there are a great many possible implementations of the invention , too many to describe herein . some possible implementations that are presently preferred are described below . it cannot be emphasized too strongly , however , that these are descriptions of implementations of the invention , and not descriptions of the invention , which is not limited to the detailed implementations described in this section but is described in broader terms in the claims . fig1 shows the process followed in one implementation of the invention . any surgical technique for lens extraction may be used , including such conventional techniques as phacoemulsification or extracapsular cataract extraction . after the lens is extracted from the eye and all particulate lens material is removed , the anterior chamber is maintained formed with intraocular fluid or viscoelastic . the eye is then centered and an autorefracting device is used to obtain a refractive reading of the aphakic eye ( i . e ., the eye with the lens removed ). while any autorefractor can be used across a wide range of possible vertex distances , one possible implementation is to use an autorefractor with a vertex distance of 13 . 75 mm , and to take an average of multiple autorefraction measurements . autorefraction provides a spherical and a cylindrical power measurement . the power of the intraocular lens can be derived from the refraction measurements . one possible method for deriving the intraocular lens power is to use an empirically derived relationship , which could be called a predictive iol model , that relates the refraction measurements to the iol power . this can be done , for example , by first calculating the aphakic spherical equivalent of the refraction measurements from the standard formula : wherein spherical equiv is the aphakic spherical equivalent , measured spherical power is the average of the spherical power measurements made using autorefraction , and measured cylindrical power is the average of the cylindrical power measurements made using autorefraction . next , the following empirically derived relationship may be used to relate the aphakic spherical equivalent to the iol power : wherein a is the lens specific constant ( and depends on the type of intraocular lens being implanted ), c is an empirically derived constant , and b is the empirically derived linear correlation coefficient . the two empirically derived coefficients c , b may be derived using a statistical regression analysis of data relating iol power to autorefraction measurement of the spherical equivalent . for example , the regression analysis may be performed on data collected from a large population of patients ( e . g ., one hundred patients ). for each patient , the data comprise the iol power selected using conventional preoperative measurements and the spherical equivalent from an intraoperative autorefraction . other relationships between the refraction measurements and the iol power may also be used , and the necessary constants and coefficients derived either empirically or theoretically . one alternative , of course , is to simply combine the two formulas as follows : varying the vertex distance of autorefraction or modifying the optical media along the optical path ( e . g ., by inserting a different material into the anterior chamber of the eye , or by placing a temporary lens in or near the eye ) can alter the parametric variables of the relationship . in some implementations , the above formulation can be improved with additional variables to achieve better precision . parameters such as intraocular pressure , intraoperative axial length , intraoperative keratometry , preoperative keratometry , preoperative axial length , intra and preoperative anterior chamber depth can be used as supplementary correlates in the predictive model , in order to refine the iol power . for example , the following relationship could be used : iol power = a + c + b * ( spherical equiv )+ d * ( axial length )+ f *( average keratometry )+ g * ( intraoperative pressure ) in one implementation , both the surgery and the autorefraction are performed using standard available equipment . a standard surgical microscope is used for extraction of the native lens , and a standard portable autorefraction device ( e . g ., a nikon retinomax ) is used for autorefraction . both procedures may be performed while the patient remains in the same supine position . the refraction measurements are read from the autorefraction device , and the iol power is calculated using a formula such as one of those given above . fig2 shows another possible implementation in which specially designed equipment is used . an autorefraction retinoscope unit 10 is attached to the exterior of an ophthalmic surgical microscope 12 . the surgical microscope in this implementation has its own display for centration and visualization . a toggle control 13 ( and / or a pedal control ) is provided for xyz centration of the microscope and the retinoscope unit . the microscope has the usual lens array 15 . the autorefraction unit can be a conventional automated retinoscopic apparatus of the type conventionally used to measure the dioptric deficiency and optical state of the phakic eye . the retinoscopic apparatus would be configured to operate with the patient in the supine position , intraoperatively , and to be moved out of the way of the microscopic surgical device when not in use , but configured so that its position and orientation is adjustable using the toggle control 13 . a display unit 14 is integrated with the autorefraction unit 10 and also attached to the surgical microscope 12 . the display unit presents the results of the iol power determination . a processing unit 16 is electrically connected to the autorefraction unit and the display . cables 18 make the electrical connections between the autorefraction unit 10 , display unit 14 , and processing unit 16 . the processing unit receives measurement data from the autorefraction unit , and uses a predictive model ( e . g ., one of those described by the above formulas ) to calculate the iol power for display on the display unit . an alternative to the arrangement shown in fig2 would be to have the autorefraction unit , display unit , and processing unit fully integrated into the ophthalmic surgical microscope . for example , the same display unit can serve both for centration and visualization during surgery and for controlling and displaying results from the autorefraction unit and processing unit during iol power determination . the equipment of fig2 or alternative implementations may be used to perform the eye surgery , to make the intraoperative refraction measurement , and to calculate the iol power for achieving the desired emmetropia or postoperative refraction . many other implementations of the invention other than those described above are within the invention , which is defined by the following claims . for example , as earlier noted , completely separate surgical and autorefraction equipment may be used ( e . g ., with the microscope moved away , and the autorefraction equipment moved into place ), and the iol measurement may be calculated from the refraction measurements without using a special processor or display unit . autorefraction may also be used after the intraocular lens is implanted ( pseudophakic eye ), to confirm whether a satisfactory choice has been made for the iol power . if the autorefraction shows a residual error , the surgeon could immediately remove the implanted lens , and substitute another . various types of autorefraction may be used to make the intraoperative refraction measurement of the aphakic eye .
apparatus for performing intraocular implant surgery , including surgical apparatus for performing intraocular implant surgery , an autorefraction device associated with the surgical apparatus , wherein the autorefraction device is configured to perform autorefraction on the aphakic eye to provide one or more aphakic refraction measurements , and a processor connected to the autorefraction device , wherein the processor is configured to process the aphakic refraction measurements and provide the user of the apparatus with information regarding the power of the intraocular lens .