<PAGE>   1
                                                                   Exhibit 10.79

                                         Nightingale & Associates, LLC
                                         Soundview Plaza
                                         1266 East Main Street
                                         Stamford, Connecticut 06902

                                         Tel: 203.359.3855
                                         Fax: 203.359.4551
                                         Email: info@nightingale-associates.org

                                         Principals:
                                         Stephen J. Hopkins
                                         Michael R. D'Appolonia
                                         Kevin I. Dowd
                                         Dennis J. Duckett
                                         Howard S. Hoffmann
                                         S. Douglas Hopkins
November 24, 1999
                                         Senior Advisors:
                                         William J. Nightingale
                                         Tor B. Arneberg

Mr. Theodore N. Gillette
Chief Executive Officer
Vision Twenty-One Inc.
7360 Bryan Dairy Road
Largo, FL 33777

Dear Ted:

         Pursuant to various discussions, Nightingale & Associates, LLC ("N&A")
understands that the Board of Directors of Vision Twenty-One Inc. ("Vision21" or
the "Company), with the approval of the Company's secured lenders, desires to
retain N&A to assume the role of interim CFO with full responsibility for
financial oversight and reporting. The following represents in more specific
terms our understanding of the scope of such an engagement and the terms under
which we would propose to assume such responsibilities.

I.       SCOPE

         N&A will immediately assign Howard S. Hoffmann to assume the position
         of interim CFO, reporting directly to the Board of Directors of the
         Company.

         Working closely in conjunction with you, Bruce Maller and other
         Vision21 senior managers and staff, N&A's responsibilities will
         include:

         1.       Manage The Implementation Of Cash Flow Forecasting And Control
                  Procedures And The Development Of Improved Financial And
                  Management Reporting.

         2.       Review And To The Extent Necessary Refine The Detailed
                  Operating Plans For Fiscal 2000.

         3.       Support And Actively Participate In Due Diligence And Deal
                  Negotiations With Potential Providers Of Long Term Capital
                  And/Or Potential Buyers Of The Company

                  a.       Develop Contingency Plan In The Event That Sufficient
                           Long Term Capital Cannot

                                                     Finding Solutions to
                                                     Complex Business Situations
                                                     Since 1975




<PAGE>   2

Mr. Theodore N. Gillette
Vision Twenty-One Inc.
November 24, 1999
Page 2

                           Be Raised Or Sale Transaction Consummated In The Time
                           Frame Available

         4.       Assist With The Implementation Of The Exit From The PPM
                  Business

         5.       Oversee Financial Statement Preparation And Other
                  Financially-Based Reporting Requirements.

         6.       Assume Management Supervision Over The MIS Department. This
                  Will Be In Addition To the Usual Managerial Duties Associated
                  with the CFO Position

         7.       If Necessary And When Appropriate, Assist In The Recruitment
                  Of A Permanent CFO.

         8.       Provide Such Other Counsel, Assistance, And Services As ISC
                  May From Time To Time Request.

II.      DISCUSSION

         It would not be our intention to prepare extensive and detailed written
         reports because such reports are both time consuming and costly to
         prepare. Rather, we would submit a highly summarized bullet-point
         narrative highlight report, supported by factual or pro forma exhibits,
         covering preliminary findings, conclusions, and recommendations,
         including recommended next steps, augmented by extensive verbal
         dialogue and discussion.

         N&A approaches all assignments such as the one under discussion as a
         team effort with the management and employees of the Company involved.
         It would be our intention and practice to utilize Company management
         and employees to undertake fact finding and analysis on our mutual
         behalf to the greatest extent possible.

         In addition, we would utilize work done by the Company or its
         professionals and other consultants, to the extent it may be available,
         in order to avoid or minimize duplication of work. As noted above, with
         the cooperation of the Company's bank lenders, we would also work with
         the banks' professionals with the same objective.

III.     RESPONSIBILITY AND STAFFING FOR THE WORK

         Howard S. Hoffmann will be the Officer-In-Charge of this assignment
         with overall responsibility for the N&A work on the engagement. Michael
         R. D'Appolonia will provide oversight and senior guidance as needed.
         Due to the accelerated, crisis nature of the project and the present
         lack of information regarding the availability and/or capability of
         Company personnel to assist with completion of various urgent tasks, it
         may be necessary to utilize the services of additional N&A Associates
         on the project. N&A agrees that it confer with the Company before
         adding additional Associates to the project team.




<PAGE>   3

Mr. Theodore N. Gillette
Vision Twenty-One Inc.
November 24, 1999
Page 3

IV.      ESTIMATE OF TIME AND COST

         In a highly fluid situation such as is the case with Vision21, it is
         difficult to provide a definitive estimate of time and cost. However,
         assuming staffing of the project as indicated below, and that each N&A
         staff member devotes the time ranges shown below, we estimate N&A
         professional time fees will range from $62,000 to $86,000 per month. It
         is N&A's intention to utilize as much as possible information and
         analyses previously generated, and every effort will be made to avoid
         duplication of work.

<TABLE>
<CAPTION>

                               TIME ESTIMATE - PER MONTH
-------------------------------------------------------------------------------------
                                    Hourly Billing        Est. Time         Est. Work
N&A Staff Members                        Rates                %                Days
-----------------                   --------------       -----------        ---------
<S>                                 <C>                  <C>                <C>
H. S. Hoffmann                           $325            80% - 100%          16 - 22

M. R. D'Appolonia                        $350            80% - 100%           0 - ??

Associate                                $225              0% - ??%           0 - ??
</TABLE>

         In addition to professional time fees, out-of-pocket expenses are
         billed at cost, and generally range from 10% to 20% of professional
         time fees, depending on the amount of travel involved. Out-of-pocket
         expenses consist primarily of travel and transportation, meals,
         lodging, telephone, specifically assignable office assistance and
         report production.

         Invoices are submitted weekly, and are due and payable upon
         presentation. Prompt payment of N&A invoices is a prerequisite for
         N&A's continued work on an engagement.

         Exhibit I, attached, is a summary of N&A professional time billing
         rates, and terms and conditions for engagement of our firm, and is an
         integral part of this Engagement Letter.

         N&A fully understands that the Company desire to keep costs to a
         minimum, commensurate with achieving the objectives of the assignment
         and given a reasonable degree of comfort relative to the judgments,
         conclusions, and recommendations involved. You should know that the
         above cost estimate is just that, an estimate, and is not a guaranteed
         firm professional time fee cost. Every effort will be made to keep
         costs to a minimum. The work will be accomplished in less time and at
         less cost than estimated if it is feasible to do so. Conversely, if
         circumstances dictate that additional N&A staff is required, or that
         more time than estimated above is required, the cost estimate could be
         exceeded. We will advise you as far in advance as possible should we
         perceive that such a situation could occur.








<PAGE>   4

Mr. Theodore N. Gillette
Vision Twenty-One Inc.
November 24, 1999
Page 4

VI.      ADVANCE DEPOSIT

         N&A requires an Advance Deposit for all assignments of the type
         described above. Given this situation, N&A requires an Advance Deposit
         of $50,000 which must be paid simultaneously with beginning project
         work. At the completion of the project and at the direction of the
         Company, N&A will either apply the Deposit to any outstanding invoices
         or, if there are no unpaid invoices owing to N&A, promptly return the
         Deposit to the Company.

VII.     PERFORMANCE FEES

         For information, N&A charges a Performance Fee, in addition to
         professional time fees, for selected types of assignments. Assignments
         where performance fees are charged include acquisitions, divestitures,
         mergers, refinancing, interim management, and asset recovery
         management.

         Based on past practices and policies of our firm, N&A proposes a
         Performance Fee equal to:

                  A.       Options to purchase 100,000 shares of the common
                           stock of Vision21, at current market values. All of
                           the unvested options issued under this Paragraph A
                           will become fully vested upon the earlier of 1) the
                           completion of a sale transaction involving the
                           entire managed care division, the entire refractive
                           surgery/ASC division or the entire company or the
                           consummation of a capital infusion of at least $25
                           million during the term of the engagement or within
                           60 days following the termination of the engagement,
                           provided such termination occurs on or after January
                           31, 2000 or 2) December 31, 2000.

                  B.       Options to purchase an additional 50,000 shares of
                           the common stock of Vision21, at current market
                           values, if the Company overcomes the immediate
                           liquidity crisis without the utilization of bridge
                           financing from potential buyers of the managed care
                           or refractive surgery units or their affiliates. All
                           of the options issued under this Paragraph B will be
                           fully vested upon issuance.

VIII.    INDEMNIFICATION

         Given the nature of this assignment, N&A will require a release in the
         form of a "Release and Indemnification" agreement from Vision
         Twenty-One Inc. prior to undertaking the project. A copy of the
         "Release and Indemnification" agreement we require is attached as
         Exhibit II.

         The rationale for this requirement is that, to the extent that any
         adversarial issues or proceedings occur between parties, N&A, by its
         very presence and activities, could be caught in the "cross fire." Of
         course, the indemnity excludes gross negligence and/or willful
         misconduct on the part of N&A or any of its officers, associates or
         staff.




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Mr. Theodore N. Gillette
Vision Twenty-One Inc.
November 24, 1999
Page 5

IX.      CONFIDENTIALITY OF CLIENT INFORMATION

         N&A recognizes and acknowledges that the firm and its officers and
         staff have access to proprietary and confidential information in most,
         if not all, client assignments. N&A assures clients that all such
         non-public information received by the firm, its officers, and staff
         from the Company will be held and treated in strict confidence, and
         will not knowingly be disclosed by N&A, its officers, and staff to
         third parties.

CAVEAT

         Given the nature of business turnaround/crisis management and related
         assignments, there can be no assurance that unforeseen problems may not
         be encountered. In addition, it is likely that difficult and complex
         judgments and conclusions will have to be made on a rapid basis without
         full and complete information and analysis readily available.
         Accordingly, N&A undertakes such assignments on a "Best Efforts" basis
         only, and makes no representations, warranties or guarantees relative
         to outcome, performance or results.

                         o o o o o o o o o o o o o o o o



















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Mr. Theodore N. Gillette
Vision Twenty-One Inc.
November 24, 1999
Page 6

         N&A works under an arrangement whereby our services can be terminated
by our clients or by ourselves at any time, upon verbal notice followed by
written confirmation. Of course, the Company will be responsible for
professional time and expense charges up to the time of notice of termination.
Should either party contemplate termination, reasonable advance notice is
desirable in the interest of orderly phase out and completion of work underway.

         N&A will be working on other client assignments during the period we
will be working on this assignment. However, we fully expect to be able to
arrange our schedules so that work on this matter will proceed at a mutually
satisfactory pace.

         If this Engagement Letter conforms to your understanding of the terms
and conditions of our retention, please have the appropriate party signify
agreement by signing and returning the enclosed extra copy of this Engagement
Letter.

         We look forward to working with the Company on this challenging
assignment.


                                                         Sincerely,


                                                         Howard S. Hoffmann


cc: S. J. Hopkins
    M. R. D'Appolonia


READ, UNDERSTOOD AND AGREED TO BY:


Vision Twenty-One Inc.

By: /s/ Theodore Gillette
------------------------------

Title: Chief Executive Officer
------------------------------

Date: 11-26-99
------------------------------




<PAGE>   7

                                    EXHIBIT I


                          NIGHTINGALE & ASSOCIATES, LLC.

                  SUMMARY OF COMPENSATION AND FEE ARRANGEMENTS


I.       PROFESSIONAL TIME FEES AND EXPENSES

         Nightingale & Associates, LLC ("N&A") charges professional time fees on
         an hourly basis for all assignments. Professional time fees on an
         hourly basis for Principals and certain Associates of the firm are as
         shown below:

<TABLE>

         <S>                               <C>         <C>                        <C>
         Mr. Stephen J. Hopkins            $400        Mr. Charles F. Kuoni       $300
         Mr. Michael R. D'Appolonia        $350        Mr. Eugene A. Reilly       $275
         Mr. Howard S. Hoffmann            $325        Mr. Michael C. Yeager      $225
</TABLE>

         Hourly time fees for Associates range from $175 to $350 per hour.

         Out-of-pocket expenses are billed at cost, and generally range from 10%
         to 15% of professional time fees, depending on the amount of travel
         involved. Out-of-pocket expenses consist primarily of transportation
         costs, meals, lodging, telephone, specific client-related office
         assistance and report production and, in the case of divestiture
         related assignments, advertising and mailing costs. Out-of-pocket
         expenses also apply to N&A staff members who reside out of the area
         when working out of N&A's office in Stamford on a client project. For
         assignments undertaken for clients domiciled in the State of
         Connecticut, a 6% professional service tax on professional time fees
         and Performance Fees also applies.

         Invoices are submitted weekly and are due and payable upon
         presentation. Prompt payment of invoices is a prerequisite for N&A's
         continued work on an assignment.

II.      CONTINGENT PERFORMANCE FEES

         For certain types of assignments, including divestitures, interim
         management, asset recovery management, licensing, acquisitions,
         mergers, joint ventures, and refinancing, N&A charges a contingent
         Performance Fee in addition to per diem professional time fees.

         The rationale for the contingent Performance Fee is that N&A can
         usually materially assist a client in the achievement of more favorable
         results and returns than would otherwise be the case. N&A brings unique
         skills and creativity, along with proven and highly successful
         experience, to those transaction and interim management oriented
         assignments where Performance Fees are charged.

         The Performance Fee is based upon the size, circumstances, and
         complexity of each particular situation, and is established and agreed
         to by mutual consent between the client and prior to formal engagement.

                              ********************




<PAGE>   8

                                   EXHIBIT I


III.     OTHER ENGAGEMENT TERMS AND CONDITIONS

         o       N&A works under a policy whereby the services of our firm can
                 be terminated by the client, or by N&A, at any time upon verbal
                 notice, followed by written confirmation.

                  -   The client is responsible for professional time fees and
                      expense charges up to the time of notification of
                      termination. In addition, Performance Fee payments, if
                      applicable, are due and payable on a pro rata basis in the
                      event of unilateral termination by the client.

                  -   Should N&A resign during the course of an assignment, we
                      agree to remain active and provide every reasonable
                      assistance during a designated transition period to phase
                      in, on an orderly basis, a replacement organization of the
                      client's choosing.

         o        Given the nature and complexity of our work, there can be no
                  assurance that unforeseen problems and issues may not be
                  encountered, or that difficult and complex operating judgments
                  and decisions may not have to be made and recommended.
                  Accordingly, N&A undertakes assignments on a "Best Efforts"
                  basis only, and makes no representations, warranties, or
                  guarantees relative to operating results or other performance
                  achieved.

o        For most types of assignments, including Company Viability Evaluations
         for third parties, Interim Management, Operational Turnaround and Asset
         Recovery/Liquidation Management assignments, N&A requires a broad
         Indemnity Agreement from the client or other financially responsible
         party.

                  -   The rationale for requiring an Indemnity Agreement is that
                      by their very nature, Viability Evaluations, Interim
                      Management, Operational Turnaround and Asset Recovery
                      Management assignments require a great many decisions and
                      operating judgments to be made on a day to day basis, and
                      the firm necessarily acts as the Agent or representative
                      of its client. To the extent any real or potential
                      adversarial issues or proceedings are related to the
                      situation N&A, by its very presence, could be caught in
                      the "crossfire."

                         o o o o o o o o o o o o o o o o









<PAGE>   9

                                   EXHIBIT II

                           RELEASE AND INDEMNIFICATION

The undersigned, Vision Twenty-One Inc. (the "Company"), acknowledging that
Nightingale & Associates, LLC ("N&A") has been engaged to render services to the
Company, for and on behalf of itself and its subsidiaries, and the successors
and assigns of the Company and its subsidiaries, hereby waives and releases any
and all claims or causes of action that it may now have or which may arise in
the future against any "Consultant Party" which shall consist of, collectively,
N&A and each of its contractors and subcontractors, and all of the employees,
officers, directors, shareholders and principals of N&A) arising out of or
relating in any way to "Covered Services" (which shall consist of services
rendered by any Consultant Party pursuant to the attached agreement relating to
the Company or any aspect of its business or assets (whether such services
consist of consulting services, management services, or any other type of
services) including, without limitation, any loss or claim thereof arising or
allegedly incurred as a result of actions taken or omitted to be taken by the
Company, its shareholders, or any other party, based in any way upon any
recommendations or suggestions by any Consultant Party relating to the Company
or any aspect of its business or assets, but excluding from the foregoing waiver
and release any claim or cause of action arising out of any act of gross
negligence or willful misconduct of any Consultant Party. The Company further
hereby agrees to indemnify and hold harmless each of the judgments, suits,
costs, expenses and disbursements of any kind or nature whatsoever which may be
imposed upon, incurred by or asserted against any of the Consultant Parties
arising out of or relating in any way to Covered Services pursuant to the
attached agreement including, without limitation, any loss or claim thereof
arising or allegedly incurred as a result of actions taken or omitted to be
taken by the Company, its shareholders, or any other party, based in any way
upon any recommendations or suggestions by any Consultant Party relating to the
Company or any aspect of its business or assets; but excluding from the
foregoing indemnification obligation any matter arising out of any act of gross
negligence or willful misconduct of any Consultant Party.

Dated: November 26, 1999

VISION TWENTY-ONE INC.

By /s/ Theodore Gillette
--------------------------------

Theodore Gillette
--------------------------------
Name

CEO
--------------------------------
Title