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Thread: Eye Drops- How many drops per ml (Aprox!)?

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    lmcder is offline Active Member
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    Eye Drops- How many drops per ml (Aprox!)?

    Could anyone please give me an aproximate to the amount of drops in a ml of eye drops, i am doing my MUR accrediation and in my case my fictitious case study patient is having difficulty using her teoptic drops, she gets 10ml every two months, i am supplying her with an autodrop thing to aid her technique, but will 10 ml last 112 drops, ie one drop each eye bd, if she stops spilling it down her face?
    Cannot find an aprox conversion, i know it varies between drops etc, any advice id appreciate it.
    Thanks X
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    JonF is offline Registered Pharmacist
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    Re: Eye Drops- How many drops per ml (Aprox!)?

    Drops in ml

    According to above link about 20 drops per ml is a good rule of thumb

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    Band6 is online now Fantastic Member
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    Re: Eye Drops- How many drops per ml (Aprox!)?

    20 drops per ml is what I've always used. I would imagine that the eyedrop bottles are calibrated that way. Be careful with viscous drops though! Also be careful using 20 drops/ml for IV infusions - I've found some giving sets calibrated at 22/23 drops/ml.

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    Re: Eye Drops- How many drops per ml (Aprox!)?

    I thought the number of drops per ml had nothing to do with the physical properties of the dropper used, but was solely determined by the viscosity and surface tension of the liquid in question?
    Although these guys want to beg to differ...:
    Blackwell Synergy - Oph Phys Optics, Volume 17 Issue 3 Page 196-204, May 1997 (Article Abstract)
    Ze genuine Article, present & perfect!

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    Band6 is online now Fantastic Member
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    Re: Eye Drops- How many drops per ml (Aprox!)?

    The size of the hole and the dropper head ( and I would imagine the hydrophobic/philic properties of the material used in the droppers manufacture) must have something to do with it, otherwise the viscosity and density of the drop would have nothing to act on.

    Wasn't there a drug recall recently from an eyedrop manufacturer regarding the dropper heads and dose?

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    Re: Eye Drops- How many drops per ml (Aprox!)?

    Quote Originally Posted by Band6 View Post
    The size of the hole and the dropper head ( and I would imagine the hydrophobic/philic properties of the material used in the droppers manufacture) must have something to do with it, otherwise the viscosity and density of the drop would have nothing to act on.
    No, that's where surface tension comes into play, and Poiseuille's Law.
    I've found one of my old Pharmacy textbooks with a table of "Number of drops per gram" for a whole list of liquids:
    Acetone: 60 drops/g; Benzene: 50; Chloroform:59; Creosote 41; ether 93; eucalyptol 53; glycerin 26; liquid paraffin 45; castor oil 44; Fowler's Arsenical solution 44; methyl salycilate 37; and many more...
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    womble is offline Registered Pharmacist
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    Talking Re: Eye Drops- How many drops per ml (Aprox!)?

    And just to further the possibilities, the NZ Prescription Pricing Authority system allows for 60 drops per 5 ml.
    (The actual justification for this I don't know but 1 drop in each eye for 1/12 = 1x5ml bottle regardless of how many the GP prescribes for payment purposes)

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    Re: Eye Drops- How many drops per ml (Aprox!)?

    Quote Originally Posted by womble View Post
    And just to further the possibilities, the NZ Prescription Pricing Authority system allows for 60 drops per 5 ml.
    Ah, yes, but the earth's gravitational pull may be slightly different in the southern hemisphere, therefore affecting a liquid's relative density and/or its surface tension...(That'll be the Pinot Grigio talking, sorry! )
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