<PAGE>   1
                                                                    Exhibit 4.36


                               September 29, 2000



Vision Twenty-One, Inc.
7360 Bryan Dairy Road, Suite 200
Largo, FL 33777

Attention: Bruce Maller, Chairman of the Board

Gentlemen:

         We refer to the Amended and Restated Credit Agreement dated as of July
1, 1998, as amended, between you and us (the "Credit Agreement"). All
capitalized terms used herein without definition shall have the same meaning
herein as such terms are defined in the Credit Agreement.

         The Borrower has advised the Banks that the Borrower is currently
working on a revised business plan which will include, among other things, a
request to restructure the Obligations owing to the Banks on terms and
conditions mutually agreed upon by the Borrower and the Banks. While the
Borrower and the Banks have initiated discussions concerning the proposed
restructuring of the Obligations, the Borrower acknowledges that the Banks have
not agreed to any terms and conditions relating to any restructuring of the
Obligations. In the meantime, however, the Borrower intends to continue to sell
the remaining physician practice management groups operated by the Borrower and
its Subsidiaries (collectively being referred to herein as the "PPM
Businesses") and use a portion of the proceeds from the sale of the PPM
Businesses to meet its reasonable and necessary operating expenses.

         To afford the Borrower an opportunity to proceed with the transactions
described above, the Borrower has requested that (i) the Banks extend the
temporary waiver period provided for in Sections 2.1 and 2.2 of that certain
Seventh Amendment and Waiver to Credit Agreement dated as of December 10, 1999,
among the Borrower, the Banks, and the Agent (the "Seventh Amendment") (as
further amended, in part, by a December 30, 1999, letter agreement, a February
29, 2000, letter agreement, a March 24, 2000, letter agreement, an April 14,
2000, letter agreement, a May 5, 2000, letter agreement, a May 19, 2000, letter
agreement, a June 1, 2000, letter agreement, a June 9, 2000, letter agreement,
a June 16, 2000, letter agreement, a June 29, 2000, letter agreement, a July
21, 2000, letter agreement, an August 11, 2000, letter agreement, and a
September 8, 2000, letter agreement, in each case between the Borrower, the
Banks and the Agent) and, in addition, that the Banks temporarily waive any
non-compliance by the Borrower as of December 31, 1999, as of March 31, 2000,
as of June 30, 2000, and as of September 30, 2000, with Sections 8.8 (Total
Funded Debt/Adjusted EBITDA Ratio), 8.10 (Interest Coverage Ratio), and 8.11
(Debt Service Coverage Ratio) of the Credit Agreement and the Borrower's
non-compliance with Section 8.5(b) of the Credit Agreement with respect to the
timely delivery



<PAGE>   2

Vision Twenty-One, Inc.
September 29, 2000
Page 2




of the Borrower's March 31, 2000, financial statements, in each case to October
13, 2000 (the "Waiver Termination Date"), (ii) Bank of Montreal extend the
Bridge Loan Period from September 29, 2000, to the Waiver Termination Date, and
(iii) amend the due date for the payment of principal, interest and unused
commitment fees otherwise due on or before September 30, 2000, with respect to
the Revolving Credit and the Term Loans (including such payments described in
Sections 2.1 and 2.2 of the Seventh Amendment) to the Waiver Termination Date.
By signing below, the Banks (including Bank of Montreal with respect to the
Bridge Loan Commitment) hereby agree to extend the waiver period provided in
Sections 2.1 and 2.2 of the Seventh Amendment from September 29, 2000, to the
Waiver Termination Date, temporarily waive any non-compliance by the Borrower
as of December 31, 1999, as of March 31, 2000, as of June 30, 2000, and as of
September 30, 2000, with Sections 8.8 (Total Funded Debt/Adjusted EBITDA
Ratio), 8.10 (Interest Coverage Ratio), and 8.11 (Debt Service Coverage Ratio)
of the Credit Agreement and the Borrower's non-compliance with Section 8.5(b)
of the Credit Agreement with respect to the timely delivery of the Borrower's
March 31, 2000, financial statements through the period ending on the Waiver
Termination Date, agree to extend the Bridge Loan Period to the Waiver
Termination Date, and agree to amend the due date for the payment of principal,
interest, and unused commitment fees otherwise due on or before September 30,
2000, with respect to the Revolving Credit and the Term Loans (including such
payments described in Sections 2.1 and 2.2 of the Seventh Amendment) to the
Waiver Termination Date, provided that:

                  (a)      until the Obligations are paid in full, the Borrower
         shall provide to the Banks a weekly Budget pursuant to Section 1.14(f)
         of the Credit Agreement and such Budget shall be subject to the
         Approved Budget and reconciliation procedures set forth therein,
         regardless of whether or not then being accompanied by a request for a
         Borrowing of Bridge Loans;

                  (b)      at all times on and after the date hereof (i) all
         proceeds from the sale of any assets of the Borrower and its
         Subsidiaries (including, without limitation, proceeds from the sale of
         the PPM Businesses or any part thereof), and (ii) cash receipts
         arising from the operation of the business of the Borrower and its
         Subsidiaries not applied pursuant to an Approved Budget, shall in each
         case be remitted promptly upon receipt to the Agent; and

                  (c)      except to the extent applied to payments pursuant to
         an Approved Budget or applied to the Obligations owing to the Banks,
         proceeds received pursuant to clause (c) above shall be held by the
         Agent as collateral for the remaining Obligations owing to the Banks
         (the Agent hereby being granted a Lien on and right of set-off for the
         benefit of the Banks against all such amounts so held).


<PAGE>   3

Vision Twenty-One, Inc.
September 29, 2000
Page 3




The Borrower hereby acknowledges and agrees to the foregoing conditions. The
Borrower also hereby acknowledges and agrees that (i) any restructuring of the
terms and conditions relating to the Obligations shall be subject to the Banks'
consent, which may be given or withheld in their discretion and (ii) any sale
of the Borrower's or its Subsidiaries' assets or businesses shall be subject to
the prior written consent of the Banks, and all proceeds from any such sale
represent proceeds of the Banks' Collateral, to be held by the Agent or applied
to the Obligations pursuant to the terms of the Credit Agreement as modified
hereby.

         Except as specifically modified hereby, all of the terms and
conditions of the Credit Agreement and the other Loan Documents shall stand and
remain unchanged and in full force and effect. This waiver shall become
effective upon the execution and delivery hereof by each of the Banks and the
Borrower as set forth below. This waiver may be executed in counterparts and by
different parties on separate counterpart signature pages, each of which shall
be an original and all of which taken together shall constitute one and the
same instrument. This waiver shall be governed by, and construed in accordance
with, the laws of the State of Illinois.



                          [SIGNATURE PAGES TO FOLLOW]



<PAGE>   4
Vision Twenty-One, Inc.
September 29, 2000
Page 4



         This waiver letter is entered into by and among the parties hereto as
of the date first above written.


BANK OF MONTREAL, in its individual           BANK ONE TEXAS, N.A.
capacity as a Bank and as Agent


By: /s/ Jack J. Kane                        By: /s/ Ronnie Kaplan
   -------------------------------             -------------------------------
Name:   Jack J. Kane                        Name:   Ronnie Kaplan
      ----------------------------                ----------------------------
Title:  Director                            Title:  Vice President
      ----------------------------                ----------------------------

PACIFICA PARTNERS I, L.P.                   PILGRIM PRIME RATE TRUST

By: Imperial Credit Asset Management,       By: Pilgrim Investments, Inc.,
    as its Investment Manager                   as its Investment Manager


By: /s/ Dean K. Kawai                       By: /s/ Charles E. LeMieux
   -------------------------------             -------------------------------
Name:   Dean K. Kawai                       Name:   Charles E. LeMieux, CFA
      ----------------------------                ----------------------------
Title:  Vice President                      Title:  Vice President
      ----------------------------                ----------------------------


PILGRIM AMERICA HIGH INCOME                 MERRILL LYNCH BUSINESS
INVESTMENTS LTD.                            FINANCIAL SERVICES, INC.

By: Pilgrim Investments, Inc.,              By: /s/ T. G. Kopczynski
    as its Investment Manager                  -------------------------------
                                            Name:   T. G. Kopczynski
By: /s/ Charles E. LeMieux                       -----------------------------
   -------------------------------          Title:  Vice President
Name:   Charles E. LeMieux, CFA                   ----------------------------
      ----------------------------
Title:  Vice President
      ----------------------------




Acknowledged and agreed to as of the date first above written.

                                              VISION TWENTY-ONE, INC.


                                              By: /s/ Bruce Maller
                                                 ------------------------------
                                              Name:   Bruce Maller
                                                   ----------------------------
                                              Title:  Chairman
                                                    ---------------------------