ASSIGNMENT AND SECURITY AGREEMENT

         THIS ASSIGNMENT AND SECURITY  AGREEMENT (this  "Agreement") is made and
entered into as of the 1 day of September, 1999, by and between Prime Medical
Operating,  Inc.,  a  Delaware  corporation  (the  "Secured  Party")  and  LASIK
Investors, L.L.C., a Delaware limited liability company ("LASIK").

                                                     RECITALS:

         A. LASIK and Secured  Party have  executed and  delivered  that certain
Contribution  Agreement  dated  effective  September 1, 1999,  between and among
LASIK,  Secured  Party,  Prime/BDR  Acquisition,   L.L.C.,  a  Delaware  limited
liability  company (the  "Debtor"),  Prime  Medical  Services,  Inc., a Delaware
corporation  ("PMSI"),  Prime/BDEC  Acquisition,   L.L.C.,  a  Delaware  limited
liability company, Barnet Dulaney Eye Center,  P.L.L.C., an Arizona professional
limited liability company,  David D. Dulaney,  M.D., Ronald W. Barnet, M.D., and
Mark Rosenberg (the "Contribution Agreement"), and Debtor and Secured Party have
executed and delivered that certain Loan  Agreement,  dated September ____, 1999
(the "Loan  Agreement"),  pursuant to which Secured Party agrees to make certain
loans to Debtor on the terms and subject to the conditions provided therein.

     B. Secured Party has requested that LASIK pledge the Collateral (as defined
below) to secure  certain  obligations  and  liabilities  that Debtor may now or
hereafter have to Secured Party, including,  without limitation, any obligations
arising under loans made pursuant to the Loan Agreement.

         C. LASIK desires to enter into this Agreement as a material  inducement
to Secured Party's extension of credit under the Loan Agreement.

                                                    AGREEMENT:

         NOW, THEREFORE, in consideration of the foregoing and the covenants and
agreements hereinafter set forth, and other good and valuable consideration, the
receipt and  sufficiency  of which LASIK  acknowledges,  LASIK and Secured Party
agree as follows:

                                                     ARTICLE I
                                        COLLATERAL AND SECURED OBLIGATIONS

     1.1 Grant of  Security  Interest.  LASIK  hereby  assigns,  transfers,  and
pledges to Secured  Party,  and LASIK hereby  grants to Secured Party a security
interest   in,   the   following   described   collateral   (collectively,   the
"Collateral"): --------------------------

     (a) Interest in  Subsidiary.  All  ownership  interests of LASIK in Debtor,
whether now existing or hereafter  acquired and including,  without  limitation,
that certain 40% membership interest in Debtor; ----------------------

          (b) Accounts. All accounts and rights now or hereafter attributable to
     any of the Collateral  described in (a) above,  and all rights of LASIK now
     or hereafter  arising  under any  agreement  pertaining  to the  Collateral
     described in (a) above,  including  without  limitation all  distributions,
     proceeds,  fees,  dividends,  preferences,  payments  or other  benefits of
     whatever  nature  which LASIK is now or may  hereafter  become  entitled to
     receive with respect to any Collateral described in (a) -------- above;

                  (c) Additional  Property.  "Collateral" shall also include the
following property (collectively, the "Additional Property") which LASIK becomes
entitled to receive or shall  receive as a result of its  ownership of any other
Collateral:  (i) any stock or other  ownership  certificate,  including  without
limitation,  any certificate representing a stock dividend or any certificate in
connection with any recapitalization,  reclassification,  merger, consolidation,
conversion,  sale of assets,  combination,  stock split, reverse stock split, or
spin-off;  (ii) any  option,  warrant,  subscription  or  right,  whether  as an
addition to or in substitution of any other  Collateral;  (iii) any dividends or
distributions  of any kind whatsoever,  whether  distributable in cash, stock or
other property;  (iv) any interest,  premium or principal payments;  and (v) any
conversion or redemption proceeds; and

          (d)  Proceeds.  All proceeds  (cash and  non-cash)  arising out of the
     sale,  exchange,  collection or other  disposition of all or any portion of
     the  Collateral  described  in (a),  (b) or (c)  above,  including  without
     limitation  proceeds  in  the  form  of  stock,  accounts,  chattel  paper,
     instruments, documents, goods, inventory and equipment. --------

The security interest in the Collateral hereby granted by LASIK to Secured Party
may sometimes be referred to in this Agreement as the "Security Interest".

          1.2 Obligations. This Agreement and the Security Interest shall secure
     full and punctual  payment and  performance of the following  indebtedness,
     duties and obligations (collectively, the "Obligations"): -----------

          (a) All  liabilities  and  obligations  of  Debtor  to  Secured  Party
     (including,  without limitation,  any principal,  interest,  fees and other
     amounts,  and  any  other  obligations)  under  and  pursuant  to the  Loan
     Agreement  and each  promissory  note  (collectively,  the  "Note")  issued
     pursuant to the Loan Agreement; and

          (b) All liabilities and obligations of LASIK to Secured Party, PMSI or
     any Prime  Indemnified  Parties (as defined in the Contribution  Agreement)
     under and pursuant to the Contribution Agreement or this Agreement.

                                   ARTICLE II
        LASIK'S REPRESENTATIONS AND WARRANTIES WITH RESPECT TO COLLATERAL

         LASIK hereby represents and warrants to Secured Party as follows:

          2.1 Ownership of Collateral.  LASIK has good and  marketable  title to
     the  Collateral   free  and  clear  of  any  liens,   security   interests,
     shareholders  agreement,  calls,  charge,  or encumbrance,  except for this
     Security  Interest.  No financing  statement or other instrument similar in
     effect  covering  all or any  part  of the  Collateral  is on  file  in any
     recording  office,  except as may have been filed in favor of Secured Party
     relating to this Agreement. -----------------------

          2.2  Power  &  Authority.  LASIK  has the  lawful  right,  power,  and
     authority to grant the Security Interest in the Collateral. This Agreement,
     together  with all filings and other  actions  necessary  or  desirable  to
     perfect and protect  such  security  interest,  which have been duly taken,
     create a valid  and  perfected  first  priority  security  interest  in the
     Collateral  securing  the  payment  and  performance  of  the  Obligations.
     -----------------

          2.3 No  Agreements.  The  Interests  are not  subject  to any right of
     redemption,  or any call or put options, voting trust, proxy,  shareholders
     agreement, right of first refusal, or any other document or agreement which
     would in any way impair or adversely  affect this Security  Interest or the
     rights of Secured Party under this Agreement. -------------

          2.4 Securities.  Any  certificates  evidencing  securities  pledged as
     Collateral are valid and genuine and have not been altered.  All securities
     pledged as Collateral  have been duly  authorized and validly  issued,  are
     fully  paid and  non-assessable,  and were not issued in  violation  of the
     preemptive  rights of any party or of any  agreement  by which LASIK or the
     issuer  thereof is bound.  Except as  expressly  provided  otherwise in the
     Contribution  Agreement or any Transaction  Document (as therein ----------
     defined),  no restrictions or conditions exist with respect to the transfer
     or voting of any securities pledged as Collateral.

                                                    ARTICLE III
                                   LASIK'S OTHER REPRESENTATIONS AND WARRANTIES

         3.1  Solvency of LASIK.  As of the date  hereof,  (i) LASIK is solvent;
(ii) the fair saleable  value of LASIK's assets  exceeds its  liabilities  (both
fixed and  contingent);  (iii)  LASIK has  sufficient  capital to satisfy all of
LASIK's obligations as they become due; (iv) no receiver,  trustee, or custodian
has been appointed for, or taken possession of, all or substantially  all of the
assets of LASIK,  either in a  proceeding  brought  by LASIK or in a  proceeding
brought  against  LASIK;  (v) LASIK is not the subject of a petition  for relief
under  the  United  States  Bankruptcy  Code or any  similar  federal  or  state
insolvency  law,  including  without  limitation a petition  filed by LASIK or a
petition filed by a third party seeking relief against LASIK; and (vi) LASIK has
no intention of filing a petition for relief under the United States  Bankruptcy
Code or any  similar  federal or state  insolvency  law, or of seeking any other
form of creditor relief.

          3.2  Authority and  Compliance.  LASIK has full power and authority to
     enter into this Agreement. LASIK has full power and authority to enter into
     and perform its obligations under each Other Agreement.  No further consent
     or approval is required as a condition to the validity of this Agreement or
     any Other  Agreement.  LASIK is in  compliance  with all  applicable  laws,
     ordinances, statutes, orders, regulations,  judgments, writs, or decrees of
     any governmental entity to which it is subject. ------------------------

          3.3  Binding  Agreement.  This  Agreement  and  each  Other  Agreement
     constitute  valid and legally  binding  obligations of LASIK, in accordance
     with  their  terms,  subject  to  the  applicable  bankruptcy,  insolvency,
     reorganization,  moratorium,  and similar laws affecting  creditors' rights
     generally. -----------------

          3.4 Litigation.  There are no proceedings pending or, to the knowledge
     of LASIK,  threatened before any court or administrative  agency which will
     or may have a material  adverse effect on the financial  condition of LASIK
     or upon LASIK's ability to perform its obligations  under this Agreement or
     any Other Agreement. ----------

          3.5 No Conflicting Agreements. There are no provisions of any existing
     agreement,  mortgage,  indenture or contract  binding on LASIK or affecting
     its  property,  which  would  conflict  with  or in  any  way  prevent  the
     execution,  delivery, or carrying out of the terms of this Agreement or any
     Other Agreement. -------------------------

          3.6  Ownership  of  Assets.  LASIK  has  good  and  full  title to the
     Collateral,  and the Collateral is owned free and clear of liens,  charges,
     claims, security interests, and other encumbrances. -------------------

          3.7 Taxes.  LASIK has filed all tax  returns  required  to be filed by
     LASIK.
                                                    ARTICLE IV
                                   LASIK'S COVENANTS WITH RESPECT TO COLLATERAL

         LASIK  covenants  and  agrees  that from the date  hereof and until the
payment  and  performance  in  full  of the  Obligations  unless  Secured  Party
otherwise consents in writing:

          4.1 Delivery of  Instruments  and/or  Certificates.  Contemporaneously
     herewith,  LASIK  covenants  and agrees to  deliver  to  Secured  Party any
     certificates,  documents,  or  instruments  representing  or evidencing the
     Collateral,  with LASIK's  endorsement thereon and/or accompanied by proper
     instruments   of  transfer   and   assignment   duly   executed  in  blank.
     -------------------------------------------

         4.2 Further Assurances. LASIK will contemporaneously with the execution
hereof and from time to time  thereafter  at its  expense  promptly  execute and
deliver all  further  instruments  and  documents  and take all  further  action
necessary  or  appropriate  or that  Secured  Party may  request in order (i) to
perfect and protect the  security  interest  created or  purported to be created
hereby and the first priority of such security interest,  (ii) to enable Secured
Party to exercise  and enforce its rights and  remedies  hereunder in respect of
the  Collateral,  and (iii) to otherwise  effect the purposes of this Agreement,
including  without  limitation:  (A)  executing  and  filing  any  financing  or
continuation  statements,  or any  amendments  thereto;  (B)  obtaining  written
confirmation  from the issuer of any  securities  pledged as  Collateral  of the
pledge of such securities,  in form and substance satisfactory to Secured Party;
(C)  cooperating  with Secured Party in registering the pledge of any securities
pledged as Collateral with the issuer of such securities;  (D) delivering notice
of Secured Party's security interest in any securities  pledged as Collateral to
any securities or financial  intermediary,  clearing  corporation or other party
required by Secured Party, in form and substance  satisfactory to Secured Party;
and  (E)  obtaining  written  confirmation  of  the  pledge  of  any  securities
constituting Collateral from any securities or financial intermediary,  clearing
corporation  or other party  required by Secured  Party,  in form and  substance
satisfactory to Secured Party.

         4.3 Additional Property. All Additional Property, as defined in Section
1.1(c)  above,  received  by LASIK shall be received in trust for the benefit of
Secured Party.  All Additional  Property and all  certificates  or other written
instruments or documents  evidencing and/or representing the Additional Property
that is received by LASIK, together with such instruments of transfer as Secured
Party may request,  shall  immediately be delivered to or deposited with Secured
Party and held by Secured Party as Collateral under the terms of this Agreement.
If the  Additional  Property  received by LASIK and  delivered to Secured  Party
pursuant  to this  Section  shall be shares of stock or other  securities,  such
shares  of  stock  or  other  securities  shall  be duly  endorsed  in  blank or
accompanied by proper  instruments  of transfer and assignment  duly executed in
blank with, if requested by Secured Party,  signatures guaranteed by a member or
member organization in good standing of an authorized Securities Transfer Agents
Medallion  Program,  all in form and substance  satisfactory  to Secured  Party.
Secured Party shall be deemed to have possession of any Collateral in transit to
Secured Party or its agent.

         4.4  Sale,  Transfer,  Encumbrance.  LASIK  will  not  sell,  transfer,
mortgage,  or otherwise  encumber any  Collateral or impair the value thereof in
any manner without  Secured  Party's prior written  consent,  including  without
limitation by purchase, lease, barter, trade, payment deferral, or the creation,
assumption  or guarantee of  indebtedness  or other  lending of credit.  Secured
Party's written consent to any sale,  mortgage,  transfer,  or encumbrance shall
not be construed to be a waiver of this  provision in respect to any  subsequent
proposed sale, mortgage, transfer, or encumbrance.

          4.5 Liens.  Neither LASIK nor any person acting on LASIK's behalf has,
     or shall have any  right,  power,  or  authority  to and shall not  create,
     incur, or permit to be placed or imposed, upon the Collateral,  any lien of
     any type or nature  whatsoever,  other  than the liens in favor of  Secured
     Party. -----

          4.6 Matters or  Occurrences  Affecting  Collateral or this  Agreement.
     LASIK  will  promptly  notify  Secured  Party  of any  and all  matters  or
     occurrences  that may have a material adverse effect on the status or value
     of the  Collateral or this  Agreement,  including  without  limitation  the
     occurrence of an Event of Default, or an event which, with giving of notice
     or  lapse  of  time,  or  both,  would  constitute  an  Event  of  Default.
     -------------------------------------------------------------

          4.7 Agreements  Pertaining to Collateral.  LASIK will not transfer any
     voting  rights  pertaining  to the  Collateral  to any  person  or  entity.
     -----------------------------------

         4.8 Dilution of Ownership.  As to any securities pledged as Collateral,
LASIK  will not  consent to or approve  of the  issuance  of (i) any  additional
interests  or  shares  of any  class  of  securities  of such  issuer,  (ii) any
instrument  convertible  voluntarily by the holder thereof or automatically upon
the occurrence or non-occurrence of any event or condition into, or exchangeable
for, any such  securities,  or (iii) any warrants,  options,  contracts or other
commitments  entitling any third party to purchase or otherwise acquire any such
securities.

          4.9  Restrictions  on  Securities.  LASIK  will  not  enter  into  any
     agreement  creating,  or  otherwise  permit to exist,  any  restriction  or
     condition upon the transfer, voting or control of any securities pledged as
     Collateral,  except as consented to in writing by Secured Party.  As to any
     securities  pledged as collateral,  LASIK will not consent to or approve of
     any stock split, reverse stock split, stock dividend, reclassification,  or
     other  similar  act  or   transaction   regarding   the  Interests   unless
     -------------------------- consented to in writing by Secured Party.

                                                     ARTICLE V
                                           LASIK'S AFFIRMATIVE COVENANTS

         Until payment and performance of all  Obligations,  LASIK covenants and
agrees that it shall promptly  advise Secured Party in writing of any litigation
filed  against  LASIK  and of any  condition,  event or act  which  comes to its
attention  that  would  or might  have a  material  adverse  effect  on  LASIK's
financial condition.

                                                    ARTICLE VI
                                                NEGATIVE COVENANTS

         Until payment and performance of all  Obligations,  LASIK covenants and
agrees that LASIK will not,  without the prior written  consent of Secured Party
grant, suffer, or permit liens on, or security interests in, the Collateral.


                                                    ARTICLE VII
                                               DEFAULT AND REMEDIES

          7.1 Events of Default.  An Event of Default  (herein so called)  shall
     exist  if  any  one  or  more  of  the   following   events   shall  occur:
     -----------------

          (a) The failure of Debtor to pay any amount  required to be paid under
     the Loan Agreement or any Note (including,  without limitation,  principal,
     interest and fees due thereunder)  within ten (10) calendar days after such
     amount is due;

          (b) The failure of LASIK to pay any  Obligation  described  in Section
     1.2(b)  within ten (10)  calendar  days after such  amount is due (and,  if
     applicable  under  the  terms  of any  contractual  agreement  creating  or
     governing  such  Obligation,  after  the  expiration  of  any  cure  period
     expressly required);

                  (c)      LASIK's breach of a covenant in this Agreement;

          (d) Any  representation  or warranty  made by LASIK in this  Agreement
     shall be false or materially  misleading,  as determined in the  reasonable
     discretion of Secured Party;

          (e) Any  event of  default  shall  occur  under  the terms of the Loan
     Agreement  and shall not be cured  within the time  expressly  provided for
     with respect thereto in the Loan Agreement;

                  (f) If LASIK or Debtor,  or any other party  obligated  to pay
any portion of the Obligations:  (i) becomes  insolvent,  or makes a transfer in
fraud of  creditors,  or makes an assignment  for the benefit of  creditors,  or
admits in  writing  its  inability  to pay its debts as they  become  due;  (ii)
generally is not paying its debts as such debts become due and Secured Party, in
good faith,  determines  that such event or  condition  could lead to a material
impairment  of the  Collateral,  or any part  thereof,  or of any other  payment
security for any of the Obligations;  (iii) has a receiver, trustee or custodian
appointed for, or take possession of, all or substantially  all of the assets of
such  party or any of the  Collateral,  either in a  proceeding  brought by such
party or in a proceeding  brought against such party and such appointment is not
discharged or such possession is not terminated within sixty (60) days after the
effective  date  thereof  or  such  party  consents  to or  acquiesces  in  such
appointment  or  possession;  (iv) files a petition  for relief under the United
States  Bankruptcy  Code  or any  other  present  or  future  federal  or  state
insolvency,  bankruptcy  or  similar  laws  (all  of the  foregoing  hereinafter
collectively called "Applicable  Bankruptcy Law") or an involuntary petition for
relief is filed against such party under any Applicable  Bankruptcy Law and such
involuntary  petition is not  dismissed  within sixty (60) days after the filing
thereof,  or an order  for  relief  naming  such  party  is  entered  under  any
Applicable  Bankruptcy  Law,  or  any  composition,   rearrangement,  extension,
reorganization or other relief of debtors now or hereafter existing is requested
or consented to by such party;  (v) fails to have discharged  within a period of
sixty (60) days any  attachment,  sequestration  or similar writ levied upon, or
any claim against or affecting, any property of such party; or (vi) fails to pay
within ninety (90) days any final money judgment against such party; or

          (g) The  issuer  of any  securities  constituting  Collateral  files a
     petition for relief under any  Applicable  Bankruptcy  Law, an  involuntary
     petition for relief is filed  against any such issuer under any  Applicable
     Bankruptcy Law and such involuntary petition is not dismissed within thirty
     (30) days after the filing thereof,  or an order for relief naming any such
     issuer is entered under any Applicable Bankruptcy Law.

          7.2  Secured  Party's  Remedies.  Upon the  occurrence  of an Event of
     Default:

          (a)  Secured  Party  may  declare  the  Obligations  in  whole or part
     immediately  due and may enforce  payment and  performance  of the same and
     exercise  any rights  under the Texas UCC,  rights and  remedies of Secured
     Party under this Agreement, or otherwise.

                  (b) Secured  Party may, at Secured  Party's  option and at the
expense of LASIK,  either in Secured  Party's  own right or in the name of LASIK
and in the same manner and to the same extent that LASIK might reasonably so act
if this Agreement had not been made: (i) do all things requisite, convenient, or
necessary to enforce the performance and observance of all rights,  remedies and
privileges of LASIK arising from the Collateral, or any part thereof,  including
without limitation compromising,  waiving,  excusing, or in any manner releasing
or discharging  any  obligation of any party to or arising from the  Collateral;
(ii) take possession of the books,  papers,  chattel paper,  documents of title,
and accounts of LASIK, wherever located,  relating to the Collateral;  (iii) sue
or otherwise collect and receive money attributable to the Collateral;  and (iv)
exercise  any other  lawfully  available  powers or  remedies,  and do all other
things which Secured Party deems requisite, convenient or necessary or which the
Secured Party deems proper to protect the Security Interest.

                  (b) Secured Party may foreclose  this  Agreement in the manner
now or  hereafter  provided  or  permitted  by law and may upon such  reasonable
notification  prior thereto as may be required by  applicable  law (LASIK hereby
agreeing  that ten  days'  notice is  commercially  reasonable),  sell,  assign,
transfer,  or otherwise  dispose of the Collateral at public or private sale, in
whole  or in  part,  and  Secured  Party  may,  in its own  name  or as  LASIK's
attorney-in-fact  effectively  assign and transfer the  Collateral,  or any part
thereof,   absolutely,  and  execute  and  deliver  all  necessary  assignments,
conveyances,  bills of sale, and other  instruments with power to substitute one
or more persons or  corporations  with like power.  Any such  foreclosure  sale,
assignment,  transfer,  or other  disposition  shall, to the extent permitted by
law,  be a  perpetual  bar,  both at law and in  equity,  against  LASIK and all
persons and  corporations  lawfully  claiming by or through or under LASIK.  Any
such foreclosure sale may be adjourned from time to time. Upon any sale, Secured
Party may bid for and purchase the  Collateral,  or any part  thereof,  and upon
compliance with the terms of sale may hold,  retain,  possess and dispose of the
Collateral, in its absolute right without further accountability.  Secured Party
shall have the right to be  credited  on the  amount of its bid a  corresponding
amount of the Obligations as of the date of such sale.

                  (c) If, in the opinion of Secured Party, there is any question
that a public sale or  distribution  of any Collateral will violate any state or
federal  securities  law,  Secured  Party  (i) may  offer  and  sell  securities
privately to purchasers who will agree to take them for investment  purposes and
not with a view to distribution  and who will agree to imposition of restrictive
legends on the  certificates  representing  the security,  or (ii) may sell such
securities in any type of offering  which  complies  with, or is exempt from the
registration requirements of, the Securities Act of 1933, and no sale so made in
good faith by Secured Party shall be deemed to be not "commercially  reasonable"
because so made.

          (d) Not in  limitation  of any  other  provision  of  this  Agreement,
     Secured  Party shall have all rights and remedies of a secured  party under
     the Texas UCC.

         7.3  Application  of Proceeds.  Secured Party may apply the proceeds of
any foreclosure  sale hereunder or from any other  permitted  disposition of the
Collateral  or any part  thereof as  follows:  (a) first,  to the payment of all
reasonable  costs and expenses of any foreclosure  and collection  hereunder and
all proceedings in connection  therewith,  including reasonable attorneys' fees;
(b) then, to the  reimbursement of Secured Party for all  disbursements  made by
Secured Party for taxes,  assessments or liens superior to the Security Interest
and  which  Secured  Party  shall  deem  expedient  to  pay;  (c)  then,  to the
reimbursement of Secured Party of any other  disbursements made by Secured Party
in accordance  with the terms hereof or under the  Contribution  Agreement,  the
Loan Agreement or any Note; (d) then, to or among the amounts of fees,  interest
and  principal  then owing and unpaid in  respect  of the  Obligations,  in such
priority as Secured Party may determine in its discretion; and (e) the remainder
of such  proceeds,  if any,  shall be paid to LASIK.  If such proceeds  shall be
insufficient to discharge the entire  Obligations,  Secured Party shall have any
other available  legal recourse  against LASIK under, or for the performance of,
the Contribution Agreement, the Loan Agreement and any Note, for the deficiency,
together with interest  thereon at the maximum rate permitted  under  applicable
law.

          7.4  Enforcement of  Obligations.  Nothing in this Agreement or in any
     other document or agreement  shall affect or impair the  unconditional  and
     absolute right of Secured Party to enforce the  Obligations as and when the
     same shall become due. --------------------------

                                                   ARTICLE VIII
                                              RIGHTS OF SECURED PARTY

          8.1 Subrogation.  Upon the occurrence of an Event of Default,  Secured
     Party,  at its election,  may subrogate to all of the interest,  rights and
     remedies  of LASIK,  in  respect  to any of the  Collateral  or  agreements
     pertaining thereto. -----------

         8.2 Secured Party  Appointed  Attorney-in-Fact.  LASIK hereby  appoints
Secured Party as attorney-in-fact of LASIK, with full authority in the place and
stead of LASIK and in the name of LASIK,  Secured Party or otherwise,  from time
to time on Secured  Party's  discretion  and upon the  occurrence of an Event of
Default,  to take any action and to execute any  instrument  which Secured Party
may deem  necessary or advisable to accomplish  the purposes of this  Agreement,
including without  limitation:  (a) to ask, demand,  collect,  sue for, recover,
compound, receive and give acquittance and receipts for moneys due and to become
due under or in respect of any of the Collateral;  (b) to receive,  endorse, and
collect  any  drafts or other  instruments,  documents  and  chattel  paper,  in
connection  with clause (a) of this  Section 8.2; (c) to file any claims or take
any action or institute any proceeding which Secured Party may deem necessary or
desirable for the  collection  of any of the  Collateral or otherwise to enforce
the rights of Secured Party against any of the Collateral; and (d) to assign and
transfer the  Collateral,  or any part  thereof,  absolutely  and to execute and
deliver  endorsements,   assignments,  conveyances,  bills  of  sale  and  other
instruments  with power to substitute  one or more persons or  corporation  with
like power.

          8.3  Performance  by Secured  Party.  If LASIK  fails to  perform  any
     agreement contained herein,  Secured Party may itself perform, or cause the
     performance  of, such  agreement,  and the  reasonable  expenses of Secured
     Party  incurred  in  connection  therewith  shall be payable by LASIK under
     Section 8.8. In no event, however,  shall Secured Party have any obligation
     or  duties  whatsoever  to  perform  any  covenant  or  agreement  of LASIK
     contained  herein,  and any such  performance  by  Secured  Party  shall be
     ---------------------------- wholly discretionary with Secured Party.

          8.4 Duties of Secured Party.  The powers  conferred upon Secured Party
     hereunder  are solely to protect its interest in the  Collateral  and shall
     not impose any duty upon it to  exercise  any such  powers.  Except for the
     safe custody of any  Collateral in its  possession  and the  accounting for
     money actually  received by it hereunder,  Secured Party shall have no duty
     as to any Collateral or as to the taking of any necessary steps to preserve
     rights  against prior  parties or any other rights  -----------------------
     pertaining to any Collateral.

         8.5 No  Liability  of Secured  Party.  Neither the  acceptance  of this
Agreement by Secured Party,  nor the exercise of any rights hereunder by Secured
Party,  shall be construed in any way as an  assumption  by Secured Party of any
obligations, responsibilities, or duties of LASIK arising in connection with the
Collateral assigned hereunder or otherwise bind Secured Party to the performance
of any obligations respecting the Collateral, it being expressly understood that
Secured  Party shall not be obligated  to perform,  observe,  or  discharge  any
obligation, responsibility, duty, or liability of LASIK in respect of any of the
Collateral,  including without limitation  appearing in or defending any action,
expending  any money or incurring any expense in  connection  therewith.  TO THE
FULLEST  EXTENT  PERMITTED  BY  APPLICABLE  LAW,  LASIK  SHALL AND DOES AGREE TO
INDEMNIFY, PROTECT, DEFEND AND HOLD HARMLESS SECURED PARTY AND ITS SUBSIDIARIES,
AND EACH OF  THEIR  OFFICERS,  DIRECTORS,  REPRESENTATIVES,  AGENTS,  EMPLOYEES,
LENDERS,  SUCCESSORS  AND  ASSIGNS,  FROM AND AGAINST ALL  LIABILITIES,  CLAIMS,
DAMAGES,  LOSSES,  FINES,  PENALTIES,  CAUSES OF ACTIONS,  SUITS,  JUDGMENTS AND
EXPENSES  (INCLUDING COURT COSTS,  ATTORNEY'S FEES AND COST OF INVESTIGATION) OF
ANY NATURE, KIND OR DESCRIPTION OF ANY PERSON OR ENTITY, DIRECTLY OR INDIRECTLY,
ARISING OUT OF,  CAUSED BY OR RESULTING  FROM (IN WHOLE OR IN PART),  ANY ACT OR
OMISSION  OF SECURED  PARTY,  OR ANYONE  ACTING ON BEHALF OF SECURED  PARTY,  IN
CONNECTION  WITH  THE  COLLATERAL,   INCLUDING  WITHOUT  LIMITATION  ANY  MARKET
FLUCTUATIONS  IN THE  COLLATERAL  AS A RESULT  OF  SECURED  PARTY'S  SALE OF, OR
FAILURE TO SELL, THE INTERESTS AT ANY  PARTICULAR  TIME WHEN IT HAS THE RIGHT TO
DO  SO.  THE  FOREGOING  INDEMNITY  SHALL  SURVIVE  THE  EXPIRATION  OR  EARLIER
TERMINATION OF THIS AGREEMENT.

          8.6  Right of  Secured  Party to  Defend  Action  Affecting  Security.
     Secured Party may, at the expense of LASIK, appear in and defend any action
     or proceeding  at law or in equity  purporting  to affect  Secured  Party's
     Security          Interest          under          this          Agreement.
     ----------------------------------------------------------

         8.7 Right of Secured Party to Prevent or Remedy Default. If LASIK shall
fail to perform any of the covenants,  conditions and agreements  required to be
performed and observed by LASIK under any Other Agreement,  or in respect of the
Collateral  (subject to any applicable  default cure period),  Secured Party (a)
may but shall not be obligated to take any action Secured Party deems  necessary
or  desirable  to prevent or remedy any such  default by LASIK or  otherwise  to
protect the Security  Interest,  and (b) shall have the  absolute and  immediate
right to take  possession  of the  Collateral or any part thereof (to the extent
Secured Party has not previously  taken  possession) to such extent and as often
as the Secured Party,  in its sole  discretion,  deems necessary or desirable in
order to prevent or to cure any such  default by LASIK,  or otherwise to protect
the security of this Agreement. Secured Party may advance or expend such sums of
money for the  account of LASIK as Secured  Party in its sole  discretion  deems
necessary for any such purpose.

          8.8  Secured  Party's  Expenses.   All  reasonable  advances,   costs,
     expenses,  charges and attorneys' fees which Secured Party may make, pay or
     incur under any  provision  of this  Agreement  for the  protection  of its
     security or for the enforcement of any of its rights hereunder,  including,
     without limitation,  in foreclosure  proceedings commenced and subsequently
     abandoned. ------------------------

          8.9. Remedies.  No right or remedy herein reserved to Secured Party is
     intended to be exclusive  of any other right or remedy,  but each and every
     such  remedy  shall be  cumulative,  not in lieu of, but in addition to any
     other rights or remedies  given under this Agreement and all other security
     documents.  Any and all of  Secured  Party's  rights  and  remedies  may be
     exercised  from  time to time  and as  often  as such  exercise  as  deemed
     necessary or desirable by Secured Party. --------

         8.10 LASIK's  Waivers.  LASIK waives notice of the  creation,  advance,
increase,  existence,  extension,  or  renewal  of, and of any  indulgence  with
respect to, the  Obligations;  waives notice of intent to accelerate,  notice of
acceleration,  notice  of  intent  to  demand,  presentment,  demand,  notice of
dishonor,  and  protest;   waives  notice  of  the  amount  of  the  Obligations
outstanding  at any time,  notice of any change in  financial  condition  of any
person liable for the  Obligations  or any part thereof,  notice of any Event of
Default,  and all other  notices  respecting  the  Obligations;  and agrees that
maturity of the Obligations  and any part thereof may be accelerated,  extended,
or renewed one or more times by Secured Party in its discretion,  without notice
to Debtor.

         8.11 Other Parties and Other Collateral.  No renewal or extension of or
any other  indulgence  with respect to the  Obligations or any part thereof,  no
release  of any  security,  no  release  of any  person  (including  any  maker,
endorser,  guarantor,  or  surety)  liable  on  the  Obligations,  no  delay  in
enforcement  of payment,  and no delay or admission or lack of diligence or care
in exercising any right or power with respect to the Obligations or any security
therefor  or  guaranty  thereof or under this  Agreement  shall in other  manner
impair  or affect  the  rights  of  Secured  Party  under  the law,  under  this
Agreement,  or under any other  document or  agreement  pertaining  to the other
security for the  Obligations,  before  foreclosing  upon the Collateral for the
purpose of paying the  Obligations.  LASIK waives any right to the benefit of or
to require or control application of any other security or proceeds thereof, and
LASIK agrees that  Secured  Party shall have no duty or  obligation  to LASIK to
apply to the Obligations any such other security or proceeds thereof.

                                                    ARTICLE IX
                                                   MISCELLANEOUS

          9.1 Terms Commercially  Reasonable.  The terms of this Agreement shall
     be deemed  commercially  reasonable  within  the  meaning of the Texas UCC.
     -----------------------------


         9.2 Notices.  Any notices or demands  required or permitted to be given
hereunder  shall be  deemed  sufficiently  given if in  writing  and  personally
delivered or mailed (with all postage and charges prepaid), addressed to Secured
Party or to LASIK their  respective  addresses set forth below, or at such other
address as the above parties may from time to time  designate by written  notice
to the other given in  accordance  with this Section  9.2.  Any such notice,  if
personally  delivered or  transmitted  by telex or telegram,  shall be deemed to
have been given on the date so delivered or transmitted or, if mailed, be deemed
to have been given on the day after such  notice is placed in the United  States
mail in accordance with this Section 9.2.

            Secured Party:             1301 Capital of Texas Hwy., Suite C-300
                                       Austin, Travis County, Texas 78746
                                       Attn: President

                  with copy to:        Timothy L. LaFrey, Esq.
                                       Akin, Gump, Strauss, Hauer & Feld, L.L.P.
                                       1900 Frost Bank Plaza
                                       816 Congress Avenue
                                       Austin, Texas 78701

                  LASIK:               LASIK Investors, L.L.C.
                                       4800 North 22nd Street
                                       Phoenix, Arizona  85016

         9.3 Parties Bound.  Secured Party's rights under this Agreement and the
Security Interest shall inure to the benefits of its successors and assigns, and
in the event of any  assignment  or  transfer of any of the  Obligations  or the
Collateral,  Secured  Party  thereafter  shall  be  fully  discharged  from  any
responsibility  with respect to the Collateral so assigned or  transferred,  but
Secured  Party shall  retain all rights and powers  hereby given with respect to
any of the  Obligations  or  Collateral  not so  assigned  or  transferred.  All
representations,  warranties, and agreements of LASIK if more than one are joint
and several, and all shall be binding upon the personal representatives,  heirs,
successors, and assigns of LASIK.

          9.4 Waiver. No delay of Secured Party in exercising any power or right
     shall operate as a waiver thereof; nor shall any single or partial exercise
     of any power or right  preclude  other or further  exercise  thereof or the
     exercise  of any other  power or right.  No waiver by Secured  Party of any
     right hereunder of any default by LASIK shall be binding upon Secured Party
     unless in writing, and no failure by Secured Party to exercise any power or
     right hereunder or waiver of any default by LASIK ------ shall operate as a
     waiver  of any  other or  further  exercise  of such  right or power of any
     further default.

          9.5 Agreement Continuing. This Agreement shall constitute a continuing
     agreement, applying to all future as well as existing transactions, whether
     or not of the character contemplated at the date of this Agreement,  and if
     all  transactions  between  Secured  Party and LASIK shall be closed at any
     time,  shall be  equally  applicable  to any new  transactions  thereafter.
     --------------------

          9.6 Definitions.  Unless the context indicated otherwise,  definitions
     in the Texas  Business and Commerce  Code ("Texas  UCC") apply to words and
     phrases in this  Agreement;  if Texas UCC definitions  conflict,  Chapter 9
     definitions apply. -----------

          9.7  Miscellaneous.   In  this  Agreement,  whenever  the  context  so
     requires,  the neuter gender  includes the masculine and feminine,  and the
     singular  number  includes  the  plural and vice  versa.  The  headings  of
     paragraphs  herein are inserted  only for  convenience  and shall in no way
     define,  describe  or limit the scope of intent of any  provisions  of this
     Agreement. No change, amendment,  modification,  cancellation, or discharge
     of any provision of this  Agreement  shall be valid unless  consented to in
     ------------- writing by Secured Party.

          9.8 Assignment of Secured Party's  Interest.  Secured Party shall have
     the right to assign  all or any  portion  of its  rights in this  Agreement
     without approval or consent.  LASIK acknowledges that Secured Party intends
     to make a collateral  assignment of its rights under this Agreement for the
     benefit of one or more of its lenders.  LASIK may not assign this Agreement
     or any of its rights or  obligations  hereunder  without the express  prior
     written     consent     of    Secured     Party    in    each     instance.
     --------------------------------------

          9.9 Applicable Laws. THIS AGREEMENT SHALL BE GOVERNED BY AND CONSTRUED
     IN ACCORDANCE  WITH THE LAWS OF THE STATE OF TEXAS AND THE APPLICABLE  LAWS
     OF THE UNITED STATES OF AMERICA. ---------------

          9.10 ENTIRE AGREEMENT.  THIS AGREEMENT,  THE LOAN AGREEMENT,  THE NOTE
     AND THE  CONTRIBUTION  AGREEMENT  (AND THE  OTHER  AGREEMENTS  CONTEMPLATED
     THEREIN)  REPRESENT THE FINAL AGREEMENT  BETWEEN THE PARTIES AND MAY NOT BE
     CONTRADICTED  BY EVIDENCE OF PRIOR,  CONTEMPORANEOUS,  OR  SUBSEQUENT  ORAL
     AGREEMENTS OF THE PARTIES.  THERE ARE NO UNWRITTEN ORAL AGREEMENTS  BETWEEN
     THE PARTIES. ----------------

                                             [Signature page follows]




<PAGE>


                                SIGNATURE PAGE TO
                                 ASSIGNMENT AND
                               SECURITY AGREEMENT

         EXECUTED this ___ day of September, 1999.

DEBTOR:                                         LASIK Investors, L.L.C.


                                           By:  /s/ Ronald W. Barnet, M.D.
                                                Ronald W. Barnet, M.D., manager


                                           By:  /s/ David D. Dulaney, M.D.
                                                David D. Dulaney, M.D., manager



SECURED PARTY:                                   Prime Medical Operating, Inc.

                                           By: /s/ Cheryl Williams

                                           Name:Cheryl Williams

                                           Title:Treasurer




<PAGE>