MEMBERSHIP INTEREST

                         TRANSFER RESTRICTION AGREEMENT

     This Membership Interest Transfer Restriction  Agreement (this "Agreement")
is entered into  effective as of the 1st day of  September,  1999,  by and among
LASIK Investors,  L.L.C., a Delaware limited  liability company (the "Company"),
Prime  Medical  Operating,  Inc., a Delaware  corporation  ("Prime"),  Ronald W.
Barnet, M.D.  ("Barnet"),  David D. Dulaney,  M.D.  ("Dulaney"),  Mark Rosenberg
("Rosenberg"),  Scott A. Perkins, M.D. ("Perkins"),  and Robert B. Pinkert, O.D.
("Pinkert").  Barnet, Dulaney, Rosenberg, Perkins and Pinkert, together with any
subsequent  Members in the Company who  hereafter  execute this  Agreement,  are
collectively referred to herein as the "Members".

                                R E C I T A L S:

             WHEREAS,  Barnet, Dulaney,  Rosenberg,  Perkins and Pinkert own all
the  issued  and  outstanding  membership  interests  of the  Company  (all such
membership  interests,  together with any hereafter  acquired,  are  hereinafter
referred to as the "Membership Interests"); and

             WHEREAS, this Agreement is a "Transaction  Document," as defined in
that  certain  Contribution  Agreement  (the  "Contribution   Agreement")  dated
effective September 1, 1999, by and among Prime, Prime Medical Services, Inc., a
Delaware corporation ("PMSI"), the Company, Barnet Dulaney Eye Center, P.L.L.C.,
an  Arizona  professional  limited  liability  company,  Prime/BDR  Acquisition,
L.L.C., a Delaware limited liability company, Prime/BDEC Acquisition,  L.L.C., a
Delaware limited liability company, Barnet, Dulaney and Rosenberg.

             WHEREAS,  the  Members,  the Company and Prime desire to enter into
this Agreement to control the distribution of ownership interests in the Company
and to promote the harmonious management of the Company's affairs.

             NOW,  THEREFORE,  in  consideration  of the  foregoing,  the mutual
covenants and agreements contained herein, and for other valuable consideration,
the receipt and sufficiency of which are hereby acknowledged, the parties hereto
agree as follows:

                                    ARTICLE I

               PERMITTED TRANSFERS; RESTRICTIONS AGAINST TRANSFER

As used in this Agreement,  "Permitted Transfers" shall mean any transfer of all
or any  part of any  Member's  Membership  Interest  to (i) the  members  of the
immediate  family of the Member or a trust or trusts for the  benefit of members
of the immediate family of the Member, provided that after any such transfer the
Member  retains  the sole  express  right to vote,  or direct  the votes of, the
Membership  Interest,  (ii) any other  Member,  provided that after any transfer
pursuant to this subsection  (ii) is consummated,  Barnet and Dulaney (or trusts
that hold Membership Interests as a result of Permitted Transfers subsection (i)
above) must  collectively own in the aggregate at least fifty-one  percent (51%)
of the total outstanding  Membership  Interests of the Company,  or (iii) Prime.
Any Member  transferring all or a portion of its Membership Interest pursuant to
a  Permitted  Transfer  shall  give  written  notice of the  Permitted  Transfer
(containing the same  information as required for notice under Section 2.1.1) to
Prime and the other Members fifteen (15) days prior to the effective date of the
Permitted Transfer. Except for a Permitted Transfer, or as otherwise provided in
this Agreement, a Member shall not transfer, assign, pledge,  hypothecate, or in
any way alienate any  Membership  Interest,  or any  interest  therein,  whether
voluntarily  or by operation of law, or by gift or otherwise,  without the prior
written consent of the Company,  the other Members and Prime,  which consent may
be withheld in their sole and absolute  discretion.  Any  purported  transfer in
violation of any  provision  of this  Agreement  shall be void and  ineffectual,
shall not operate to transfer any interest or title to the purported transferee,
and shall give the Company, the other Members and Prime options to purchase such
Membership Interest in the manner and on the conditions hereinafter provided. As
used in this Agreement,  "Option  Members" shall mean all Members of the Company
except  (i) the Member  who,  prior to the  proposed  transfer  or the  incident
resulting in the proposed transfer of all or a portion of a Membership Interest,
owned such interest and (ii) Rosenberg.

                                   ARTICLE II

                                     OPTIONS

2.1          OPTION UPON VOLUNTARY TRANSFER.

             2.1.1  Notice of  Intention  to  Transfer.  If a Member  intends to
voluntarily  transfer any of its Membership  Interest,  other than pursuant to a
Permitted  Transfer,  to any person other than the Company,  and does not obtain
the written consents required in ARTICLE I hereof, the Member shall give written
notice to the other  Members,  Rosenberg  and Prime stating (i) the intention to
transfer a Membership  Interest,  (ii) the amount of  Membership  Interest to be
transferred,  (iii) the name,  business  and  residence  address of the proposed
transferee,  (iv) the nature and amount of the consideration,  and (v) the other
terms of the proposed sale.

             2.1.2 Option to Purchase.  The Option  Members shall have,  and may
exercise  within 30 days after  receipt of the notice of intent to transfer,  an
option  to  purchase  all  or  any  portion  of  the  Membership   Interest  the
transferring Member intends to transfer,  for the price and upon the other terms
stated in the notice of intent to transfer.  If the Option Members fail,  within
such 30-day period,  to exercise  their purchase  option (by delivery of written
notice) with respect to the entire Membership  Interest being  transferred,  the
Option  Members shall be deemed to have elected not to exercise  their  purchase
option with respect to such unpurchased Membership Interest.  Upon any notice of
non-exercise (or deemed  non-exercise) by the Option Members,  Rosenberg (if not
the transferring  Member) shall have, and may exercise within 30 days of receipt
of notice of such non-exercise (or deemed  non-exercise),  an option to purchase
all or any portion of such unpurchased  Membership  Interest upon the same terms
and conditions.  If Rosenberg fails,  within such 30-day period, to exercise his
purchase  option (by  delivery  of written  notice)  with  respect to the entire
unpurchased  Membership Interest,  Rosenberg shall be deemed to have elected not
to  exercise  his  purchase  option  with  respect to any  remaining  Membership
Interest. Upon any notice of non-exercise (or deemed non-exercise) by Rosenberg,
Prime shall have,  and may exercise  within 30 days of receipt of notice of such
non-exercise  (or  deemed  non-exercise),  an  option  to  purchase  all of such
remaining Membership Interest upon the same terms and conditions.

             2.1.3 Death Before Closing.  If a Member who proposed to transfer a
Membership  Interest  dies  prior  to the  closing  of  the  sale  and  purchase
contemplated  by this  Section  2.1, the  Membership  Interest of such  deceased
Member shall be the subject of sale and purchase under Section 2.3.

             2.1.4 Allowable  Consideration.  All parties hereto acknowledge and
agree that it would be  impractical  to exercise  an option to purchase  arising
pursuant to this Section 2.1 whenever the proposed  consideration to be received
by the transferring  Member is other than cash or cash  equivalents.  Therefore,
the parties agree that no transfer  shall be permitted and no option shall arise
pursuant to this Section 2.1 whenever the  consideration to be received from the
proposed transferee is other than cash or cash equivalents.

2.2          OPTION UPON CERTAIN INVOLUNTARY TRANSFERS.

             2 2.1  Exercise  Event and  Notice.  The filing of a  voluntary  or
involuntary petition of bankruptcy by or on behalf of a Member, an assignment by
a Member of any of its Membership Interest, or of any right or interest therein,
for the benefit of creditors, or the voluntary transfer,  transfer by law or any
other transfer,  of any Membership Interest, or of any right or interest therein
(other  than  transfers  governed by ARTICLE I or  Sections  2.1,  2.3 or 2.4 or
ARTICLE  VII  hereof),  shall give the other  Members,  Rosenberg  and Prime the
option to  purchase  the  Membership  Interest of such  bankrupt  Member or such
transferred  Membership  Interest  as  provided  herein.  Upon the  filing  of a
voluntary or  involuntary  petition of bankruptcy by or on behalf of a Member or
an assignment by Member of any of its  Membership  Interest,  or of any right or
interest  therein,  for the  benefit of  creditors,  the Member or its  personal
representative  shall  promptly  give written  notice of such  occurrence to the
other  Members,  Rosenberg  and Prime.  In the event of a transfer of Membership
Interest,  as described above, the Member  transferring such Membership Interest
shall  promptly  give  written  notice of such  transfer  to the other  Members,
Rosenberg and Prime.

             2.2.2 Option to Purchase.  The Option  Members shall have,  and may
exercise  within 30 days after receipt of the notice of the applicable  exercise
event,  an option to purchase all or any portion of the Membership  Interest the
bankrupt or transferring Member intends to transfer,  for the price and upon the
other terms hereinafter provided. If the Option Members fail, within such 30-day
period,  to exercise their purchase  option (by delivery of written notice) with
respect to the entire Membership Interest being transferred,  the Option Members
shall be deemed to have  elected  not to  exercise  their  purchase  option with
respect to such unpurchased Membership Interest. Upon any notice of non-exercise
(or deemed  non-exercise) by the Option Members,  Rosenberg (if not the bankrupt
or  transferring  Member) shall have, and may exercise within 30 days of receipt
of notice of such non-exercise (or deemed  non-exercise),  an option to purchase
all or any portion of such  unpurchased  Membership  Interest  for the price and
upon the other terms  hereinafter  provided.  If  Rosenberg  fails,  within such
30-day period,  to exercise his purchase  option (by delivery of written notice)
with respect to the entire unpurchased  Membership Interest,  Rosenberg shall be
deemed to have elected not to exercise  his purchase  option with respect to any
remaining  Membership  Interest.  Upon any  notice of  non-exercise  (or  deemed
non-exercise) by Rosenberg, Prime shall have, and may exercise within 30 days of
receipt of notice of such  non-exercise (or deemed  non-exercise),  an option to
purchase all of such  remaining  Membership  Interest for the price and upon the
other terms hereinafter provided.

2.3          PURCHASE AND SALE OF MEMBERSHIP INTEREST UPON DEATH.

             2.3.1  Notice  of  Death.  Upon  the  death  of  the  Member,   the
representative  of the estate of the deceased Member shall promptly give written
notice of the death to the other Members, Rosenberg and Prime.

             2.3.2 Option to Purchase.  The Option  Members shall have,  and may
exercise  within 30 days  after  receipt  of the  notice of death,  an option to
purchase all or any portion of the Membership  Interest of the deceased  Member,
for the price and upon the  other  terms  hereinafter  provided.  If the  Option
Members fail,  within such 30-day period,  to exercise their purchase option (by
delivery of written  notice)  with  respect to the  entirety of such  Membership
Interest,  the Option  Members  shall be deemed to have  elected not to exercise
their purchase option with respect to such unpurchased Membership Interest. Upon
any notice of  non-exercise  (or  deemed  non-exercise)  by the Option  Members,
Rosenberg (but not his estate if he is the deceased  Member) shall have, and may
exercise  within 30 days of  receipt of notice of such  non-exercise  (or deemed
non-exercise),  an option to  purchase  all or any  portion of such  unpurchased
Membership Interest for the price and upon the other terms hereinafter provided.
If Rosenberg fails,  within such 30-day period,  to exercise his purchase option
(by  delivery  of  written  notice)  with  respect  to  the  entire  unpurchased
Membership  Interest,  Rosenberg shall be deemed to have elected not to exercise
his purchase option with respect to any remaining Membership Interest.  Upon any
notice of non-exercise (or deemed non-exercise) by Rosenberg,  Prime shall have,
and may exercise  within 30 days of receipt of notice of such  non-exercise  (or
deemed  non-exercise),  an option to purchase all of such  remaining  Membership
Interest for the price and upon the other terms hereinafter provided.

2.4  OPTION UPON DEATH OF A MEMBER'S SPOUSE, TERMINATION OF MARITAL RELATIONSHIP
     OR PARTITION OF COMMUNITY PROPERTY.

             2.4.1  Death of  Member's  Spouse.  Each  Member and each  Member's
spouse  agree that in the event the spouse of a Member  predeceases  such Member
and such Member does not succeed by the spouse's  last will and  testament or by
operation of law to any interest  (including,  without  limitation,  a community
property interest) of the spouse in the Membership  Interest,  such Member shall
have, and may exercise  within 60 days after the death of the spouse,  an option
to purchase all or any portion of the  spouse's  interest for the price and upon
the other terms hereinafter  provided.  If the Member fails,  within such 60-day
period,  to exercise  his purchase  option (by delivery of written  notice) with
respect to the entirety of such spouse's  interest,  that Member shall be deemed
to have  elected  not to  exercise  his  purchase  option  with  respect to such
spouse's interest.  Upon any notice of non-exercise (or deemed  non-exercise) by
the Member,  the Option Members shall then have, and may exercise within 30 days
after  receipt  of such  non-exercise  (or  deemed  non-exercise),  an option to
purchase all or any portion of the deceased spouse's interest, for the price and
upon the other terms  hereinafter  provided.  If the Option Members fail, within
such 30-day period,  to exercise  their purchase  option (by delivery of written
notice) with respect to the entirety of such  deceased  spouse's  interest,  the
Option  Members shall be deemed to have elected not to exercise  their  purchase
option with respect to such unpurchased  deceased  spouse's  interest.  Upon any
notice of non-exercise (or deemed non-exercise) by the Option Members, Rosenberg
(if not the Member whose spouse is deceased) shall have, and may exercise within
30 days of receipt of notice of such non-exercise (or deemed  non-exercise),  an
option to purchase  all or any  portion of such  unpurchased  deceased  spouse's
interest  for the  price  and upon the  other  terms  hereinafter  provided.  If
Rosenberg fails,  within such 30-day period, to exercise his purchase option (by
delivery of written  notice)  with  respect to the entire  unpurchased  deceased
spouse's interest, Rosenberg shall be deemed to have elected not to exercise his
purchase option with respect to any remaining  portion of the deceased  spouse's
interest. Upon any notice of non-exercise (or deemed non-exercise) by Rosenberg,
Prime shall have,  and may exercise  within 30 days of receipt of notice of such
non-exercise  (or  deemed  non-exercise),  an  option  to  purchase  all of such
remaining  portion of the deceased  spouse's interest for the price and upon the
other terms hereinafter provided.

             2.4.2 Termination of Marital Relationship or Partition of Community
Property. In the event a divorce,  annulment or other proceeding for termination
of the  marital  relationship  is  filed by or  against  a  Member,  or upon the
initiation  of any voluntary or  involuntary  attempt to partition the community
property  estate between a Member and such Member's  spouse for any reason,  the
Member shall promptly give written notice to the other Members,  Rosenberg,  and
Prime, of such event.  The Member shall have, and may exercise within 60 days of
giving of such notice, an option to purchase all or any portion of the departing
spouse's interest in such Membership  Interest (including without limitation any
community  property interest,  for purposes of this Section),  for the price and
upon the other terms  hereinafter  provided.  If the Member  fails,  within such
60-day period,  to exercise his purchase  option (by delivery of written notice)
with respect to the  entirety of such  spouse's  interest,  that Member shall be
deemed to have elected not to exercise his purchase  option with respect to such
spouse's interest.  Upon any notice of non-exercise (or deemed  non-exercise) by
the Member,  the Option Members shall then have, and may exercise within 30 days
after  receipt  of such  non-exercise  (or  deemed  non-exercise),  an option to
purchase all or any portion of the departing  spouse's  interest,  for the price
and upon the other  terms  hereinafter  provided.  If the Option  Members  fail,
within such 30-day period,  to exercise  their  purchase  option (by delivery of
written  notice)  with  respect  to the  entirety  of  such  departing  spouse's
interest,  the Option  Members  shall be deemed to have  elected not to exercise
their  purchase  option  with  respect to such  unpurchased  departing  spouse's
interest. Upon any notice of non-exercise (or deemed non-exercise) by the Option
Members, Rosenberg (if not the Member whose spouse is departing) shall have, and
may exercise within 30 days of receipt of notice of such non-exercise (or deemed
non-exercise),  an option to  purchase  all or any  portion of such  unpurchased
departing  spouse's  interest for the price and upon the other terms hereinafter
provided.  If  Rosenberg  fails,  within such  30-day  period,  to exercise  his
purchase  option (by  delivery  of written  notice)  with  respect to the entire
unpurchased  departing  spouse's  interest,  Rosenberg  shall be  deemed to have
elected not to  exercise  his  purchase  option  with  respect to any  remaining
portion of the departing spouse's interest.  Upon any notice of non-exercise (or
deemed non-exercise) by Rosenberg,  Prime shall have, and may exercise within 30
days of receipt of notice of such  non-exercise  (or  deemed  non-exercise),  an
option to  purchase  all of such  remaining  portion of the  departing  spouse's
interest for the price and upon the other terms hereinafter provided.

2.5          ALTERNATE NOTICES.

             The failure of any  person,  whether a party to this  Agreement  or
otherwise,  to give notice of the occurrence of an Exercise Event (as defined in
Section 4.3) as contemplated herein shall not operate to prevent the creation of
any option which would otherwise arise pursuant to this ARTICLE II. Any party to
this  Agreement who has actual  knowledge of the occurrence of an Exercise Event
may give the required written notice of the occurrence of an Exercise Event, and
upon the giving of such written  notice the options  shall be created and become
exercisable  to the  same  extent  as if such  notice  was  given  by the  party
initially contemplated above. For instance, and purely by way of example, in the
event of the death of a Member,  another  Member having actual  knowledge of the
Member's  death  may give the  notice  initially  contemplated  to be given by a
representative  of the estate of the deceased  Member  pursuant to Section 2.3.1
above,  whereupon the Option  Members'  option  described in Section 2.3.2 would
arise and become  exercisable to the same extent as if the notice had been given
by the representative of the estate of the deceased Member.

                                   ARTICLE III

                   EXERCISE OF OPTIONS; EFFECT OF NON-EXERCISE

3.1          MANNER OF EXERCISE OF OPTIONS.

             All options granted in, or arising pursuant to, ARTICLE II shall be
exercised by a written notice to that effect  delivered within the time provided
for the exercise of the option.

3.2          COMPLETE EXERCISE OF OPTIONS.

             Notwithstanding  anything  herein to the  contrary,  the holders of
options granted in, or arising pursuant to, ARTICLE II must,  either alone or in
the  aggregate,  exercise the options in such a manner as to purchase all of the
Membership  Interest (or interest therein) subject to such options,  and failure
to do so shall cause a forfeiture of the options.

3.3          MULTIPLE OPTION HOLDERS.

             In cases  where an option is held by more than one  Option  Member,
each  purchasing  Option  Member  shall  be  entitled  to  purchase  his  or her
proportionate  share of the Membership Interest subject to the option. An Option
Member's  proportionate  share  shall  equal  the  total  amount  of  Membership
Interests  subject to the option multiplied by a fraction the numerator of which
is the  amount  of  Membership  Interests  held by such  Option  Member  and the
denominator  of which shall be the amount of  Membership  Interests  held by all
Option Members electing to exercise the option.

3.4          EFFECT OF NON-EXERCISE OF OPTIONS.

             If the  holders of options  granted  or  arising  pursuant  to this
Agreement do not exercise  their  options,  or such  options are  forfeited,  as
provided herein,  the person or persons  acquiring the Membership  Interests (or
interest  therein)  that  were  the  subject  of the  options  shall  execute  a
counterpart  of this  Agreement  and  become a party  hereto and shall hold such
Membership  Interests  subject to all the terms and conditions  provided herein,
and any transfer of such Membership  Interests (or interest  therein) shall only
be made in accordance  with the terms and  conditions  provided  herein.  In the
event the person or persons  acquiring  the  Membership  Interests  (or interest
therein)  fail to execute a  counterpart  of this  Agreement  and become a party
hereto,  such transfer shall be void and  ineffectual,  and shall not operate to
transfer any interest or title to the purported  transferee and such  Membership
Interests shall thereafter be subject to cancellation and  extinguishment by the
Company,  without  consideration  therefor.  In  addition,  in  the  event  of a
voluntary  transfer  subject to the provisions of Section 2.1, upon the lapse or
forfeiture of the options arising pursuant to that Section, the Member proposing
the  transfer  shall have the right to  effectuate  the  transfer of  Membership
Interests  in  accordance  with the  terms  stated  in the  notice  of intent to
transfer,  and the  transferee of such  Membership  Interests  shall execute and
become a party to this  Agreement  and  shall  hold  such  Membership  Interests
subject to all of its terms and conditions.  Provided further, however, any such
transfer of Membership  Interests shall be void and  ineffectual,  and shall not
operate to transfer any interest or title to the  purported  transferee,  if (i)
the  transfer  is not upon the terms or is not to the  transferee  stated in the
notice of intent to transfer,  or (ii) the transfer is not closed within 10 days
of receipt of written notice of the election not to exercise,  or the forfeiture
of, all applicable options.

                                   ARTICLE IV

                                 PURCHASE PRICE

4.1          PURCHASE PRICE.

             The  purchase  price of the  Membership  Interests  to be purchased
pursuant to options granted, held or exercised pursuant to Sections 2.2, 2.3 and
2.4  hereof,  shall be the amount  calculated  in  accordance  with  Section 4.2
hereof.

4.2          CALCULATION OF PURCHASE PRICE.

             When  determined in accordance  with this Section 4.2, the purchase
price for the Membership  Interest or any portion  thereof or spouse's  interest
therein shall be equal to the Appraised  Value of the Membership  Interest as of
the Valuation Date (as defined in Section 4.3 hereof), reduced when necessary to
reflect the purchase of less than a one hundred  percent (100%) interest in each
of the Membership Interests to be transferred (for example:  reduced by one-half
when a  spouse's  interest  is only an  undivided  one-half  community  property
interest in each of the Membership  Interests of a Member spouse).  For purposes
of this Agreement,  the "Appraised Value" of a Membership  Interest shall be (i)
based on the overall value of the Company as a going concern, expressed in a per
Membership Interest unit amount without  consideration to whether the Membership
Interest,  or interest therein,  being transferred  constitutes a controlling or
minority  interest in the Company,  and (ii) determined by a certified  business
appraiser,  selected  by the  Company,  that is a member of either the  American
Society of Appraisers or the Institute of Business  Appraisers;  but if a Member
or Prime  disagrees  with such  determination  that  Member or Prime may, at its
expense,  have another certified  business  appraiser that is a member of one or
both of the above named professional  organizations  determine the value, and if
the two appraisers cannot agree upon a value, they shall mutually select a third
certified  business  appraiser  (that  meets  the  above  described   membership
requirements) who shall,  together with the first two appraisers,  determine the
value of the  Membership  Interest by majority  vote.  The expense of such third
appraiser  shall  also be paid by the  Member or Prime,  as the case may be, who
disagrees  with the value  determination  of the Company's  original  appraiser,
unless the appraised value ultimately  determined is more than ten percent (10%)
greater than the value determined by the Company's original appraiser.

4.3          CERTAIN DEFINITIONS.

             As used herein,  the term "Valuation  Date" shall mean and refer to
the end of the fiscal year of the Company  immediately  preceding  the  Exercise
Event,  unless the purchasing party elects to use the alternate  valuation date,
in which  event the  Valuation  Date  shall be the end of the month  immediately
preceding the Exercise  Event. As used herein,  the term "Exercise  Event" shall
mean and refer to the event or  circumstance  described  in  ARTICLE  II of this
Agreement, as a result of which the Company, a Member, or Prime, as the case may
be in the first  instance,  becomes  entitled  to  exercise  a  purchase  option
hereunder.

                                    ARTICLE V

                          PAYMENT OF THE PURCHASE PRICE

5.1          PAYMENT.

             Except as otherwise  provided in this Agreement,  including Section
2.1, the purchase price for a Membership Interest to be purchased from a selling
party shall either: (i) be paid in cash; or (ii) at the option of the purchasing
party,  up to seventy  percent (70%) of the purchase  price may be deferred with
the remainder paid in cash at the closing.

5.2          PROMISSORY NOTE.

             If the purchasing  party elects to defer part of the purchase price
by the execution and delivery of a promissory  note, the deferred portion of the
price shall be evidenced by the promissory  note of the purchasing  party to the
order of the selling party payable in sixty (60) equal monthly  installments  of
principal  and interest on or before the first day of each month  beginning  the
month next following the date of closing. The interest rate for such installment
promissory  note shall be equal to the prime or base rate on corporate  loans at
large U.S.  money center  commercial  banks as  published  in the "Money  Rates"
column of the Wall  Street  Journal  on the date of  exercise  of the  option to
purchase  (or, if such option is not  exercised  on a date on which such rate is
published, the next following date on which such rate is published). In no event
shall the interest rate exceed the maximum legal  interest rate then  prevailing
for such obligations in the state of Texas. The note shall be secured by a first
lien security interest in the Membership Interest transferred and the purchasing
party shall  deliver  certificates  evidencing  the  Membership  Interest to the
selling party and take such further action as is reasonably necessary to perfect
the security interest.

                                   ARTICLE VI

                                   THE CLOSING

             Unless otherwise agreed by the parties, the closing of the sale and
purchase of a Membership  Interest shall take place at the principal  offices of
the Company within sixty (60) days after the exercise of any option  provided by
this Agreement.  Each party hereto  (including the spouses of the Members) shall
bear its own transaction  costs,  including  legal and accounting  fees, if any,
attributable to any transfer of a Membership Interest,  or any interest therein,
pursuant to this  Agreement.  Upon the closing,  the selling party shall deliver
its  Membership  Interest  to the  purchaser  free and  clear of all  liens  and
encumbrances,  and shall deliver to the Company its  resignation and that of all
of its nominees, if any, as officers and directors of the Company and any of the
Company's subsidiaries.  The selling party shall deliver to the purchasing party
at closing, all appropriate documents of transfer,  including without limitation
bills of sale, assignments or other instruments of conveyance. As a condition to
any closing of the sale and purchase of a  Membership  Interest (or any interest
therein) pursuant to this Agreement:  (i) the selling party shall be indemnified
by the purchasing party (in a form reasonably satisfactory to the selling party)
for all the Company's liabilities,  whether fixed or contingent,  to lenders and
others,  incurred prior to the closing of the  transaction,  (ii) the purchasing
party and/or the Company  shall cause the release of any personal  guaranties by
the  selling  party that the  selling  party may have  granted to the  Company's
lenders or other  creditors  or which may have  otherwise  been  provided by the
selling party for the benefit of the Company,  and (iii) if the selling party is
a creditor of the Company, the purchasing party shall unconditionally  guarantee
the debt of the Company to the  selling  party and execute  such  documents  and
instruments   of  guarantee  as  may  be  necessary  in  connection   therewith.
Furthermore,  and as a condition to closing, in the event the selling party owes
any amounts to the Company at the time of closing,  such  indebtedness  shall be
paid in full by the selling party at or prior to the closing, or may be deducted
from and offset  against the  purchase  price by the  purchasing  party,  in the
purchasing  party's  sole  discretion.  In the event of a failure  to close as a
result of the  non-satisfaction  of the  conditions to closing set forth herein,
this  Agreement  shall  remain  in full  force  and  effect  and all  Membership
Interests  shall remain  subject to the  restrictions  contained  herein and, in
addition,  the parties hereto shall be entitled to such other remedies as may be
available in the event the failure to close constitutes a breach hereof.

                                   ARTICLE VII

                             LEGEND ON CERTIFICATES

             All Membership  Interests now or hereafter owned by the Members, or
their  permitted  transferees,  shall  be  subject  to the  provisions  of  this
Agreement,  and any  certificates  representing  same shall  bear the  following
legend:

             "THE  MEMBERSHIP   INTEREST   REPRESENTED   HEREBY  AND  THE  SALE,
             ASSIGNMENT,  TRANSFER,  PLEDGE  OR OTHER  DISPOSITION  THEREOF  ARE
             SUBJECT TO CERTAIN RESTRICTIONS  CONTAINED IN A MEMBERSHIP INTEREST
             TRANSFER  RESTRICTION  AGREEMENT  AMONG THE  COMPANY AND THE WITHIN
             NAMED MEMBER, AND ANY AMENDMENT  THERETO.  THE AGREEMENT LIMITS THE
             USE OF THIS MEMBERSHIP  INTEREST AS COLLATERAL FOR ANY LOAN WHETHER
             BY PLEDGE,  HYPOTHECATION  OR OTHERWISE.  A COPY OF THE  MEMBERSHIP
             INTERES   TRANSFER   RESTRICTION   AGREEMENT  AND  ALL   APPLICABLE
             AMENDMENTS  THERETO  WILL BE FURNISHED BY THE COMPANY TO THE HOLDER
             HEREOF  WITHOUT  CHARGE UPON WRITTEN  REQUEST TO THE COMPANY AT ITS
             PRINCIPAL PLACE OF BUSINESS OR REGISTERED OFFICE."

                                  ARTICLE VIII

                            TERMINATION OF AGREEMENT

             This Agreement and all restrictions on Membership Interest transfer
created hereby shall terminate on the occurrence of any of the following events:

             (a)             The bankruptcy or dissolution of the Company.

     (b) The ownership by one person of all of the  Membership  Interests of the
Company which are then subject to this Agreement.

             (c) The execution of a written  instrument  by the Company,  all of
the Members who then own Membership  Interests  subject to this  Agreement,  and
Prime which terminates the same.

     (d) The date  twenty-one (21) years after the death of the last survivor of
all individuals who are parties to this Agreement.

                                   ARTICLE IX

                               GENERAL PROVISIONS

9.1          REMEDIES FOR BREACH.

             The  Membership  Interests are unique  chattels,  and each party to
this Agreement shall have the remedies which are available to him, her or it for
the violation of any of the terms of this Agreement,  including, but not limited
to, the equitable remedy of specific performance.

9.2          BINDING EFFECT.

             This  Agreement  is binding  upon and inures to the  benefit of the
Company,  its  successors  and  permitted  assigns,  to the  Members  and  their
respective heirs,  personal  representatives,  successors and permitted assigns,
and to Prime,  its successors and permitted  assigns.  This Agreement may not be
assigned,  in whole or in part, by any party hereto without the express  written
consent of all parties hereto.

9.3          PRIOR AGREEMENTS.

             This  Agreement  supersedes  all prior written and oral  agreements
between the parties regarding the subject matter hereof.

9.4          GOVERNING LAWS.

             This Agreement is executed under,  and in conformity with, the laws
of the State of Texas and shall be governed  thereby.  If any  provision of this
Agreement  shall be determined to be invalid or  unenforceable  or prohibited by
the laws of the State of Texas, this Agreement shall be considered  divisible as
to such provisions and such  provisions  shall be inoperative and shall not be a
part of the consideration  moving from any party to another party. The remaining
provisions  shall be valid and binding upon the parties and be of like effect as
though such invalid,  unenforceable  or prohibited  provisions were not included
herein.

9.5          AMENDMENT.

             This  Agreement  may be  amended  in whole  or in part  only by the
written consent of all the parties.  Such amendment shall be effective as of the
date then  determined by the parties and shall  supersede any provisions  herein
contained which are in conflict.

9.6          CAPTIONS AND GENDER.

             The captions and titles herein are for convenience only and are not
intended to include or  conclusively  define the subject matter of the text. All
pronouns and  references  thereto shall refer to the  masculine,  feminine,  and
neuter  genders,  singular  or plural,  as the  identification  of the  persons,
entities, and companies may require. The term "person" as used in this Agreement
shall include natural persons, companies,  partnerships, trusts, estates and any
other form of entity.

9.7          NOTICES.

             All notices  required to be given  hereunder  shall be deemed to be
duly given by  personally  delivering  such notice or by mailing it by certified
mail, to the Company,  to the Members,  and to Prime at the following  addresses
(which  may be  changed  by giving  written  notice of such  change to all other
parties hereto):

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

             To Barnet:      Ronald W. Barnet, M.D.
                             4800 North 22nd Street
                             Phoenix, Arizona 85016

             To Dulaney:     David D. Dulaney, M.D.
                             4800 North 22nd Street
                             Phoenix, Arizona 85016

             To Rosenberg:   Mark Rosenberg
                             4800 North 22nd Street
                             Phoenix, Arizona 85016

             To Perkins:     Scott A. Perkins, M.D.
                             4800 North 22nd Street
                             Phoenix, Arizona 85016

             To Pinkert:     Robert B. Pinkert, O.D.
                             4800 North 22nd Street
                             Phoenix, Arizona 85016

             To Prime:        Prime Medical Operations, Inc.
                              Attention: President
                              1301 Capital of Texas Highway
                              Austin, Texas 78746

9.8  BINDING EFFECT OF THIS AGREEMENT ON ADDITIONAL MEMBERSHIP INTEREST ACQUIRED
     BY A MEMBER.

             In the event a Member acquires,  contracts to acquire,  or receives
any Membership  Interests of the Company which are not subject to this Agreement
at the time of acquisition,  such additional  Membership Interests of the Member
shall  be   automatically   subject  to  this  Agreement  and  any  certificates
representing  such Membership  Interests shall bear the legend prescribed herein
and this Agreement shall be amended, if necessary, to reflect the acquisition of
such Membership Interests by the Member.

9.9          EXECUTION OF DOCUMENTS.

             Whenever Membership Interests are to be purchased by the Company, a
Member, or Prime pursuant to this Agreement,  the transferor shall do all things
and execute and deliver all documents and make all transfers as may be necessary
to consummate such purchase.  In the event that the transferor  refuses to abide
by the terms and  conditions  specified  herein,  the  purchaser(s)  may  tender
payment  for such  Membership  Interest by mailing  payment to the  transferor's
attention  at the  address  of the  Company's  registered  office on file at the
office of the Texas Secretary of State.  After payment is tendered  accordingly,
the Company shall be entitled to cancel such  Membership  Interest on its books,
and reissue such Membership Interest to the purchaser(s) or, if the purchaser is
the Company,  the Company may hold such Membership Interest as treasury stock or
cancel such Membership Interest.

9.10         ACTIONS BY THE COMPANY.

             Any decision by the Company to exercise any purchase  option,  give
any notice or otherwise enforce any provisions of this Agreement,  shall be made
by a majority  vote of Members who are not then in breach of this  Agreement and
whose Membership Interests are not then the subject of any option or requirement
of notice of an Exercise Event.

                            [Signature pages follow]


<PAGE>


S-2

                                SIGNATURE PAGE TO

                               MEMBERSHIP INTEREST

                         TRANSFER RESTRICTION AGREEMENT

             EXECUTED as of the date first mentioned above.

             COMPANY:                        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

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

                                                 Ronald W. Barnet, M.D.


             DULANEY:                           /s/ David D. Dulaney, M.D.

                                                 David D. Dulaney, M.D.

             ROSENBERG:                         /s/ Mark Rosenberg

                                                 Mark Rosenberg

             Perkins:                           /s/ Scott A. Perkins, M.D.

                                                 Scott A. Perkins, M.D.


             Pinkert:                           /s/ Robert B. Pinkert, O.D.

                                                 Robert B. Pinkert, O.D.


             PRIME:                              Prime Medical Operating, Inc.

                                             By: /s/ Cheryl Williams
                                                 Printed Name:  Cheryl Williams
                                                 Title:  Treasurer



<PAGE>


                                SPOUSAL CONSENTS

             The  undersigned   spouse  of  Ronald  W.  Barnet,   M.D.  hereunto
subscribes her name in evidence of her agreement and consent to the  disposition
made of any interest she may have,  including any community property  interests,
in the  membership  interest  of LASIK  Investors,  L.L.C.,  referred  to in the
foregoing Agreement, and to all other provisions of such Agreement.

                                       Signature: /s/ Teri Barnet
                                       Printed Name: Teri Barnet

             The  undersigned   spouse  of  David  D.  Dulaney,   M.D.  hereunto
subscribes her name in evidence of her agreement and consent to the  disposition
made of any interest she may have,  including any community property  interests,
in the  membership  interest  of LASIK  Investors,  L.L.C.,  referred  to in the
foregoing Agreement, and to all other provisions of such Agreement.

                                       Signature: /s/ Anna Maria Dulaney
                                       Printed Name: Anna Maria Dulaney

             The undersigned  spouse of Mark Rosenberg  hereunto  subscribes her
name in evidence of her  agreement  and consent to the  disposition  made of any
interest  she may have,  including  any  community  property  interests,  in the
membership  interest of LASIK  Investors,  L.L.C.,  referred to in the foregoing
Agreement, and to all other provisions of such Agreement.

                                       Signature: /s/ J. Rosenberg
                                       Printed Name: J. Rosenberg

             The  undersigned   spouse  of  Scott  A.  Perkins,   M.D.  hereunto
subscribes her name in evidence of her agreement and consent to the  disposition
made of any interest she may have,  including any community property  interests,
in the  membership  interest  of LASIK  Investors,  L.L.C.,  referred  to in the
foregoing Agreement, and to all other provisions of such Agreement.

                                       Signature: /s/ Lourdes S. Perkins
                                       Printed Name: Lourdes S. Perkins

             The  undersigned  spouse  of  Robert  B.  Pinkert,   O.D.  hereunto
subscribes her name in evidence of her agreement and consent to the  disposition
made of any interest she may have,  including any community property  interests,
in the  membership  interest  of LASIK  Investors,  L.L.C.,  referred  to in the
foregoing Agreement, and to all other provisions of such Agreement.

                                       Signature: /s/ Jodi C. Pinkert
                                       Printed Name: Jodi C. Pinkert