ASSIGNMENT AND SECURITY AGREEMENT

         THIS ASSIGNMENT AND SECURITY  AGREEMENT (this  "Agreement") is made and
entered  into  as of the  31st  day of  January,  2000,  by  and  between  Prime
Refractive  Management,  L.L.C.,  a  Delaware  limited  liability  company  (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,  Prime  Medical  Operating,   Inc,  a  Delaware  corporation,   Prime/BDR
Acquisition,  L.L.C.,  a  Delaware  limited  liability  company,  Prime  Medical
Services, Inc., a Delaware corporation ("PMSI"), Prime/BDEC Acquisition, L.L.C.,
a Delaware  limited  liability  company,  Prime  Refractive,  L.L.C., a Delaware
limited liability company (the "Debtor"),  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  (as amended by that certain First
Amendment to  Contribution  Agreement  dated as of January 31,  2000,  among the
foregoing parties, the "Contribution  Agreement"),  and Debtor and Secured Party
have executed and delivered that certain Loan Agreement, dated as of January 31,
2000 (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.

     1.3  Subordination.  Liens created hereby are subordinate to liens in favor
of  Lenders  (as such term is  defined  in that  certain  Loan  Agreement  for a
$14,000,000 advancing term loan, entered into by Secured Party, Bank of America,
N.A., as administrative agent, BankBoston, N.A., as documentation agent and such
Lenders).
                                   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>


S-1



                                SIGNATURE PAGE TO

                                 ASSIGNMENT AND

                               SECURITY AGREEMENT

         EXECUTED as of this 31st day of January, 2000.

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 Refractive Management, L.L.C.

                                   By:/s/ Cheryl Williams

                                   Name: Cheryl Williams

                                   Title: Chief Financial Officer