
<PAGE>   1
                                  EXHIBIT 4.5

                            HEATON STOCK OPTION PLAN

Effective Date of Grant                                          Expiration Date
-----------------------                                          ---------------
July 22, 1993                                                      July 22, 2003

TO: Don Heaton ("Optionee")

    WHEREAS, Quest Medical, Inc., (the "Company") wishes to recognize the
contributions of the Optionee to the Company and to encourage the Optionee's
sense of proprietorship in the Company by owning the Common Stock, par value
$.05 per share (the "Common Stock"), of the Company;

    WHEREAS, the Company and the Optionee are parties to an employment
Agreement and Agreement regarding Competition dated as of July 22, l993 (the
"Employment Agreement");

    NOW, THEREFORE, in consideration of the mutual agreements and covenants
contained herein and in the Employment Agreement, the Company hereby grants to
the Optionee a stock option to purchase up to a total of 30,000 shares of the
Common Stock at a price per share of $3.75 (the "Option Price") on the terms
and conditions and subject to the restrictions set forth in this Agreement.

l.  TERM OF OPTION.  The term of this option shall expire ten years from the
Effective Date of Grant, or on the date set forth in the upper right hand
corner on page l of this Agreement, except as such term may be otherwise
shortened by the other provisions of this Agreement.

2.  EXERCISE OF OPTION.

    a.       Exercise.        Except as otherwise provided in this Agreement,
this option shall only become exercisable after one year of continued service
with the Company immediately following the Effective Date of Grant in the
installments set forth below.  Each installment shall include the number of
shares and shall become exercisable (in whole or in part) upon and after the
dates set forth below.

<TABLE>
<CAPTION>
                 Date                                       Shares
                 ----                                       ------
    <S>                                          <C>
    One year from the Effective                  one-half of the number
    Date of Grant                                of shares subject to the option

    Two years from the Effective                 one-half of the number
    Date of Grant                                of shares subject to the option
</TABLE>

The installments shall be exercisable as to any or all shares covered by an
installment, at any time or times after an installment becomes exercisable and
until expiration or termination of this





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option; provided, however, that the option may not be exercised as to less than
1,000 shares at any one time (or the remaining shares then purchasable under
the option, if less than 1,000 shares).

    b.       Method of Exercise.      This option may be exercised only by
written notice (the "Exercise Notice") by the Optionee to the Company at its
principal executive office.  The Exercise Notice shall be deemed given when
deposited in the U.S. mails, postage prepaid, addressed to the Company at its
principal executive office, or if given other than by deposit in the U.S.
mails, when delivered in person to an officer of the Company at that office.
The date of exercise of the option (the "Exercise Date") shall be the date of
the postmark if the notice is mailed or the date received if the notice is
delivered other than by mail.  The Exercise Notice shall state the number of
shares in respect of which the option is being exercised and, if the shares for
which the option is being exercised are to be evidenced by more than one stock
certificate, the denominations in which the stock certificates are to be
issued.  The Exercise Notice shall be signed by the Optionee and shall include
the complete address of such person, together with such person's social
security number.

    This option may be exercised either by tendering cash in the amount of the
Option Price or, with the Company's consent, by tendering shares of Common
Stock (which may include shares previously acquired upon exercise of part of
the option).  The Exercise Notice shall be accompanied by payment of the
aggregate option Price of the shares purchased by cash, a certified cashiers
check or, at the Company's option, by delivery of shares of Common Stock having
a Fair Market Value on the date immediately preceding the exercise date equal
to the Option Price.

    If the shares to be purchased are covered by an effective registration
statement under the Securities Act of 1933, as amended, the option may be
exercised by a broker-dealer acting on behalf of an Optionee if (a) the
broker-dealer has received from the Optionee or the Company a fully- and
duly-endorsed agreement evidencing such option, together with instructions
signed by the Optionee requesting the Company to deliver the shares of Common
Stock subject to such option to the broker-dealer on behalf of the Optionee and
specifying the account into which such shares should be deposited; (b) adequate
provision has been made with respect to the payment of any withholding taxes
due upon such exercise, and (c) the broker-dealer and the Optionee have
otherwise complied with Section 220.3(e)(4) of Regulation T, 12 CFR Part 220,
or any successor provision.

    The certificates for shares of Common Stock as to which this option shall
have been so exercised shall be registered in the name of the Optionee and
shall be delivered to the Optionee at the address specified in the Exercise
Notice.  In the case of the exercise of the option by an Optionee who is
employed by the Company on the Exercise Date, the Optionee in exercising such
option shall make payment or other arrangements (including, but not limited to,
requesting that the Company withhold shares of Common Stock that were to be
issued to the Optionee upon such exercise) satisfactory to the Company for
withholding federal and state taxes, if applicable, with respect to the shares
acquired upon exercise of the option.  In the case of options exercised when
the Optionee is no longer employed by the Company, such option exercise shall
be valid





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only if accompanied by payment or other arrangement satisfactory to the Company
with respect to the Company's obligations, if any, to withhold federal and
state taxes with respect to the exercise of the option.  In the event the
person exercising the option is a transferee of the Optionee by will or under
the laws of descent and distribution, the Exercise Notice shall be accompanied
by appropriate proof of the right of such transferee to exercise this Option.

3.  TERMINATION OF OPTION.

    a.       Optionee's Death.  In the event of the Optionee's death, the
option may be exercised by the Optionee's estate, personal representative or
beneficiary to the fullest extent that the Optionee was entitled to exercise
the same at any time within the one-year period commencing on the day next
following the Optionee's death.  After the Optionee's death, this option shall
be exercisable only by the executor or administrator of the Optionee's estate,
or if the Optionee's estate is not in administration, by the person or persons
to whom the Optionee's rights shall have passed by the Optionee's will or under
the laws of descent and distribution of the state where the Optionee was
domiciled at the date of death.

    b.       Suspension of Option.  The Company may suspend for a reasonable
period or periods the time during which this option may be exercised if, in the
opinion of the Company, such suspension is required to enable the Company to
remain in compliance with regulatory requirements relating to the issuance of
shares of Common Stock subject to this option.  The option is subject to the
requirement that, if at any time the Company shall determine, in its
discretion, that the listing, registration or qualification of the shares of
common stock subject to the option upon any securities exchange or under any
state or federal law, or the consent or approval of any government regulatory
body, is necessary or desirable as a condition of, or in connection with, the
granting or exercise of the option or the issue or purchase of shares under the
option, the option may not be exercised in whole or in part until such listing,
registration, qualification, consent or approval shall have been effected or
obtained free of any conditions not acceptable to the Company.  The Company
shall be under no obligation to effect or obtain any such listing,
registration, qualification, consent or approval if the Company shall
determine, in its discretion, that such action would not be in the best
interest of the Company.  The Company shall not be liable for damages due to a
delay in the delivery or issuance of any stock certificates for any reason
whatsoever, including, but not limited to, a delay caused by listing,
registration or qualification of the shares of Common Stock subject to an
option upon any securities exchange or under any federal or state law or the
effecting or obtaining of any consent or approval of any governmental body with
respect to the granting or exercise of the option or the issue or purchase of
shares under the option.

4.  NO RIGHTS AS SHAREHOLDER.  Neither the Optionee nor any person claiming
under or through the Optionee shall be or have any rights or privileges of a
shareholder of the Company in respect of any of the shares issuable upon the
exercise of the option, unless and until certificates representing such shares
shall have been issued (as evidenced by the appropriate entry on the books of
the Company or of a duly authorized transfer agent of the Company).





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5.  STATE AND FEDERAL SECURITIES REGULATION.  Optionee hereby represents that
if he exercises this option, then any purchases of stock hereunder shall be for
investment purposes and not with a view of resale or distribution.  In
addition, no shares shall be issued by the Company upon the exercise of this
option unless and until (a) any then- applicable requirements of state and
federal laws and regulatory agencies shall have been fully complied with to the
satisfaction of the Company and its counsel, and (b) if requested to do so by
the Company, the person exercising the option shall execute and deliver to the
Company a letter of investment intent in such form and substance as the Company
may require unless the issuance and sale of the stock have been registered
under the Securities Act.  If shares are issued upon exercise of an option
without registration under the Securities Act, subsequent registration of such
shares shall automatically relieve the purchaser thereof of any investment
restrictions or representations made upon the exercise of such option.

6.  ADMINISTRATION.  The Option and this Agreement shall be administered by the
Company's Stock Option Committee or in the absence thereof, by the Company's
Board of Directors.  The Committee shall have complete authority to construe,
interpret and administer this Agreement and to make all other determinations
necessary or deemed advisable in the administration of this Agreement.  The
determinations, interpretations and constructions made by the Committee shall
be final and conclusive.

7.  WITHHOLDING OF TAXES.  The Company may make such provisions and take such
steps as it may deem necessary or appropriate for the withholding of any taxes
which the Company is required by any law or regulation of any governmental
authority, whether federal, state or local, domestic or foreign, to withhold in
connection with any option, including, but not limited to, the withholding of
the issuance of all or any portion of the shares of Common Stock subject to the
option until the Optionee reimburses the Company for the amount the Company is
required to withhold with respect to such taxes, canceling any portion of the
issuance in an amount sufficient to reimburse the Company for the amount it is
required to so withhold, or taking any other action reasonably required to
satisfy the withholding obligation of the Company.

8.  CONTINUED EMPLOYMENT NOT PRESUMED.  Nothing in this Agreement or any
document describing it nor the grant of an option shall give the Optionee the
right to continue in employment with the Company or affect the right of the
Company to terminate the employment of the Optionee with or without cause.

9.  DILUTION OR OTHER ADJUSTMENTS.  In the event that there is any change in
the Common Stock subject to this Agreement or subject to the option granted
hereunder as the result of any stock dividend on, dividend of or stock split or
stock combination of, or any like change in, stock of the same class or in the
event of any change in the capital structure of the Company, the board of
Directors or the Committee shall make such adjustments with respect to the
Option as it deems appropriate to prevent dilution or enlargement of option
rights.





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10. RESTRICTIONS ON ISSUANCE OF SHARES.

    (a)      The Company shall not be obligated to sell or issue any shares
upon the exercise of the option granted under this Agreement unless:

             (i)     the shares with respect to which such option is being
    exercised have been registered under applicable federal securities laws or
    are exempt from such registration;

             (ii)    the prior approval of such sale or issuance has been
    obtained from any state regulatory body having jurisdiction; and

             (iii)   in the event the Common Stock has been listed on any
    exchange, the shares with respect to which such option is being exercised
    have been duly listed on such exchange in accordance with the procedure
    specified therefor.

If the shares to be issued upon the exercise of the option are intended to be
issued by the Company in reliance upon the exemptions from the registration
requirements of applicable federal securities laws, the Optionee, if so
requested by the Company, shall furnish to the Company such evidence and
representations, including an opinion of counsel, satisfactory to it, as the
Company may reasonably request.

    (b)      The option shall not be transferable by the Optionee other than by
will or the laws of descent and distribution or pursuant to a qualified
domestic relations orders as defined by the Code or Title I of the Employee
Retirement Income Security Act, or the rules thereunder.

11. GOVERNING LAW.  This Agreement has been executed in, and shall be deemed to
be performable in, Dallas, Dallas County, Texas.  The parties agree that this
Agreement shall be governed by and construed in accordance with the laws of the
State of Texas.  The parties further agree that the courts of the State of
Texas, and any courts whose jurisdiction is derivative on the jurisdiction of
the courts of the State of Texas, shall have personal jurisdiction over all
parties to this Agreement.

12. ENTIRE AGREEMENT.  This Agreement constitutes the entire agreement between
the parties pertaining to the precise subject matter contained in it and
supersedes all prior and contemporaneous agreements, representations and
understandings of the parties.  No supplement, modification or amendment of
this Agreement shall be binding unless executed in writing by the party to be
charged therewith.  No waiver of any of the provisions of this Agreement shall
be deemed, or shall constitute a waiver of any other provision, whether or not
similar, nor shall any waiver constitute a continuing waiver.

13. DUPLICATE ORIGINALS.  Duplicate originals of this document shall be
executed by both the Company and the Optionee, each of which shall retain one
duplicate original.

14. NOTICE.  Other than any Exercise Notice, any notice required or permitted
to be given under this Agreement shall be in writing and delivered in person or
sent by registered or certified





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mail, return receipt requested, first-class postage prepaid, (i) if to the
Optionee, at the address shown on the books and records of the Company, or (ii)
if to the Company, at 4103 Billy Mitchell Drive, Dallas, Texas 75244,
Attention: President, or any other address that may be given by either party to
the other party by notice pursuant to this Section.  Any notice, if sent by
registered or certified mail, shall be deemed to have been given at the time of
mailing.

                                        QUEST MEDICAL, INC.


                                        By:  /s/ F. Robert Merrill             
                                             -----------------------------------
                                        Title:  Secretary

ACCEPTED:

DON HEATON  /s/ Don Heaton         
            ---------------------




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