<PAGE>   1
                                                                EXHIBIT 10.35







                              EMPLOYMENT AGREEMENT


         EMPLOYMENT AGREEMENT made this 30th day of April, 1989 between ESCALON
OPHTHALMICS, INC., a Pennsylvania corporation (the "Employer") and STERLING
C.JOHNSON (the "Employee").

                                 R E C I T A L

         The parties desire to enter into this Agreement to provide for the
employment of the Employee by the Employer and for certain matters in
connection with such employment, all as set forth more fully in this Agreement.

         NOW, THEREFORE, in consideration of the premises and covenants set
forth herein and intending to be legally bound hereby, the parties to this
Agreement hereby agree as follows:

         1.      DUTIES.  The Employer agrees that the Employee shall be
employed by the Employer during the term of this Agreement (as defined in
Section 2 hereof) to serve as President and Chief Executive Officer of the
Employer.  During the term of this Agreement, the Employee shall also be
recommended to the stockholders of the Employer for election to the Board of
Directors (the "Board") of the Employer.  The Employee agrees to be so employed
by the Employer and to devote his best efforts and substantially all of his
business time to advance the interests of the Employer and discharge adequately
his duties hereunder.

         2.      TERM.  Subject to Sections 4 and 5 hereof, the initial term of
the Employee's employment hereunder shall commence on January 1, 1990 and shall
continue for a term of five (5) years.  This Agreement shall be renewed
automatically upon the expiration of its initial term and each renewal term for
successive terms of one year unless either party notifies the other party in
writing at least 90 days prior to the expiration of any term of such party's
determination not to renew this Agreement beyond the then existing term.

         3.      COMPENSATION.

         (a)     Salary.  During the term of his employment under this
Agreement, the Employee shall be paid an annual salary. The 1990 salary shall
be $140,000 provided the Employer has successfully completed a fund raising
program, or a lesser sum to be determined by the Board if funding of the
Employer is delayed beyond January 1,1990. Such salary shall be reviewed
annually thereafter by the Board and shall be increased each year by a
percentage not less than the sum of (i) the percentage increase in the cost of
living index for the Philadelphia area for the year then ended and (ii) 2%.
The Employee's salary shall be paid in accordance with the
<PAGE>   2

Employer's regular payroll practices.  In addition, the Employee may be paid an
annual performance bonus as determined by the Board in its sole discretion.

         (b)     Stock.  The Employee shall be granted an option to purchase
from the Employer at a price of $0.01 per share, in cash, 300,000 shares of the
Employer's Common Stock (the "Shares") according to the following vesting
schedule:

<TABLE>
                 <S>                    <C>
                 Execution of Agreement - 60,000 Shares
                 January 1,1991         - 60,000 Shares
                 January 1,1992         - 60,000 Shares
                 January 1,1993         - 60,000 Shares
                 January 1,1994         - 60,000 Shares
</TABLE>

                 In addition, the Employee may be offered additional rights
(including options) to purchase additional equity securities of the Employer as
determined by the Board in its sole discretion.

         (c)     Fringe Benefits.  The Employee, to the extent he is insurable,
shall be entitled to the following fringe benefits:

                 (i)  Medical and dental insurance coverage for the Employee
and/or his family, at no cost to the Employee and in accordance with Company
policy;

                 (ii)  Long-term disability insurance based upon the Employee's
salary, commencing when compensation ceases under Section 4(b);

                 (iii) Term life insurance coverage equal to two times the
Employee's salary;

                 (iv) Participation in such other fringe benefit programs or
profit sharing programs of the Employer to the extent and on the same terms and
conditions as are accorded to other officers and key employees of the Employer.

         In the event the Employer/Employee is uninsurable for medical
insurance purposes, the Employer shall pay up to $10,000 of medical expenses of
the Employee during each year of this Agreement.

         (d)     Reimbursement of Expenses.  The Employee shall be reimbursed
for all normal items of travel and entertainment and miscellaneous expenses
reasonably incurred by him on behalf of the Employer upon presentation or
appropriate vouchers and substantiation therefor, including the use of a
personal car on business of the Employer.





                                      -2-
<PAGE>   3
         (e)     Moving Expenses.  If, during the term of this Agreement, the
Employer decides to locate the Employer's principal place of business in a
location that requires the Employee to move the location of his principal
residence, the Employer agrees to pay the reasonable and necessary moving
expenses of the Employee, including reasonable and necessary selling expenses
associated with the sale of his present principal residence and the reasonable
purchase expenses associated with the purchase of his new residence.  Expenses
may including, but are not limited to, broker commissions, legal fees and
mortgage related expenses.

         (f)     Entire Compensation.  The compensation provided for in this
Agreement shall constitute full payment for the services to be rendered by the
Employee to the Employer hereunder.

         4.      DEATH OR TOTAL DISABILITY OF THE EMPLOYEE.

         (a)     Death.  In the event of the death of the Employee during the
term of this Agreement, this Agreement shall terminate effective as of the date
of the Employee's death, and the Employer shall not have any further obligation
or liability under this Agreement except that the Employer shall pay to the
Employee's estate any portion of the Employee's salary for the period up to the
Employee's date of death that remains unpaid.

         (b)     Total Disability.  In the event of the Total Disability (as
that term is hereinafter defined) of the Employee for a period of 90
consecutive days at any time during the term of this Agreement, the Employer
shall have the right to terminate the Employee's employment hereunder by giving
the Employee 30 days' written notice thereof, and, upon expiration of such
30-day period, the Employer shall not have any further obligation or liability
under this Agreement except that the Employer shall pay to the Employee any
portion of the Employee's salary for the period up to the date of termination
that remains unpaid.

                 The term "Total Disability" when used herein, shall mean a
mental or physical condition which in the reasonable opinion of the Board of
the Employer, including the advice of an outside licensed physician renders the
Employee unable or incompetent to carry out the job responsibilities required
by his position as President and Chief Executive Officer.





                                      -3-
<PAGE>   4

         5.      TERMINATION OF EMPLOYEE.

         (a)     For Cause; Resignation.  The Employer may discharge the
Employee and thereby terminate his employment hereunder for cause which shall
be deemed to include the following:

                 (i)     habitual intoxication;

                 (ii)    drug addiction;

                 (iii)   conviction of a felony;

                 (iv)    failure to execute such duties as are within the scope
                 of this Agreement and are reasonably required of an employee
                 holding his positions;

                 (v)     a breach by the Employee of any material term of this
                 Agreement;

                 (vi)    engaging in conduct that, in the reasonable opinion of
                 the Board of the Employer and as supported by an unrelated
                 third party assessment, has injured or would injure the
                 business or reputation of the Employer or would otherwise
                 adversely affect its interests; or

                 (vii)    misappropriation of any corporate funds or property
of the Employer, theft embezzlement or fraud.

In the event that the Employer shall discharge the Employee for cause pursuant
to this Section 5(a), or in the event that Employee shall resign his employment
with the Employer, the Employer shall not have any further obligation or
liability to the Employee under this Agreement, except that the Employer shall
pay to the Employee any portion of the Employee's salary for the period up to
the date of termination that remains unpaid.

         (b)     Without Cause.  If the Employer discharges the Employee
without cause hereunder (i.e., for a reason other than as set forth in Section
5(a)), the Employer shall not have any further obligation or liability to the
Employee under this Agreement, except that:

                 (i)     the Employer shall pay to the Employee any portion of
                 the Employee's salary and fringe benefits for the period up to
                 the date of termination that remains unpaid; and





                                      -4-
<PAGE>   5
                 (ii)    the Employer shall continue the Employee's salary and
                 fringe benefits for a period of one year after termination.

         6.  NON-DISCLOSURE AND NON-COMPETITION.

         (a)     Non-Disclosure.  The Employee recognizes and acknowledges that
he will have access to certain confidential information of the Employer and
that such information constitutes valuable, special and unique property of the
Employer.  The Employee agrees that he will not, for any reason or purpose
whatsoever, during or after the term of his employment, disclose any such
confidential information to any person without express authorization of the
Employer, except (i) as necessary in the ordinary course of performing his
duties hereunder or (ii) with regard to information that is in the public
domain or that the Employee learns outside of the scope of his employment.  The
Employee also agrees to abide by the terms of any non-disclosure agreements
entered into by the Employer with any third parties.

         (b)     Non-Competition.  The Employee agrees that:

                 (i)     during his employment by the Employer hereunder; and

                 (ii)    for an additional period of two years after the
                 termination of the Employee's employment hereunder,

neither the Employee nor any firm or corporation in which he may be interested
as a partner, trustee, director, officer, employee, agent, shareholder, lender
of money or guarantor, or for which he performs services in any capacity
(including as a consultant or independent contractor) shall at any time during
such period be engaged, directly or indirectly, in any Competitive Business (as
that term is hereinafter defined); provided, however, that the business
activities of the Employee on behalf of any other entity that is in control of,
controlled by or under common control with the Employer shall not be deemed to
violate the Employee's undertakings as set forth in this Section 6(b).  Nothing
herein contained shall be deemed to prevent the Employee from investing in or
acquiring one percent or less of any class of securities of any company is such
class of securities is listed on a national securities exchange or is quoted on
the NASDAQ system.  For purposes of this Section 6(b), the term "Competitive
Business" shall mean any business that develops, produces, or markets
ophthalmic products, devices or equipment, whether of a diagnostic,
prophylactic or therapeutic nature, which are competitive with the





                                      -5-
<PAGE>   6
Employer's products at the time of termination.  Notwithstanding the foregoing,
this Section 6(b) shall not apply if the Employee is terminated by the Employer
without cause under Section 5(b).

         (c)     Injunctive Relief.  The Employee acknowledges that his
compliance with the agreements in Sections 6(a) and 6(b) hereof is necessary to
protect the good will and other proprietary interests of the Employer and that
he is the Chief Executive Officer of the Employer and conversant with its
affairs, its trade secrets, its customers and other proprietary information.
The Employee acknowledges that a breach of his agreements in Sections 6(a) and
6(b) hereof will result in irreparable and continuing damage to the Employer
for which there will be no adequate remedy at law; and the Employee agrees that
in the event of any breach of the aforesaid agreements, the Employer and its
successors and assigns shall be entitled to injunctive relief and to such other
and further relief as may be proper.

         (d)     Survival of Covenants.  The provisions of this Section 6 shall
survive the termination of this Agreement.

         7.      SUPERSEDES OTHER AGREEMENTS.

         This Agreement supersedes and is in lieu of any and all other
employment arrangements between Employee and the Employer, but shall not
supersede any existing confidentiality or non-disclosure agreements between the
Employee and the Employer.

         8.      AMENDMENTS.

         Any amendment to this Agreement shall be made in writing an signed by
the parties hereto.

         9.      ENFORCEABILITY.

         If any provision of this Agreement shall be invalid or unenforceable,
in whole or in part, then such provision shall be deemed to be modified or
restricted to the extent and in the manner necessary to render the same valid
and enforceable, or shall be deemed excised from this Agreement, as the case
may require, and this Agreement shall be construed, and enforced to the maximum
extent permitted by law as if such provision had been originally incorporated
herein as so modified or restricted or as if such provision had not been
originally incorporated herein, as the case may be.





                                      -6-
<PAGE>   7
         10.     CONSTRUCTION.

         The Agreement shall be construed and interpreted in accordance with
the internal laws of the State of New Jersey.

         11.     ASSIGNMENT.

         (a)     By the Employer.  The rights and obligations of the Employer
under this Agreement shall inure to the benefit of, and shall be binding upon,
the successors and assigns of the Employer.

         (b)     By the Employee.  This Agreement and the obligations created
hereunder may not be assigned by the Employee.

         12.     NOTICES.

         All notices required or permitted to be given hereunder shall be in
writing and shall be deemed to have been given when mailed by certified mail,
return receipt requested, or delivered by a national overnight delivery service
addressed to the intended recipient as follows:



         IF TO THE EMPLOYEE:

                 Sterling C. Johnson
                 36 Richmond Drive
                 Skillman, New Jersey 08558

         IF TO THE EMPLOYER:

                 Escalon Ophthalmics, Inc.
                 1608 Walnut Street
                 Suite 1702
                 Philadelphia, PA  19103
                 Attn:  Richard J. DePiano

         WITH A COPY TO:

                 Sheldon M. Bonovitz, Esquire
                 Duane, Morris & Heckscher
                 One Liberty Place
                 Philadelphia, PA  19102






                                      -7-
<PAGE>   8
Any party may from time to time change its address for the purpose of notices
to that party by a similar notice specifying a new address, but no such change
shall be deemed to have been given until it is actually received by the party
sought to be charged with its contents.

         13.     WAIVERS.

         No claim or right arising out of a breach or default under this
Agreement shall be discharged in whole or in part by a waiver of that claim or
right unless the waiver is supported by consideration and is in writing and
executed by the aggrieved party hereto or his or its duly authorized agent.  A
waiver by any party hereto of a breach or default by the other party hereto of
any provision of this Agreement shall not be deemed a waiver of future
compliance therewith, and such provisions shall remain in full force and
effect.

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


                                                      ESCALON OPHTHALMICS, INC.
                                                                               
                                                      By:                      
                                                         ----------------------
                                                         Chairman of the Board 
                                                                               
                                                                               
                                                      By:                      
                                                         ----------------------
                                                         STERLING C. JOHNSON   
                                              
                                              






                                      -8-
<PAGE>   9



                    FIRST AMENDMENT TO EMPLOYMENT AGREEMENT


         FIRST AMENDMENT TO EMPLOYMENT AGREEMENT dated as the lst day of
January, 1991, by and between ESCALON OPHTHALMICS, INC.  ("Employer") and
STERLING C. JOHNSON ("Employee").


                                 R E C I T A L

         WHEREAS, by Employment Agreement dated April 30, 1989, Employee became
an employee of Employer; and

         WHEREAS, pursuant to Section 3(b) of the Employment Agreement,
Employee was granted options to purchase up to 300,000 shares of common stock
of Employer over five years in accordance with the vesting schedule set forth
therein (the "Options"); and

         WHEREAS, Employee will recognize ordinary income under Section 83 of
the Internal Revenue Code of 1986, as amended (the "Code") upon exercise of the
Options equal to the difference between the then fair market value of the
shares of common stock received and the exercise price; and

         WHEREAS, Employer desires to reimburse Employee for the federal and
state income taxes imposed on Employee by reason of such recognition of such
ordinary income.

         NOW, THEREFORE, the parties hereto, intending to be legally bound
hereby, agree as follows:

                 1.       (a)  Employer shall reimburse Employee, as additional
compensation, an amount sufficient to enable Employee to pay the aggregate
federal and state income taxes imposed on Employee by reason of the recognition
of ordinary income under Section 83 of the Code upon exercise of the Options
received by Employee pursuant to the Employment Agreement.

                          (b)  The amount of such reimbursement shall include
an amount sufficient to enable Employee to pay the federal and state income
taxes imposed on the reimbursement itself, that is, the reimbursement shall be
"grossed up" to reflect the income taxes imposed on the reimbursement itself.

                          (c)  The reimbursement for federal taxes shall take
into account any deduction available to Employee for the payment of state
income taxes.

<PAGE>   10
                          (d)  Employer shall also reimburse Employee for the
cost and expense of obtaining personal tax advice regarding the tax treatment
and the proper reporting of the tax consequences upon receipt and exercise of
the Options.

                 2.       In the event of any disagreement between Employer and
Employee regarding the computation of the reimbursement required to be made in
paragraph 1 hereof, such disagreement shall be resolved by Employer's
accountants, whose determination shall be binding on Employee and Employer and
their respective heirs, personal representatives, successors and assigns.

                 3.       Employee shall cooperate with Employer in furnishing
all information required to enable Employer to compute the reimbursement
required to be made pursuant to paragraph 1 hereof.

                 4.       In all other respects, the Employment Agreement is
hereby ratified and affirmed by the parties.

         IN WITNESS WHEREOF, this First Amendment has been executed by the
parties as of the date first above written.



                                            ESCALON OPHTHALMICS, INC.
                                            
                                            
                                            By:                             
                                                ----------------------------
                                                   Chairman of the Board
                                            
                                            
                                                                            
                                            --------------------------------
                                                  Sterling C. Johnson

<PAGE>   11




                    SECOND AMENDMENT TO EMPLOYMENT AGREEMENT


         This SECOND AMENDMENT TO EMPLOYMENT AGREEMENT ("Second Amendment")
dated this 1st day of January, 1995 is executed between ESCALON OPHTHALMICS,
INC., a Pennsylvania corporation (the "Employer") and STERLING C.JOHNSON (the
"Employee").

                                    RECITALS

         Whereas the Employer and the Employee executed an initial Employment
Agreement ("Agreement") dated April 30, 1989, and a First Amendment on January
1, 1991, which Agreement and First Amendment terminated on December 31, 1994;
and,

         Whereas the parties have agreed that the Employee should continue to
render services to the Employer for an additional term of employment; and,

         Whereas the parties desire to enter into this Second Amendment to the
Agreement ("Second Amendment") to provide for the continued employment of the
Employee by the Employer, and for certain matters in connection with such
employment, all as set forth more fully in this Second Amendment.

         NOW, THEREFORE, in consideration of the premises and covenants set
forth herein and intending to be legally bound hereby, the parties to this
Second Amendment hereby agree as follows:


         1.      NEW TERM.  Subject to Sections 4 and 5 of the Agreement, the
new term of the Employee's employment hereunder the Second Amendment shall
commence on January 1, 1995 and shall continue for a term of three (3) years.
Employment shall be automatically renewed upon the expiration of the term of
the Second Amendment and each renewal term for successive terms of one year
unless either party notifies the other party in writing at least 90 days prior
to the expiration of any term of such party's determination not to renew this
Second Amendment beyond the then existing term.

         2.      COMPENSATION AND AUTOMOBILE.  During the term of his
employment under this Second Amendment, the Employee shall be paid an annual
salary. The 1995 salary shall be $154,000, plus the costs associated with the
lease of an automobile, not to exceed $500.00 per month. Such salary shall be
reviewed annually thereafter by the Board and shall be increased each year at
the sole discretion of the Board.  The Employee's salary shall be paid in
accordance with the Employer's regular payroll practices.  In addition, the
Employee may be paid an annual performance bonus as determined by the Board in
its sole discretion.
<PAGE>   12
SECOND AMENDMENT
PAGE TWO


         3.      BACK PAY.  The Employer agrees that during the term of the
Agreement (1990 to 1994) the Employee was not paid all the salary due him.  The
total unpaid compensation exceeds $118,000, including $33,046 for 1994. In
order for the Employee to be duly compensated for past services the parties
agree that the Employer will issue the Employee 50,000 shares of Escalon common
stock, and pay the Employee $60,000 by December 31, 1996, or, in the event of a
merger of the Employer with another company, within thirty (30) days following
the closing of the merger. The sum of the back pay is shown as Attachment I to
this Second Amendment.

         4.      STOCK.  The Employee shall be continue to be eligible to
receive incentive stock options to granted the Employee at the sole discretion
of the Employer as approved by the Board of Directors.

         All other terms and conditions of the Agreement and First Amendment
remain the same.

         IN WITNESS WHEREOF, this Second Amendment has been executed by the
parties as of the date first above written.


                                                ESCALON OPHTHALMICS, INC.
                                                
                                                By:                       
                                                   -----------------------
                                                   Jay L. Federman, M.D.
                                                   Chairman of the Board
                                                
                                                By:                       
                                                   -----------------------
                                                   STERLING C. JOHNSON






                                      -2-
<PAGE>   13
                                  ATTACHMENT I



<TABLE>
<CAPTION>
Cost of Living Change By Year
-----------------------------
<S>                      <C>
1991 versus 1990         4.2%
1992 versus 1991         3.0%
1993 versus 1992         3.2%
1994 versus 1993         2.9%
</TABLE>

<TABLE>
<CAPTION>
Year             Base Salary                                Amount Paid                       Shortfall
----             -----------                                -----------                       ---------
<S>              <C>                                        <C>                               <C>
1990             $140,000                                   $ 98,115                          $ 41,885
1991              148,680                                    145,569                             3,111
1992              156,114                                    152,403                             3,711
1993              164,232                                    146,968                            17,264
1994              172,279                                    120,207                            52,072
                                                                                              --------
                                                            Total Shortfall                   $118,043
</TABLE>


                 * The formula in the Employment Agreement is that the base
salary was $140,000 for the year 1990, and was to increase by a minimum of the
Cost of Living Index (COLI) for the Philadelphia Area plus two percent (2%).
For example, the COLI change of from 1990 to 1991 of 4.2% plus 2% equals 6.2%.
This number times the base of $140,000 in 1990 equals $148,680 in 1991.





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