Biomedical Engineering Reference
In-Depth Information
of six test eyes is needed for evaluation at the end of a 6-month
implantation period. Therefore, one extra animal each for the test
and control groups (total of seven) should be considered to account
for any inadvertent animal loss during the study.
The study animals should be anesthetized, prepared, and
draped under aseptic techniques. After insertion of a lid speculum,
a fornix-based conjunctival flap is dissected between the insertions
of two adjacent rectus muscles. The shunt is sutured to the sclera an
appropriate distance posterior to the limbus and is inserted into the
anterior chamber through an appropriately sized needle tract. A
patch graft may be placed over the anterior portion of the tube. The
conjunctival wound is closed, and the eye is treated with an anti-
bacterial or steroid ointment.
Gross examination of the eyes should be done at 1 and 3 days
postsurgery; both slit-lamp biomicroscopic and indirect ophthalmo-
scopic examinations should be at done 1 and 4 weeks, and at 3 and 6
months postsurgery. The observations should include at a minimum
flare, cell adhesions, neovascularization, corneal edema, and location
of the tube and implant. After the 6-month interval, the animals
should be euthanized; at least three enucleated eyes should be
immediately fixed in neutral-buffered formalin for storage. The
retrieved eyes should be sectioned equatorially and examined noting
the location/placement of the shunt. Histopathological evaluations
should be done at the anterior and posterior segments of the eyes.
The explanted shunts should be examined for cellular and fibrinous
deposits, especially inside and at the tube/implant junctions. At least
two shunts should have pressure/flow testing, and the structural
integrity of the shunts should be evaluated. The aqueous shunt
material will be judged biocompatible if implantation in the eye
does not produce a significant local response, and does not have
any detectable changes in flow properties.
The US FDA uses a classification system (Class 1, 2, and 3) for
ophthalmic medical devices [
26
] which is based on how much
regulatory control or risk is applicable for clinical use. For example,
Class 1 devices require the least regulatory control such as dist-
ometers, visual acuity charts, ophthalmic trial lens sets, and a cor-
neal radius measuring device. Class 2 devices require a 510(k)
premarket application and have functions that either contact the
eye directly (e.g., corneal electrode or thermal cautery unit) or have
impact on eye care if there are malfunctions (e.g., ophthalmoscope,
AC-powered slit-lamp biomicroscope, or visual field laser). Class 3
ophthalmic devices have the most stringent testing requirements,
and a Premarket application is needed that assures that the device is
safe and effective for its clinical use. Examples of Class 3 ophthalmic
devices include excimer lasers,
3.5 Ophthalmic
Instruments
intraocular pressure measuring
device, and intraocular gas.
