FIRST AMENDMENT TO FACILITY USE AGREEMENT

         THIS FIRST  AMENDMENT  ("Amendment")  TO THE FACILITY USE  AGREEMENT is
made and entered into as of July __, 2000 (the "Effective  Date"),  by and among
Caster One, L.L.C., a Delaware limited liability company,  (hereinafter referred
to as "Newco"),  Andrew Caster, M.D. (hereinafter referred to as "Provider") and
Caster  Eye  Center  Medical  Group,  a  California   professional   corporation
(hereinafter referred to as "Caster PC"). Newco, Provider and Caster PC shall be
referred to collectively as the "Parties".

                                    RECITALS:

         WHEREAS,  the Parties entered into that certain  Facility Use Agreement
(the "Agreement"),  dated as of March 1, 2000, by and among Newco,  Provider and
Caster PC, that allows  Caster PC and  Provider  to use  Newco's  facilities  in
connection with providing Refractive Surgery and related services;

         WHEREAS, the Billing Staff of Newco, as defined hereafter, shall assume
responsibility  of billing and  collecting on behalf of Newco and the remittance
of payment of the Professional Fee and the unreimbursed reimbursable expenses to
Provider and Caster PC;

         WHEREAS,  the  Parties  concur  that  the  assumption  by  Newco of its
responsibility  for billing and collecting,  in accordance with the terms of the
Agreement,  as further clarified by the terms of this Amendment,  is in the best
interest of the Parties;

         WHEREAS,  the  Parties  further  concur  that the  Agreement  should be
amended to provide that Newco shall  retain the Facility  Usage Fee from amounts
collected by it,  while  remitting  the  Professional  Fee and the  unreimbursed
reimbursable expenses to Provider and Caster PC;

         NOW, THEREFORE,  for and in consideration of the recitals above and the
mutual covenants and conditions  contained  herein,  the parties hereto agree to
amend the Agreement as follows:

                             STATEMENT OF AMENDMENT

     1.  Section 3.3 of the  Agreement is amended by the  addition,  immediately
after the first paragraph, of the following two (2) paragraphs:

                  Newco billing staff ("Billing Staff") located in the office at
         9100 Wilshire Blvd., Suite 265E, Beverly Hills,  California 90212 shall
         furnish all billing and collecting  services to Provider and Caster PC.
         On a day of the week designated by Provider in consultation with Newco,
         Provider  shall furnish to Billing  Staff,  in a form  satisfactory  to
         Newco,  a procedure  data sheet (the "Data  Sheet") for the week ending
         upon close of business on the previous day (the "Billing  Week").  Such
         Data Sheet shall enumerate each procedure  performed by Provider during
         the  Billing  Week;  the  total  fee  charged  for  the  procedure,  as
         determined by Provider;  the name,  address and telephone number of the
         patient;  and any additional  information required by Billing Staff for
         purposes  of proper  and timely  billing  for  Provider's  professional
         medical  services in the performance of Refractive  Surgery and related
         services.

                  Provider and Caster PC hereby designate Newco as their billing
         agent during the term of the  Agreement,  and Newco hereby accepts such
         assignment.  Billing Staff shall maintain complete and accurate records
         of charges  billed and amounts  collected,  and shall furnish  Provider
         with copies of all billing  statements issued on Provider's  behalf, as
         well as  copies  of bank  receipts  for all  payments  deposited  in an
         account designated by Newco. When payments are received,  Billing Staff
         shall be  responsible  for  recording  and  depositing  the receipts in
         Newco's  account  and making  payment to  Provider  of the agreed  upon
         amounts constituting compensation for Provider's professional services,
         which shall be calculated  as described in Section  4.1(a) or 4.1(b) as
         the case may be (the "Professional  Fee"). The Parties  acknowledge and
         agree that the entire  amount of the  Professional  Fee shall,  in each
         case,  represent fair market value for  Refractive  Surgery and related
         services  performed by Provider and shall include no additional payment
         for any other purpose.

     2.  Section 4.1 of the  Agreement  is hereby  restated  in its  entirety as
follows:
                  Section 4.1  Facility  Fees.  Subject to  modification  in the
         manner  prescribed by Section 8.9 of Newco's Limited  Liability Company
         Agreement,  the fees  payable  to Newco by  Caster PC and  Provider  in
         return for use of the Facilities made available by Newco hereunder (the
         "Facility Usage Fee") shall be determined on a per procedure basis. The
         Facility Usage Fee shall be remitted by Billing Staff on a weekly basis
         to an account  designated by Newco, less the unreimbursed  reimbursable
         expenses,  pursuant to Section 4.2,  incurred by Caster PC and Provider
         during the same time period as the  procedures  were performed on which
         the current  Facility  Usage Fee was based.  The amount of the Facility
         Usage  Fee  with  respect  to any  procedure  shall  be  determined  in
         accordance with the following:

                           (a) As long as Caster PC's standard, undiscounted fee
                           charged to the patient  (determined without reference
                           to the fee  charged  for any  single  procedure,  the
                           "Patient  Fee")  has  at  all  prior  times  remained
                           between  the  amounts  of $2,400  per  procedure  and
                           $2,275 per  procedure,  the  Facility  Usage Fee with
                           respect  to any one  procedure  shall  equal  (i) the
                           amount  actually  collected for such procedure  minus
                           (ii) $400.

                           (b) At  all  times  following  any  reduction  of the
                           Patient  Fee  to  an  amount  less  than  $2,275  per
                           procedure,  or any  increase in the Patient Fee to an
                           amount  greater  than  $2,400  per   procedure,   the
                           Facility  Usage Fee with respect to any one procedure
                           shall  equal (i) the amount  actually  collected  for
                           such  procedure  minus (ii) an amount up to seventeen
                           and 58/100  percent  (17.58%)  of such  Patient  Fee;
                           provided,   however,  that  in  no  event  shall  the
                           Facility  Usage Fee be below the fair market value of
                           the use of the Facilities in the aggregate.

                           (c) At the  conclusion of the Billing  Week,  Billing
                           Staff shall  calculate the total  Facility  Usage Fee
                           for that week based on the total number of procedures
                           performed  and the  charge per  procedure.  The total
                           Facility    Usage   Fee,   less   the    unreimbursed
                           reimbursable  expenses  accruing  during the  Billing
                           Week, shall constitute Newco's Facility Usage Fee for
                           such Billing Week.

                           (d) The  differing  amounts  reflected in  subsection
                           (ii)  of  each  of  subsections  (a)  and  (b)  above
                           represent the range of contemplated Professional Fees
                           for  any one  procedure.  At the  conclusion  of each
                           Billing Week, the total  Professional  Fees allocated
                           to Provider per procedure during that week,  together
                           with  the  amount  of the  unreimbursed  reimbursable
                           expenses  incurred during the Billing Week,  shall be
                           remitted to an account designated by Provider.

                           (e) Notwithstanding the foregoing  provisions of this
                           Section 4.1, or any other  contrary  provision of any
                           Transaction  Document,  Provider shall be entitled to
                           perform  procedures  for free and refund amounts paid
                           for  procedures on a limited basis in a manner and to
                           the extent  Provider  has done so in the past,  or as
                           otherwise  consented to by Newco.  The Facility Usage
                           Fee  with  respect  to  such   procedures   shall  be
                           eliminated,  as long as the aggregate  Facility Usage
                           Fee paid hereunder  equals or exceeds the fair market
                           value of the use of the Facilities.

     3. Full Force and Effect.  With the  exception of the above,  the Agreement
shall remain in full force and effect in its original form.

         4.  Consideration.  The Parties acknowledge and agree that the Facility
Usage  Fee  was  originally  intended,  in  accordance  with  the  terms  of the
Agreement,  to cover all of the management and administration  services provided
by Newco, which expressly included billing and collecting  services as indicated
in the second  Recital  herein.  Accordingly,  no  additional  consideration  is
required  on  account  of  Newco's   undertaking,   at  the  present  time,  the
responsibility  for billing and  collecting  services on behalf of Provider  and
Caster PC, as provided in the Agreement.

5.       Miscellaneous.

a.   Entire Agreement. This Amendment, together with the Agreement; that certain
     Limited  Liability Company Agreement dated as of March 1, 2000 by and among
     Newco, Prime Refractive,  L.L.C., a Delaware limited liability company, and
     Caster Eye Center Medical Group, a California professional corporation; and
     that certain contribution agreement (the "Contribution Agreement") dated as
     of March 1, 2000,  by and among Prime  Medical  Services,  Inc., a Delaware
     corporation,   Prime  Refractive,  L.L.C.,  a  Delaware  limited  liability
     company,  Newco, Provider and Caster PC, supersedes all previous contracts,
     agreements  and  understandings  and  constitutes  the entire  agreement of
     whatsoever  kind or  nature  existing  between  or among  the  parties  and
     representing  the within subject matter,  and no party shall be entitled to
     benefits other than those specified herein or therein.

b.   Counterparts.  This Amendment may be executed in two or more  counterparts,
     each and all of which shall be deemed an original and all of which together
     shall constitute but one and the same instrument.

c.   All capitalized terms not defined herein shall have the same definitions as
     supplied in the Agreement or the Contribution Agreement.

         THE PARTIES  HERETO have executed this Amendment as of the day and year
first above written.

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Newco:                              Caster One, L.L.C.

                                By: ____________________________________________
                                    Teena Belcik, signing as a manager of Newco
                                         and on behalf of Prime, as a member
                                         of Newco


                                By: ____________________________________________
                                    Andrew Caster, signing as both a manager
                                        and, on behalf of Caster, PC, as a
                                        member of Newco



Provider:                        _______________________________________________
                                            Andrew Caster, M.D.



Caster PC:                       Caster Eye Center Medical Group

                                     By:
                                           Andrew Caster, M.D., President