Biomedical Engineering Reference
In-Depth Information
Examinations of the rabbit eyes are done using a Draize scor-
ing system on days 1-7, 9-14, and 16-21 just prior to lens
removal. Additional examinations of the eyes can be performed
based on any findings noted during the study. On days 8, 15, and
22 after lens removal, eyes are fluorescein stained and slit-lamp
examinations using the McDonald-Shadduck scoring system
are conducted. The animals are euthanized after the eye examina-
tions on day 22, and the eyes are fixed in an appropriate fixative
(e.g. Davidson's solution, 10% neutral-buffered formalin). Micro-
scopic examination of the cornea, conjunctivae, iris, and lens is
conducted.
Evaluation of corneal metabolism may be important safety data
based on the nature of the test article (e.g., extended wear contact
lenses). It is suggested that a minimum of three additional rabbits
(test and control eyes) are used if the effects on corneal metabolism
are tested in this 22-day study.
A specific ISO standard 11979-5 [
12
] was written to address the
biocompatibility evaluation of IOLs. The requirements in this stan-
dard include evaluation of physicochemical properties that are rele-
vant to biocompatibility and guidance on conducting an ocular
implantation study.
Prior to biocompatibility testing for any device, an initial risk
assessment (ISO 14971) [
24
] should be conducted also taking into
account the history of material in clinical use and animal models to
test the long-term stability of the materials. To address any gaps in
the risk assessment, the following physicochemical tests, which are
described in the ISO standard for IOLs, should be considered.
1. Exhaustive extraction test
The IOL material should be tested for extractables under
exhaustive conditions, and the extraction media should be
analyzed.
2. Test for leachables
The purpose of this testing is to detect and quantify extractable
additives and other leachables from IOL material under physi-
ologic conditions.
3. Test for hydrolytic stability
This test should determine the stability of an IOL material in an
aqueous environment through detection and quantification of
possible degradation products from hydrolysis and changes in
physical appearance, optical properties, and chromatographic
characteristics.
4. Photostability test
The purpose of this test is to determine the photostability of
IOL materials when irradiated over
3.2 Intraocular
implants
a wavelength of
300-400 nm.
