Document:

PROMISSORY NOTE
Austin, Texas                    (LINE OF CREDIT)             September 1, 1999

PROMISE TO PAY: For value  received,  the undersigned  Borrower  (whether one or
more) promises to pay to the order of Lender the Principal Amount, to the extent
advanced by Lender, together with interest on the unpaid balance of such amount,
in lawful  money of the United  States of America,  in  accordance  with all the
terms, conditions,  and covenants of this Note and the Loan Documents identified
below.

     BORROWER:  Prime/BDR  Acquisition,  L.L.C.,  a Delaware  limited  liability
company
     BORROWER'S ADDRESS FOR NOTICE:  1301 Capital of Texas Highway,  Suite C-300
Austin, Texas 78746 Attention: President
LENDER:           Prime Medical Operating, Inc., a Delaware corporation

     LENDER'S ADDRESS FOR PAYMENT:  1301 Capital of Texas Highway,  Suite C-300,
Austin, Texas 78746 Attention: Chief Financial Officer
PRINCIPAL AMOUNT:  Two Hundred Thousand Dollars ($200,000)

INTEREST RATE:  Fifteen Percent (15%)

PAYMENT  TERMS:  Interest on the unpaid  balance of this Note is due and payable
quarterly,  beginning  November 1, 1999, and continuing  regularly and quarterly
thereafter on or before the first day of February,  May, August, until September
1, 2000 (the "Maturity  Date"),  when the outstanding  principal balance and all
accrued  interest shall be due and payable in full.  Interest will be calculated
on the unpaid  principal  balance.  Each payment  will be credited  first to the
accrued interest and then to the reduction of principal.

REVOLVING  LINE OF  CREDIT:  This Note  evidences  a  revolving  line of credit.
Subject to the terms of the Loan Agreement  between  Borrower and Lender of even
date  herewith,  all or any portion of the Principal  Amount of this Note may be
borrowed, paid, prepaid, repaid, and reborrowed,  from time to time prior to the
Maturity  Date and in accordance  with the Loan  Documents.  Each  borrowing and
repayment  hereunder will be (i) endorsed on an attachment to this Note, or (ii)
entered  in the books and  records of  Lender.  The books and  records of Lender
shall be prima facie  evidence  of all sums due  Lender.  If an event of default
exists  under  this Note or any Loan  Document,  then  Lender  shall be under no
obligation to make any advance under this Note.

     LOAN  AGREEMENT:  This Note is executed  pursuant to and is governed by the
terms of the Loan  Agreement  of even date  herewith,  executed by Borrower  and
Lender, as amended (collectively, the "Loan Agreement").
1.       INTEREST PROVISIONS:

Rate:  The  principal  balance of this Note from time to time  remaining  unpaid
prior to maturity  shall bear  interest at the  Interest  Rate per annum  stated
above.  Interest  shall be  calculated  on the  amount  of each  advance  of the
Principal Amount of this Note from the date of each such advance.

Maximum  Lawful Interest:  The term "Maximum Lawful Rate" means the maximum rate
         of interest  and the term  "Maximum  Lawful  Amount"  means the maximum
         amount  of  interest  that is  permissible  under  applicable  state or
         federal law for the type of loan  evidenced  by this Note and the other
         Loan  Documents.  If the Maximum Lawful Rate is increased by statute or
         other governmental action subsequent to the date of this Note, then the
         new  Maximum  Lawful  Rate  shall be  applicable  to this Note from the
         effective date thereof, unless otherwise prohibited by applicable law.

Spreadingof Interest:  Because of the possibility of irregular periodic balances
         of principal or premature payment,  the total interest that will accrue
         under this Note cannot be determined in advance. Lender does not intend
         to contract for,  charge,  or receive more than the Maximum Lawful Rate
         or Maximum Lawful Amount  permitted by applicable state or federal law,
         and to prevent such an  occurrence  Lender and Borrower  agree that all
         amounts of interest,  whenever  contracted for, charged, or received by
         Lender, with respect to the loan of money evidenced by this Note, shall
         be spread,  prorated,  or  allocated  over the full period of time this
         Note is unpaid,  including  the period of any renewal or  extension  of
         this Note.  If demand for payment of this Note is made by Lender  prior
         to the full stated term, the total amount of interest  contracted  for,
         charged,  or  received  to the time of such  demand  shall  be  spread,
         prorated, or allocated along with any interest thereafter accruing over
         the full period of time that this Note  thereafter  remains  unpaid for
         the purpose of determining if such interest  exceeds the Maximum Lawful
         Amount.

Excess   Interest:  At maturity  (whether by  acceleration  or  otherwise) or on
         earlier  final  payment of this Note,  Lender  shall  compute the total
         amount of interest that has been contracted for,  charged,  or received
         by Lender or  payable by  Borrower  under  this Note and  compare  such
         amount to the Maximum  Lawful  Amount  that could have been  contracted
         for, charged, or received by Lender. If such computation  reflects that
         the total amount of interest that has been contracted for, charged,  or
         received  by Lender or payable by Borrower  exceeds the Maximum  Lawful
         Amount,  then Lender  shall apply such excess to the  reduction  of the
         principal balance and not to the payment of interest; or if such excess
         interest  exceeds the unpaid  principal  balance,  such excess shall be
         refunded to Borrower. This provision concerning the crediting or refund
         of excess  interest  shall control and take  precedence  over all other
         agreements  between  Borrower and Lender so that under no circumstances
         shall the total interest contracted for, charged, or received by Lender
         exceed the Maximum Lawful Amount.

Interest After Default:  At Lender's option,  the unpaid principal balance shall
         bear interest after maturity  (whether by acceleration or otherwise) at
         the "Default  Interest  Rate." The Default  Interest  Rate shall be, at
         Lender's  option,  (i) the Maximum  Lawful Rate, if such Maximum Lawful
         Rate is established by applicable law; or (ii) the Interest Rate stated
         on the first page of this Note plus five (5) percentage  points,  if no
         Maximum Lawful Rate is established by applicable law; or (iii) eighteen
         percent (18%) per annum; or (iv) such lesser rate of interest as Lender
         in its sole  discretion  may choose to charge;  but never more than the
         Maximum  Lawful Rate or at a rate that would  cause the total  interest
         contracted  for,  charged,  or received by Lender to exceed the Maximum
         Lawful Amount.

Daily Computation of Interest: To the extent permitted by applicable law, Lender
at its option will  calculate  the per diem interest rate or amount based on the
actual  number of days in the year (365 or 366, as the case may be),  and charge
that per diem interest rate or amount each day. In no event shall Lender compute
the interest in a manner that would cause  Lender to contract  for,  charge,  or
receive interest that would exceed the Maximum Lawful Rate or the Maximum Lawful
Amount

DEFAULT PROVISIONS:

EVENTS OF DEFAULT AND  ACCELERATION  OF MATURITY:  LENDER MAY, AFTER THIRTY (30)
DAYS'  WRITTEN  NOTICE TO BORROWER  AND  BORROWER'S  FAILURE TO CURE WITHIN SUCH
30-DAY  PERIOD  AND  WITHOUT  FURTHER  NOTICE OR DEMAND,  (except  as  otherwise
required  by  statute),  ACCELERATE  THE  MATURITY  OF THIS NOTE AND DECLARE THE
ENTIRE UNPAID PRINCIPAL BALANCE AND ALL ACCRUED INTEREST AT ONCE DUE AND PAYABLE
IF:

         There is  default  in the  payment  of any  installment  of  principal,
interest,  or any other sum  required to be paid under the terms of this Note or
any of the Loan Documents; or

         There is a breach or  default  (other  than by Lender or Prime  Medical
Services,  Inc.)  under this Note or any of the Loan  Documents,  including  any
instrument  securing the payment of this Note or any loan agreement  relating to
the advance of loan proceeds.

WAIVER   BY  BORROWER:  EXCEPT AS PROVIDED IN  PARAGRAPH  2(a) HEREOF AND IN ANY
         OTHER LOAN  DOCUMENT,  BORROWER AND ALL OTHER  PARTIES  LIABLE FOR THIS
         NOTE  WAIVE,  DEMAND,  NOTICE  OF  INTENT TO  DEMAND,  PRESENTMENT  FOR
         PAYMENT,  NOTICE OF  NONPAYMENT,  PROTEST,  NOTICE OF  PROTEST,  GRACE,
         NOTICE OF DISHONOR,  NOTICE OF INTENT TO ACCELERATE MATURITY, NOTICE OF
         ACCELERATION  OF MATURITY,  AND  DILIGENCE IN  COLLECTION.  EACH MAKER,
         SURETY,  ENDORSER,  AND GUARANTOR OF THIS NOTE WAIVES AND AGREES TO ONE
         OR MORE  EXTENSIONS  FOR ANY PERIOD OR PERIODS OF TIME, AND ANY PARTIAL
         PAYMENTS, BEFORE OR AFTER MATURITY,  WITHOUT PREJUDICE TO THE HOLDER OF
         THIS NOTE. EACH MAKER, SURETY, ENDORSER, AND GUARANTOR WAIVES NOTICE OF
         ANY AND ALL RENEWALS, EXTENSIONS,  REARRANGEMENTS, AND MODIFICATIONS OF
         THIS NOTE.

Non-Waiver by Lender:  Any previous extension of time,  forbearance,  failure to
pursue some  remedy,  acceptance  of late  payments,  or  acceptance  of partial
payment by Lender,  before or after  maturity,  does not  constitute a waiver by
Lender of its subsequent  right to strictly  enforce the collection of this Note
according to its terms.

Other  Remedies Not  Required:  Lender shall not be required to first file suit,
exhaust all  remedies,  or enforce its rights  against any  security in order to
enforce payment of this Note.

Joint and Several  Liability:  Each Borrower who signs this Note, and all of the
other  parties  liable  for the  payment  of  this  Note,  such  as  guarantors,
endorsers,  and sureties,  are jointly and  severally  liable for the payment of
this Note.

Attorney's  Fees: If Lender  requires the services of an attorney to enforce the
payment of this Note or the performance of the other Loan Documents,  or if this
Note is collected through any lawsuit,  probate,  bankruptcy,  or other judicial
proceeding,  Borrower  agrees to pay  Lender an amount  equal to its  reasonable
attorney's fees and other collection  costs.  This provision shall be limited by
any applicable statutory  restrictions  relating to the collection of attorney's
fees.

3.       MISCELLANEOUS PROVISIONS:

Subsequent Holder: All references to Lender in this Note shall also refer to any
subsequent owner or holder of this Note by transfer, assignment, endorsement, or
otherwise.

Transfer:Borrower  acknowledges and agrees that Lender may transfer this Note or
         partial   interests  in  the  Note  to  one  or  more   transferees  or
         participants,  including without  limitation  transfers provided for in
         Section  8.10 of the Loan  Agreement.  Borrower  authorizes  Lender  to
         disseminate  to any  such  transferee  or  participant  or  prospective
         transferee or participant any information it has pertaining to the loan
         evidenced  by  this  Note,   including,   without  limitation,   credit
         information  on Borrower and any  guarantor of this Note and any of the
         type of information described in Section 8.10 of the Loan Agreement.

Other  Parties  Liable:  All  promises,  waivers,   agreements,  and  conditions
applicable  to Borrower  shall  likewise be  applicable  to and binding upon any
other  parties  primarily  or  secondarily  liable for the payment of this Note,
including all guarantors, endorsers, and sureties.

Successors  and Assigns:  The  provisions of this Note shall be binding upon and
for the benefit of the successors, assigns, heirs, executors, and administrators
of Lender and Borrower.

No Duty or Special  Relationship:  Borrower acknowledges that Lender has no duty
of good faith to Borrower,  and Borrower acknowledges that no fiduciary,  trust,
or other special relationship exists between Lender and Borrower.

Modifications:  Any modifications agreed to by Lender relating to the release of
liability of any of the parties primarily or secondarily  liable for the payment
of this Note, or relating to the release,  substitution, or subordination of all
or part of the security for this Note,  shall in no way  constitute a release of
liability  with  respect to the other  parties or  security  not covered by such
modification.

Entire  Agreement:  Borrower  warrants and  represents  that the Loan  Documents
constitute the entire agreement  between Borrower and Lender with respect to the
loan  evidenced  by this Note and agrees  that no  modification,  amendment,  or
additional  agreement  with  respect  to such loan or the  advancement  of funds
thereunder will be valid and  enforceable  unless made in writing signed by both
Borrower and Lender.

Borrower's  Address  for Notice:  All  notices  required to be sent by Lender to
Borrower shall be sent by U.S. Mail, postage prepaid,  to Borrower's Address for
Notice stated on the first page of this Note, until Lender shall receive written
notification from Borrower of a new address for notice.

Lender's  Address for  Payment:  All sums payable by Borrower to Lender shall be
paid at Lender's  Address for Payment  stated on the first page of this Note, or
at such other address as Lender shall designate from time to time.

Business Use:  Borrower  warrants and  represents to Lender that the proceeds of
this Note will be used solely for business or commercial purposes, and in no way
will the proceeds be used for personal, family, or household purposes.

Chapter 15 Not Applicable:  It is understood that Chapter 15 of the Texas Credit
Code relating to certain  revolving credit loan accounts and tri-party  accounts
is not applicable to this Note.

APPLICABLE  LAW: THIS NOTE HAS BEEN EXECUTED AND DELIVERED IN TEXAS AND SHALL BE
CONSTRUED IN ACCORDANCE  WITH THE APPLICABLE  LAWS OF THE STATE OF TEXAS AND THE
LAWS OF THE UNITED STATES OF AMERICA APPLICABLE TO TRANSACTIONS IN TEXAS.

4.       LOAN DOCUMENTS:

This Note.

The Loan Agreement and the Loan Documents as defined therein.

All      other  documents  signed in connection  with the Loan  Agreement or the
         loan  evidenced  by this  Note,  including,  without  limitation,  that
         certain  Contribution  Agreement,  dated  effective  September 1, 1999,
         between and among Borrower,  Lender,  Prime Medical  Services,  Inc., a
         Delaware  corporation,   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,   LASIK  Investors,
         L.L.C., a Delaware limited liability company,  David D. Dulaney,  M.D.,
         Ronald  W.  Barnet,   M.D.,  and  Mark  Rosenberg  (the   "Contribution
         Agreement") and each  Transaction  Document (as such term is defined in
         the Contribution Agreement).

                                              [Signature page follows]

<PAGE>

                                                  SIGNATURE PAGE TO
                                                   PROMISSORY NOTE

EXECUTED this 1 day of September, 1999.

                 BORROWER:

             PRIME/BDR ACQUISITION, L.L.C., a Delaware limited liability company

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

                                  Printed Name: Ronald W. Barnet, M.D.

                                  Title: Manager

<PAGE>COLLOCATION AGREEMENT

                                 BY AND BETWEEN

                       BARNET DULANEY EYE CENTER, P.L.L.C.

                                       AND

                         PRIME/BDEC ACQUISITION, L.L.C.

<PAGE>

                                   COLLOCATION
                                    AGREEMENT

     This COLLOCATION  AGREEMENT  ("Agreement"),  effective as of the 1st day of
September,  1999 (the  "Effective  Time"),  is by and between BARNET DULANEY EYE
CENTER,  P.L.L.C.,  an Arizona  professional limited liability company ("BDEC"),
and  PRIME/BDEC  ACQUISITION,  L.L.C.,  a  Delaware  limited  liability  company
("Company").

                                               W I T N E S S E T H:

     WHEREAS,  the  Company  has been  organized  for the  purpose of  providing
facilities,  equipment  and  non-physician  personnel  for  the  performance  by
physicians  of  Refractive  Surgery  (as  defined  herein),  for the  marketing,
scheduling  and  management of Refractive  Surgery,  for the  credentialing  and
scheduling  of  physicians  to perform  Refractive  Surgery and for the billing,
collecting  and   accounting  for  the  use  of  the  facility,   equipment  and
non-physician personnel (the "Business");

     WHEREAS,  BDEC has owned or leased assets for the performance by physicians
of Refractive Surgery, including, without limitation, certain space located in a
building at 4800 North 22nd Street,  Phoenix,  Arizona  85016 and certain  space
located in a building at 555 East River Road,  Tucson,  Arizona  (individually a
"Facility"  and  collectively  the  "Facilities")  and in  connection  with each
Facility, equipment,  instruments, computer software used in connection with the
equipment, certain leases and contracts, the leasehold improvements,  furniture,
fixtures and other fixed assets and items of personal property used primarily in
or  materially  relied  on  for  the  performance  of  Refractive  Surgery  (the
"Equipment and Personalty");

     WHEREAS, BDEC employs  non-physician  personnel (the "BDEC Employees") with
expertise  and  experience  in  assisting   physicians  in  the  performance  of
Refractive  Surgery,   in  credentialing  and  scheduling   physicians  for  the
performance  of  Refractive  Surgery  in  the  Facilities,   in  performing  the
scheduling of patients for Refractive  Surgery in the Facilities,  in performing
marketing,  accounting,  billing  and  collection  services  for  the use of the
Facilities  and in managing  the  Facilities  and all  non-physician  aspects of
Refractive Surgery in the Facilities (the "Support Services");

     WHEREAS,   BDEC  employs  physician  and   non-physician   executives  (the
"Managers")  with expertise and experience in the management of the  Facilities,
the Equipment and Personalty,  the Support  Services and all other elements of a
Refractive Surgery center (the "Management Services");

     WHEREAS,  BDEC, Prime Medical  Operating,  Inc.("Prime") and others entered
into that certain Contribution  Agreement dated effective September 1, 1999 (the
"Contribution  Agreement"),  pursuant  to  which  Prime,  BDEC and  others  have
participated in a series of transactions that were completed simultaneously with
the execution and delivery of this Agreement,  in which transactions the Company
became the owner of the  Equipment  and  Personalty  and the business  conducted
therewith,  excluding the practice of medicine,  and in which  transactions BDEC
agreed to provide to the Company the  Facility and the  Management  Services and
Support Services on the terms and conditions set forth in this Agreement;

     NOW, THEREFORE,  for and in consideration of the mutual covenants set forth
herein, and other good and valuable  consideration,  the receipt and adequacy of
which are hereby forever acknowledged and confessed, the parties hereto agree as
follows:

                                                     ARTICLE I
                                                    DEFINITIONS

     1.1 Agreement shall mean this Collocation Agreement between the Company and
BDEC  and  any  amendments  hereto  as may  from  time to  time  be  adopted  as
hereinafter provided.

     1.2 BDEC shall mean Barnet Dulaney Eye Center, P.L.L.C.

     1.3 Buildings shall mean Building P and Building T.

     1.4 Building P shall mean the  building  located at 4800 North 22nd Street,
Phoenix, Arizona 85016, and known generally as the Barnet Dulaney Eye Center.

     1.5  Building T shall  mean the  building  located at 555 East River  Road,
Tucson, Arizona, and known generally as the Barnet Dulaney Eye Center.

     1.6  Business  shall  mean  the  provision  of  facilities,  equipment  and
non-physician  personnel for the performance by physicians of Refractive Surgery
(as defined  herein),  the  marketing,  scheduling  and management of Refractive
Surgery,  the credentialing  and scheduling of physicians to perform  Refractive
Surgery and the billing,  collecting and accounting for the use of the facility,
equipment and non-physician personnel.

         1.7 Business  Expense shall mean all  out-of-pocket  costs and expenses
incurred by BDEC solely and  exclusively  in the  performance  of its duties and
obligations  under,  and in accordance  with, this Agreement.  Business  Expense
shall also  include  that portion  (allocated  based on the relative  percentage
amount of each such  employee's  time spent working  directly on the Business of
the Company) of salaries,  wages and  benefits for those  personnel  employed by
BDEC to provide  services  hereunder,  but only to the extent such employees (i)
work  directly on the  Business  of the  Company  and (ii) are either  listed on
Exhibit B hereto or are  subsequently  employed to replace such listed employees
or are  added  in the  same  service  categories  related  to  the  Business  as
corresponds  to the service  categories  applicable to the  employees  listed on
Exhibit B. Business  Expense  shall also include a reasonable  allocation of the
out-of-pocket   costs  incurred  by  BDEC  related  to  hiring  such  personnel.
Notwithstanding the foregoing, Business Expense shall not include any portion of
the salaries,  wages or benefits related to any personnel  employed or otherwise
retained or contracted by BDEC who work in any of the following  departments  or
fall  within any of the  following  categories:  (a)  accounting,  (b)  accounts
receivable,  (c) purchasing, (d) practice operations, (e) management information
systems and facilities support, (f) human resources,  (g) credentialing,  or (h)
executive management.  Furthermore,  Business Expense shall not include any rent
or other costs or expenses  incurred by BDEC  pursuant to the Base  Leases.  For
illustration  purposes,  the parties agree that Business Expense for the Phoenix
Refractive  Surgery  center  based on the pro forma  annualized  facility  model
attached  hereto  as  Exhibit  A for the  first  full  year of the  Term of this
Agreement  would be  $1,663,638,  being the sum of the  categories  on Exhibit A
marked  with an  asterisk.  It is the  intention  of the parties  that  Business
Expense be consistent with the methodology reflected in Exhibit A.

     1.8 Company shall mean Prime/BDEC Acquisition, L.L.C.

     1.9  Facility  and  Facilities  shall have the  meaning  given to it in the
recitals to this Agreement.

     1.10 Premises P shall mean the Facility and other space located in Building
P to which the right to use is granted in Section 2.3 hereof.

     1.11 Premises T shall mean the Facility and other space located in Building
T to which the right to use is granted in Section 2.3 hereof.

     1.12 Refractive Surgery shall mean, collectively, any current and/or future
surgical procedures intended to correct myopia,  hyperopia or astigmatism of the
eye, excluding procedures aimed only at restoring accommodation (presbyopia) and
procedures  to  treat  only  cataracts,   glaucoma,   oculoplastics  or  retinal
abnormality.

     1.13 Services Fee shall mean BDEC's compensation  established and described
in Article VI hereof.

     1.14 State shall mean the State of Arizona.

     1.15 Term shall mean the  initial  and any  renewal  periods of duration of
this Agreement as described herein.

                                   ARTICLE II
                            RIGHT TO USE THE PREMISES

     2.1 Base Lease.  Section 2.3  contains a grant of a right to use Premises P
and Premises T and is subject and  subordinate  to the terms and  conditions  of
those certain  leases as amended ("Base  Leases")  pursuant to which BDEC leases
the Building P and Building T.

     2.2 Users of  Buildings.  Building P and  Building T are used for  multiple
activities, including, but not limited to, Refractive Surgery, office and clinic
activities of BDEC  physicians and other  professionals,  an ambulatory  surgery
center ("ASC") and marketing,  accounting,  management and other  administrative
activities.  The various  activities  in each Building do not  necessarily  have
specific or identified space and, in some instances, more than one activity uses
a space at the same time or at different times.  BDEC designates,  schedules and
modifies  the  location  and the times that each  activity  can use space in the
Buildings.

         2.3 Grant of Right to Use. In  consideration  of  Company's  payment to
BDEC of the Purchase Price, as defined in the Contribution Agreement, and on the
terms and  conditions of this  Agreement,  BDEC hereby grants to the Company the
non-exclusive  right to use for  Refractive  Surgery the spaces in the Buildings
where the  Equipment  and  Personalty  are located at the times  during  regular
business  hours and in the manner  designated by BDEC (but in no event less than
forty percent (40%) of the of the business hours during each week),  which might
require the using of such space while the same or adjoining  space is being used
by an ASC or on a  cooperative  schedule  with an ASC.  BDEC also  grants to the
Company the non-exclusive  right to use and to permit its guests and invitees to
use the common areas in accordance  with the Base Leases.  Notwithstanding  that
the foregoing grants are  non-exclusive,  BDEC covenants and agrees that it will
not allow any person or entity,  other than the Company, to utilize any space in
the  Buildings,  any Equipment and Personalty or any BDEC Employees for purposes
of conducting any component of the Business.

     2.4 Term and Conditions of Grant. The grants set forth in Section 2.3 above
are each for the term and on the conditions, requirements,  covenants, rules and
regulations  of the Base Leases and subject to  Company's  paying its  allocated
portion of the rent,  common area  charges and other  payments  required of BDEC
under the Base Leases.

     2.5 Maintenance of Base Leases. Throughout the Term of this Agreement, BDEC
covenants  and agrees to  maintain  all Base  Leases in full  force and  affect,
without any breach or default by BDEC thereunder.

                                                    ARTICLE III
                                         APPOINTMENT AND AUTHORITY OF BDEC

     3.1 Appointment. The Company hereby appoints BDEC as its sole and exclusive
agent  for the  management  and  performance  of  day-to-day  operations  of the
Business in the  Facilities,  using the  Equipment and  Personalty,  through the
provision of Management  Services and Support Services,  as defined herein,  and
BDEC hereby accepts such appointment,  subject at all times to the provisions of
this Agreement.

         3.2  Authority.  Consistent  with  the  provisions  of this  Agreement,
directions given by the Company and operating and capital budgets established by
the Company,  BDEC shall have the responsibility  and commensurate  authority to
provide,  or  cause  to be  provided,  personnel,  business  and  administrative
services  for the  Company,  which shall  include  those  services  set forth in
Article  III hereof.  BDEC is hereby  expressly  authorized  to provide all such
services  in  whatever  manner  BDEC,  in  good  faith,  deems  appropriate  and
consistent  with  commercially  reasonable  standards  to  meet  the  day-to-day
requirements  of  the  business  functions  of the  Company  or  related  to the
Business.  The  authority  of BDEC  shall  extend no further  than is  expressly
provided  herein,  and  shall  not be  extended  by  implication  or  otherwise.
Notwithstanding  anything  contained herein to the contrary,  BDEC shall have no
authority  to speak on behalf of, or to bind,  the Company  with  respect to any
third party.

     3.3 Retained Authority.  The Company shall at all times retain the ultimate
responsibility  for the  operation of the Business  and,  except as delegated to
BDEC herein or by resolution of Company's  managers,  shall retain the authority
and power and to make all decisions with respect to its assets and rights.

     3.4  Nature of  Relationship.  The  parties  acknowledge  and agree that no
partnership  or other form of entity,  or any joint and  several  liability,  is
intended to be created by or between them by the  execution or operation of this
Agreement, and none of the foregoing should be implied.

                                                    ARTICLE IV
                                                 COVENANTS OF BDEC

     4.1  Management  and Support  Services.  BDEC shall provide the  Management
Services  and  Support  Services  necessary  to operate  the  Business as it was
operated by BDEC prior to the Effective Time, including,  but not limited to the
following:

     4.1.1 Marketing and Scheduling.  BDEC shall conduct  marketing  efforts for
the Facility and shall schedule patient treatment in the Facility, in the manner
that such services were performed prior to the Effective Time.

     4.1.2  Physician  Matters.  BDEC  shall  credential  physicians  to perform
Refractive  Surgery in the Facility  and shall  schedule  physicians  to use the
Facility in the manner that such services were performed  prior to the Effective
Time.

     4.1.3 Supplies.  As agent for the Company, BDEC shall obtain all reasonable
medical,  office, and other supplies,  including stationery and forms, and shall
ensure that the Company is at all times adequately stocked with such supplies as
are reasonably necessary and appropriate for the operation of the Business.

     4.1.4  Licenses and Permits.  BDEC shall  coordinate  all  development  and
planning  processes,  and apply for and use  BDEC's  best  efforts to obtain and
maintain all federal,  state, and local licenses and regulatory permits required
for or in connection with the operation of the Business.

     4.1.5 Contract  Negotiations.  BDEC shall negotiate,  either directly or on
the Company's  behalf, as appropriate,  all contractual  arrangements with third
parties as are reasonably necessary and appropriate for the Business.

     4.1.6 Financial  Matters.  BDEC shall  establish and administer  accounting
procedures,  controls,  and  systems  for  the  development,   preparation,  and
safekeeping  of records and books of accounts  relating to the  Company,  all of
which shall be prepared and  maintained in accordance  with  generally  accepted
accounting  principles  consistently  applied. BDEC shall prepare and deliver to
the Company,  and each of its members,  within thirty (30) days after the end of
each fiscal year of the Company,  a balance sheet, a profit and loss  statement,
and a  statement  of sources  and  applications  of funds and changes in working
capital reflecting the financial status of the Company and as of the end of such
prior fiscal year,  all of which shall be prepared in accordance  with generally
accepted accounting principles  consistently applied.  Additionally,  BDEC shall
prepare and deliver to the board of  managers  of the  Company,  and each of the
Company's members,  monthly financial  statements within ten (10) days after the
end of each month, and shall prepare and deliver to the board of managers of the
Company,  and each of the Company's members,  such other financial statements or
records  as BDEC may  from  time to time  deem  appropriate  or as the  board of
managers of the Company,  or its members,  may reasonably  request. On or before
ninety (90) days prior to the end of each fiscal year of the Company,  BDEC will
prepare and deliver to the board of  managers  of the  Company,  and each of the
Company's  members,  a  proposed  operating  budget of  projected  expenses  and
revenues  of  the  Company  for  the  next  fiscal  year  of  the  Company,  and
representatives of BDEC shall make themselves  reasonably available to the board
of managers and the members of the Company to explain such  proposed  budget and
the underlying assumptions.

     4.1.7 Billing and Collection.  BDEC shall be solely responsible for billing
and  collecting  for all  services  provided  by Company  and for the use of the
Facility and Equipment and  Personalty.  Company shall be entitled to all monies
collected by BDEC on behalf of Company.

     4.1.8 Information Systems.  BDEC shall provide and maintain the information
systems it deems  necessary to operate the Business.  BDEC shall have reasonable
discretion to select hardware and software,  provided such hardware and software
shall be adequate to operate the Business in a commercially  reasonable  manner,
and BDEC  shall be  responsible  for  training  employees  to  operate  any such
systems.

     4.1.9 Legal  Actions.  As requested  by the Company,  BDEC shall advise and
assist the Company in instituting  or defending  legal actions or proceedings by
or  against  third  parties  arising  out of the  Business,  including,  without
limitation,  those actions necessary for the protection and continued  operation
of the Company.  BDEC shall have no authority to initiate,  compromise or settle
any legal  action in the name of the  Company,  or to confess a judgment  in the
name of, or on behalf of, the Company.

     4.1.10  Insurance.  (a) BDEC shall  obtain and  maintain  professional  and
comprehensive  general liability  insurance and other insurance covering Company
for the  risks  and in the  amounts  typically  carried  by  others  in the same
business as Company.

     (b) BDEC  shall  obtain  and  maintain  appropriate  workers'  compensation
coverage for BDEC's  personnel and shall carry  professional  and  comprehensive
general  liability  insurance  covering all BDEC  personnel in amounts that BDEC
deems necessary, the cost of which insurance shall be a Business Expense.

         4.2  Personnel.  BDEC shall  employ or otherwise  retain,  and shall be
responsible  for  interviewing,   selecting,   hiring,  training,   supervising,
scheduling,  and terminating,  non-physician  personnel as BDEC deems reasonably
necessary and appropriate for the performance of Management Services and Support
Services.  Such personnel may include  temporary or "floater"  personnel who are
retained by BDEC to  substitute  for permanent  personnel.  BDEC shall have sole
responsibility  for determining the salaries,  wages, and fringe benefits of all
such  personnel,  for paying such  salaries and wages,  and for  providing  such
fringe benefits,  and for  withholding,  as required by law, any sums for income
tax, unemployment insurance,  social security, or any other withholding required
by applicable law or governmental  requirement.  BDEC shall have sole discretion
in decisions  regarding the termination of personnel employed by BDEC to provide
services  to the  Company.  BDEC shall  indemnify  the  Company and the Compan s
managers and members and hold them  harmless from and against any claim or cause
of action  which  alleges  or is based upon any act or  omission  by BDEC or its
owners, managers,  directors, officers or employees with respect to any employee
or  former  employee  of BDEC.  This  indemnity  obligation  shall  survive  any
termination or expiration of this Agreement.

     4.2.1  Non-Exclusivity.  In  recognition  of the fact  that  the  personnel
retained by BDEC to provide services pursuant to this Agreement may from time to
time perform  services for others,  this  Agreement  shall not prevent BDEC from
performing  such services for others or restrict BDEC from using such  personnel
in the  performance  of  services  for other  parties  which are not in the same
business as Company.

                  4.2.2 Equal Employment Opportunity.  Without limitation of any
provision set forth herein,  BDEC expressly agrees,  for itself and on behalf of
the  Company,  to abide by any and all  applicable  federal  and/or  State equal
employment  opportunity  statutes,  rules, and regulations,  including,  without
limitation,  Title VII of the Civil  Rights  Act of 1964,  the Equal  Employment
Opportunity Act of 1972, the Age  Discrimination  in Employment Act of 1967, the
Equal  Pay Act of 1963,  the  National  Labor  Relations  Act,  the  Fair  Labor
Standards  Act, the  Rehabilitation  Act of 1973,  the  Occupational  Safety and
Health Act of 1970,  and the Americans  with  Disabilities  Act, all as may from
time-to-time be modified or amended.

     4.2.3  Labor  Reports.  BDEC shall for its own  account or on behalf of the
Company, as appropriate,  prepare,  maintain, and file all requisite reports and
statements  regarding income tax withholdings,  unemployment  insurance,  social
security, workers' compensation,  equal employment opportunity, or other reports
and statements  required with respect to personnel  provided by BDEC pursuant to
this Agreement and with respect to all personnel  employed or otherwise retained
by the Company.

     4.3 Conduct of Business.  BDEC  represents and warrants to the Company that
it is  authorized  to enter  into and  perform  this  Agreement  and its  duties
hereunder  without the consent or approval of any third party which has not been
obtained.  BDEC covenants and agrees to provide all of the services  required of
it hereunder, and to perform all of its obligations hereunder, in a commercially
reasonable  manner  and  in  compliance  with  all  applicable  laws  and  legal
requirements.

                                                   ARTICLE V
                                              COVENANTS OF COMPANY

     5.1 Notices to BDEC.  Company will give BDEC timely notice of operating and
capital  budgets  approved by the Company and directions or requests that it has
with respect to the conduct of the Business or the manner in which BDEC performs
its duties hereunder in order that BDEC shall have an opportunity to comply with
such budgets, directions or requests.

     5.2 Invoices and  Payment.  BDEC shall  deliver to the board of managers of
the Company, and to each of the members of the Company, monthly invoices setting
forth the Services  Fee, Use Fees,  and expense  reimbursement  due BDEC for the
immediately  preceding  month,  together with such supporting  documentation  as
shall be reasonably necessary to document the calculation and incurrence of such
amounts in accordance with the terms of this Agreement. The Company will pay, or
authorize BDEC in writing to pay, the invoiced  amounts  properly due within ten
(10)  days  after  receipt  of such  invoice,  unless  any of such  amounts  are
contested in good faith.

                                                   ARTICLE VI
                                             FINANCIAL ARRANGEMENT

     6.1 Amount of Services Fee. As  compensation  (the "Services  Fee") for the
Management Services and Support Services to be rendered hereunder, BDEC shall be
entitled to receive  from the Company an amount equal to Two percent (2%) of the
Company's Net Revenues (as hereinafter defined).

         6.2  Determination  of Net Revenues.  For purposes of Section 6.1, "Net
Revenues" shall mean the total operating  revenues of the Company net of revenue
deductions  which  include  without  limitation  an  allowance  for  contractual
allowances,  discounts,  professional fees, co-management fees and staff managed
fees and other uncollectible  amounts,  all as determined in accordance with the
methodology  used in the  preparation  of  Exhibit  A hereto  and  otherwise  in
accordance with generally accepted accounting  principles  consistently applied.
For illustration  purposes,  the parties agree that Net Revenues for the Phoenix
Refractive  Surgery  center  based on the pro forma  annualized  facility  model
attached  hereto  as  Exhibit  A for the  first  full  year of the  Term of this
Agreement would be $5,968,627.

     6.3 Business Expenses. In addition to the Services Fee described in Section
6.1, the Company shall reimburse BDEC, upon submission by BDEC of an invoice and
necessary supporting  documentation,  for any Business Expense properly incurred
by BDEC in accordance with this Agreement.

     6.4 Use  Payment.  Company  agrees to pay (the "Use  Payment") to BDEC on a
monthly  basis as  compensation  for BDEC's grant to Company of the right to use
the Premises and common areas of the Buildings. The Use Payment for the Premises
in Building P shall be twelve percent (12%),  and for the Premises in Building T
shall be  thirty-six  percent (36%) of the rent and all other costs and expenses
incurred by BDEC pursuant to the Base Lease for each of the respective building.
The Use  Payment  shall be paid in advance  and shall be due and  payable on the
first day of each month during the Term.

                                                  ARTICLE VII
                                              TERM AND TERMINATION

     7.1 Term.  This  Agreement  shall be effective  for an initial  period (the
"Term") commencing on the Effective Date and ending September 1, 2004.

     7.2 Termination.  The Company may terminate this Agreement immediately upon
the occurrence of one of the following events:

     (1) the dissolution or bankruptcy of BDEC; or

     (2) after the  expiration  of a ninety  (90) day  period in which  BDEC has
failed to remedy its failure to perform its duties  under this  Agreement  after
having received written notice from the Company of BDEC's failure to perform its
duties under this Agreement, which notice must specify the failure to perform.

     7.3  Termination  by  Agreement.  In the event the  Company  and BDEC shall
mutually  agree  in  writing,  this  Agreement  may be  terminated  on the  date
specified in such written agreement.

         7.4 Effects of  Termination.  Upon  termination of this  Agreement,  as
hereinabove  provided,  no party  shall have any further  obligations  hereunder
except for (i) obligations  accruing prior to the date of termination,  and (ii)
obligations,  promises, or covenants set forth herein that are expressly made to
extend beyond the Term, including, without limitation,  payment of accrued money
due under  Article VI, if any, and the  authority  and limited power of attorney
granted to BDEC herein, which shall survive until such time as such obligations,
promises,  or  covenants  shall  be  fully  paid  and  satisfied  (all of  which
provisions  shall survive the  expiration  or  termination  of this  Agreement).
Notwithstanding  anything  to the  contrary  herein,  upon  termination  of this
Agreement for any reason,  all accrued Service Fees,  Business  Expenses and Use
Payments,  if any,  shall  become  immediately  due and payable to BDEC  without
demand or notice.

                                                  ARTICLE VIII
                                                  MISCELLANEOUS

     8.1 Notices. Any notice, request, demand,  instruction,  communication,  or
other document required, permitted, or desired to be given hereunder shall be in
writing  and,  except  as  otherwise  provided  for  herein,   shall  be  deemed
effectively  given:  (a) on receipt if  delivered  personally  or by  commercial
courier service or if sent by prepaid telex,  telegram, by facsimile or by other
instantaneous  electronic  transmission  device,  or (b) on the  fifth day after
deposit (unless a different date is shown on the return receipt) if sent postage
prepaid registered or certified United States mail, return receipt requested, as
follows:

                  Company:                  Prime/BDEC Acquisition, L.L.C.
                                            1301 Capital of Texas Highway
                                            Suite C-300
                                            Austin, Texas 78746

                                            Attn.:            President
                                            Facsimile:  (512) 314-4398

                  BDEC:                     Barnet Dulaney Eye Center, P.L.L.C..
                                            4800 North 22nd Street
                                            Phoenix, Arizona  85016
                                            Attn.: Mark Rosenberg
                                            Facsimile:  (602) 508-4889

or to such other  address,  or to the attention of such other person or officer,
as either party may by written notice designate.

     8.2 Governing  Law. This  Agreement has been executed and delivered in, and
shall be governed by, and construed and enforced in accordance with, the laws of
the State of Texas.  Proper venue for any action with respect to this  Agreement
shall be Dallas County, Texas.

     8.3  Assignment.  Except  as may be  herein  specifically  provided  to the
contrary,  this Agreement  shall inure to the benefit of and be binding upon the
parties  hereto and their  respective  legal  representatives,  successors,  and
assigns;  provided,  however,  that  neither  party may  assign  its  rights and
obligations under this Agreement without the prior written consent of the other.

     8.4 No Waiver.  The failure of either  party to insist at any time upon the
strict  observance  or  performance  of any  provision  of this  Agreement or to
exercise any right or remedy as provided in this Agreement  shall not impair any
right or  remedy of such  party or be  construed  as a waiver or  relinquishment
thereof with respect to subsequent defaults or breaches.  Every right and remedy
given by this Agreement to the parties hereto may be exercised from time to time
and as often as may be deemed xpedient by the appropriate party.

     8.5  Consents,  Approvals,  and  Exercise of  Discretion.  Except as may be
herein specifically  provided to the contrary,  whenever this Agreement requires
any consent or approval to be given by either party, or either party must or may
exercise  discretion,  the parties agree that such consent or approval shall not
be unreasonably  withheld or delayed,  and such  discretion  shall be reasonably
exercised.

     8.6  Severability.  In the event any provision of this Agreement is held to
be invalid,  illegal,  or unenforceable for any reason and in any respect,  such
invalidity,  illegality,  or unenforceability  shall not affect the remainder of
this  Agreement,  if the remainder of this  Agreement can be enforced to achieve
its purposes equitably to both parties.

     8.7 Divisions and Headings.  The division of this  Agreement into articles,
sections,  and  subsections  and the use of captions and headings in  connection
therewith are solely for convenience and shall not affect in any way the meaning
or interpretation of this Agreement.

     8.8 Sales and Use Tax.  BDEC and the  Company  acknowledge  and agree  that
certain of the services to be provided by BDEC hereunder may be subject to state
sales and use taxes and that BDEC may have a legal  obligation  to collect  such
taxes from the Company and to remit same to the State. The Company agrees to pay
the  applicable  state  sales and use taxes in  respect  of the  portion  of the
Services  Fee  attributable  to such  services,  and  grants  BDEC the  right to
withdraw and disburse from the bank accounts of the Company amounts necessary to
timely and fully pay such taxes.

         8.9  Entire  Agreement.  With  respect  to the  subject  matter of this
Agreement,  this Agreement supersedes all previous contracts and constitutes the
entire  agreement  between  the  parties.  Neither  party  shall be  entitled to
benefits other than those specified  herein. No oral statements or prior written
material not specifically  incorporated herein shall be of any force and effect,
and no changes in or  additions to this  Agreement  shall be  recognized  unless
incorporated  herein by amendment  in writing and signed by all parties  hereto.
Such  amendment(s)  shall  become  effective  on the  date  stipulated  in  such
amendment(s).  The parties  specifically  acknowledge that, in entering into and
executing this Agreement,  the parties rely solely upon the  representations and
agreements contained in this Agreement and no others.

         8.10 Audit Rights.  During the Term of this  Agreement and for a period
of two (2) years after any  termination  or  expiration of this  Agreement,  the
Company and each of its members shall be entitled to audit and inspect the books
and records of BDEC for purposes of  determining  the  propriety of all Business
Expenses,  Services  Fees and Use  Payments  charged to the  Company  under this
Agreement.  BDEC agrees to maintain,  throughout such period,  detailed  records
supporting  all amounts  charged to, or reimbursed  by, the Company  pursuant to
this  Agreement  and to  cooperate  fully with,  and to make its  employees  and
records  available  during  normal  business  hours to,  the  auditors  or other
representatives  of the Company or its  members  performing  such  audit.  Audit
rights may not be exercised  more  frequently  than once in every  eighteen (18)
month period and all costs and expenses  associated  therewith shall be borne by
the party  exercising  audit rights unless any such inspection  reveals that the
Company has overpaid,  by at least  $25,000,  any amounts which should have been
properly  paid or  reimbursed  to BDEC in  accordance  with  the  terms  of this
Agreement.  BDEC shall be entitled  to receive at least  thirty (30) days' prior
written  notice of the exercise of audit  rights prior to the  beginning of such
inspection.

                                             [Signature page follows]

<PAGE>

                                                 SIGNATURE PAGE TO
                                               COLLOCATION AGREEMENT

     IN WITNESS WHEREOF, the parties have executed this Agreement as of the date
first written above.

     COMPANY:                   PRIME/BDEC ACQUISITION, L.L.C.

                                By: /s/ Cheryl Williams

                                Name: Cheryl Williams

                                Title: Treasurer

     BDEC:                      BARNET DULANEY EYE CENTER, P.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

<PAGE>

                                                     EXHIBIT A

                                               Pro Forma Annualized
                                                  Facility Model

<PAGE>

                                                     EXHIBIT B

                                                     EMPLOYEES

<PAGE>

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