Biomedical Engineering Reference
In-Depth Information
5. Nd-YAG laser exposure test
Laser therapy may be given to patients with IOLs, and this test
is designed to evaluate any physical or chemical effects or
leakage from IOLs after Nd-YAG laser exposure.
6. Evaluation of insoluble inorganics
The IOL material should be evaluated for the presence of
residual insoluble inorganics on and in the lens from
manufacturing and process aids. If any are identified, then the
residuals should be identified.
Based on risk assessment of the materials, the following bio-
compatibility endpoints should be considered for IOLs: cytotoxic-
ity, genotoxicity, local effects after implantation, and sensitization
potential. Since IOLs are extremely small (approximately 20 mg),
no testing is required to evaluate systemic or chronic toxicity.
Details on the conduct of the cytotoxicity, genotoxicity, and sensi-
tization studies were discussed earlier in this chapter.
Because of the target tissue for IOLs, an ocular implantation
study is the likely choice for evaluation of local effects. This specific
guidance on IOLs describes an ocular implantation study in rabbits.
As is ideal for biocompatibility studies, the test article should be a
finished IOL, and the control article should be an IOL of a similar
design with at least 5 years of successful marketed use. A minimum
of six test IOL eyes and six control IOL eyes should be evaluated for
the study; the control IOL should be implanted in contra-lateral
eye from the test IOL.
If the rabbit is chosen as the model, then the implantation
study duration should be 6 months; the rabbit is prone to fibrin
formation and rapid lens regrowth which complicates a longer-term
assessment. Any other animal model used for this study should have
a duration of 1 year. The implantation procedure should be as close
to the clinical use as possible; however, due to the rabbit model and
ocular geometry, the IOL material can alternatively be located at
another ocular site with adequate justification.
After implantation, slit-lamp biomicroscopy is used to monitor
the eyes after 7 days, 4 weeks, 3 months, 6 months, and at the end of
the follow-up period (if longer than 6 months). The observations
should include fibrin, flare, cells, adhesions, neovascularization, cor-
neal edema, material clarity, location of the haptic, and centration of
the IOL. At the conclusion of the study, the eyes are enucleated,
dissected, examined, and fixed for histopathologic examination. Dur-
ing dissection, the IOLs are removed and examined by light micros-
copy for cells, debris, and fibrinous deposits. Half of the lenses are
cleaned and examined for optical properties as described in ISO
standard 11979-2 [
12
]. The remaining lens samples are evaluated
by scanning electron microscopy for signs of calcification.
