emulsion having properties meeting the objectives of this invention is unsuitable as it causes discomfort to the patient when added to the eye . examples 4 and 5 illustrate that primary surfactants unsuitable for formation of a dry eye emulsion can be made functional when used in combination with the secondary surfactants of the invention regardless of the arithmetic hlb . this example illustrates that various surfactant combinations may be used that meet certain of the guidelines set forth above , especially those relating to hlb , but still fail to provide a meta stable emulsion able to withstand the elevated temperatures required for sterilization of the formulation . a mixture of myrj - 52 , a polyoxyethylene ( 40 ) stearate , and glycerol monostearate ( gms ), were used as primary surfactants to form a dry eye treatment emulsion with mineral oil as the oil phase . myrj - 52 has a high hlb value ( 15 - 16 . 9 ) and is water - soluble . glycerol monostearate ( gms nf ) has a low hlb value ( 3 - 5 ) and is therefore oil soluble suggesting that the combination should form a suitable oil in water emulsion . these surfactants have an identical lipophilic group ( stearate ) but different hydrophilic groups , and thus will have different physical behavior in terms of partitioning into the oil or water phases as suggested by the difference in the hlb value of the two surfactants . this combination of surfactants was evaluated by formation of 11 emulsions utilizing 5 . 5 % (± 0 . 3 %) of drakeol - 35 , a commercially available mineral oil at two different total surfactant concentrations − 0 . 15 % and 0 . 30 %. the non - polar oil phase of drakeol - 35 mineral oil and the aqueous phase of 0 . 67 % nacl and 0 . 05 % of anhydrous na 2 hpo 4 were common to all 11 of these formulations ; the ph was adjusted with diluted hcl as required . the relative concentration of the two individual surfactants was varied to evaluate the effect of the average hlb on emulsion quality as shown in table 1 . emulsification of the 11 formulations was performed using a commercial homogenizer ( pro250 ) from proscientific , inc ., with a ¾ horsepower motor which drove a 30 mm rotor - stator generator , by combining all of the reactants into one vessel and raising the temperature to approximately 90 ° c . table 1 provides the formulations and the compositions ( in grams ) for the 11 test formulations utilizing the myrj - 52 and gms primary surfactant systems . 3 . drakeol refers to a series of nf mineral oils available from penreco co . of butler , pa . the numeral following the letters represents the average molecular weight of the oil , and is an indication of the viscosity of the fluid . the formulations of table 1 produced emulsions which all met the first criterion of separation when at rest for several minutes . they also appeared to meet the second criterion of the emulsion returning to its original dispersed form after simple agitation . however , after periods of 60 minutes to 1 day , some of the oil phase in the formulations with the higher hlb values evidenced significant oil breakout , where the individual oil droplets were broken , resulting in the formation of an oil film on the surface . the formulations with the lower hlb values provided emulsions that did not evidence the oil film after similar periods of time . however , when agitated with mechanical shaking to simulate transportation effects , the oil film was visible on the surface within a time period that precluded a commercially viable product . in general , an increasing value of the calculated hlb produced poorer quality emulsions upon standing or upon agitation . however , no formulation in table 1 was found to be adequate because of the degradation of the individual oil droplets and the subsequent formation of a surface oil layer . further , microscopic studies and photographs of these formulae taken before and after both autoclaving and shaking demonstrated that the oil droplets were degraded either by being subjected to autoclaving at 121 ° c . or by shaking on the platform rocker shaker by vari - mix for less than one day . the above example illustrates that for the materials of this example , hlb values alone proved to be an unreliable parameter of complex formulation issues in the development of the intended dry eye treatment composition . while hlb values are generally useful as a formulation development guide , it was obvious that further considerations are required for the development of a dry eye treatment composition suitable for purposes of this invention . resolution of the above described problem would likely require significantly higher surfactant concentrations but it was known that increasing the concentration of myrj - 52 % would result in ocular discomfort — i . e . significant stinging . for this reason , the formulation was not evaluated clinically . polysorbate - 80 ( trade name tween - 80 ), a stearyl ether of a polysorbate , was evaluated as a sole primary surfactant for forming a dry eye treatment emulsion utilizing a total concentration of 7 . 0 % of a mineral oil mixture of draekol - 15 and draekol - 35 . in this study , polysorbate - 80 concentrations of 0 . 2 %, 1 . 0 %, and 1 . 5 % were utilized in the base formula as displayed in table 2 as formulae c1 through c6 . these formulations were prepared with and without disodium edta . emulsification of the 6 formulations was carried out with a commercial homogenizer ( pro250 ) from proscientific , inc ., using a ¾ horsepower motor that drove a 30 mm rotor - stator generator , by combining all of the reactants into one vessel and raising the temperature to approximately 90 ° c . table 2 provides the formulations and the compositions ( in grams ) for the 6 test formulations utilizing tween - 80 as the sole surfactant , 1 . drakeol refers to a series of nf mineral oils available from penreco co . of butler , pa . the numeral following the letters represents the average molecular weight of the oil , and is an indication of the viscosity of the fluid 2 . polysorbate - 80 is a stearyl ether of a polysorbate and is sold under the tradename tween - 80 by ici ( now known as uniqema , new castle , de ) in wilmington , de . the six emulsions prepared using polysorbate - 80 as a sole primary surfactant were found to meet the first criterion of providing appropriate separation of the oil and aqueous phases upon resting in the container for several minutes . the second criterion of reconstitution by simple product agitation was also met . however , these formulae failed to meet the third criterion because all were destabilized ( as evidenced by surface oil film formation ) when agitated for short periods of time on the laboratory shaker or when autoclaved for 30 minutes at 121 ° c . increased polysorbate - 80 content in the formulae to 1 . 50 decreased oil droplet instability , but still failed to meet the third criterion . the failure to meet the third criterion was confirmed in post autoclaved and post shaken samples , in that that the surface oil film formed by droplet coalescence prevented the reconstitution of the emulsion by simple shaking as required by the second criterion . these formulae thus did not meet the requirements for the desired eye treatment solution . it was found that when using only polysorbate - 80 as a sole primary surfactant , a higher concentration of polysorbate - 80 was required with the following undesirable results : ( 1 ) the emulsion was not autoclave stable , ( 2 ) the higher concentration of the polysorbate - 80 led to stinging on the eye and ( 3 ) the higher concentration of the polysorbate - 80 degraded the performance of the meta stable emulsion on the eye . thus , thee performance of these samples failed by a wide margin to meet the criterion of maintaining the original emulsion characteristics after agitation for a period of time . therefore , the use of polysorbate - 80 as a sole surfactant for the non - polar oil formula was judged inadequate and was not evaluated clinically . though this example does not illustrate the formation of an emulsion , it does illustrate the basis for rejection of a primary surfactant that would otherwise appear to be suitable for formation of an oil in water emulsion . the example describes the evaluation of span 20 , a highly viscous water insoluble sorbitan monolaurate , for suitability as a surfactant system for use on the eye . the hlb of 8 . 6 of this surfactant , and its reported use in ophthalmic products suggested that it would be a suitable surfactant for formation of an oil in water emulsion using mineral oil . five concentrations of span 20 , from 0 . 05 % to 1 . 00 % wv were prepared in a buffered normal saline vehicle for evaluation of comfort on the eye . the vehicle used for all formulations was unisol 4 , a buffered saline solution marketed by alcon laboratories , fort worth , tex . unisol 4 had previously been studied and found to be the most comfortable normal saline product for use on the ocular surface . it was therefore used as a vehicle for the test formulations , and was also used as a control . a drop of each of the 5 test formulations was placed on to the ocular surfaces of each subject , utilizing a 15 ml dropper container that delivered a drop of 40 μl to the ocular surface . the subject was asked to describe the sensation as one of : pleasant , neutral , slight sting , moderate sting , or severe sting . the results obtained with 6 subjects , all of whom evaluated each of the test formulation on two different days are summarized in table 3 . in view of the sting when applied to the eye and ocular surfaces , even in concentrations ≦ 0 . 10 %, the use of span 20 was rejected as a suitable surfactant for an eye treatment composition . this example illustrates that polysorbate - 80 found unsatisfactory for purposes of this invention in example 2 can be made suitable by combination with a secondary surfactant , in this case octoxynol - 40 . the example determines the optimum ratio of a mixed surfactant system comprising polysorbate - 80 as a primary and octoxynol - 40 as a secondary surfactant to maximize the stability of the oil / water interface in the ocular emulsion systems . formulae utilizing 2 . 4 % drakeol - 15 and 4 . 8 % drakeol - 35 with both octoxynol - 40 and polysorbate - 80 were evaluated at different concentrations . octoxynol - 40 has an hlb of 19 and polysorbate - 80 has an hlb of 15 . the two surfactants combined will yield an arithmetic hlb above the hlb believed suitable for formation of a stable oil in water emulsion . the samples were made both with and without disodium edta , keeping the concentrations of the other additives at the levels required for eye treatment compositions . the emulsification of the four formulations prepared was carried out with a commercial homogenizer ( pro250 ) from proscientific , inc ., using a ¾ horsepower motor which drove a 30 mm rotor - stator generator , by combining all of the reactants into one vessel and raising the temperature to approximately 60 ° c . table 4 sets forth the formulations and the compositions ( in grams ) for the 4 test formulations utilizing the octoxynol - 40 and polysorbate - 80 surfactant systems . 1 . drakeol refers to a series of nf mineral oils available from penreco co . of butler , pa . the numeral following the letters represents the average molecular weight of the oil , and is an indication of the viscosity of the fluid . 2 . octoxynol - 40 is polyethylene glycol ( 40 ) p - isooctylphenyl ether sold under the tradename synperonic op - 40 by ici ( now known as uniqema , new castle , de ) in wilmington , de . 3 . polysorbate - 80 is a stearyl ether of a polysorbate sold under the tradename tween - 80 by ici ( now known as uniqema , new castle , de ) in wilmington , de . all 4 formulations met the three pre - clinical criteria of proper separation , reconstitution of the emulsion by gentle shaking and maintaining the original emulsion characteristics when agitated for a period of time of at least 72 hours on the laboratory platform rocker shaker by vari - mix , or when autoclaved for 30 minutes at 121 ° c . microscopic studies and photographs of the samples - before and after autoclaving and shaking demonstrated that the oil droplets were not degraded by being subjected to autoclaving at 121 ° c ., or by shaking on the platform rocker shaker by vari - mix for 288 hours . since this formulation of non - polar oil with the surfactant system of octoxynol - 40 and polysorbate - 80 satisfied the pre - clinical criteria , formulae d1 and d3 were evaluated clinically and were found to adequately augment and restore the lipid layer thickness . the results of the clinical evaluations of formulations d1 and d4 are given in the following table : the clinical evaluations of patient numbers 1 to 14 indicated that the surfactant system of octoxynol - 40 and polysorbate - 80 were efficacious in forming and restoring a lipid layer of improved characteristics and that both formulations were essentially equally effective . the subjective sensation realized with both formulations was evaluated as comfortable , and without any form of adverse sensation . the studies of example 3 indicated that the addition of the surfactant octoxynol - 40 as a second surfactant in combination with polysorbate - 80 satisfied the criteria for a dry eye treatment composition . this study was directed to determining the optimal concentrations of the mixed primary and secondary surfactant system of polysorbate - 80 ( tween - 80 ) and octoxynol - 40 for an optimal dry eye treatment formulation . six formulations were prepared . each was formed using a commercial homogenizer ( pro250 ) from proscientific , inc ., using a ¾ horsepower motor which drove a 30 mm rotor - stator generator , by combining all of the reactants into one vessel and raising the temperature to approximately 60 ° c . table 5 illustrates 6 formulations , where the concentration of polysorbate - 80 is held constant at 0 . 40 %, while the concentration of octoxynol - 40 is varied at 0 . 30 %, 0 . 60 % and 1 . 20 % surfactant levels . the 0 . 40 % polysorbate - 80 concentration was chosen from the result of prior experiments that established that this concentration , when used with higher levels of octoxynol - 40 , met the pre - clinical requirements , while lower concentrations of polysorbate - 80 had resulted in minimal but detectable oil droplet degradation after being subjected to autoclaving at 121 ° c ., or by shaking on the platform rocker shaker by vari - mix for periods of time from 3 days to 288 hours . it was also considered desirable to utilize the lowest concentrations of both polysorbate - 80 and octoxynol - 40 for a dry eye treatment composition , while meeting the previously described requirements , since the sensitivity of the ocular surface cells and the immune response of the eye can be expected to increase with increasing concentration to any compound placed on the eye . these phenomena may also be exacerbated in dry eye states , since the surface epithelial cells are frequently compromised by the desiccation and lack of lubrication accompanying dry eye states . table 5 provides the formulations and the compositions ( in grams ) for the 6 test formulations : 3 . drakeol refers to a series of nf mineral oils available from penreco co . of butler , pa . the numeral following the letters represents the average molecular weight of the oil , and is an indication of the viscosity . 4 . p / o is the molar ratio of the polysorbate - 80 to octoxynol - 40 components . the lowest concentration of 0 . 30 grams octoxynol - 40 with 0 . 40 grams polysorbate - 80 was found to optimally satisfy the 3 criteria . the low surfactant concentration is desirable due to the possibility of irritancy of ocular tissue , where the sensitivity to a compound placed on the eye can be expected to increase with increasing concentration .
this invention relates to an emulsion composition for the formation of an artificial tear film over the ocular surface of the eye capable of providing mechanical lubrication for the ocular surface while reducing evaporation of fluid therefrom . the emulsion is desirably in the form of a meta stable emulsion and is characterized by the use of a surfactant comprising a combination of a primary and secondary surfactant where the primary surfactant permits formation of the emulsion and the secondary surfactant permits autoclaving of the surfactant . the invention also includes a method for the formation of such an emulsion .