<PAGE>

                                                               Exhibit 4.3

                          OCULEX PHARMACEUTICALS, INC.


                          REGISTRATION RIGHTS AGREEMENT


                                 MARCH __, 1997

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                                TABLE OF CONTENTS
<TABLE>
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                                                                                                               PAGE
<S>                                                                                                            <C>
I.  GENERAL.......................................................................................................1
         1.1      Definitions.....................................................................................1

II.  REGISTRATION.................................................................................................2
         2.1      Demand Registration.............................................................................2
         2.2      Piggyback Registrations.........................................................................3
                  2.2.1    Underwriting...........................................................................3
                  2.2.2    Right to Terminate Registration........................................................3
         2.3      Expenses of Registration........................................................................3
         2.4      Obligations of the Company......................................................................3
         2.5      Termination of Registration Rights..............................................................4
         2.6      Delay of Registration; Furnishing Information...................................................4
         2.7      Indemnification.................................................................................4
         2.8      Assignment of Registration Rights...............................................................6
         2.9      Amendment of Registration Rights................................................................6
         2.10     "Market Stand-Off" Agreement....................................................................7

III.  MISCELLANEOUS...............................................................................................7
         3.1      Governing Law...................................................................................7
         3.2      Survival........................................................................................7
         3.3      Successors and Assigns..........................................................................7
         3.4      Severability....................................................................................7
         3.5      Amendment and Waiver............................................................................7
         3.6      Delays or Omissions.............................................................................8
         3.7      Notices.........................................................................................8
         3.8      Attorneys' Fees.................................................................................8
         3.9      Titles and Subtitles............................................................................8
         3.10     Counterparts....................................................................................8
         3.11     Entire Agreement................................................................................8
</TABLE>


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                          OCULEX PHARMACEUTICALS, INC.

                          REGISTRATION RIGHTS AGREEMENT


         THIS REGISTRATION RIGHTS AGREEMENT (the "Agreement") is entered into as
of the _____ day of March, 1997, by and between OCULEX PHARMACEUTICALS, INC., a
California corporation (the "Company") and TJOA THIAN SONG, (the "Investor").

                                    RECITALS

         WHEREAS, the Company sold to Investor One Million Thirty Four Thousand
Four Hundred Eighty Three (1,034,483) shares of its Series B Preferred Stock
("Series B Preferred") in a Stock Purchase Agreement dated June 25, 1996, by and
between the Company and the Investor (the "Purchase Agreement"); and

         WHEREAS, the Company wishes to grant registration rights to the
Investor in consideration for a Market Stand-Off Agreement.

         NOW, THEREFORE, in consideration of the mutual promises,
representations, warranties, covenants and conditions set forth in this
Agreement, the parties mutually agree as follows:

                                  I. GENERAL

         1.1      DEFINITIONS. As used in this Agreement the following terms
shall have the following respective meanings:

         "EXCHANGE ACT" means the Securities Exchange Act of 1934, as amended.

         "HOLDER" means any person owning of record Registrable Securities that
have not been sold to the public or any assignee of record of such Registrable
Securities.

         "INITIAL OFFERING" means the Company's first firm commitment
underwritten public offering of its Common Stock registered under the Securities
Act.

         "REGISTER," "REGISTERED," and "REGISTRATION" refer to a registration
effected by preparing and filing a registration statement in compliance with the
Securities Act, and the declaration or ordering of effectiveness of such
registration statement or document.

         "REGISTRABLE SECURITIES" means (i) Common Stock of the Company issued
or issuable upon conversion of the Shares; and (ii) any Common Stock of the
Company issued as (or issuable upon the conversion or exercise of any warrant,
right or other security which is issued as) a dividend or other distribution
with respect to, or in exchange for or in replacement of, such above-described
securities. Notwithstanding the foregoing, Registrable Securities shall not
include any securities sold by a person to the public either pursuant to a
registration statement or Rule 144 or sold in a private transaction in which the
transferror's rights under Section 2 of this Agreement are not assigned.

         "REGISTRATION EXPENSES" shall mean all expenses incurred by the Company
in complying with Sections 2.1 and 2.2 hereof, including, without limitation,
all registration and filing fees, printing expenses, fees and disbursements of
counsel for the Company, blue sky fees and expenses.


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         "SECURITIES ACT" shall mean the Securities Act of 1933, as amended.

         "SELLING EXPENSES" shall mean all underwriting discounts and selling
commissions applicable to the sale.

         "SHARES" shall mean the Company's Series B Preferred issued pursuant to
the Purchase Agreement.

         "SEC" or "COMMISSION" means the Securities and Exchange Commission.


                               II. REGISTRATION

         2.1      DEMAND REGISTRATION.

                  2.1.1   If the Company shall receive a written request from
the Investor that the Company file a registration statement under the
Securities Act covering the registration of Registrable Securities having an
aggregate offering price to the public in excess of $5,000,000, then the
Company shall use its best efforts to effect, as soon as practicable, the
registration under the Securities Act of all Registrable Securities that the
Investor requests to be registered.

                  2.1.2   The Company shall not be required to effect a
registration pursuant to this Section 2.1:

                          (i)    prior to the third anniversary of the date of
this Agreement; or

                          (ii)   after the Company has effected one
registration pursuant to this Section 2.1, and such registration has been
declared or ordered effective; or

                          (iii)  during the period starting with date of
filing of, and ending on the date one hundred eighty (180) days following the
effective date of the registration statement pertaining to the Initial Offering;
provided that the Company makes reasonable good faith efforts to cause such
registration statement to become effective; or

                          (iv)   if within thirty (30) days of receipt of a
written request from the Investor pursuant to Section 2.1.1, the Company gives
notice to the Investor of the Company's intention to make its Initial Offering
within ninety (90) days; or

                          (v)    if the Company shall furnish to the Investor
a certificate stating that in the good faith judgment of the Board of Directors
of the Company, it would be seriously detrimental to the Company and its
shareholders for such registration statement to be effected at such time, in
which event the Company shall have the right to defer such filing for a period
of not more than ninety (90) days after receipt of the request of the Investor;
provided that such right to delay a request shall be exercised by the Company
not more than once in any twelve (12) month period.

         2.2      PIGGYBACK REGISTRATIONS. The Company shall notify the
Investor in writing at least thirty (30) days prior to the filing of any
registration statement under the Securities Act for purposes of a public
offering of securities of the Company (including, but not limited to,
registration statements relating to secondary offerings of securities of the
Company, but excluding registration statements relating to employee benefit
plans or with respect to corporate reorganizations or

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other transactions under Rule 145 of the Securities Act) and will afford the
Investor an opportunity to include in such registration statement all or part
of such Registrable Securities held by the Investor. If the Investor desires
to include in any such registration statement all or any part of the
Registrable Securities held by the Investor, Investor shall, within fifteen
(15) days after the above-described notice from the Company, so notify the
Company in writing. Such notice shall state the intended method of
disposition of the Registrable Securities by the Investor. If the Investor
decides not to include all of his Registrable Securities in any registration
statement thereafter filed by the Company, the Investor shall nevertheless
continue to have the right to include any Registrable Securities in any
subsequent such registration statement or registration statements as may be
filed by the Company with respect to offerings of its securities, all upon
the terms and conditions set forth herein.

                  2.2.1   UNDERWRITING. If the registration statement under
which the Company gives notice under this Section 2.2 is for an underwritten
offering, the Company shall so advise the Investor. In such event, the right
of the Investor to be included in a registration pursuant to this Section 2.2
shall be conditioned upon the Investor's participation in such underwriting
and the inclusion of the Investor's Registrable Securities in the
underwriting to the extent provided herein. The Investor shall enter into an
underwriting agreement in customary form with the underwriter or underwriters
selected for such underwriting by the Company. Notwithstanding any other
provision of the Agreement, if the underwriter determines in good faith that
the inclusion of the Registrable Securities would jeopardize the successful
sale of such other securities proposed to be sold by such underwriter or
underwriters, the Company shall not be obligated to include the Registrable
Securities in the registration.

                  2.2.2   RIGHT TO TERMINATE REGISTRATION. The Company shall
have the right to terminate or withdraw any registration initiated or
withdraw any registration initiated by it under this Section 2.2 prior to the
effectiveness of such registration whether or not the Investor has elected to
include securities in such registration. The Registration Expenses of such
withdrawn registration shall be borne by the Company in accordance with
Section 2.3 hereof.

         2.3      EXPENSES OF REGISTRATION. Except as specifically provided
herein, all Registration Expenses incurred in connection with any
registration, qualification or compliance pursuant to Section 2.1 or any
registration under Section 2.2 herein shall be borne by the Company. All
Investor related Selling Expenses incurred in connection with any
registrations hereunder shall be borne by the Investor. The Company shall
not, however, be required to pay for expenses of any registration proceeding
begun pursuant to Section 2.1, the request of which has been subsequently
withdrawn by the Investor unless the withdrawal is based upon material
adverse information concerning the Company of which the Investor was not
aware at the time of request or the Investor agrees to forfeit the demand
registration right pursuant to Section 2.1.

         2.4      OBLIGATIONS OF THE COMPANY. Whenever required to effect the
registration of any Registrable Securities, the Company shall, as
expeditiously as reasonably possible:

                  2.4.1   Prepare and file with the SEC a registration statement
with respect to such Registrable Securities and use all reasonable efforts to
cause such registration statement to become effective.

                  2.4.2   Prepare and file with the SEC such amendments and
supplements to such registration statement and the prospectus used in connection
with such registration statement as may be necessary to comply with the
provisions of the Securities Act with respect to the disposition of all
securities covered by such registration statement.


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                  2.4.3   Furnish to the Investor such number of copies of a
prospectus, including a preliminary prospectus, in conformity with the
requirements of the Securities Act, and such other documents as he may
reasonably request in order to facilitate the disposition of Registrable
Securities owned by him.

                  2.4.4   Use all reasonable efforts to register and qualify the
securities covered by such registration statement under such other securities or
Blue Sky laws of such jurisdictions as shall be reasonably requested by the
Investor, provided that the Company shall not be required in connection
therewith or as a condition thereto to qualify to do business or to file a
general consent to service of process in any such states or jurisdictions.

                  2.4.5   In the event of any underwritten public offering,
enter into and perform its obligations under an underwriting agreement, in
usual and customary form, with the managing underwriter(s) of such offering.
The Investor participating in such underwriting shall also enter into and
perform its obligations under such an agreement.

                  2.4.6   Notify the Investor of Registrable Securities covered
by such registration statement at any time when a prospectus relating thereto
is required to be delivered under the Securities Act of the happening of any
event as a result of which the prospectus included in such registration
statement, as then in effect, includes an untrue statement of a material fact
or omits to state a material fact required to be stated therein or necessary
to make the statements therein not misleading in the light of the
circumstances then existing.

         2.5      TERMINATION OF REGISTRATION RIGHTS. All registration rights
granted under this Section 2 shall terminate and be of no further force and
effect three (3) years after the date of the Company's Initial Offering. In
addition, the Investor's registration rights shall expire if (i) the Company
has completed its Initial Offering and is subject to the provisions of the
Exchange Act, (ii) the Investor (together with his affiliates, partners and
former partners) holds less than 1% of the Company's outstanding Common Stock
(treating all shares of convertible Preferred Stock on an as converted basis)
and (iii) all Registrable Securities held by and issuance to the Investor may
be sold under Rule 144 during any ninety (90) day period.

         2.6      DELAY OF REGISTRATION; FURNISHING INFORMATION.

                  2.6.1   The Investor shall not have any right to obtain or
seek an injunction restraining or otherwise delaying any such registration as
the result of any controversy that might arise with respect to the
interpretation or implementation of this Section 2.

                  2.6.2   It shall be a condition precedent to the obligations
of the Company to take any action pursuant to Section 2.1 or 2.2 that the
Investor shall furnish to the Company such information regarding himself, the
Registrable Securities held by him and the intended method of disposition of
such securities as shall be required to effect the registration of their
Registrable Securities.

         2.7      INDEMNIFICATION. In the event any Registrable Securities
are included in a registration statement under Sections 2.1 or 2.2:

                  2.7.1   To the extent permitted by law, the Company will
indemnify and hold harmless the Investor, against any losses, claims, damages,
or liabilities (joint or several) to which he may become subject under the
Securities Act, the Exchange Act or other federal or state law, insofar as such
losses, claims, damages or liabilities (or actions in respect thereof) arise out
of or are based upon any of the


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following statements, omissions or violations (collectively a "Violation") by
the Company: (i) any untrue statement or alleged untrue statement of a
material fact contained in such registration statement, including any
preliminary prospectus or final prospectus contained therein or any
amendments or supplements thereto, (ii) the omission or alleged omission to
state therein a material fact required to be stated therein, or necessary to
make the statements therein not misleading, or (iii) any violation or alleged
violation by the Company of the Securities Act, the Exchange Act, any state
securities law or any rule or regulation promulgated under the Securities
Act, the Exchange Act or any state securities law in connection with the
offering covered by such registration statement; and the Company will
reimburse the Investor for any legal or other expenses reasonably incurred by
them in connection with investigating or defending any such loss, claim,
damage, liability or action; provided however, that the indemnity agreement
contained in this Section 2.7.1 shall not apply to amounts paid in settlement
of any such loss, claim, damage, liability or action if such settlement is
effected without the consent of the Company, which consent shall not be
unreasonably withheld, nor shall the Company be liable in any such case for
any such loss, claim, damage, liability or action to the extent that it
arises out of or is based upon a Violation which occurs in reliance upon and
in conformity with written information furnished expressly for use in
connection with such registration by the Investor.

                  2.7.2   To the extent permitted by law, the Investor will, if
Registrable Securities held by the Investor are included in the securities as to
which such registration qualifications or compliance is being effected,
indemnify and hold harmless the Company, each of its directors, its officers,
and legal counsel and each person, if any, who controls the Company within the
meaning of the Securities Act, any underwriter and any other Holder selling
securities under such registration statement or any of such other Holder's
partners, directors or officers or any person who controls such Holder, against
any losses, claims, damages or liabilities (joint or several) to which the
Company or any such director, officer, controlling person, underwriter or other
such Holder, or partner, director, officer or controlling person of such other
Holder may become subject under the Securities Act, the Exchange Act or other
federal or state law, insofar as such losses, claims, damages or liabilities (or
actions in respect thereto) arise out of or are based upon any Violation, in
each case to the extent (and only to the extent) that such Violation occurs in
reliance upon and in conformity with written information furnished by the
Investor under an instrument duly executed by the Investor and stated to be
specifically for use in connection with such registration; and the Investor will
reimburse any legal or other expenses reasonably incurred by the Company or any
such director, officer, controlling person, underwriter or other Holder, or
partner, officer, director or controlling person of such other Holder in
connection with investigating or defending any such loss, claim, damage,
liability or action if it is judicially determined that there was such a
Violation; provided, however, that the indemnity agreement contained in this
Section 2.7.2 shall not apply to amounts paid in settlement of any such loss,
claim, damage, liability or action if such settlement is effected without the
consent of the Investor, which consent shall not be unreasonably withheld;
provided further, that in no event shall any indemnity under this Section 2.7
exceed the proceeds from the offering received by the Investor.

                  2.7.3   Promptly after receipt by an indemnified party under
this Section 2.7 of notice of the commencement of any action (including any
governmental action), such indemnified party will, if a claim in respect thereof
is to be made against any indemnifying party under this Section 2.7, deliver to
the indemnifying party a written notice of the commencement thereof and the
indemnifying party shall have the right to participate in, and, to the extent
the indemnifying party so desires, jointly with any other indemnifying party
similarly noticed, to assume the defense thereof with counsel mutually
satisfactory to the parties; provided, however, that an indemnified party shall
have the right to retain its own counsel, with the fees and expenses to be paid
by the indemnifying party, if representation of such indemnified party by the
counsel retained by the indemnifying party would be inappropriate due to actual
or potential differing interests between such indemnified party and any other
party represented by such counsel in such proceeding. The failure to deliver
written notice to the indemnifying party within a reasonable time


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of the commencement of any such action, if materially prejudicial to its
ability to defend such action, shall relieve such indemnifying party of any
liability to the indemnified party under this Section 2.7, but the omission
so to deliver written notice to the indemnifying party will not relieve it of
any liability that it may have to any indemnified party otherwise than under
this Section 2.7.

                  2.7.4   If the indemnification provided for in this Section
2.7 is held by a court of competent jurisdiction to be unavailable to an
indemnified party with respect to any losses, claims, damages or liabilities
referred to herein, the indemnifying party, in lieu of indemnifying such
indemnified party thereunder, shall to the extent permitted by applicable law
contribute to the amount paid or payable by such indemnified party as a
result of such loss, claim, damage or liability in such proportion as is
appropriate to reflect the relative fault of the indemnifying party on the
one hand and of the indemnified party on the other in connection with the
Violation(s) that resulted in such loss, claim, damage or liability, as well
as any other relevant equitable considerations. The relative fault of the
indemnifying party and of the indemnified party shall be determined by a
court of law by reference to, among other things, whether the untrue or
alleged untrue statement of a material fact or the omission to state a
material fact relates to information supplied by the indemnifying party or by
the indemnified party and the parties' relative intent, knowledge, access to
information and opportunity to correct or prevent such statement or omission;
provided, that in no event shall any contribution by a Holder hereunder
exceed the proceeds from the offering received by such Holder.

                  2.7.5   The obligations of the Company and Holders under this
Section 2.7 shall survive completion of any offering of Registrable Securities
in a registration statement. No Indemnifying Party, in the defense of any such
claim or litigation, shall, except with the consent of each Indemnified Party,
consent to entry of any judgment or enter into any settlement which does not
include as an unconditional term thereof the giving by the claimant or plaintiff
to such Indemnified Party of a release from all liability in respect to such
claim or litigation. In the event any offering of Registrable Securities is
underwritten, and the underwriting agreement provides for indemnification and/or
contribution by the Company and the Holders offering securities thereunder, the
indemnification and/or contribution obligations of the Company and the Holders
hereunder shall in no event exceed the obligations of the parties set forth in
such underwriting agreement.

         2.8    ASSIGNMENT OF REGISTRATION RIGHTS. The rights to cause the
Company to register Registrable Securities pursuant to this Section 2 may be
assigned by a Holder to a transferee or assignee of Registrable Securities
which acquires at least five hundred thousand (500,000) shares of Registrable
Securities (adjusted for stock splits and combinations); provided however,
(A) the transferor shall, within ten (10) days after such transfer, furnish
to the Company written notice of the name and address of such transferee or
assignee and the securities with respect to which such registration rights
are being assigned and (B) such transferee shall agree to be subject to all
restrictions set forth in this Agreement.

         2.9    AMENDMENT OF REGISTRATION RIGHTS. Any provision of this
Section 2 may be amended or terminated and the observance thereof may be
waived (either generally or in a particular instance and either retroactively
or prospectively), only with the written consent of the Company and the
Investor. Any amendment, termination or waiver effected in accordance with
this Section 2.8 shall be binding upon the Investor and the Company. By
acceptance of any benefits under this Section 2, the Investor hereby agrees
to be bound by the provisions hereunder.

         2.10   "MARKET STAND-OFF" AGREEMENT. If requested by the Company as
the representative of the underwriters of Common Stock (or other securities)
of the Company, the Investor shall not sell or otherwise transfer or dispose
of any Shares or Common Stock (or other securities) of the Company held by
the Investor (other than those included in the registration) for a

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<PAGE>

period specified by the representative of the underwriters not to exceed one
hundred eighty (180) days following the effective date of a registration
statement of the Company filed under the Securities Act, provided however,
that all officers and directors of the Company enter into similar agreements.
The Company may impose stop-transfer instructions with respect to the shares
of Common Stock (or other securities) subject to the foregoing restriction
until the end of said one hundred eighty (180) day period.

                              III. MISCELLANEOUS

         3.1      GOVERNING LAW. This Agreement shall be governed by and
construed under the laws of the State of California without giving effect to
principles of conflicts of laws thereof.

         3.2      SURVIVAL. The representations, warranties, covenants, and
agreements made herein shall survive any investigation made by the Investor
and the closing of the transactions contemplated hereby. All statements as to
factual matters contained in any certificate or other instrument delivered by
or on behalf of the Company pursuant hereto in connection with the
transactions contemplated hereby shall be deemed to be representations and
warranties by the Company hereunder solely as of the date of such certificate
or instrument.

         3.3      SUCCESSORS AND ASSIGNS. Except as otherwise expressly
provided herein, the provisions hereof shall inure to the benefit of, and be
binding upon, the successors, assigns, heirs, executors, and administrators
of the parties hereto and shall inure to the benefit of and be enforceable by
each person who shall be a holder of Registrable Securities from time to
time; provided, however, that prior to the receipt by the Company of adequate
written notice of the transfer of any Registrable Securities specifying the
full name and address of the transferee, the Company may deem and treat the
person listed as the holder of such shares in its records as the absolute
owner and holder of such shares for all purposes, including the payment of
dividends or any redemption price.

         3.4      SEVERABILITY. In case any provision of the Agreement shall
be invalid, illegal, or unenforceable, the validity, legality, and
enforceability of the remaining provisions shall not in any way be affected
or impaired thereby.

         3.5      AMENDMENT AND WAIVER.

                  3.5.1   Except as otherwise expressly provided, this Agreement
may be amended or modified only upon the written consent of the Company and the
Investor.

                  3.5.2   Except as otherwise expressly provided, the
obligations of the Company and the rights of the Investor under this
Agreement may be waived only with the written consent of the Investor.

                  3.5.3   Notwithstanding the foregoing, this Agreement may be
amended with only the written consent of the Company to include additional
purchasers of Shares as "Investors," "Holders" and parties hereto.

         3.6      DELAYS OR OMISSIONS. It is agreed that no delay or omission
to exercise any right, power, or remedy accruing to the Investor, upon any
breach, default or noncompliance of the Company under this Agreement shall
impair any such right, power, or remedy, nor shall it be construed to be a
waiver of any such breach, default or noncompliance, or any acquiescence
therein, or of any similar breach, default or noncompliance thereafter
occurring. It is further agreed that any waiver, permit, consent, or approval
of any kind or character on Investor's part of any breach, default or
noncompliance under the Agreement or any waiver on Investor's part of any
provisions or conditions

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<PAGE>

of this Agreement must be in writing and shall be effective only to the
extent specifically set forth in such writing. All remedies, either under
this Agreement, by law, or otherwise afforded to Investor, shall be
cumulative and not alternative.

         3.7      NOTICES. All notices required or permitted hereunder shall
be in writing and shall be deemed effectively given: (i) upon personal
delivery to the party to be notified, (ii) when sent by confirmed telex or
facsimile if sent during normal business hours of the recipient; if not, then
on the next business day, (iii) five (5) days after having been sent by
registered or certified mail, return receipt requested, postage prepaid, or
(iv) one (1) day after deposit with a nationally recognized overnight
courier, specifying next day delivery, with written verification of receipt.
All communications shall be sent to the party to be notified at the address
as set forth on the signature pages hereof or at such other address as such
party may designate by ten (10) days advance written notice to the other
parties hereto.

         3.8      ATTORNEYS' FEES. In the event that any dispute among the
parties to this Agreement should result in litigation, the prevailing party
in such dispute shall be entitled to recover from the losing party all fees,
costs and expenses of enforcing any right of such prevailing party under or
with respect to this Agreement, including without limitation, such reasonable
fees and expenses of attorneys and accountants, which shall include, without
limitation, all fees, costs and expenses of appeals.

         3.9      TITLES AND SUBTITLES. The titles of the sections and
subsections of this Agreement are for convenience of reference only and are
not to be considered in construing this Agreement.

         3.10     COUNTERPARTS. This Agreement may be executed in any number
of counterparts, each of which shall be an original, but all of which
together shall constitute one instrument.

         3.11     ENTIRE AGREEMENT. This Agreement, the Purchase Agreement
and the other documents delivered pursuant thereto constitute the full and
entire understanding and agreement between the parties with regard to the
subjects hereof and no party shall be liable or bound to any other in any
manner by any representations, warranties, covenants and agreements except as
specifically set forth herein and therein.

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<PAGE>

         IN WITNESS WHEREOF, the parties hereto have executed this Registration
Rights Agreement as of the date set forth above.



COMPANY:                                                    INVESTOR:

OCULEX PHARMACEUTICALS, INC.                TJOA THIAN SONG



By: /s/ Jerry B. Gin                         By: /s/ Tjoa Thian Song
   -------------------------------              -------------------------------
         President                                     Tjoa Thian Song


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