<PAGE>   1
                              CALL OPTION AGREEMENT

                                TABLE OF CONTENTS

<TABLE>
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                                                                                                  PAGE
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<S>                                                                                               <C>
SECTION 1: DEFINITIONS........................................................................      1

         1.1      Certain Definitions.........................................................      1
         1.2      Pronouns....................................................................      3

SECTION 2:  CALL OPTION.......................................................................      3

         2.1      Grant of Call Option; Exercise Price........................................      3
         2.2      Manner of Exercising Call Option............................................      4
         2.3      Management Shares and Management Options....................................      4
         2.4      Extension of Call Option....................................................      5
         2.5      Issuance of ACS Series C Preferred Stock....................................      5
         2.6      Shareholder Approval........................................................      5

SECTION 3:  PUT OPTION........................................................................      5

         3.1      Grant of Put Option.........................................................      5
         3.2      Exercise of Put Option;  Closing Date.......................................      5
         3.3      Management Shares and Management Options....................................      6
         3.4      Issuance of ACS Series C Preferred Stock....................................      6
         3.5      Shareholder Approval........................................................      6

SECTION 4:  TRANSFER..........................................................................      6

         4.1      Legend......................................................................      6
         4.2      No Transfer.................................................................      6

SECTION 5:  ANTIDILUTION......................................................................      7

         5.1      Adjustments.................................................................      7

SECTION 6:  REGISTRATION RIGHTS...............................................................      7

         6.1      Registration Rights.........................................................      7

SECTION 7:  REPRESENTATIONS AND WARRANTIES....................................................      7

         7.1      Representations and Warranties of ACS.......................................      7
         7.2      Representations and Warranties of the Company...............................      8
         7.3      Representations and Warranties of the Preference Holders....................      9

CALL OPTION AGREEMENT

SECTION 8: MISCELLANEOUS......................................................................     11

         8.1      No Inconsistent Agreements..................................................     11
         8.2      Remedies....................................................................     11
         8.3      Amendments and Waivers......................................................     11
         8.4      Successors and Assigns......................................................     11
         8.5      Severability................................................................     11
         8.6      Counterparts................................................................     11
         8.7      Descriptive Headings........................................................     11
         8.8      Governing Law...............................................................     12
         8.9      Notices.....................................................................     12
         8.10     Entire Agreement............................................................     13
         8.11     Further Action..............................................................     13
         8.12     Tax Consequences............................................................     13
</TABLE>












THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED. THEY MAY NOT BE SOLD, OFFERED FOR SALE, PLEDGED OR HYPOTHECATED IN THE
ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT AS TO THE SECURITIES UNDER SAID
ACT OR AN OPINION OF COUNSEL REASONABLY SATISFACTORY TO THE CORPORATION THAT
SUCH REGISTRATION IS NOT REQUIRED.


                              CALL OPTION AGREEMENT

        THIS CALL OPTION AGREEMENT (this "Agreement") is made and entered into
this 27th day of June, 1997 (the "Effective Date") by and among Advanced Corneal
Systems, Inc., a California corporation ("ACS"), Visionex Pte. Ltd., a Singapore
corporation (the "Company") and each individual or entity listed on the attached
Exhibit A (the "Preference Holders").

                                    RECITALS

        WHEREAS, subject to the conditions set forth herein, the Preference
Holders hereby grant to ACS an option to purchase all Preference Shares owned by
the Preference Holders.

        WHEREAS, subject to the conditions set forth herein, ACS hereby grants
to the Preference Holders the right to require ACS to purchase all Preference
Shares owned by the Preference Holders.

        WHEREAS, the Company desires to facilitate the transactions contemplated
herein.

        NOW THEREFORE, in consideration of the mutual promises, covenants and
agreements contained herein, the parties hereto agree as follows:

                             SECTION 1: DEFINITIONS

        1.1 Certain Definitions.

        "ACS Common Stock" means the number of shares of Common Stock of ACS to
be issued in accordance with the terms of this Agreement.

        "ACS Series C Shares" means the number of shares of Series C Preferred
Stock of ACS which may be issued in accordance with the terms of this Agreement.

        "Annual Revenues" shall mean the product of four (4) times revenues of
the Company determined in accordance with generally accepted accounting
principles for the fiscal quarter immediately preceding the Call Option Exercise
Date.

        "Call Option" shall have the meaning set forth in Section 2.1 of this
Agreement.

        "Call Option Closing Date" shall have the meaning set forth in Section
2.2 of this



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<PAGE>   2

Agreement.

        "Call Option Exercise Date" means the date ACS gives notice to the
Company and the Preference Holders in accordance with Section 2.2 of this
Agreement.

        "Call Option Period" means the two (2) year period commencing on the
third anniversary of the Effective Date and ending on the fifth anniversary of
the Effective Date.

        "Call Option Record Date" means the date which is twenty (20) days
following the Call Option Exercise Date.

        "Delaying Holders" shall have the meaning set forth in Section 2.4 of
this Agreement.

        "Effective Date" shall have the meaning set forth in the first paragraph
of this Agreement.

        "Exercising Holder" shall have the meaning set forth in Section 3.2 of
this Agreement.

        "Management Options" means options to purchase Ordinary Shares of the
Company issued to officers, employees, or directors of the Company pursuant to a
plan or arrangement approved by the board of directors of the Company.

        "Management Shares" means Ordinary Shares of the Company issued (i)
directly to officers, employees, or directors of the Company and (ii) upon the
exercise of Management Options.

        "Nasdaq National Market Issuer" shall have the meaning set forth in Rule
4460 of the National Association of Securities Dealers, Inc. Manual.

        "Ordinary Shares" means the ordinary shares in the share capital of the
Company.

        "Preference Holders" shall have the meaning set forth in the first
paragraph of this Agreement.

        "Preference Shares " means (i) all Ordinary Shares issued or issuable
upon conversion of the Company's Preference Shares purchased by a Preference
Holder directly from the Company or acquired pursuant to a transfer in
accordance with Section 4.2 hereof and (ii) all outstanding Preference Shares.

        "Purchase Agreement" shall have the meaning set forth in Section 2.5 of
this Agreement.

        "Put Option" shall have the meaning set forth in Section 3.1 of this
Agreement.

        "Put Option Closing Date"shall have the meaning set forth in Section 3.2
of this Agreement.

        "Put Option Exercise Date" means the date an Exercising Holder delivers
the Put Option Exercise Notice.



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<PAGE>   3

        "Put Option Period" means the three (3) year period commencing on the
second anniversary of the Effective Date and ending on the fifth anniversary of
the Effective Date.

        "Put Option Record Date" means the date which is five (5) days following
the Put Option Exercise Date.

        1.2 Pronouns. When used herein, the pronoun "his" shall mean his, her or
its, as appropriate and "him" and "he" have corresponding meanings.

                             SECTION 2: CALL OPTION

        2.1 Grant of Call Option; Exercise Price. Subject to the terms and
conditions herein set forth, each Preference Holder hereby grants ACS an option
to purchase the number of Preference Shares as set forth for such Preference
Holder on Exhibit A (the "Call Option "). The per share purchase price to be
paid by ACS for each Preference Share shall be a fraction, the numerator of
which is the number of shares of ACS Common Stock corresponding to Annual
Revenues or, subject to Section 2.5 herein, ACS Series C Shares, as set forth in
Table 2.1(a) below, and the denominator of which is the number of Preference
Shares that are outstanding on the Call Option Record Date.

                                  TABLE 2.1(a)


<TABLE>
<CAPTION>
    ANNUAL REVENUES (1)                       ACS COMMON STOCK ISSUABLE UPON
(in millions of U.S. dollars)                          EXERCISE (2)
<S>                                           <C>
          0-8                                           2,252,694
          8-9                                           2,386,027
          9-10                                          2,519,361
         10-11                                          2,652,694
         11-12                                          2,786,028
         12-13                                          2,919,361
         13-14                                          3,052,694
         14-15                                          3,186,028
         15+                                            3,319,361
</TABLE>

(1) The upper value of each range includes the endpoint. The lower value of each
range does not include the endpoint.

(2) The number of shares of ACS Common Stock or ACS Series C Shares issuable
upon exercise of the Call Option shall be decreased by the number of shares of
ACS Common Stock or ACS Series C Shares issued previously pursuant to the Put
Option.

        2.2 Manner of Exercising Call Option. Except as provided in Section 2.4,
ACS may exercise the Call Option at any time during the Call Option Period, by
giving notice, in substantially the form attached hereto as Exhibit B, to the
Company and the Preference Holders. The purchase of the Preference Shares by ACS
shall take place on the date which shall be not less than ten (10) nor more than
thirty (30) days after the Call Option Record Date (the "Call Option Closing
Date"); provided, however, the Call Option Date shall not occur before the
requirements of Section 2.6 have


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<PAGE>   4

been satisfied, if applicable. ACS may purchase all, but not less than all, of
the Preference Shares that are outstanding on the Call Option Record Date. For
purposes of determining the number and owners of Preference Shares, the Company
shall, within five (5) days following the Call Option Record Date, certify in
writing to ACS the number of Preference Shares owned of record or beneficially
by each Preference Holder and the address of each Preference Holder. On the Call
Option Closing Date, each Preference Holder shall deliver all Preference Shares
owned by such Preference Holder duly endorsed for transfer to ACS and free and
clear of any imperfections of title, lien, claim, encumbrance, restriction or
charge other than restrictions on transfer imposed by the securities laws of the
United States or the Republic of Singapore.

        2.3 Management Shares and Management Options.

             (a) Obligation to Purchase and Assume. If at the time ACS exercises
the Call Option the aggregate purchase price for the Preference Shares is equal
to 3,319,361 shares of ACS Common Stock, less the number of shares of ACS Common
Stock issued previously pursuant to, or issuable upon, the exercise of the Put
Option, then ACS shall (i) purchase all Management Shares outstanding on the
Call Option Closing Date and (ii) assume all the Management Options outstanding
on the Call Option Closing Date. Each Management Share shall be exchanged for
0.26 shares of ACS Common Stock; provided, however, that in no event shall ACS
exchange more than 650,000 shares of ACS Common Stock pursuant to this Section
2.3, and each holder of a Management Share shall deliver all Management Shares
owned by such holder duly endorsed for transfer to ACS and free and clear of any
imperfections of title, lien, claim, encumbrance, restriction or charge other
than restrictions on transfer imposed by the securities laws of the United
States or the Republic of Singapore. Each Management Option assumed by ACS shall
be exercisable upon the same terms and conditions as under the Management Option
except that (i) such Management Option shall entitle the holder to purchase from
ACS the number of shares of ACS Common Stock (rounded down to the nearest whole
number of such shares) that equals the product of 0.26 times the number of
Ordinary Shares subject to such Management Option and (ii) the exercise price
per share of the Management Option shall be an amount (rounded down to the
nearest whole number) equal to the exercise price per share of the Management
Option divided by 0.26. As promptly as practicable following the Call Option
Closing Date, ACS shall issue to each holder of a Management Option a written
instrument informing such holder of the assumption by ACS of such Management
Option.

             (b) Option to Purchase and Assume. If at the time ACS exercises the
Call Option the aggregate purchase price for the Preference Shares is less than
3,319,361 shares of ACS Common Stock less the number of shares of ACS Common
Stock issued previously pursuant to, or issuable upon, the exercise of the Put
Option, then ACS shall have the right, but shall not be obligated, to (i)
purchase all Management Shares and (ii) assume all the Management Options, on
the terms set forth in Section 2.3(a).

        2.4 Extension of Call Option. If within ten (10) days following the Call
Option Exercise Date the holders of a majority of the then outstanding
Preference Shares (the "Delaying Holders") provide ACS with written notice of
their election to defer the date on which ACS may exercise the Call Option, then
ACS's right to exercise the Call Option shall be deferred, for a period not to
exceed two years after the Call Option Exercise Date, to a new Call Option
Exercise Date selected by the Delaying Holders at the time such notice is given;
provided, however, that the


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<PAGE>   5

Preference Holders may not utilize this right more than once during the term of
this Agreement.

        2.5 Issuance of ACS Series C Preferred Stock. If on the Call Option
Closing Date, ACS's outstanding Series C Preferred Stock shall not have been
automatically converted pursuant to paragraph IV.4(b) (or any successor
provision) of ACS's then current Articles of Incorporation, then ACS Series C
Shares and not shares of ACS Common Stock shall be issued to the holders of the
Preference Shares at such closing.

        2.6 Shareholder Approval. If ACS is a Nasdaq National Market Issuer as
of the Call Option Exercise Date, then ACS shall, if required, obtain
shareholder approval to issue the shares of ACS Common Stock pursuant to this
Section 2 prior to such issuance.

                              SECTION 3: PUT OPTION

        3.1 Grant of Put Option. ACS hereby grants each Preference Holder the
right to require ACS to purchase at any time during the Put Option Period the
number of Preference Shares as set forth for such Preference Holder on Exhibit A
(the "Put Option"). The per share purchase price to be paid by ACS for each
Preference Share shall be the number of shares of ACS Common Stock or, subject
to Section 3.4 herein, ACS Series C Shares, equal to the quotient of (A) divided
by (B), where (A) equals 2,252,694 shares of ACS Common Stock and (B) equals the
total number of Preference Shares as set forth on Exhibit A.

        3.2 Exercise of Put Option; Closing Date. Each Preference Holder may
exercise the Put Option by giving notice (an "Exercising Holder"), in
substantially the form attached hereto as Exhibit C (the "Put Option Exercise
Notice"), to ACS at any time during the Put Option Period. The purchase of the
Preference Shares by ACS shall take place on the date selected by ACS, which
shall be not less than ten (10) nor more than thirty (30) days after the Put
Option Exercise Date (the "Put Option Closing Date"); provided, however, the Put
Option Closing Date shall not occur before the requirements of Section 3.5 have
been satisfied, if applicable. ACS will purchase the number of Preference Shares
from each Exercising Holder set forth in the Put Option Exercise Notice;
provided, however, that the number of Preference Shares to be purchased by ACS
shall not be less than fifty percent (50%) of the Preference Shares as set forth
for the Exercising Holder on Exhibit A. On the Put Option Closing Date, the
Exercising Holder shall deliver the number of Preference Shares set forth in the
Put Option Exercise Notice duly endorsed for transfer to ACS and free and clear
of any imperfections of title, lien, claim, encumbrance, restriction or charge
other than restrictions on transfer imposed by the securities laws of the United
States or the Republic of Singapore.

        3.3 Management Shares and Management Options. If at the time of the Put
Option Exercise Date each Preference Holder exercises its right to require ACS
to purchase all Preference Shares as set forth for such Preference Holder on
Exhibit A, then ACS shall have the right, but shall not be obligated, to (i)
purchase all Management Shares and (ii) assume all the Management Options, on
the terms set forth in Section 2.3(a).

        3.4 Issuance of ACS Series C Preferred Stock. If on the Put Option
Closing Date, ACS's outstanding Series C Preferred Stock shall not have been
automatically converted pursuant to



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<PAGE>   6

paragraph IV.4(b) (or any successor provision) of ACS's then current Articles of
Incorporation, then shares of ACS Series C Preferred Stock and not ACS Common
Stock shall be issued to the holders of the Preference Shares at such closing.

        3.5 Shareholder Approval. If ACS is a Nasdaq National Market Issuer as
of the Call Option Exercise Date, then ACS shall obtain shareholder approval to
issue the shares of ACS Common Stock pursuant to this Section 2 prior to such
issuance.

                               SECTION 4: TRANSFER

        4.1 Legend. The certificates representing the Preference Shares held by
the Preference Holders shall have endorsed thereon the following legend:

                "The securities represented by this certificate are subject to
                purchase by ACS in accordance with the terms of a Call Option
                Agreement dated June 27, 1997 by and among the Company, ACS, and
                the Preference Holders listed on Exhibit A attached thereto, as
                may be amended from time to time, a copy of which is on file
                with the Secretary of the Company."

             The Company hereby covenants to place a stop transfer order against
the Preference Shares held by the Preference Holders, and each Preference Holder
hereby irrevocably authorizes the Company to do so.

        4.2 No Transfer. Except for the sale of the Preference Shares to ACS in
accordance with the terms of this Agreement, no Preference Holder shall
alienate, sell, give, transfer, assign, bequeath, pledge or hypothecate any
Preference Shares beneficially owned by him or create or permit to exist any
lien thereon or security interest therein, other than by will or intestacy. Any
attempted transfer or other act in violation of this Section 4.2 shall be of no
effect and the attempted transferee or other party shall receive no rights in
the Preference Shares or under this Agreement. The Company agrees that it will
not transfer any Preference Shares held by the Preference Holders on the stock
transfer records of the Company. Notwithstanding the above, the Preference
Shares held by the Preference Holders may be assigned by a Preference Holder to
a limited partner, general partner or other affiliate of a Preference Holder,
provided that such assignee has agreed to be bound by the terms and conditions
of this Agreement. Subject to the foregoing, this Agreement shall be binding
upon and inure to the benefit of the parties hereto, their successors and
assigns.

                             SECTION 5: ANTIDILUTION

        5.1 Adjustments. All shares of ACS Common Stock or ACS Series C
Preferred Stock issued upon exercise of the Call Option or Put Option shall be
adjusted for stock splits, stock dividends, recapitalizations, reorganizations
and combinations. With respect to these shares, it is the intent of the Company,
ACS and the Preference Holders that no such adjustment shall result in an
increase or decrease in the aggregate value to be received by the Preference
Holders in the form of shares of ACS Common Stock or ACS Series C Preferred
Stock to be issued in exchange for the Preference Shares on the Call Option
Closing Date or Put Option Closing Date, as applicable.



                                       6
<PAGE>   7

                         SECTION 6: REGISTRATION RIGHTS

        6.1 Registration Rights. The Preference Holders are parties to that
certain Investors Rights Agreement with ACS, dated June 27, 1997, entered into
pursuant to the ACS Series C Preferred Stock Purchase Agreement, dated June 27,
1997, and the shares of ACS Common Stock issuable under this Agreement are and
ACS shall procure that such securities remain "Registrable Securities" under the
terms of such Investors Rights Agreement.

                    SECTION 7: REPRESENTATIONS AND WARRANTIES

        7.1 Representations and Warranties of ACS. ACS represents and warrants
to the Company and the Preference Holders as of the date hereof as follows:

             (a) Organization. ACS is a corporation duly incorporated, validly
existing and in good standing under the laws of the State of California, and is
duly qualified to do business and is in good standing in each of the other
jurisdictions in which it owns or leases property or conducts business except
where the failure to be so qualified would not have a material adverse effect on
its business.

             (b) Authorization. ACS has all requisite corporate power and
authority to own, lease and operate its properties and to carry on its business
as now being conducted, and possesses all licenses, franchises, rights and
privileges material to the conduct of its business. ACS has all requisite
corporate power and authority to enter into this Agreement and to consummate the
transactions contemplated hereby. The execution and delivery of this Agreement,
and the consummation of the transactions contemplated hereby have been duly
authorized by all necessary corporate action on the part of ACS. This Agreement
has been duly executed and delivered by ACS and constitutes a valid and binding
obligation of ACS enforceable in accordance with its terms, except as may be
limited by applicable bankruptcy, insolvency or similar laws affecting the
enforcement of creditors rights in general.

             (c) Governmental Consents. No consent, approval, order or
authorization of, or registration, declaration or filing with, any governmental
entity is required by or with respect to ACS in connection with the execution
and delivery of this Agreement by ACS or the consummation by ACS of the
transactions contemplated hereby, except for (i) such consents, approvals,
orders, authorizations, registrations, declarations and filings as may be
required under applicable federal and state securities laws, and (ii) such other
consents, authorizations, filings, approvals and registrations which if not
obtained or made would not have a material adverse effect on ACS taken as a
whole.

             (d) No Conflict. The execution and delivery of this Agreement by
ACS and the performance of its obligations hereunder (i) will not be in
violation or breach of, and will not conflict with or constitute a default
under, any of the terms of the Articles of Incorporation or Bylaws of ACS, or
any note, debt instrument, security agreement, lease, deed of trust or mortgage,
or any other contract, agreement or commitment binding upon ACS or any of its
assets or properties; (ii) will not result in the creation or imposition of any
lien, encumbrance, equity or restriction in favor of any


                                       7
<PAGE>   8

third party upon any of the assets or properties of ACS; and (iii) will not
conflict with or violate any applicable law, rule, regulation, judgment, order
or decree of any government, governmental instrumentality or court having
jurisdiction over ACS or any of its assets or properties other than any such
conflicts, violations, defaults, terminations, cancellations or accelerations
which individually or in the aggregate would not have a material adverse effect
on ACS taken as a whole. No consents, waivers or approvals of third parties
material to the operations of ACS are required to be obtained by ACS in
connection with the execution and delivery of this Agreement and the performance
of ACS's obligations hereunder.

             (e) Issuance of the Common Stock of ACS. The shares of ACS Common
Stock and Series C Preferred Stock issuable upon exercise of the Call Option or
the Put Option hereunder and the shares of ACS Common Stock issuable upon
conversion of such shares of Series C Preferred Stock have been duly and validly
reserved for issuance and when issued pursuant to this Agreement, will be duly
and validly authorized and issued, fully paid and nonassessable.

        7.2 Representations and Warranties of the Company. The Company
represents and warrants to ACS and the Preference Holders as of the date hereof
as follows:

             (a) Organization. The Company is a corporation duly incorporated,
validly existing and in good standing under the laws of the country of
Singapore, and is duly qualified to do business and is in good standing in each
of the other jurisdictions in which it owns or leases property or conducts
business except where the failure to be so qualified would not have a material
adverse effect on its business.

             (b) Capitalization. The authorized, issued and outstanding capital
stock of the Company on the Effective Date of this Agreement is as set forth on
Exhibit D hereto. All of such issued and outstanding shares of capital stock
have been duly authorized and validly issued and are fully paid and
nonassessable.

             (c) Authority. The Company has all requisite corporate power and
authority to own, lease and operate its properties and to carry on its business
as now being conducted, and possesses all licenses, franchises, rights and
privileges material to the conduct of its business. The Company has all
requisite corporate power and authority to enter into this Agreement and to
consummate the transactions contemplated hereby. The execution and delivery of
this Agreement, and the consummation of the transactions contemplated hereby
have been duly authorized by all necessary corporate action on the part of the
Company. This Agreement has been duly executed and delivered by the Company and
constitutes a valid and binding obligation of the Company enforceable in
accordance with its terms, except as may be limited by applicable bankruptcy,
insolvency or similar laws affecting the enforcement of creditors rights in
general.

             (d) Governmental Consents. No consent, approval, order or
authorization of, or registration, declaration or filing with, any governmental
entity is required by or with respect to the Company in connection with the
execution and delivery of this Agreement by the Company or the consummation by
the Company of the transactions contemplated hereby, except for (i) such
consents, approvals, orders, authorizations, registrations, declarations and
filings as may be required


                                       8
<PAGE>   9

under applicable federal and state securities laws, and (ii) such other
consents, authorizations, filings, approvals and registrations which if not
obtained or made would not have a material adverse effect on the Company taken
as a whole.

             (e) No Conflict. The execution and delivery of this Agreement by
the Company and the performance of its obligations hereunder (i) will not be in
violation or breach of, and will not conflict with or constitute a default
under, any of the terms of the Articles of Incorporation or Bylaws of the
Company, or any note, debt instrument, security agreement, lease, deed of trust
or mortgage, or any other contract, agreement or commitment binding upon the
Company or any of its assets or properties; (ii) will not result in the creation
or imposition of any lien, encumbrance, equity or restriction in favor of any
third party upon any of the assets or properties of the Company; and (iii) will
not conflict with or violate any applicable law, rule, regulation, judgment,
order or decree of any government, governmental instrumentality or court having
jurisdiction over the Company or any of its assets or properties other than any
such conflicts, violations, defaults, terminations, cancellations or
accelerations which individually or in the aggregate would not have a material
adverse effect on the Company taken as a whole. No consents, waivers or
approvals of third parties material to the operations of the Company are
required to be obtained by the Company in connection with the execution and
delivery of this Agreement and the performance of the Company's obligations
hereunder.

             (f) Issuance of the Preference Shares. The Preference Shares were
duly and validly authorized and issued, fully paid and nonassessable.

             (g) Full Disclosure. The information furnished by or on behalf of
the Company pursuant to this Agreement at any time prior to the Closing, taken
as a whole, does not and will not contain any untrue statement of a material
fact, and does not and will not omit to state any material fact necessary to
make any statement, in light of the circumstances under which such statement was
made, not misleading.

        7.3 Representations and Warranties of the Preference Holders. Each
Preference Holder represents and warrants, severally and not jointly, to ACS and
the Company as of the date hereof as follows:

             (a) Authority. This Agreement constitutes a valid and binding
obligation enforceable in accordance with its terms, except as may be limited by
applicable bankruptcy, insolvency or similar laws affecting the enforcement of
creditors rights in general.

             (b) Ownership of Preference Shares; No Conflict. Each Preference
Holder represents and warrants as of this date, and covenants that (i) he has
the right to enter into this Agreement, to transfer to ACS all or any part of
the Preference Shares as set forth for such Preference Holder on Exhibit A, free
and clear of any imperfections of title, lien, claim, encumbrance, restriction
or charge (other than restrictions on resale that may arise under applicable
federal and state securities laws); (ii) the Preference Shares, are not and will
not be subject to any right of first


                                       9
<PAGE>   10

refusal, right of repurchase or any similar right granted to, or retained by,
the Preference Holder, any shareholder of the Company or any other person, other
than the certain right of first refusal set forth in Section 9 of the Joint
Venture Agreement entered into by and among the Company and the Preference
Holders; and (iii) there is no provision of any existing agreement, and the
Preference Holder will not enter into an agreement, by which the Preference
Holder is or would be bound (or to which the Preference Holder is or would
become subject) that conflicts or would conflict with this Agreement or the
performance of the Preference Holder's obligations under this Agreement.

             (c) Additional Representations. If ACS's counsel reasonably deems
it necessary, the transfer of any of the shares of ACS Common Stock upon the
exercise of either the Call Option or the Put Option may be conditioned upon the
Preference Holder representing to ACS that:

                    (i) the shares of ACS Common Stock are being acquired (a)
for the Preference Holders's own account, not for the account of any other
person, and (b) for investment and not with a view to distribution or resale
except in compliance with applicable laws regulating securities;

                    (ii) the Preference Holder is capable of evaluating the
merits and risks of its investment in the shares of ACS Common Stock and the
amount of such investment is within the Preference Holder's risk capital means;

                    (iii) the Preference Holder understands and acknowledges
that an investment in ACS as represented by the shares of ACS Common Stock is
highly speculative in nature and is subject to a high degree of risk of loss in
whole or in part;

                    (iv) the Preference Holder understands and acknowledges that
he must bear the economic risk of investment for an indefinite period of time
because the transfer to the Preference Holder of the shares of ACS Common Stock
has not been registered under the Securities Act of 1933, as amended (the
"Act"), and such shares cannot be transferred by the Preference Holder unless
such transfer is registered under the Act or registration is not required in
connection with such transfer; and

                    (v) such other representations as are required in the
opinion of ACS's counsel, reasonably satisfactory to the Preference Holder, to
comply with applicable state or federal securities laws.

             (d) Full Disclosure. The information furnished by or on behalf of
each Preference Holder pursuant to this Agreement, taken as a whole, does not
and will not contain any untrue statement of a material fact, and does not and
will not omit to state any material fact necessary to make any statement, in
light of the circumstances under which such statement was made, not misleading.

                            SECTION 8: MISCELLANEOUS

        8.1 No Inconsistent Agreements. Neither the Company nor ACS nor any
Preference Holder will hereafter enter into any agreement which is inconsistent
with this Agreement.



                                       10
<PAGE>   11

        8.2 Remedies. Any party having rights under any provision of this
Agreement shall have all rights and remedies set forth in this Agreement, and
all rights and remedies which such party has been granted at any time under any
other agreement or contract and all of the rights which such party has under any
law. Any party having any rights under any provision of this Agreement shall be
entitled to enforce such rights specifically (without posting a bond or other
security), to recover damages by reason of any breach of any provisions of this
Agreement and to exercise all other rights granted by law.

        8.3 Amendments and Waivers. Except as otherwise provided herein, the
provisions of this Agreement may be amended or waived only upon the prior
written consent of the Company, ACS and holders of at least a majority of the
Preference Shares outstanding at the time of the amendment or waiver; provided,
however, that any amendment to or waiver of any provision of this Agreement that
would adversely affect a particular Preference Holder in a manner different from
the other Preference Holders shall require the approval of the Preference
Holders so adversely affected. Any such amendment or waiver shall bind the
Company, ACS and the Preference Holders.

        8.4 Successors and Assigns. All covenants and agreements in this
Agreement by or on behalf of any of the parties hereto will bind and inure to
the benefit of the respective successors and assigns of the parties hereto
whether so expressed or not.

        8.5 Severability. Whenever possible, each provision of this Agreement
will be interpreted in such manner as to be effective and valid under applicable
law, but if any provision of this Agreement is held to be prohibited by or
invalid under applicable law, such provision will be ineffective only to the
extent of such prohibition or invalidity, without invalidating the remainder of
this Agreement.

        8.6 Counterparts. This Agreement may be executed simultaneously in two
or more counterparts, any one of which need not contain the signatures of more
than one party, but all such counterparts taken together will constitute one and
the same Agreement.

        8.7 Descriptive Headings. The descriptive headings of this Agreement are
inserted for convenience only and do not constitute a part of this Agreement.

        8.8 Governing Law. The corporate law of California will govern all
issues concerning the relative rights of the Company, ACS and the Preference
Holders. All other questions concerning the construction, validity and
interpretation of this Agreement and the Exhibits and Schedules hereto will be
governed by and construed in accordance with the domestic laws of the State of
California, without giving effect to any choice of law or conflict of law
provision or rule (whether of the State of California or any other jurisdiction)
that would cause the application of the laws of any jurisdiction other than the
State of California. In furtherance of the foregoing, the internal law of the
State of California shall control the interpretation and construction of this
Agreement, even though under that jurisdiction's choice of law or conflict of
law analysis, the substantive law of some other jurisdiction would ordinarily
apply.

        8.9 Notices. All notices and other communications hereunder shall be in
writing and


                                       11
<PAGE>   12

shall be deemed given (i) upon personal delivery; (ii) upon transmission by
facsimile (receipt verified); (iii) upon the fifth day following deposit by
registered or certified mail (return receipt requested), postage prepaid, and,
if delivered to a party overseas, by air mail; or (iv) upon the second day
following dispatch by express courier service (receipt verified), to the parties
at the following addresses (or at such other address for a party as shall be
specified by like notice; provided, that notices of a change of address shall be
effective only upon receipt thereof):

                           To ACS:

                           ACS Corporation
                           15279 Alton Parkway, Suite 100
                           Irvine, CA  92618
                           Attn:    John Parrish

                           With Copies to:

                           Wilson Sonsini Goodrich & Rosati
                           650 Page Mill Road
                           Palo Alto, CA 94304-1050
                           Attention: J. Casey McGlynn
                           Telephone. (415) 493-9300
                           Facsimile: (415) 493-6811

                           To the Company:

                           Visionex Pte. Ltd.
                           1 Robinson Road, #18 - 00 AIA Tower
                           Singapore 048542


                           To the Preference Holders:
                           At the addresses set forth on Exhibit A.

                           With Copies to:

                           Heller, Ehrman, White & McAuliffe
                           50 Raffles Place, #17-04
                           Singapore  048623
                           Telephone:  (65) 538-1756
                           Facsimile:    (65) 538-1537

        8.10 Entire Agreement. This Agreement (including the documents referred
to herein) constitutes the entire agreement between the parties hereto and
supersedes any prior understandings, agreements or representations by or between
such parties, written or oral, that may have related in any way to the subject
matter hereof.



                                       12
<PAGE>   13

        8.11 Further Action. Each party hereto shall take such further action
and shall execute and deliver such further documents as reasonably may be
requested by any other party in order to carry out the provisions and purposes
of this Agreement.

        8.12 Tax Consequences. To the extent any Preference Holder is required
to include in income currently upon an exercise of the Call Option or Put Option
any amount attributable to its share pursuant to Section 367(b) of the Internal
Revenue Code and the Temporary Regulations in effect as of the date hereof
("Section 367(b)"), ACS shall issue to such Preference Holder additional shares
of Common Stock of ACS (the "Additional Shares") having a value equal to the
amount of tax liability actually incurred by any individual Preference Holder or
individual or nonexempt entity partner of such Preference Holder pursuant to
Section 367(b).




                                       13

<PAGE>   14
                                       14


        IN WITNESS WHEREOF, the parties have executed this Agreement as of the
date first above written.

ADVANCED CORNEAL SYSTEMS, INC.


By:

Title:
         President


VISIONEX PTE. LTD.


By:

Title:
         President


<PAGE>   15
                                       15


                             DP III ASSOCIATES, L.P.
                             By:  One Palmer Square Associates III, L.P.

                             By:

                             Its:

                             BIOTECHNOLOGY INVESTMENTS LIMITED
                             By:  Old Court Limited

                             By:

                             Its:

                             DOMAIN PARTNERS III, L.P.
                             By:  One Palmer Square Associates III, L.P.

                             By:

                             Its:

                             SANDERLING VENTURE PARTNERS III, L.P.

                             By:

                             Its:

                             SANDERLING III LIMITED PARTNERSHIP

                             By:

                             Its:


                             SANDERLING III BIOMEDICAL, L.P.

<PAGE>   16
                             16

                             By:

                             Its:

                             SANDERLING VENTURE PARTNERS IV, L.P.

                             By:

                             Its:

                             SANDERLING IV LIMITED PARTNERSHIP

                             By:

                             Its:

                             SANDERLING FERI TRUST VENTURE
                             PARTNERS IV, L.P.

                             By:

                             Its:

                             SANDERLING IV BIOMEDICAL, L.P.

                             By:

                             Its:

                             SANDERLING VENTURE MANAGEMENT LLC

                             By:

                             Its:


<PAGE>   17
                             17


                             CHANCELLOR VENTURE CAPITAL II, L.P.

                             By:

                             Its:

                             KME VENTURE III, L.P.

                             By:

                             Its:

                             DRAKE & CO. F/B/O CITIVENTURE PRIVATE
                             PARTICIPATION III LIMITED

                             By:

                             Its:

                             ECICS VENTURES PTE. LTD.

                             By:  ECICS Management Pte. Ltd.

                             By:

                             Title:

                             ECICS VENTURES 2 LIMITED
                             By:  ECICS Management Pte. Ltd.

                             By:
                             Title:

                             OCBC, WEARNES & WALDEN INVESTMENTS
                                           (SINGAPORE) LIMITED
                             O,W&W INVESTMENTS LIMITED

<PAGE>   18
                             18


                             By:  OCBC, Wearnes & Walden Management
                             (Singapore) Pte. Ltd.

                             By:

                             Title:

                             UOB VENTURE INVESTMENTS LIMITED

                             UOB VENTURE INVESTMENTS II LIMITED

                             By:  UOB Venture Management Pte. Ltd.

                             By:

                             Title:

                             SINGAPORE BIO-INNOVATIONS PTE. LTD.

                             By:

                             Title:

                             VERTEX ASIA LIMITED

                             VERTEX INVESTMENT (II) LIMITED

                             HWH INVESTMENT PRIVATE LIMITED

                             By:  Vertex Management, Inc.

                             By:

                             Title:


<PAGE>   19



                                    EXHIBIT A

                              SCHEDULE OF INVESTORS


<TABLE>
<CAPTION>
                                                            Number of         Total Purchase Price
                 Name and Address                       Preference Shares      (Singapore Dollars)
<S>                                                     <C>                   <C>

DP III Associates, L.P.                                       44,588            S$     63,760.84
Biotechnology Investments Limited                          1,333,334            S$  1,906,667.62
Domain Partners III, L.P.                                  1,288,751            S$  1,842,913.93
c/o Brian Dovey
One Palmer Square
Princeton, NJ 08542

Sanderling Venture Partners III, L.P.                        389,357            S$    556,780.51
Sanderling III Limited Partnership                           201,689            S$    288,415.27
Sanderling III Biomedical, L.P.                               67,104            S$     95,958.72
Sanderling Venture Partners IV, L.P.                       1,046,912            S$  1,497,084.16
Sanderling IV Limited Partnership                            408,429            S$    584,053.47
Sanderling Feri Trust Venture
   Partners IV, L.P.                                         116,156            S$    166,103.08
Sanderling IV Biomedical, L.P.                               407,560            S$    582,810.80
Sanderling Ventures Management LLC                            29,480            S$     42,156.40
c/o Robert G. McNeil, Ph.D
2730 Sand Hill Road, Suite 200
Menlo Park, CA 94025

Chancellor Venture Capital II, L.P.                          366,301            S$    523,810.43
KME Venture III, L.P.                                         51,282            S$     73,333.26
Drake & Co. f/b/o Citiventure Private                        915,755            S$  1,309,529.65
   Participation III Limited
c/o Peggy Segal
1166 Avenue of the Americas
New York, NY 10036

Singapore Bio-Innovations Pte. Ltd.                        1,333,334            S$  1,906,667.62
250 North Bridge Road, #24-00
Raffler City Tower
Singapore 179101
Attention:  Mr. Yong Sea Teoh

Vertex Asia Limited                                          533,335            S$    762,669.05
Vertex Investment (II) Limited                               533,335            S$    762,669.05
HWH Investment Private Limited                               133,335            S$    190,669.05
c/o Ms. Christina Lim
Vertex Management, Inc.
3 Lagoon Drive, Suite 220
Redwood City, CA 94065
</TABLE>


                                       19
<PAGE>   20

<TABLE>
<S>                                                         <C>                 <C>
UOB Venture Investments Limited                              333,335            S$    476,669.05
UOB Venture Investments II Limited                           333,335            S$    476,669.05
c/o Kim Seng Tan
UOB Venture Management Pte. Ltd.
80 Raffles Place 10th Storey
UOB Plaza 1
Singapore 048624

OCBC, Wearnes & Walden Investments
   (Singapore) Limited                                       233,335            S$    333,669.05
O,W&W Investments Limited                                    233,335            S$    333,669.05
c/o OCBC, Wearnes & Walden
Management
   (Singapore) Pte. Ltd.
65 Chulia Street #39-01
OCBC Centre
Singapore 049513
Attention:  Daniel Ong

ECICS Ventures Pte. Ltd.                                     111,115            S$    158,894.45
ECICS Ventures 2 Limited                                     222,225            S$    317,781.75
c/o ECICS Management Pte. Ltd.
7 Temasek Boulevard #11-01
Suntec Tower One
Singapore 038987
Attention:  Patrick Yang




TOTAL:                                                    10,666,717            S$ 15,253,405.31
</TABLE>


                                       20


<PAGE>   21
                                       21


                                    EXHIBIT B

                           CALL OPTION EXERCISE NOTICE


Date:

TO:      VISIONEX PTE. LTD.
         and the holders of Preference Preferred Stock of VISIONEX PTE. LTD.

        Pursuant to the Call Option Agreement dated as of June 27, 1997 by and
among Visionex Pte. Ltd. (the "Company"), Advanced Corneal Systems, Inc. ("ACS")
and the Preference Holders (the "Agreement"), ACS hereby gives notice of its
election to exercise the Call Option to purchase all of the Preference Shares
owned by the Preference Holders. Capitalized terms used in this notice shall
have the meanings as defined in the Agreement.

        In accordance with Section 2 of the Agreement, ACS requests that five
(5) days after the Call Option Record Date, the Company provide to ACS, in
writing, a certification as to the number of outstanding Preference Shares on
the Call Option Record Date, the owners of the outstanding Preference Shares on
the Call Option Record Date, and the address of each Preference Holders.

        The Call Option Closing Date shall be _______________. ACS hereby
requests that the Preference Holders provide to ACS a written certification by
each Preference Holder that the representations and warranties made by the
Preference Holder in the Agreement are true and correct as of the date of the
Preference Holder's certification and will be true and correct as of the Call
Option Closing Date. For this purpose, a Preference Holder may sign and return a
copy of this letter on the space provided.

Very truly yours,

ADVANCED CORNEAL SYSTEMS, INC.


        The undersigned Preference Holder hereby certifies that the
representations and warranties made by him in the Agreement are true and correct
as of the date Preference Holder signs this certification and will be true and
correct as of the Call Option Closing Date.



Signature


Printed Name


<PAGE>   22
                                       22


                                    EXHIBIT C

                           PUT OPTION EXERCISE NOTICE


Date:

TO:      ADVANCED CORNEAL SYSTEMS, INC.
         AND VISIONEX PTE. LTD.

        Pursuant to the Call Option Agreement dated as of June 27, 1997 by and
among Visionex Pte. Ltd. (the "Company"), Advanced Corneal Systems, Inc. ("ACS")
and the Preference Holders (the "Agreement"), the undersigned Preference Holder
gives notice of its election to exercise the Put Option to require ACS to
purchase Preference Shares owned by the undersigned Preference Holder, which
number of shares constitutes at least 50% of the Preference Shares as set forth
for the undersigned Preference Holder on Exhibit A of the Agreement. Capitalized
terms used in this notice shall have the meanings as defined in the Agreement.

Very truly yours,


Signature


Printed Name

<PAGE>   23



                                    EXHIBIT D

                   VISIONEX PTE. LTD. CAPITALIZATION SCHEDULE


<TABLE>
<CAPTION>
                                                        Number of
            Name/Address                            Preference Shares
<S>                                                 <C>

DP III Associates, L.P.                                    44,588
Biotechnology Investments Limited                       1,333,334
Domain Partners III, L.P.                               1,288,751
c/o Brian Dovey
One Palmer Square
Princeton, NJ 08542
Sanderling Venture Partners III, L.P.                     389,357
Sanderling III Limited Partnership                        201,689
Sanderling III Biomedical, L.P.                            67,104
Sanderling Venture Partners IV, L.P.                    1,046,912
Sanderling IV Limited Partnership                         408,429
Sanderling Feri Trust Venture
   Partners IV, L.P.                                      116,156
Sanderling IV Biomedical, L.P.                            407,560
Sanderling Venture Management LLC                          29,480
c/o Robert G. McNeil, Ph.D
2730 Sand Hill Road, Suite 200
Menlo Park, CA 94025
Chancellor Venture Capital II, L.P.                       366,301
KME Venture III, L.P.                                      51,282
Drake & Co. f/b/o Citiventure Private                     915,755
   Participation III Limited
c/o Peggy Segal
1166 Avenue of the Americas
New York, NY 10036
Singapore Bio-Innovations Pte. Ltd.                     1,333,334
250 North Bridge Road, #24-00
Raffler City Tower
Singapore 179101
Attention:  Mr. Yong Sea Teoh
Vertex Asia Limited                                       533,335
Vertex Investment (II) Limited                            533,335
HWH Investment Private Limited                            133,335
c/o Ms. Christina Lim
Vertex Management, Inc.
3 Lagoon Drive, Suite 220
Redwood City, CA 94065
</TABLE>



                                       23
<PAGE>   24

<TABLE>
<S>                                                    <C>

UOB Venture Investments Limited                           333,335
UOB Venture Investments II Limited                        333,335
c/o Kim Seng Tan
UOB Venture Management Pte. Ltd.
80 Raffles Place 10th Storey
UOB Plaza 1
Singapore 048624
OCBC, Wearnes & Walden Investments
   (Singapore) Limited                                    233,335
O,W&W Investments Limited                                 233,335
c/o OCBC, Wearnes & Walden Management
   (Singapore) Pte. Ltd.
65 Chulia Street #39-01
OCBC Centre
Singapore 049513
Attention:  Daniel Ong
ECICS Ventures Pte. Ltd.                                  111,115
ECICS Ventures 2 Limited                                  222,225
c/o ECICS Management Pte. Ltd.
7 Temasek Boulevard #11-01
Suntec Tower One
Singapore 038987
Attention:  Patrick Yang


           Total Preference Shares Outstanding         10,666,717
</TABLE>



                                       24