Document:

<PAGE>   1

                                                                    EXHIBIT 4.28

                                  May 19, 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 has entered into
an Agreement and Plan of Merger and Reorganization, dated as of February 10,
2000 (the "Merger Agreement"), among the Borrower, Opticare Health Systems, Inc.
(the "Parent"), and OC Acquisition Corp., a wholly-owned subsidiary of the
Parent ("Merger Sub"), pursuant to which the parties intend to merge Merger Sub
with and into the Borrower subject to the terms and conditions thereof which
include, among other things, restructuring 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 and due diligence
concerning the Merger and any proposed restructuring of the Obligations, the
Borrower acknowledges that the Banks have not consented to the Merger nor have
the Banks 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, and an April 14,
2000, letter agreement, and a May 5, 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,
and as of March 31, 2000, with Sections 8.8 (Total

<PAGE>   2

Vision Twenty-One, Inc.
May 19, 2000
Page 2

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, in each
case to the earlier of June 2, 2000, or the termination of the Merger Agreement
pursuant to its terms (the earlier of such dates being referred to herein as the
"Waiver Termination Date"), (ii) Bank of Montreal extend the Bridge Loan Period
from May 19, 2000, to the Waiver Termination Date, and (iii) postpone the due
date for the payment of principal, interest and unused commitment fees otherwise
due on or before May 19, 2000, 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 May 19, 2000, to the Waiver Termination
Date, temporarily waive any non-compliance by the Borrower as of December 31,
1999, and March 31, 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 postpone the due date for the payment of
principal, interest, and unused commitment fees otherwise due on or before May
19, 2000, to the Waiver Termination Date, provided that:

                  (a)      the Borrower agrees to promptly provide to the Banks
         copies of any instruments and documents entered into or proposed to be
         entered into in connection with the Merger (including, without
         limitation, any executed shareholder lock-up agreements) and to
         promptly advise the Banks of any termination, amendment, or waiver of
         the Merger Agreement or of any material breach thereof by any party
         thereto, in each case subject to its directors' fiduciary duties;

                  (b)      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;

                  (c)      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

<PAGE>   3

Vision Twenty-One, Inc.
May 19, 2000
Page 3

                  (d)      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).

The Borrower hereby acknowledges and agrees to the foregoing conditions. The
Borrower also hereby acknowledges and agrees that (i) the consummation of the
Merger and of any restructuring of the terms and conditions relating to the
Obligations shall in each case 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.
May 19, 2000
Page 4

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

<TABLE>
<CAPTION>

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

<S>                                                   <C>
                                                      By: /s/ Ronnie Kaplan
By: /s/ Jack J. Kane                                      Name:  Ronnie Kaplan
    Name:  Jack J. Kane                                   Title: Vice President
    Title: Director

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

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

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

By:     Pilgrim Investments, Inc., as its
        Investment Manager                           By:  /s/ Gary L. Stewart
                                                          Name:  Gary L. Stewart
                                                          Title: Vice President
By: /s/ Charles E. LeMieux
    Name:  Charles E. LeMieux, CFA
    Title: Assistant Vice President
</TABLE>

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

                                                      VISION TWENTY-ONE, INC.

                                                      By: /s/ Bruce Maller
                                                          Name:  Bruce Maller
                                                          Title: Chairman<PAGE>   1

                                                                    EXHIBIT 4.29

                                  June 1, 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 has entered into
an Agreement and Plan of Merger and Reorganization, dated as of February 10,
2000 (the "Merger Agreement"), among the Borrower, Opticare Health Systems, Inc.
(the "Parent"), and OC Acquisition Corp., a wholly-owned subsidiary of the
Parent ("Merger Sub"), pursuant to which the parties intend to merge Merger Sub
with and into the Borrower subject to the terms and conditions thereof which
include, among other things, restructuring 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 and due diligence
concerning the Merger and any proposed restructuring of the Obligations, the
Borrower acknowledges that the Banks have not consented to the Merger nor have
the Banks 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, and a May 19, 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, and as of March 31, 2000,

<PAGE>   2

Vision Twenty-One, Inc.
June 1, 2000
Page 2

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, in each case to the earlier of June 9, 2000, or the termination of
the Merger Agreement pursuant to its terms (the earlier of such dates being
referred to herein as the "Waiver Termination Date"), (ii) Bank of Montreal
extend the Bridge Loan Period from June 2, 2000, to the Waiver Termination Date,
and (iii) postpone the due date for the payment of principal, interest and
unused commitment fees otherwise due on or before June 2, 2000, 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 June 2, 2000, to
the Waiver Termination Date, temporarily waive any non-compliance by the
Borrower as of December 31, 1999, and March 31, 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 postpone the due date
for the payment of principal, interest, and unused commitment fees otherwise due
on or before June 2, 2000, to the Waiver Termination Date, provided that:

                  (a)      the Borrower agrees to promptly provide to the Banks
         copies of any instruments and documents entered into or proposed to be
         entered into in connection with the Merger (including, without
         limitation, any executed shareholder lock-up agreements) and to
         promptly advise the Banks of any termination, amendment, or waiver of
         the Merger Agreement or of any material breach thereof by any party
         thereto, in each case subject to its directors' fiduciary duties;

                  (b)      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;

                  (c)      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

<PAGE>   3

Vision Twenty-One, Inc.
June 1, 2000
Page 3

                  (d)      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).

The Borrower hereby acknowledges and agrees to the foregoing conditions. The
Borrower also hereby acknowledges and agrees that (i) the consummation of the
Merger and of any restructuring of the terms and conditions relating to the
Obligations shall in each case 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.
June 1, 2000
Page 4

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

<TABLE>
<CAPTION>

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

<S>                                                   <C>
                                                      By: /s/ Ronnie Kaplan
By: /s/ Jack J. Kane                                      Name:  Ronnie Kaplan
     Name:  Jack J. Kane                                  Title: Vice President
     Title: Director

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

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

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

By:      Pilgrim Investments, Inc., as its
         Investment Manager                           By: /s/ Gary L. Stewart
                                                          Name:  Gary L. Stewart
                                                          Title: Vice President

By: /s/ Charles E. LeMieux
     Name:  Charles E. LeMieux, CFA
     Title: Assistant Vice President
</TABLE>

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

                                                      VISION TWENTY-ONE, INC.

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

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