Surgery – Instruments – Light application
Reexamination Certificate
2001-02-21
2004-01-27
Farah, A. (Department: 3739)
Surgery
Instruments
Light application
C606S004000, C606S003000, C607S088000
Reexamination Certificate
active
06682523
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of glaucoma therapy and more particularly to a laser-based system and technique for clearing cellular and other debris from a patient's obstructed trabecular meshwork to increase aqueous outflows through the meshwork to lower intraocular pressures. The system and method introduce exogenous chromophores, preferably in the form of uniformly dimensioned nanocrystalline particles, into meshwork spaces to provide photoabsorption of a selected wavelength to thereby deliver energy directly to media within spaces in the trabecular meshwork.
2. Description of Related Art
Glaucoma is a general term given to a group of debilitating eye diseases that afflict approximately 1%-2% of the U.S. population and an estimated 67 million people worldwide. In the U.S., the incidence of glaucoma rises with age to over 6% of the Caucasian population 75 years and older, and about 11% of the population of African descent 75 years and older. Glaucoma represents a significant health care issue, with millions of people worldwide at risk of vision loss.
The principal sign of glaucoma is elevated intraocular pressure (IOP) that ultimately can damage the optic nerve and result in impairment to, or loss of, normal visual function. Aqueous humor aq is the clear nutrient fluid that circulates within the anterior chamber ac of an eye to nourish ocular tissues. The aqueous aq is produced by the ciliary body cb and is drained through the trabecular meshwork tin and Schlemm's canal sch (see FIG.
1
A). In a glaucoma condition, drainage of aqueous through the trabecular meshwork tin is insufficient to balance aqueous production, and therefore fluid intraocular pressure can be elevated and eventually damage the optic nerve.
Primary open-angle glaucoma is the most prevalent open-angle glaucoma in the U. S, representing approximately 37% of total U.S. cases, or about 1.2 million people, with an estimated 63,000 new cases annually. The pathophysiological mechanisms underlying primary open-angle glaucoma are not fully understood. It is believed that one or more factors play a role, for example, (i) that as a patient ages, the trabecular meshwork undergoes biostructural changes and loses its ability to regulate outflows, or (ii) that naturally elevated IOP levels can be tolerated initially, but after a long period begin to cause irreversible damage.
Another form of ocular hypertension is caused by exfoliation syndrome or exfoliation glaucoma. In this condition, the iris rubs against the lens and dislodges white flakes form the lens surface that are carried by the aqueous humor into the trabecular meshwork It is believed that the exfoliated flakes build up in the trabecular meshwork and block outflow facility, eventually leading to a rise in IOP and fill-blown glaucoma. This type of exfoliation glaucoma accounts for approximately 20% of total U.S. glaucoma cases or about 660,00 people. An estimated 34,000 new cases are diagnosed annually in the U.S.
Pigmentary glaucoma is caused by pigment dispersion syndrome wherein abrasive contact between the iris and lens sheds pigment into the anterior chamber and aqueous humor. The pigment again can clog the trabecular meshwork and increase IOP. Pigmentary glaucoma accounts for approximately 3% of total U.S. glaucoma cases or about 100,000 people with an estimated 5,000 new cases per year.
The ability of the trabecular meshwork in filtering aqueous flows play a central role in many forms of glaucoma. The meshwork consists of about 25 layers of perforated trabecular sheets (ts
1
. . . ts
25
) around the filtration angle of the anterior chamber ac, having a width of about 1,000 &mgr;m to 1,500 &mgr;m (1.0 nm. to 1.5 nm.) in a circumference ranging from 35,000 to 40,000 &mgr;m (see FIGS.
1
A-
1
B).
FIG. 1C
shows an enlarged micrograph of trabecular cords and openings.
FIG. 1E
is a representation of the endothelial layer el of a trabecular cord tc or beam wherein its core comprises predominantly collagen microfibrils.
FIG. 1D
illustrates that each successively deeper trabecular sheet ts of the meshwork has smaller openings or pores p between trabecular cords tc than more superficial trabecular sheets. Further, the intrasheet spacing iss diminishes between successively deeper trabecular sheets ts. The meshwork thus serves as a filtration mechanism wherein cellular detritus and other debris in the aqueous flow is captured before it passes into Schlemm's canal sch wherein the outflows are carried away from the anterior chamber.
FIG. 1D
includes a graphic representation of exfoliated detritus indicated at d accumulating within spaces in the meshwork that are believed responsible for reducing outflow facility through the meshwork and for collapsing intrasheet spacing.
Various laser therapies have been developed or proposed for treating a patient's trabecular meshwork. These laser approaches rely on trans-corneal irradiation of a series of spots on the surface of meshwork tm exposed to the anterior chamber. The ophthalmologist utilizes a goniolens to direct the laser beam to strike exposed trabecular sheets at an oblique angle. For example, argon laser trabeculoplasty (ALT) and selective laser trabeculoplasty (SLT) have been tested and compared in several trials. ALT was introduced in the 1980's and uses an argon laser operating at a wavelength (&lgr;) range of about 512 nm with a pulse duration of about 0.10 second to irradiate a series of about 50 spots only around 180° of the meshwork The more recently developed trans-corneal laser approach, called SLT, uses a short-pulse 532 nm laser with pulse duration of 3-10 nanoseconds and energy levels that range from 0.60 mJ to 1.20 mJ. This approach was disclosed by Latina in U.S. Pat. No. 5,549,596. Yet another trans-corneal laser approach was disclosed by Hsia et al. in U.S. Pat. No. 6,059,772. Hsia disclosed three experimental trials on a limited set of human patients using an 800 nm laser beam with microsecond pulse durations, and varied energy levels. TABLE A below compares the laser parameters used in the various approaches, arranged in order of increasing wavelengths (&lgr;).
TABLE A
&lgr;
Pulse Duration
Power
Beam Size
ALT
514 nm
0.1 second (100 ms)
various powers
50 &mgr;m
settings
SLT
532 nm
3 ns-10 ns
0.6-1.2 mJ/
300-400 &mgr;m
pulse
Hsia et al.
800 nm
1 microsecond
30-80 mJ/pulse
100-200 &mgr;m
A recent series of articles provides a comparative evaluation of ALT and SLT and investigates the mechanisms of action that underlie ALT and SLT to lower intraocular pressure (see
Ocular Surgery News
, Mar. 1, 2000). The results of these evaluations also can be instructive as to the probable mechanisms of action underlying the laser approach, if eventually proven under FDA regulatory schemes, that was proposed by Hsia in U.S. Pat. No. 6,059,772.
The ALT and SLT approaches use very similar wavelengths—514 nm for ALT vs. 532 nm for ALT. Still, as reported by Dr. J. Alvarado, the laser-tissue interactions in trabecular meshwork tissues of glaucoma patients differ markedly between ALT and SLT. (See Alvarado, J. A,
Mechanical and Biological Comparison of ALT and SLT; Ocular Surgery News
, Mar. 1, 2000). The ALT treatment modality produces a discrete burn or photocoagulation-type injury in trabecular sheets that are impacted by the laser irradiation. The damage is clearly visible to the ophthalmologist through a slit-lamp biomicroscope. In contrast to ALT, the SLT method produces no laser burns—the trabecular meshwork appears undamaged and without tissue reaction to the incident radiation. Dr. Alvarado stated that “[d]espite differences in the interaction of the laser light with the treated tissues, early clinical outcome comparisons of SLT and ALT have shown that the treatments are similar in the capacity to lower the intraocular pressure (IOP) of glaucoma patients.” Id. at p.1. From TABLE A, it is readily apparent that the main difference between ALT and SLT is the pulse duration and the hence the energy deliv
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