EXHIBIT A
                                                             TO SUPPLEMENT TO
                                                             SECURITIES PURCHASE
                                                             AGREEMENT

                   SUPPLEMENT TO REGISTRATION RIGHTS AGREEMENT

         SUPPLEMENT TO REGISTRATION RIGHTS AGREEMENT (this "SUPPLEMENT"),  dated
as of  May  23,  1997  by  and  among  PALOMAR  MEDICAL  TECHNOLOGIES,  INC.,  a
corporation organized under the laws of the State of Delaware, with headquarters
located at 66 Cherry Hill Drive,  Beverly,  Massachusetts 01915 (the "COMPANY"),
RGC INTERNATIONAL INVESTORS, LDC ("RGC") and the other Initial Investors.

         WHEREAS:

        A. The Company and RGC are parties to a  Registration  Rights  Agreement
dated as of March 27, 1997 (the "ORIGINAL  REGISTRATION RIGHTS AGREEMENT" and as
supplemented by this Supplement,  the "REGISTRATION  RIGHTS AGREEMENT") pursuant
to which the  Company  granted  to RGC  certain  registration  rights  under the
Securities  Act  and the  rules  and  regulations  promulgated  thereunder,  and
applicable state securities laws;

        B.  Contemporaneous  with their  execution  and delivery of the Original
Securities  Purchase  Agreement,  the Company and RGC executed  and  delivered a
Registration  Rights  Agreement,  in  the  form  attached  as  Exhibit  B to the
Securities  Purchase Agreement (the "ORIGINAL  REGISTRATION  RIGHTS AGREEMENT"),
pursuant  to which the Company  agreed to provide  certain  registration  rights
under the Securities Act and the rules and regulations  promulgated  thereunder,
and applicable state securities laws;

        C. In connection with the Supplement to Securities Purchase Agreement of
even  date  herewith  by and  between  the  Company  and each of the  Additional
Investors (the "SECURITIES PURCHASE AGREEMENT  SUPPLEMENT" and together with the
Securities  Purchase  Agreement  dated as of March 27,  1997 by and  between the
Company and RGC, the "SECURITIES PURCHASE  AGREEMENT"),  the Company has agreed,
upon the terms and subject to the  conditions  contained  therein,  to issue and
sell to the undersigned shares of its Series H Convertible  Preferred Stock, par
value $.01 per share; and

        D. To induce the Initial Investors to execute and deliver the Securities
Purchase Agreement Supplement,  the Company has agreed to amend the terms of the
Original  Registration  Rights  Agreement to provide the Initial  Investors  the
rights and benefits set forth in the Original Registration Rights Agreement;

        E. All other  capitalized terms used herein and not otherwise defined in
this  Supplement  shall have the  respective  meanings set forth in the Original
Registration Rights Agreement.

         NOW,  THEREFORE,  in  consideration  of the  premises  and  the  mutual
covenants  contained  herein  and other  good and  valuable  consideration,  the
receipt and sufficiency of which are hereby  acknowledged,  the Company, RGC and
each of the other  Initial  Investors  hereby agree to  supplement  the Original
Registration Rights Agreement as follows:

1.       DEFINITIONS.  The definitions of the following terms contained in the
Original Registration Rights Agreement are amended as follows:

         a. "INITIAL  INVESTORS"  shall be deemed to include RGC and each of the
other Initial  Investors set forth on the Execution  Page hereto and each of the
other  Initial  Investors  set forth on Execution  Pages which may  hereafter be
appended to this Supplement in accordance with Section 4 hereof (each,  together
with their affiliates).

         b.  "PREFERRED  STOCK"  means  the  shares  of the  Company's  Series H
Convertible Preferred Stock, par value $.01 per share, issued or to be issued to
Initial Investors  pursuant to the Securities  Purchase Agreement on the initial
Closing Date or on any  Additional  Closing  Date (as defined in the  Securities
Purchase Agreement Supplement).  For the avoidance of doubt the term "Conversion
Shares"  includes all shares of Common Stock  issuable on or with respect to all
of the shares of Preferred Stock.

         c.  "REGISTRATION RIGHTS AGREEMENT" and "SECURITIES PURCHASE AGREEMENT"
 shall have the meanings set forth in the recitals to this Supplement.

         d.  "RGC" means RGC International Investors, LDC.

2. Except as expressly  supplemented  and/or modified  herein,  the terms of the
Original Registration Rights Agreement shall continue in full force and effect.

3. In the event an Additional  Closing under the Securities  Purchase  Agreement
shall not have  occurred on or before May 7, 1997,  unless each of the  original
parties hereto agrees otherwise, this Supplement shall terminate at the close of
business on such date and shall be of no further force or effect.

4. An Initial Investor shall become a party to the Registration Rights Agreement
upon execution of an Execution  Page by such Initial  Investor on or before June
19, 1997. Upon execution,  such Initial Investor shall be entitled to all of the
benefits  conferred  thereby  and  shall be  subject  to all of the  obligations
thereunder.

<PAGE>

         IN WITNESS WHEREOF,  the undersigned  Initial Investors and the Company
have  caused  this  Supplement  to be duly  executed  as of the date first above
written.


PALOMAR MEDICAL TECHNOLOGIES, INC.



By:
   -------------------------------
   Name:
   Title:




INITIAL INVESTOR:


SOUTHBROOK INTERNATIONAL INVESTMENTS, LTD.

By:
   ---------------------------------------
   Name:
   Title:


RGC INTERNATIONAL INVESTORS, LDC



By:
   --------------------------------------
   Name:
   Title: