the present invention provides an improved method for stimulating an electrical response in an eye and mitigating degradation of electrical response to light of an eye having a damaged retina . the method of the present invention may be used with a retina that is damaged due to retinitis pigmentosa , diabetic retinopathy , macular degeneration , retinal detachment , or other retinal trauma and may be implemented on any animal , having an eye with the general properties described herein . fig1 illustrates a mammal eye 100 , which includes an optic nerve 102 , a lens 104 , a cornea 106 , an iris 108 , zonules 110 , a retina 112 , and a vitreous 114 . in accordance with various embodiments of the invention , photoactive material 116 is injected into eye 100 , e . g ., using a hypodermic needle , such that the photoactive material is dispersed within vitreous 114 and proximate retina 112 . in accordance with alternative embodiments of the invention , photoactive material 116 is injected subretinally . fig2 illustrates a portion of retina 112 in greater detail , illustrating possible injection sites and resting sites for photoactive material 116 . the retina includes internal limiting member 201 , nerve - fiber layer 203 , ganglion - cell layer 205 , inner plexiform layer 207 , inner nuclear layer 209 , outer plexiform layer 211 , outer nuclear layer 213 , inner segments 215 , outer segments 208 , bruch &# 39 ; s membrane 206 , rpe 219 , and choriocapillaris 221 . as noted above , photoactive material 116 may be placed on a surface 202 of retina 112 or in a subretinal area 204 , such as a space located between a bruch &# 39 ; s membrane 206 and outer segments 208 . photoactive material 116 may be placed directly in such locations , or , as described in more detail below , the material may be coated with a bio - targeted material , which adheres to particular cells , such as ganglia or bipolar cells or photoreceptors 223 . in accordance with various embodiments of the invention , photoactive material 116 includes a quantum dot . a quantum dot is a semiconductor nanostructure that confines motion of conduction band electrons , valence band holes , or excitons ( pairs of conduction band electrons and valence band holes ) in three spatial directions . the confinement can be due to electrostatic potentials ( generated by external electrodes , doping , strain , impurities ), due to the presence of an interface between different semiconductor materials ( e . g . in the case of self - assembled quantum dots ), due to the presence of the semiconductor surface ( e . g . in the case of a semiconductor nanocrystal ), or any combination thereof . dimensions of quantum dots are typically on the order of about 1 to about 100 nanometers , and typically about 10 to about 50 nanometers for self - assembled quantum dots . the quantum dots fluoresce , emit an electrical potential or current , or a combination thereof , when exposed to light . the electrical potential is thought to stimulate rods and cones or other portions of retina 112 . the color of fluorescence and properties of the electrical potential general depend on the shape , size , and materials used to form the quantum dot . quantum dots for use with the present invention may be formed using a variety of techniques . for example , the quantum dots may be formed by creating a region of a first material having a first bandgap surrounded by a second material of a second bandgap , wherein the second bandgap is larger than the first bandgap . for example , a quantum dot may include a cadmium selenide ( cdse ) core surrounded by a zinc selenide ( zns ) shell . alternatively , self - assembled quantum dots nucleate spontaneously under certain conditions during molecular beam epitaxy ( mbe ) and metallorganic vapor phase epitaxy ( movpe ), when a material is grown on a substrate to which it is not lattice matched . the resulting strain between the grown layer and the substrate produces coherently strained islands on top of a two - dimensional “ wetting - layer .” the islands can be subsequently surrounded by a shell to form the quantum dot . individual quantum dots can also be created from two - dimensional electron or hole gases present in remotely doped quantum wells or semiconductor heterostructures . in this case , a surface is coated with a thin layer of photoresist . a lateral pattern is then defined in the resist by electron beam lithography . this pattern can then be transferred to the electron or hole gas by etching , or by depositing metal electrodes ( lift - off process ) that allow the application of external voltages between the electron gas and the electrodes . quantum dots may also be formed in quantum well structures due to monolayer fluctuations in the well &# 39 ; s thickness . fig3 illustrates a quantum dot 300 suitable for use as photoactive material 116 . quantum dot 300 includes an inner semiconductor 302 core formed of , for example , indium / gallium / phosphide , silicon , gallium arsenide , cadmium telluride , copper indium gallium selenide , indium gallium nitride , or organic materials such as polymer - fullerene heterojunctions ( e . g ., p3ht + c 60 ), organic nanocrystal solar cells ( e . g ., cadmium selenide or cadmium telluride ), dye sensitized cells ( e . g ., dye and titanium oxide or nobelium oxide ), or a tandem cell ( e . g ., copper - phthalocyanin + c 60 ); a shell 304 , formed of , for example , zinc selenide or other suitable material ; a coating 306 , formed of , for example , peg lipids or other suitable material ; and bio - functional material 308 , formed of , for example , biotin or other suitable proteins . as noted above , in accordance with various embodiments of the invention , a plurality of quantum dots exhibiting a plurality of fluorescence wavelengths or dots responsive to light of varying wavelengths are employed to stimulate photoreceptors based on incident light of multiple wavelengths . for example , a combination of nanoparticles responsive to red , blue , and green incident light may be employed . various other combinations of nanoparticles / quantum dots are also within the scope of the invention . use of photoactive nanoparticles such as quantum dots is advantageous because it allows for less invasive methods of implanting the devices , which in turn minimizes trauma and scaring of the retina . in addition , because the particles are so small , the particles block relatively little light from photoreceptors 210 ( illustrated in fig2 ). further , the quantum dots can be injected into a wider field of vision , compared to larger devices . fig4 - 7 illustrate electroretinograms ( erg ) for royal college of surgeons ( rcs ) rats with retinal degeneration , injected in vitreous 114 with about 5 μl of quantum dots 300 in saline , for a sham group , and for a control group . intravitreal injections : 0 . 5 μl injected 1 mm posterior to limbus ; subretinal injection : 0 . 1 μl injected under direct visualization subretinally . fig4 illustrates maximal dark - adapted erg , which elicits both rod and cone photoreceptor response , in rcs rats . the control group ( n = 4 ) has had no intervention , the sham group ( n = 4 ) has received intraocular injections of saline , and the qd - 540 group ( n = 6 ) has received intraocular injections of quantum dots with a biotin coating . fig4 illustrates an increase in the electrical activity of the active implant eyes in weeks 3 through 7 , compared to the sham and control groups , which progressively decline . fig5 illustrates photopic light - adapted erg results , which elicit predominantly cone photoreceptor responses , in the rcs rats . the control group ( n = 4 ) has had no interventions , the sham group ( n = 4 ) has received intraocular injections of saline , and the qd - 540 group ( n = 6 ) has received intraocular injections of quantum dots with a biotin coating . fig5 demonstrates a general trend for increasing electrical activity in the active implant group , compared with a tendency for decline in the sham and control groups over time . fig6 illustrates erg recordings week 3 after injection . line 602 indicates the erg of an rcs rat with intraocular qd - 540 , compared with recordings from a representative sham surgery eye , illustrated by line 604 . fig7 illustrates representative erg recordings at week 7 . line 702 indicates the erg of an rcs rat with intraocular qd - 540 , compared with recordings from a representative sham surgery eye , represented by line 704 . as illustrated , although the overall erg amplitudes for both sham and injected eyes have decreased , the eye with the active implants has maintained a relatively normal erg , whereas the sham eye recording is essentially flat . fig8 illustrates nuclei count following a 2 month post - implantation erg recording . the rcs rats then were euthanized and the eyes enucleated and the retina embedded in a plastic medium , then cut to 0 . 5 micron thickness and stained with toludine blue . using image analysis software , the number of nuclei present in the ganglion cell layer , inner nuclear layer , and the photoreceptor nuclear layer ( outer nuclear layer ) were measured on five sections each 100 microns in length . there were three animals in the active implant group , 2 in the sham surgery group , and 1 in the control group . fig8 shows no appreciable difference between the groups in the number of cells present in the ganglion cell layer , a trend for increased cells for both the active implant and sham surgery groups in the inner nuclear layer , and a marked increase in the photoreceptor nuclei in the active implant group . the photoreceptors are the basis of the electrophysiologic network of signals which produce the sensation of vision . increased numbers of cells in this layer in the active implant group indicates a protective effect of the active implant on these cells . this is consistent with fig4 - 7 , which depict a preservation of the electrical functioning of the retina in the active implant groups . the intraocular quantum dots appear to preserve both the function and the anatomy of the retina in this model of progressive blindness . fig9 illustrates results of the morris water maze test results for three groups . each group , consisting of one control animal and one active implant animal , was tested in a water maze . the morris water maze test is a functional test to determine whether or not the animal can see light . the test consists of a water escape pool ( 1 . 4 m diameter , 0 . 6 m deep , water at 20 deg celsius ). around the edge of the pool are six lights . the escape platform , a small pedestal approximately 12 cm in diameter , is randomly placed adjacent to one light , which is then illuminated as the rat is placed in the water . the subject then has 60 seconds to swim towards the light and climb up onto the pedestal . if the subject does not find the pedestal within 60 seconds , the animal is removed from the pool . each animal is tested a total of ten times . in the group of animals 8 weeks post - implantation , the active implant animal was able to escape an average of 30 % faster than the control animal . in the 5 week post - implantation group , the active implant group escaped an average 13 % more rapidly than the control group and in the 4 week post - implantation group , the active implant had escape times 15 % faster than the control . the results indicate that the animals receiving the active implant were consistently able to navigate the maze more rapidly than the control animals . the maze is specifically designed to eliminate any tactile or olfactory cues , and the animal must rely entirely upon sight to successfully exit . fig1 illustrates recovery round , maximal dark - adapted erg in rcs rats . this test elicits both rod and cone photoreceptor response . fig1 illustrates results from experiments involved in the intraocular injection of quantum dots to reverse blindness . the rcs rats were monitored with electroretinograms every other week until the recordings became essentially flat , indicating a loss of retinal functioning . the control group ( n = 2 ) has had no intervention , the sham group ( n = 2 ) has received intraocular injections of saline , while groups active implant 593 ( n − 2 ) and active implant 614 ( n = 2 ) have received intraocular injections of quantum dots with an amino acid coating . 593 and 614 refer to the wavelength of light to which each quantum dot exhibits a maximum response . recordings were taken the day of surgery , 2 weeks post - implantation and 4 weeks post - implantation . the graph illustrates that both the control and sham surgery groups exhibit no gain in the electrical functioning of the retina at any point post - operatively . in contrast , both active implant groups had a substantial increase in the electrical activity of the retina post - implantation . the active implant 593 group had a 2 - fold increase in the amplitude of the waveform response to light , and the active implant group 614 had a 2 . 5 - fold increase in the amplitude of the waveform response to light . fig1 illustrates morris water maze test , recovery round results for three groups , each group consisting of one representative animal , tested in a water maze . the test consists of a water escape pool ( 1 . 4 m diameter , 0 . 6 m deep , water at 20 deg celsius ). around the edge of the pool are six lights . the escape platform , a small pedestal approximately 12 cm in diameter , is randomly placed adjacent to one light , which is then illuminated as the rat is placed in the water . the subject then has 60 seconds to swim towards the light and climb up onto the pedestal . if the subject does not find the pedestal within 60 seconds , the animal is removed from the pool . each animal is tested a total of ten times . the graph indicates that the control group averaged 60 seconds , indicating that the maze was never successfully completed . the active implant 593 group averaged 50 seconds , 17 % quicker escape time than control . the active implant 614 group averaged 27 . 6 seconds , nearly twice as fast as the control group , indicating a higher level of visual functioning . the results indicate that the animals receiving the active implant were consistently able to navigate the maze more rapidly than the control animals . the maze is specifically designed to eliminate any tactile or olfactory cues , and the animal must rely entirely upon sight to successfully exit . fig1 illustrates photomicrograph of a human retina ( a ), and quantum dots adherent to human retinal photoreceptors ( b ). a whole human eye was obtained from the rocky mountain lions eye bank and examined grossly and beneath an operating microscope and found to be free of any structural abnormalities . next , 0 . 05 ml of a biotin linked quantum dot with an absorption wavelength near 528 nm and an excitation wavelength of 547 nm was injected into the subretinal space . after histological processing , the biotin linked quantum dots were visible by fluorescent light microscopy . the quantum dots could be seen adherent to the native photoreceptors ( arrow ), as well as in unbound aggregates in the subretinal space ( arrowhead ). this demonstrates that biotin linked quantum dots bind to human retinal photoreceptors when injected into an eye bank specimen . this has practical implications in the area of neural prosthetics and neural protection for targeted delivery of drugs , molecules , and electric current to photoreceptors in disease states . the present invention has been described above with reference to exemplary embodiments . those skilled in the art having read this disclosure will recognize that changes and modifications may be made to the embodiments without departing from the scope of the invention . these and other changes or modifications are intended to be included within the scope of the present invention .
an improved method for stimulating electrical activity in an eye is provided . provided is a technique for implanting small , nanometer - sized photoactive devices into an eye to improve electrical activity within an eye or mitigate degradation of electrical response in damaged eyes .