referring initially to fig1 , a system in accordance with the present invention is shown and is generally designated 10 . more specifically , as shown , the system 10 includes a laser unit 12 for generating an input laser beam 14 . for the present invention , the input laser beam 14 is preferably a pulsed laser beam wherein the pulses are ultra - short and each pulse has a duration measured in femto - seconds . further , the input laser beam 14 preferably has a wavelength ( λ i ) that is about 780 nm ( λ i = 780 nm ). fig1 also indicates that the input laser beam 14 is directed from the laser unit 12 , and onto the retina 16 of an eye 18 . as intended for the present invention , when the input light beam 14 ( λ i ) is incident on tissue in the retina 16 , it will interact with the tissue to generate a return light beam 20 . importantly , the return light beam 20 may include either , or both , of two different components that will have different wavelengths . stated differently , the return light beam 20 will include a first component having a wavelength ( λ r1 ) and a second component with a wavelength ( λ r2 ). note : λ i ≠ λ r1 ≠ λ r2 . still referring to fig1 it will be seen that , in addition to the laser unit 12 , the system 10 includes a sensor unit 22 and an active mirror 24 . specifically , these elements of the system 10 ( i . e . sensor unit 22 and active mirror 24 ) are used to pre - compensate the input beam 14 to create a diffraction limited spot on the retina 16 . on this point it is well known that the cornea 26 and lens 28 of the eye 18 will introduce optical aberrations into the input light beam 14 . also , the retina 16 will introduce phase aberrations that continue with the return light beam 20 . in order to measure the optical aberrations , the sensor unit 22 is preferably a wavefront sensor of a type well known in the pertinent art , such as a hartmann shack sensor . on the other hand , phase aberrations introduced by the retina 16 are preferably compensated for by pre - programming a computer to account for curvature of the retina 16 . it is known , however , that some phase aberrations can be detected by fluorescence wavefront analysis . therefore , the sensor unit 22 may also include this capability . once optical and phase aberrations in a return light beam 20 have been measured by the sensor unit 22 , the aberrations can then be used to program an active mirror 24 ( i . e . the computer used for operation of the active mirror 24 ). specifically , the active mirror 24 is to be programmed in a manner that will change the input light beam 14 to thereby effectively remove the aberrations from the return light beam 20 . alternatively , a customized phase plate 29 ( see fig5 ) of a type disclosed in co - pending u . s . application ser . no . 12 / 204 , 674 which is assigned to the same assignee as the present invention can be used with , or without , the active mirror 24 for this purpose . importantly , the now - compensated return light beam 20 can be used by the imaging unit 30 for imaging purposes . anatomically , an optic ( visual ) part 32 of the retina 16 comprises most of what is generally referred to as the fundus . as shown in fig2 , the sclera 34 is under the optic ( visual ) part 32 , and the optical nerve head 36 connects to the optic ( visual ) part 32 through the sclera 34 . in detail , with reference to fig2 and fig3 it will be seen that the optic ( visual ) part 32 of the retina 16 is curved and includes a retina - pigment - epithelium ( rpe ) 38 . the rpe 38 is a target tissue of interest for the present invention . anterior to the rpe 38 and identified in an anterior to posterior direction , are : nerve fibers 40 ; retinal ganglion cells 42 ; axion 44 ; bipolar cell 46 ; and a photo receptor 48 . of these , as indicated above , it is the rpe 38 with its lipofuscins that responds to the input beam ( λ i ) to generate a return beam ( λ r1 ) 20 due to tpef . referring now to fig4 , it will be seen that the optical nerve head 36 anatomically includes the lamina cribrosa ( lc ) 50 which is bounded by pre - laminar tissue 52 and post - laminar tissue 54 . as also indicated above , the lc 50 is also a target tissue of interest for the present invention . in this case , the lc 50 responds to the input beam 14 ( λ i ) to generate a return beam 20 ( λ r2 ) due to shg . additional aspects of aberration compensation for the present invention can be appreciated with reference to fig5 . there the sensor unit 22 is shown to include a lens array 56 , and a ccd camera 58 . this arrangement is typical for a wavefront sensor of the type commonly referred to as a hartmann - shack sensor . fig5 also indicates that a customized phase plate 29 can be used together with , or in lieu of , the active mirror 24 . in either case , the importance of the arrangement is to compensate the input beam 14 for aberrations that could otherwise diminish the efficacy of the imaging system 10 . anatomically , there are three sources for these aberrations ; all from the eye 18 itself . they are : 1 ] optical aberrations introduced by the anterior segment ( i . e . cornea 26 and lens 28 ); 2 ] phase aberrations introduced by the curvature of the retina 16 that relate to astigmatism ; and 3 ] phase aberrations introduced by the retina 16 . of all the aberrations introduced by an eye 18 into the input light beam 14 , optical aberrations are the most prominent , and are measured by the sensor unit 22 . to do this , a source 60 of infrared ( ir ) light radiates ir through pupil imaging optics 62 . also , the internal limiting membrane ( ilm ) 64 that defines the anterior surface of the retina 16 includes aberrational information in the light that is reflected from the retina 16 . after leaving the eye 18 , the optical aberrations that are introduced into the return beam 20 by the cornea 26 and lens 28 are processed by the sensor unit 22 . the resultant information is then programmed into the active mirror 24 . this essentially compensates for the first source of aberrations ( i . e . the anterior segments ). as for the second source of aberrations ( i . e . phase aberrations introduced by the curvature of the retina 16 ) it is well known that these aberrations can be measured in accordance with the angle of incidence , “ θ ”, between the input light beam 14 and the anterior surface of the retina 16 . accordingly , “ θ ” is determined by anatomical dimensions of the retina 16 . the resultant measurements involving “ θ ” are then also programmed into the computer - controlled active mirror 24 . the remaining aberrations from the third source ( i . e . the retina 16 ), although relatively minor , can be detected by a fluorescence wavefront sensor in the sensor unit 22 and used with the other information to further refine compensation corrections for the system 10 . as mentioned above , and as shown in fig5 , a custom phase plate 29 can be used in combination with the active mirror 24 , or in lieu thereof . in either configuration , the purpose is to pre - compensate the input light beam 14 so that aberrations introduced into the light beam 14 do not detract from the imaging capability of the system 10 . while the particular system and method for imaging retinal tissue with tissue generated light as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated , it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims .
a system and method for imaging retinal tissues in an eye generates an input light beam having ultra - short pulses and an input wavelength to stimulate the tissue . depending on the particular type tissue being imaged , the retinal tissue responds to the input beam by generating a return beam of light having first and second components of different wavelengths . an imaging unit then receives the return light and images the tissue according to the return wavelength . additionally , a sensor unit is used to evaluate light returning from the retina to measure optical and phase aberrations introduced by the eye , and to program a compensator that compensates the input beam by removing the aberrations .