Document:

<PAGE>
                                                                     EXHIBIT 4.5

                              [NEXTERA LETTERHEAD]

                                                                  March 29, 2002

Knowledge Universe, Inc.
844 Moraga Drive
Los Angeles, CA  90049
Attention: Stanley E. Maron

Dear Mr. Maron:

        This letter amends the Letter Agreement (the "Agreement"), dated as of
June 29, 2001, that was entered into by and between Nextera Enterprises, Inc., a
Delaware corporation (the "Company"), and Knowledge Universe, Inc. and
affiliates ("KU").

        All terms and provisions of the Agreement remain in full force and
effect, except that the language which provides that "If the Senior Lenders do
not approve such exchange prior to July 1, 2001, KU agrees that the Company's
right and option to exchange the Series A Preferred Stock into subordinated debt
shall be extended until ten (10) business days after the Company's receipt of
written approval from the Senior Lenders of such exchange" shall be deleted in
its entirety and replaced with the following: "If the Senior Lenders do not
approve such exchange prior to July 1, 2001, KU agrees that the Company's right
and option to exchange the Series A Preferred Stock into subordinated debt shall
be extended until no later than June 15, 2002."

        Except as specifically amended hereby, the Agreement shall continue in
full force and effect. Please sign where indicated below to evidence your
acknowledgement and agreement to the foregoing.

               Very truly yours,

               NEXTERA ENTERPRISES, INC.,
               a Delaware corporation

                   /s/ David Schneider
               --------------------------------------------
               By: David Schneider
               Title: President and Chief Executive Officer

               ACKNOWLEDGED AND AGREED

               KNOWLEDGE UNIVERSE, INC.,
               a Delaware corporation

                   /s/ Stanley E. Maron
               --------------------------------------------
               By: Stanley E. Maron
               Title: Secretary<PAGE>

                                                                     EXHIBIT 4.6

                              [NEXTERA LETTERHEAD]

                                                                   June 14, 2002

Knowledge Universe, Inc.
844 Moraga Drive
Los Angeles, CA 90049
Attention:  Stanley E. Maron

Dear Mr. Maron:

        This letter amends the Letter Agreement (the "Agreement") dated as of
June 29, 2001, that was entered into by and between Nextera Enterprises, Inc., a
Delaware corporation (the "Company"), and Knowledge Universe, Inc. and
affiliates ("KU"), which was amended pursuant to that certain letter agreement
between the Company and KU dated March 29, 2002 (the "Amendment").

        All terms and provisions of the Agreement, as amended by the Amendment,
remain in full force and effect, except that the language which provides that
"If the Senior Lenders do not approve such exchange prior to July 1, 2001, KU
agrees that the Company's right and option to exchange the Series A Preferred
Stock into subordinated debt shall be extended until no later than June 15,
2002" shall be deleted in its entirety and replaced with the following: "If the
Senior Lenders do not approve such exchange prior to July 1, 2001, KU agrees
that the Company's right and option to exchange the Series A Preferred Stock
into subordinated debt shall be extended until no later than June 30, 2002;
provided, however, that the June 30, 2002 date shall be extended until July 31,
2002 unless KU gives written notice to the Company by no later than June 27,
2002 of its decision not to extend the period past June 30, 2002."

        Except as specifically amended hereby, the Agreement shall continue in
full force and effect. Please sign where indicated below to evidence your
acknowledgement and agreement to the foregoing.

        Sincerely,

        Nextera Enterprises, Inc., a Delaware corporation

        By:     /s/ David Schneider
            --------------------------------------------
            David Schneider, Its Chief Executive Officer

        ACKNOWLEDGED AND AGREED

        Knowledge Universe, Inc., a Delaware corporation

        By:     /s/ Stanley E. Maron
            --------------------------------------------
            Stanley E. Maron, Its Secretary<PAGE>

                                  EXHIBIT 10.1

                           AMENDMENT NO. 1 AND WAIVER

               AMENDMENT NO. 1 AND WAIVER (this "Amendment"), dated as of July
19, 2002, to that certain Credit Agreement, dated as of July 26, 2001, (the
"Credit Agreement"; capitalized terms used herein and not defined shall have the
meaning set forth in the Credit Agreement), among SOLA INTERNATIONAL INC., a
Delaware corporation (the "Borrower"), the Lenders party thereto, UBS WARBURG
LLC, as sole lead arranger, UBS AG, STAMFORD BRANCH, as an Issuing Bank, and as
administrative agent (in such capacity, the "Administrative Agent"), ABN AMRO
BANK, N.V., as syndication agent, UBS AG, STAMFORD BRANCH, as collateral agent
for the Lenders, and UNION BANK OF CALIFORNIA, as documentation agent.

                              W I T N E S S E T H :

               WHEREAS, the Borrower has requested that the Lenders agree to
amend and waive certain provisions of the Credit Agreement;

               WHEREAS, pursuant to Section 9.08 of the Credit Agreement, the
Borrower and each of the undersigned Lenders hereby agree to amend and waive
certain provisions of the Credit Agreement as set forth herein;

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

               SECTION ONE - Amendments. The Borrower and the Lenders hereby
amend, subject to the satisfaction of the conditions set forth in Section Three
hereof:

               (a) Section 1.01 of the Credit Agreement by adding thereto, in
        appropriate alphabetical sequence, the following definition:

               "euro" or "E" means the single currency of participating member
        states of the European Union.

               (b) The definition of "Adjusted Leverage Ratio" in Section 1.01
        of the Credit Agreement by adding thereto, after the word "quarters" and
        before the period at the end thereof, the following phrase:

               "provided, that for the purposes of this definition, the rate of
        exchange between the euro and the dollar shall be E 0.8905 to $1.0000"

               (c) The definition of "Consolidated Interest Coverage Ratio" in
        Section 1.01 of the Credit Agreement by adding thereto, after the word
        "quarters" and before the period at the end thereof, the following
        phrase:

               "provided, that for the purposes of this definition, the rate of
        exchange between the euro and the dollar shall be E 0.8905 to $1.0000"

               (d) The definition of "Eligible Accounts Receivable" in Section
        1.01 of the Credit Agreement by deleting the words "150 days" in clause
        (d) and replacing it with the words "90 days".

               (e) The definition of "Permitted Acquisition" in Section 1.01 of
        the Credit Agreement by deleting the word "$10.0 million" in clause
        (vii) and replacing it with the word "$5.0 million", deleting the word
        "and" at the end of clause (viii) and by deleting clause (ix) and
        replacing it with the following:

<PAGE>

                      (ix) the aggregate Acquisition Consideration for all
               Permitted Acquisitions shall not exceed $30.0 million since the
               Closing Date; provided, further, that any Equity Interests
               constituting all or a portion of such Acquisition Consideration
               shall not have a cash dividend requirement on or prior to the
               Revolving Credit Maturity Date; and

                      (x) after giving effect to the closing of each such
               Permitted Acquisition, the amount of the Borrower's unrestricted
               cash and cash equivalents (as defined in the Borrower's financial
               statements filed with the Securities and Exchange Commission)
               after giving effect to such Permitted Acquisition shall exceed
               $45.0 million.

               (f) Section 2.05(c)(ii) of the Credit Agreement by adding
        thereto, after the parenthetical and before the period at the end
        thereof, the following words:

                "during the preceding month (or shorter period commencing with
        the date hereof or ending with the Revolving Credit Maturity Date or the
        date on which all Letters of Credit have been canceled or have expired
        and the Commitments of all Lenders shall have been terminated)"

               (g) Section 5.04 of the Credit Agreement by deleting clause (c)
        and replacing it with the following:

               "Monthly Reports. Within 30 days after the end of each calendar
        month (other than the last month of a fiscal quarter), the consolidated
        statements of income and cash flows and the balance sheet of the
        Borrower for such month and for the then elapsed portion of the fiscal
        year, in comparative form with the consolidated statements of income and
        cash flows and the balance sheets for the comparable periods in the
        previous fiscal year, accompanied by a certificate of a Financial
        Officer stating that such financial statements fairly present, in all
        material respects, the consolidated results of operations and cash flows
        and the balance sheet of the Borrower as of the date and for the periods
        specified in accordance with GAAP consistently applied, subject to
        normal year-end and quarter-end adjustments, and such report shall be
        marked confidential;"

               (h) Section 6.08(a) of the Credit Agreement by deleting the table
        therein and replacing it with the following:

<TABLE>
<CAPTION>
                      Fiscal Year Ended                Amount
                      -----------------                ------
                      <S>                            <C>
                        March 31, 2002               $30,000,000
                        March 31, 2003               $35,000,000
                        March 31, 2004               $30,000,000
</TABLE>

        and by deleting therefrom the third proviso in its entirety and
        replacing it with the words "provided, further, that the aggregate
        Capital Expenditures by the Borrower and its Subsidiaries shall not
        exceed $95.0 million from and after the Closing Date to the Revolving
        Credit Maturity Date".

               SECTION TWO - Waiver. Effective as of the Amendment Effective
Date (as defined below), the Lenders hereby waive compliance by the Borrower
through the Revolving Credit Maturity Date of Section 6.04 of the Credit
Agreement with respect to the Borrower agreeing to defer payment in an amount
not to exceed $3.0 million in accounts receivable due to the Borrower (the
"Deferment") from U.S. Vision, Inc. ("USV"), in connection with the financing by
the Borrower and certain banks (the "USV Lenders") to USV in connection with its
merger with Kayak Acquisition Corporation (the "USV Merger"). The Deferment
shall be expressly set forth in writing, a copy of which shall be delivered to
the Lenders. The writing shall set forth that USV will to pay to the Borrower 6%
per annum payable not less frequently than quarterly on the Deferment through
the life of the Deferment. The writ

                                      -2-
<PAGE>

ing shall further set forth that the Deferment shall not be subordinated other
than to the loans by the USV Lenders to USV in connection with the USV Merger,
in any event not to exceed $3.0 million of such financing.

               SECTION THREE - Conditions to Effectiveness. This Amendment shall
become effective as of the date first above written (the "Amendment Effective
Date") when, and only when, the Administrative Agent shall have received
counterparts of this Amendment executed by the Borrower and the Required Lenders
or, as to any of the Lenders, advice satisfactory to the Administrative Agent
that such Lender has executed this Amendment. The effectiveness of this
Amendment (other than Sections Seven, Eight and Nine hereof) is conditioned upon
the accuracy of the representations and warranties set forth in Section Five
hereof and upon payment of the fees, costs and expenses set forth in the first
sentence of Section Seven hereof.

               SECTION FOUR - Amendment Fee. Each Lender that executes and
delivers a signature page to this Amendment not later than 12:00 p.m. (New York
time) on July 17, 2002 (each, a "Qualifying Lender") will be entitled to receive
an amendment fee (the "Amendment Fee") equal to the product of .10% of the then
effective commitment of such Qualifying Lender on the Amendment Effective Date
and payable on 12:00 p.m. (New York time) on July 17, 2002. The Amendment Fee
shall be paid by the Borrower by wire transfer of immediately available funds to
the Administrative Agent and shall be distributed by the Administrative Agent to
each of the Qualifying Lenders.

               SECTION FIVE - Representations, Warranties and Covenants. In
order to induce the Lenders and the Agents to enter into this Amendment, the
Borrower represents and warrants to each of the Lenders and the Agents that
before and after giving effect to this Amendment, (x) no Default or Event of
Default has occurred and is continuing; and (y) all of the representations and
warranties in the Credit Agreement, after giving effect to this Amendment, are
true and complete in all material respects on and as of the date hereof as if
made on the date hereof (or, if any such representation or warranty is expressly
stated to have been made as of a specific date, as of such specific date). The
Borrower further represents and warrants (which representations and warranties
shall survive the execution and delivery hereof) to the Agents and each Lender
that:

               (a) It has the corporate power and authority to execute, deliver
        and perform this Amendment and have taken all corporate actions
        necessary to authorize the execution, delivery and performance of this
        Amendment;

               (b) This Amendment has been duly executed and delivered on behalf
        of the Borrower by a duly authorized officer or attorney-in-fact of the
        Borrower; and

               (c) The Borrower will not purchase any Notes unless each such
        purchase is made in compliance with all applicable law.

               SECTION SIX - Reference to and Effect on the Credit Agreement and
the Notes. On and after the effectiveness of this Amendment, each reference in
the Credit Agreement to "this Agreement," "hereunder," "hereof" or words of like
import referring to the Credit Agreement, and each reference in the Notes and
each of the other Loan Documents to "the Credit Agreement," "thereunder,"
"thereof" or words of like import referring to the Credit Agreement, shall mean
and be a reference to the Credit Agreement, as modified by this Amendment. The
Loan Documents, as specifically modified by this Amendment, are and shall
continue to be in full force and effect and are hereby in all respects ratified
and confirmed. Without limiting the generality of the foregoing, the Security
Documents and all of the Collateral described therein do and shall continue to
secure the payment of all Obligations under the Loan Documents, in each case as
modified by this Amendment. The execution, delivery and effectiveness of this
Amendment shall not, except as expressly provided herein, operate as a waiver of
any right, power or remedy of any Lender or any Agent under any of the Loan
Documents, nor constitute a waiver of any provision of any of the Loan
Documents.

               SECTION SEVEN - Costs, Expenses, Taxes and Fees. The Borrower
agrees to pay all reasonable costs and expenses of the Agents in connection with
the preparation, execution and delivery of this Amendment and

                                      -3-
<PAGE>

the other instruments and documents to be delivered hereunder, if any
(including, without limitation, the reasonable fees and expenses of Cahill
Gordon & Reindel) in accordance with the terms of Section 9.05 of the Credit
Agreement. In addition, the Borrower shall pay or reimburse any and all stamp
and other taxes payable or determined to be payable in connection with the
execution and delivery of this Amendment and the other instruments and documents
to be delivered hereunder, if any, and agrees to save each Agent and each Lender
harmless from and against any and all liabilities with respect to or resulting
from any delay in paying or omission to pay such taxes.

               SECTION EIGHT - Execution in Counterparts. This Amendment may be
executed in any number of counterparts and by different parties hereto in
separate counterparts, each of which when so executed shall be deemed to be an
original and all of which taken together shall constitute but one and the same
agreement. Delivery of an executed counterpart of a signature page to this
Amendment by telecopier shall be effective as delivery of a manually executed
counterpart of this Amendment.

               SECTION NINE - Governing Law. This Amendment shall be governed
by, and construed in accordance with, the laws of the State of New York (without
giving effect to any provisions thereof relating to conflicts of law).

                            [Signature Pages Follow]

                                      -4-
<PAGE>

               IN WITNESS WHEREOF, the parties hereto have caused this Amendment
to be executed by their respective officers thereunto duly authorized, as of the
date first above written.

                                       SOLA INTERNATIONAL INC.

                                       By:   /S/ Steven M. Neil
                                             --------------------------------
                                             Name: Steven M. Neil
                                             Title: Executive Vice President

                                      S-1
<PAGE>

                  Lender Signature page to Amendment No. 1 to
                    Sola International Inc. Credit Agreement

                                       UBS AG, STAMFORD BRANCH, as a Lender

                                       By:   /S/ Robert Reuter
                                             -----------------------------------
                                             Name: Robert Reuter
                                             Title: Executive Director

                                       By:   /S/ Renata Jacobson
                                             -----------------------------------
                                             Name: Renata Jacobson
                                             Title: Director

                                      S-2
<PAGE>

                  Lender Signature page to Amendment No. 1 to
                    Sola International Inc. Credit Agreement

                                         ABN-AMRO BANK, as a Lender

                                         By:   /S/ Dean P. Giglio
                                               ---------------------------------
                                               Name: Dean P. Giglio
                                               Title: Vice President

                                         By:   /S/ Todd J. Miller
                                               ---------------------------------
                                               Name: Todd J. Miller
                                               Title: Assistant Vice President

                                      S-3
<PAGE>

                  Lender Signature page to Amendment No. 1 to
                    Sola International Inc. Credit Agreement

                                       RZB FINANCE LLC, as a Lender

                                       By:   /S/ John A. Valiska
                                             -----------------------------------
                                             Name: John A. Valiska
                                             Title: Group Vice President

                                       By:   /S/ Eric Salat
                                             -----------------------------------
                                             Name: Eric Salat
                                             Title: Vice President

                                      S-4
<PAGE>

                  Lender Signature page to Amendment No. 1 to
                    Sola International Inc. Credit Agreement

                                    UNION BANK OF CALIFORNIA, N.A., as a Lender

                                    By:   /S/ Ryan C. Bradley
                                          --------------------------------------
                                          Name: Ryan C. Bradley
                                          Title: Vice President

                                      S-5
<PAGE>

                  Lender Signature page to Amendment No. 1 to
                    Sola International Inc. Credit Agreement

                                       WESTPAC BANKING CORPORATION, as a Lender

                                       By:   /S/ Andrew Ramsey
                                             -----------------------------------
                                             Name: Andrew Ramsey
                                             Title: Vice President

                                      S-6

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