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    <periodOfReport>2015-10-15</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0000836429</issuerCik>
        <issuerName>SYNERGETICS USA INC</issuerName>
        <issuerTradingSymbol>SURG</issuerTradingSymbol>
    </issuer>

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            <rptOwnerName>Hable David M</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O SYNERGETICS USA, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>3845 CORPORATE CENTRE DRIVE</rptOwnerStreet2>
            <rptOwnerCity>O'FALLON</rptOwnerCity>
            <rptOwnerState>MO</rptOwnerState>
            <rptOwnerZipCode>63368</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
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            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>President and CEO</officerTitle>
            <otherText></otherText>
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            <expirationDate>
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                <value>2024-12-11</value>
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    <footnotes>
        <footnote id="F1">Shares tendered for an offer price of $6.50 per share in cash (the &quot;Cash Consideration&quot;) plus one non-transferable contractual contingent value right per share (each, a &quot;CVR&quot;), which represents the right to receive up to two contingent payments, if any, of up to $1.00 in the aggregate, net to the holder in cash, upon the achievement of certain specified milestones within an agreed upon time period (less any applicable withholding taxes and without interest) (together, the &quot;Offer Price&quot;), pursuant to the tender offer consummated on September 16, 2015 according to the terms of the Agreement and Plan of Merger (the &quot;Merger&quot; Agreement&quot;), dated as of September 1, 2015, by and among Valeant Pharmaceuticals International, Blue Subsidiary Corp. and Synergetics USA, Inc.</footnote>
        <footnote id="F2">Pursuant to the terms of the Merger Agreement, on October 15, 2015, each share of restricted stock issued and outstanding immediately prior to the Effective Time (as defined in the Merger Agreement) was converted into the right to receive an amount per share equal to the Offer Price.</footnote>
        <footnote id="F3">Pursuant to the terms of the Merger Agreement, on October 15, 2015, each option outstanding immediately prior to the Effective Time (as defined in the Merger Agreement) was canceled in exchange for (i) a cash payment equal to the product of (A) the number of shares underlying the option and (B) the difference between the Cash Consideration and the exercise price of the option; and (ii) one CVR for each share underlying the option, in each case without interest and subject to any applicable tax withholding.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ David M. Hable</signatureName>
        <signatureDate>2015-10-15</signatureDate>
    </ownerSignature>
</ownershipDocument>
