Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...
Reexamination Certificate
2002-06-28
2004-02-17
Casler, Brian L. (Department: 3763)
Surgery
Means for introducing or removing material from body for...
Treating material introduced into or removed from body...
C604S294000
Reexamination Certificate
active
06692481
ABSTRACT:
1.0 BACKGROUND ART
1.1 Field of the Invention
The invention concerns apparatus and methods for treating amblyopic conditions and is particularly directed to methods that correct this visual deficiency in adults.
1.2 Description of Related Art
Amblyopia, Greek for “blunt vision”, is the failure of an anatomically intact eye to develop normal visual acuity. Amblyopia affects five to seven million individuals in the United States alone, with an estimated 70,000 new cases annually. Amblyopia accounts for more visual loss in the under-45 age group than all other ocular diseases, including trauma. In the lay press, this condition is often referred to as “lazy eye”. The term lazy eye is to be avoided, however, as it may also be used in the lay press to describe strabismus (“crossed” eye) as well. While a crossed eye may become amblyopic (strabismic amblyopia), not all crossed eyes are amblyopic nor are all amblyopic eyes crossed.
Amblyopia represents a failure of the affected eye to develop normal synaptic connections with the visual cortex (Sireteanu, 1982). This is thought to result from an abnormal outcome of the competitive process of visual development. During visual development, the roughly 1.2 million nerve fibers that make up the optic nerve of each eye compete for synaptic connections in the brain (Cynader 1982). Under normal developmental circumstances, the visual input from each eye is roughly equal to that of its counterpart therefore each eye is assigned a proportionately equal number of synapses in the visual processing areas of the brain and allowed to realize its full visual potential. In humans, this process is thought to begin at birth and continues until roughly 8 years of age.
The number of synapses available within a given area of cortex is limited and once this number of synapses is reached, the development of additional synapses cannot occur without the loss or destruction of other synapses in the same cortical area. This phenomenon is known as the conservation of total axonal arborizations (Sabel 1988). In amblyopia, one eye is disadvantaged relative to the contralateral eye. This may be due to the need for spectacle correction in one eye more so than the other (refractive amblyopia), by the presence of a crossed eye (strabismic amblyopia) or by the presence of an obstruction in the visual axis of one eye (cataract, ptosis of the upper eyelid, or presence of an eyelid mass, for example). During visual development, the better-seeing eye is therefore assigned a greater proportion of the available synapses in visual cortex than its poorer seeing counterpart. In this way, the better-seeing eye may control more synapses in the cortex than it needs for optimal vision. With a limited number of synapses available in visual cortex, the poorer-seeing eye is left with fewer synapses than it needs for normal vision. If this situation remains uncorrected beyond the critical period of visual development, these synaptic connections become fixed, and neither correction of the weaker eye's underlying disadvantage nor the patching therapy described below will return the eye to normal visual acuity. If this situation is recognized during the first years of life (before) the critical period of visual development is complete however, treatment is often possible.
The problem is typically addressed in the following manner: First, the underlying condition that initially disadvantaged the weaker eye (i.e., the need for glasses, obstruction by a ptotic eyelid, strabismus, etc) is corrected. Second, the better-seeing eye is temporarily disadvantaged relative to the amblyopic eye. This is usually accomplished via occlusion of the dominant eye with an eye patch or similar occlusive device. In lieu of a patch, it is also possible to use cycloplegic eye drops such as atropine in the dominant eye to cause visual blurring. This practice is sometimes referred to as “pharmacologic patching”. In this way, the amblyopic eye is given an opportunity to form sufficient synaptic connections to allow useful vision before the critical period is complete and synaptic connections become fixed.
If occlusion therapy is used too aggressively, however, it is possible to make the previously dominant eye amblyopic. For this reason, regular visual acuity checks are necessary throughout amblyopia therapy. As a general rule, visual acuity is checked in both eyes on a schedule of 1 week per year of patient life. For example, a 1-year old undergoing full-time occlusion therapy would have his or her vision evaluated weekly; a 4-year old undergoing full-time occlusion therapy would have his or her vision evaluated every four weeks. These checkups include an examination to ensure that the underlying cause of the amblyopia (e.g., refractive error, ptotic eyelid, strabismus, etc) is being managed appropriately, as well as an assessment of visual acuity in each eye. In older literate children, this is done with a standard eye chart. In younger children who are verbal but not yet literate, standardized picture charts are used to determine visual acuity. In preverbal children, the task is significantly more difficult and often involves the examiner observing the child's ability to fixate upon and follow a small target with each eye.
Thus the two mainstays of amblyopia management in children are the prevention of any condition that could disadvantage the vision of one eye relative to its counterpart, and occlusive therapy, whether by physical patching or pharmacologic cycloplegia. Occlusive therapy is problematic for several reasons: First, the technique is only effective during the so-called critical period during which the visual system is developing. In humans, this period begins at birth and is largely complete by eight years of age, although this limit is subject to debate. The older the patient is, the less successful occlusive therapy tends to be, with occlusive therapy in adults having little or no significant value.
Second, and of significant importance, keeping an occlusive dressing over the dominant eye of a young child is a challenge for child, parent, and physician alike. Understandably, many children fail occlusive therapy due to noncompliance. This leaves these patients with permanent visual loss in the amblyopic eye, as occlusion therapy is not efficacious in adults and there are currently no effective methods for the treatment of adult amblyopia.
1.3 Deficiencies in the Prior Art
The challenge in an amblyopic patient therefore is to improve vision in the amblyopic eye without causing significant reduction of visual acuity in the dominant eye. There is currently no such therapy available to adult patients or to pediatric patients refractory to occlusion therapy. The lack of a demonstrably effective treatment for adult amblyopia leaves many patients with severely limited, often debilitating, vision. The prevalence of adult amblyopia indicates the need to develop a therapy to improve vision in an amblyopic eye. This is of paramount importance in patients who have sustained vision loss in their dominant non-amblyopic eye from disease or trauma. Significant alleviation of the handicap caused by visual deprivation arising from this condition would allow this population of adults to function more effectively in society and to enjoy a better quality of life.
2.0 SUMMARY OF THE INVENTION
The invention addresses the need for providing a treatment for improving vision in an amblyopic eye. The method utilizes selected drugs to induce a sustained yet reversible interruption of optic nerve transmission in the dominant eye, which is sufficient to allow complete or significant visual recovery in the amblyopic eye. The disclosed procedures are particularly suitable for treatment in adults for whom conventional methods used in children are ineffective.
Accordingly, the invention in one aspect is a method of safely interfering with impulse transmission from the dominant eye to the brain. This is accomplished with a drug that effectively blocks nerve transmission. Many drugs are known to interfere with nerve conduct
Akerman & Senterfitt
Casler Brian L.
Siromns Kevin C.
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