The purpose of this research is to evaluate the number of eyedrops easily accessible per party of a selection of generally prescribed glaucoma medications.

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Six party of every glaucoma medication were tested: three each in the vertical and also horizontal orientations. Bottles to be housed in a customized force gauge device designed come mimic ballpoint fingertip call with a bottle. At a traditional rate, all drops to be expressed from each bottle and counted with an automated autumn counter. Simultaneously, party volume to be measured and also drop size and number were likewise estimated. The main outcome actions were: total variety of drops, volume per bottle and also drops per milliliter (mL) the glaucoma medication.


A total of 192 party from 32 party designs and also manufacturers to be tested. Twenty-two of the 32 party designs had actually a considerably different mean number of drops in the vertical and also horizontal positions, through 10 designs have an ext drops dispensed in the horizontal orientation and 12 in the upright orientation. 6 of the 32 bottle designs had a considerably different mean total bottle volume in the vertical and also horizontal positions, through all design having greater volume in the upright position. An adjusted ratio the mean variety of drops/mean party volume prove a range from 20.9 drops/mL to 40.8 drops/mL.


There is far-ranging variability in drops and also volume obtainable per bottle of glaucoma medication depending on both the bottle position and manufacturer. This data point to the require for circumspection in prescribing glaucoma medications and also caution in assessing therapeutic outcomes.

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Although data show improved outcomes through lowered intraocular press from proper pharmacotherapy <1, 2>, numerous patients through glaucoma struggle to adhere to your prescribed regimens. Several studies suggest patients comply through 70% or under of their glaucoma drugs <3,4,5>. Plenty of factors have been implicated <6>, but difficulty instilling drops has actually garnered recent attention <7>. Ideal eyedrop management requires eye-hand coordination and also dexterity, linking intuitive acuity with a stable hand and also accurate proprioception <8>. No surprisingly, videotape evidence demonstrated that glaucoma patient provided an average of 1.4–1.8 drops when trying to instill a single eyedrop <9, 10>. A current cross-sectional patient inspection revealed the 25% of patients reported troubles with early eyedrop bottle exhaustion and also associated compliance with therapy. One-third of patient reported the factor for early on bottle exhaustion was due to bottle related problems such as “more than one drop come out” or “size of autumn is also large”. The last complaint is sustained by literary works that displayed the volume of one eyedrop in one ophthalmic solution may vary indigenous 25 come 70 μl <11>. Given the regular tear movie volume is 7 μl and also only qualified of containing 30 μl without overflow, a far-ranging portion of an eyedrop is wasted <12>. These data suggest that a far-ranging number the glaucoma patients run out of eyedrops before a booked prescription refill and that bottle connected mechanics play a duty <13>.

Despite the importance of bottle design in appropriate use of subject therapeutics, there exists no standardization of to produce in regards come drop instillation dynamics <14>, and the only dosing requirement is come accurately label and package medication volume <15>. Being manufactured and sold on the communication of volume, eyedrops are unique from many other creates of pharmacotherapy, which are prescribed through a discrete variety of doses to guide dispensing and also refill rates. While the minimum volume of medication consumers must anticipate per container of medicine is available, this does no necessarily analyze to number of applications, and also without regulation, leads to the possibility of inconsistency in the variety of drops that medicine accessible per bottle. Number of previous studies analyzing a smaller variety of medications in a non-standardized fashion have actually found far-reaching variability in the number of drops between both brands of medication and also position the the bottle <16,17,18>. Together such, the present study to be designed to more evaluate this possibility by objectively and systematically measure up the variety of eyedrops in each party of many typical glaucoma medications.

The number of eyedrops dispensed indigenous various usual glaucoma medicines was measured. All medications were to buy at cost from the college of Kentucky study Pharmacy and represented available regional brand and generic medications. A pressure gauge device consisting that a Mecmesin M500E Motorised Tension and also Compression test Stand, Mecmesin 100 N progressed Force Gauge (Mecmesin Corporation, Sterling, VA, USA) and custom grips and compressors to be designed and also calibrated through JA King & agency (Whitsett, NC, USA) (Fig. 1). The compressors to be designed come mimic ballpoint fingertip call with a bottle. Because that each medication, the bottle was housed in the apparatus and clamps were readjusted until the ballpoint compressors were situated at mid bottle length. Because that bottles with a rectangular rather of ring shape, the diluent dimensions were favored for compression, as this represents the an approach most likely to be utilized by patients once instilling drops. Beginning at 0 kg-force (kgf) and 0 mm (mm) displacement, the gauge was progressed in 0.1 mm increments until a fall of liquid fell from the bottle, as observed subjectively and confirmed v an automated VCD-BTD drop respond to (Vernier Software and Technology, Beaverton, OR, USA) and LabQuest 2 display (Vernier Software and also Technology, Beaverton, OR, USA). At a price of about one drop/s, 10 drops were expressed, climate the apparatus to be retracted come 0 kgf. This was recurring until all drops were exhausted from the bottle.


Force Gauge Apparatus. A force gauge apparatus consisting the a Mecmesin M500E engine- Tension and Compression Stand, Mecmesin 100 N advanced Force Gauge and custom grips and compressors to be designed and calibrated through JA King & Company. a: The compressors were designed come mimic ballpoint fingertip call with a bottle tip. b: for each medication, the bottle was housed in the apparatus and clamps were changed until the ballpoint compressors were located at mid party length. The L-shaped compression clamp to be then changed until the pressure gauge sensor was centered on the crosshairs that the clamp at a 90-degree angle

Simultaneously, fall size and also number was likewise estimated utilizing the densitometric technique for volume determination <19>. In twenty fall increments, the total volume of systems expressed to be measured v a 0.0001 g analytical balance (Ohaus Corporation, Parsippany, NJ, USA). This was repeated until every drops were worn down from the bottle. A 200 uL pipette (Zhejiang Huawei clinical Instrument Co, LTD, Zhe Jiang, China) was used to remove four 100-uL aliquots of every bottle. The median of the samples was divided by 0.1 mL to calculation the volume of every drop and also each bottle by splitting the fixed of every by the calculation density. For any type of bottles v residual liquid in the container lid, this was removed with the pipette and volume was measured separately.

Six bottles of each medication were tested. Three bottles were tested in the vertical orientation v the bottle pointer at 180 degrees and also three bottles to be tested in the close to horizontal orientation v the bottle reminder at 30 degrees. The vertical and also horizontal orientations to be the beginning position for the bottle tip throughout each measurement, together compression the the party variably and also slightly readjusted the tip position.

Statistical analysis

Mean response was compared by constructing an analysis of variance for a two method layout v factors: place (horizontal versus vertical) and also bottle (all combinations of medication name and formulation). A highly far-ranging interaction between position and also bottle was derived (p 
Full size table
Full dimension table

The outcomes of this study suggest there is significant variability in the variety of drops and also volume per bottle of glaucoma medications, both in terms of which party design and manufacturer is utilized and also the place the party is held when squeezed. Because that example, if a representative patience from this region is prescribed a 5 mL party of timolol 0.5%, there are 5 different generic and also brand party designs that may be dispensed. The patient can anticipate a selection of 123–209 and also 147–166 mean drops per party in the horizontal and vertical positions, respectively. If instilled twice daily, this would suggest a difference between 25.5 come 43 days of obtainable medication relying on the manufacturer and bottle position.

This study is the an initial to our expertise to existing an objective, automated and reproducible an approach to measure the number of drops easily accessible per party of medication. Further, we measured countable drops rather of calculating the variety of drops based on volume, i m sorry was shown to it is in inaccurate. Numerous previous studies have evaluated tiny samples of bottle formulations with similar, change results. A 1994 research of patient blinded to either use of a 5 mL party of timolol maleate matches levobunolol found a 21% greater length of usage of timolol (37 matches 29 days) <16>. Another study evaluate 45 matches 90 degree administration of fabricated tear bottles and found a considerably greater number of drops every bottle using densitometric evaluation and smaller sized drop volume because that 4 the end of 5 formulations at 45 contrasted to 90 degrees. The authors suggest administration at 45 levels would result in up to $1.93 savings every bottle contrasted to 90 levels <17>. A study evaluating 2.5 ml party of prostaglandin analogues organized vertically, in ~ 45 degrees and horizontally discovered that vertical instillation resulted in an ext drops per party for bimatoprost and also latanoprost, if 45 degrees was most efficient for travaprost. Suspect 1 year the bilateral therapy at 2006 costs, the authors established use of the most effective instillation method would an outcome in yearly savings of $109–192 <18>. Lastly, a recent study found significant variability in the number of eyedrops per bottle of 4 regionally available formulations of latanoprost when measured by manually counting the number of drops to express by hand, ranging from 77.6 to 88.7 drops per bottle. The authors estimated a similarly significant difference in estimated yearly cost, varying from $184 come $1198 per formulation <20>.

Currently, there exist no federal guidelines to regulate bottle style or quantity of drops obtainable per volume of medication <14, 15>. It has actually been said that pharmacists regularly use a rough guideline of 0.05 mL per eyedrop or 20 drops every mL (written an individual communication, division of drug Information, FDA, in march 27, 2015). V that in mind, there are significantly more eyedrops per bottle in this analysis than recommended, varying from 10.4% to 45.8% more mean drops per bottle tested. This may show that manufacturers “overfill” the bottles to allow for a margin that error throughout dispensing. If true, this serves critical purpose, due to the fact that it is well-known that countless patients require much more than one eyedrop per application <9, 10>. However, this data suggests another problem has been created by this practice: far-reaching variability in the number of doses every bottle.

Aside from bottle volume, second factor affect the number of drops available per party is fall size. We found far-ranging variability in the approximated drop dimension of learned formulations, varying from 0.024 to 0.221 mL. The size of autumn dispensed from a bottle counts on three basic elements: the design of the dropper bottle and tip, properties of the consisted of solution and the place of the bottle. The surface ar area approximately the bottle tip and surface anxiety of the solution are both manufacturer managed factors that affect drop size. Patience manipulations such as the angle and also rate autumn are created are much less predictable <11>. Further, the outcomes of the current study and others imply the many economical bottle place varies indigenous one style to the following <17–19>. A last potential determinant the drop size is the force required to squeeze the bottle, which unfortunately is substantially variable in both the experimental and also clinical setup <21, 22>. With all of these influences, it might be daunting to design suitable bottle because that instillation. One professional suggestion has actually been to use a dropper guideline with a smaller outer orifice diameter the provides continual surface area for a smaller-volume autumn to fall <11>.

This study has actually several limitations. The experimental design was novel, and although dimensions were automated, they have actually not been independently verified. Due to the fact that the study was carried out in an objective and reproducible manner, it might not accurately reflect plenty of of the patient related factors in dosing; that is likely that our patient experience also greater variability in the variety of drops accessible per bottle. Only two party positions to be tested and most ophthalmic containers room not intended come be delivered in a strict horizontal position. While 192 party from 32 bottle designs to be tested, they still stand for a tiny sampling that all accessible brand and also generic ophthalmic medications.

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In summary, this research demonstrates the far-reaching variability in drops and volume available per party of glaucoma medication relying on both the bottle position and manufacturer. This unregulated practice leaves prescribing physicians and pharmacists unable to accurately suspect the amount of medicine to dispense. This may bring about patients running out of medication at an early stage or being left through excess and associated costs. The variability native one refill come the next might be a contributor to minimal compliance. The experimental architecture in this study suggests an objective, reproducible an approach to determine drop number uniformly across different bottles and also designs. It must compel more evaluation and also consideration of standardization in the industry.