the invention will now be described in detail by way of reference only to the following examples , and to the accompanying drawings . in first preferred embodiment , the method of the present invention comprises the following steps . the host cornea is optionally de - epithelialized , and a total circular conjunctival peritomy is performed . a scleral incision of between 25 % and 75 % of thickness of the sclera , or preferably up to the half thickness of the sclera is then made , just posterior to the superior limbus and extending over an arc of from about 20 ° to approximately 180 °. starting from this incision , the cornea is dissected at 25 % and 75 %, or preferably at half thickness , and a corneal flap is created in this plane extending up to the half - circle diameter . the dissection is then continued , preferably to within 0 . 5 - 3 mm of the limbus , to create an inferior intrastromal pocket , continuous with the bed of the superior flap . the free superior corneal anterior lamella is optionally reflected inferiorly and retracted gently , allowing the trephination of a circular hole through the posterior lamella of the cornea overlying the visual axis and communicating with the anterior chamber of the eye . the keratoprosthesis is then placed between the anterior and posterior lamellae , so that the transparent core lies over the circular hole . the anterior lamella is then repositioned , and the sclera is sutured . a conjunctival flap is preferably then fashioned to cover the entire anterior surface of the eye . both corneal and conjunctival flaps are preferably opened by a trephination overlying the visual axis and in line with the posterior opening , in a secondary procedure which should preferably be performed no earlier than 1 month following implantation . if a conjunctival flap cannot be created , a mucosal graft , such as buccal mucosa , can be used ; however , coverage by such a flap is much less critical than in the case of full - thickness implantation . the method is illustrated in more detail in the accompanying drawings . [ 0050 ] fig1 depicts the cornea 11 , limbus 12 and conjunctiva 13 . the conjunctival peritomy provides the conjunctival edge 14 . the scleral incision is depicted as 15 . fig2 depicts the corneal flap 21 and the inferior intrastromal pocket 22 created on the lamellar bed 23 and extending up to the edge 24 . fig3 depicts the reflected corneal flap 31 and the trephination of the opening 32 in the posterior corneal lamella . fig4 depicts the placement of the keratoprosthesis ( consisting of core 42 and skirt 43 ), covered by the corneal flap 45 and overlying the posterior opening 41 . the sutured scleral incision is depicted as 44 . the preferred method for implantation of a soft , flexible keratoprosthesis is performed as follows . the patient is anaesthetised . the cornea 11 is de - epithelialized , using a knife such as a beaver blade . a circular conjunctival 360 °- peritomy and dissection along the edge 14 are performed to expose the limbus 12 and perilimbal sclera , especially in the superior half of the eye , followed by haemostasis . using a diamond knife , a half - depth scleral incision 15 is then made , approximately 1 mm posterior to the superior limbus and extending over approximately 180 °. starting from this incision , the cornea is dissected at half thickness , using an angled pocket knife , so as to create a flap 21 , which is lifted not further than the half - circle diameter of the cornea . the dissection is continued in the same plane into the inferior half of the cornea to create an inferior semicircular intrastromal pocket 22 defined within the limits of the lamellar bed 23 , the edge 24 ( situated at a distance of 0 . 5 to 3 mm from limbus ), and the anterior corneal lamella 11 . the superior corneal flap 31 is then reflected inferiorly and retracted gently to allow the use of a trephine , such as a skin biopsy punch , in order to trephine a circular opening 32 , 2 to 5 mm in diameter , through the posterior corneal lamella 23 , overlying the central visual axis and communicating with the anterior chamber of the eye . viscoelastics may optionally be introduced into the anterior chamber . in the aphakic eye , an anterior vitrectomy may be performed if required , through the circular opening 32 . the keratoprosthesis 42 is inserted into the pocket using an instrument such as a lens - introducing forceps with non - toothed broad flat blades , taking care not to crush or damage the prosthesis , and placed so that the optic lies centred over the opening 32 in the posterior lamella . the superior corneal flap 45 is then re - placed over the prosthesis , and the pocket 22 is closed by suturing the scleral incision 44 with 10 / 0 nylon sutures . if possible , a conjunctival flap , or a flap of alternative tissue , is fashioned and used to cover the entire surface of the globe . in certain preferred embodiments , the technique comprises the use of microkeratome or laser to prepare the intrastromal pocket and / or the posterior trephination and / or the anterior circumferential incision communicating with the pocket , which may be within cornea or sclera and vary from 20 to 180 °. ophthalmic lasers and procedures pertaining to eye surgery described in the patent literature may be used to perform the incisions , trephination and stromal pocket formation . such methods and instruments , related to corneal refractive surgery but not to insertion of keratoprosthesis , are disclosed for example in u . s . pat . no . 4 , 903 , 695 ( warner et al . ); u . s . pat . no . 4 , 994 , 058 ( raven et al . ); u . s . pat . no . 5 . 336 , 215 ( hsueh et al . ); and u . s . pat . no . 5 , 549 , 632 ( lai ). postoperative care should include subconjunctival administration of steroids and antibiotics at the conclusion of surgery , and topical treatment for the next two weeks , such as anti - glaucoma medication ( as used preoperatively ), guttae chloramphenicol and prednisolone 0 . 5 % ( 4 times daily ). long - term postoperative medication , such as tetracycline 1 % ointment , and freshly - made , preservative - free guttae medroxyprogesterone 1 %, both 4 times daily , may be used until the secondary procedure is performed . approximately 1 to 5 months after implantation , the conjunctival and anterior corneal covering layers are trephined to create a circular opening , 2 to 5 mm in diameter , overlying the central visual axis and in line with the posterior corneal opening . long - term medication as disclosed above is continued indefinitely after the secondary procedure . for reviews covering the history of prosthokeratoplasty and keratoprosthetics see : day , r ., transactions of the american ophthalmological society , vol . 55 , pp . 455 - 475 ( 1957 ): “ artificial corneal implants ”; mannis , m . j . and krachmer , j . h ., survey of ophthalmology , vol . 25 , pp . 333 - 338 ( 1981 ): “ keratoplasty : a historical perspective ”; barron , b . a ., “ prosthokeratoplasty ”, in the cornea , churchill livingstone , new york , 1988 , pp . 787 - 803 ; leibowitz , h . m ., trinkaus - randall , v ., tsuk , a . g . and franzblau , c ., progress in retinal and eye research , vol . 13 , pp . 605 - 621 ( 1994 ): “ progress in the development of a synthetic cornea ”; chirila , t . v ., trends in polymer science , vol . 2 , pp . 296 - 300 ( 1994 ): “ modern artificial corneas : the use of porous polymers ”; hicks , c . r ., fitton , j . h ., chirila , t . v ., crawford , g . j . and constable , i . j ., survey of ophthalmology , vol . 42 , pp . 175 - 189 ( 1997 ): “ keratoprosthesis : advancing towards a true artificial cornea ”; caldwell , d . r ., transactions of the american ophthalmological society , vol . 95 , pp . 751 - 802 ( 1997 ): “ the soft keratoprosthesis ”; chirila , t . v . et al ., progress in polymer science , vol . 23 , pp . 447 - 473 ( 1998 ): “ artificial cornea with a porous polymeric skirt ”; and brenman , k . and parel , j . m ., anales del instituto barraquer ( barcelona ), vol . 28 ( suppl . ), pp . 187 - 192 ( 1999 ): “ toward a complication - free kpro . a critical review of kpro advancement since 1995 ”. it will be apparent to the person skilled in the art that while the invention has been described in some detail for the purposes of clarity and understanding , various modifications and alterations to the embodiments and methods described herein may be made without departing from the scope of the inventive concept disclosed in this specification . references cited herein are listed on the following pages , and are incorporated herein by this reference . [ 0061 ] patent documents u . s . pat . no . 4 , 586 , 929 binder u . s . pat . no . 4 , 693 , 715 abel u . s . pat . no . 4 , 772 , 283 white u . s . pat . no . 4 , 865 , 601 caldwell et al . u . s . pat . no . 4 , 903 , 695 warner et al . u . s . pat . no . 4 , 923 , 466 pintucci u . s . pat . no . 4 , 932 , 968 caldwell et al . u . s . pat . no . 4 , 994 , 058 raven et al . u . s . pat . no . 5 , 108 , 428 capecchi et al . u . s . pat . no . 5 , 300 , 115 py u . s . pat . no . 5 , 300 , 116 chirila et al . u . s . pat . no . 5 , 336 , 215 hsueh et al . u . s . pat . no . 5 , 458 , 819 chirila et al . u . s . pat . no . 5 , 489 , 300 capecchi et al . u . s . pat . no . 5 , 489 , 301 barber u . s . pat . no . 5 , 549 , 632 lai u . s . pat . no . 5 , 713 , 956 legeais u . s . pat . no . 5 , 843 , 185 leon rolden et al . french patent no . 2 , 649 , 605 legeais et al . australian patent no . 650156 chirila et al . day , r ., transactions of the american ophthalmological society , vol . 55 , pp . 455 - 475 ( 1957 ): “ artificial corneal implants ”. mannis , m . j . and krachmer , j . h ., survey of ophthalmology , vol . 25 , pp . 333 - 338 ( 1981 ): “ keratoplasty : a historical perspective ”. barron , b . a ., “ prosthokeratoplasty ”, in the cornea , churchill livingstone , new york , 1988 , pp . 787 - 803 . leibowitz , h . m ., trinkaus - randall , v ., tsuk , a . g . and franzblau , c ., progress in retinal and eye research , vol . 13 , pp . 605 - 621 ( 1994 ): “ progress in the development of a synthetic cornea ”. chirila , t . v ., trends in polymer science , vol . 2 , pp . 296 - 300 ( 1994 ): “ modern artificial corneas : the use of porous polymers ”. legeais , j . m ., renard , g ., parel , j . m ., savoldelli , m . and pouliquen , y ., archives of ophthalmology , vol . 113 , pp . 757 - 763 ( 1995 ): “ keratoprosthesis with biocolonizable microporous fluorocarbon haptic ”. hicks , c . r ., fitton , j . h ., chirila , t . v ., crawford , g . j . and constable , i . j ., survey of ophthalmology , vol . 42 , pp . 175 - 189 ( 1997 ): “ keratoprosthesis : advancing towards a true artificial cornea ”. caldwell , d . r ., transactions of the american ophthalmological society , vol . 95 , pp . 751 - 802 ( 1997 ): “ the soft keratoprosthesis ”. legeais , j . m . and renard , g ., biomaterials , vol . 19 , pp . 1517 - 1522 ( 1998 ): “ a second generation of artificial cornea ( biokpro ii )”. chirila , t . v . et al ., progress in polymer science , vol . 23 , pp . 447 - 473 ( 1998 ): “ artificial cornea with a porous polymeric skirt ”. brenman , k . and parel , j . m ., anales del instituto barraquer ( barcelona ), vol . 28 ( suppl . ), pp . 187 - 192 ( 1999 ): “ toward a complication - free kpro . a critical review of kpro advancement since 1995 ”. hicks , c . r ., crawford , g . j ., chirila , t . v ., lou , x ., platten , s ., vijayasekaran , s . and constable , i . j ., proceedings , the 3 rd kpro study group meeting , birmingham , 24 - 26 june 1999 , pp . 9 - 10 ( 1999 ): “ pilot study of the chirila keratoprosthesis in human patients ”. crawford , g . j ., hicks , c . r ., lou , x ., vijayasekaran , s ., tan , d ., mulholland , b ., chirila , t . v . and constable , i . j ., ophthalmology , vol . 109 , pp . 883 - 889 ( 2002 ): “ the chirila keratoprosthesis : phase i human clinical trials ”.
disclosed are improved methods of insertion of keratoprosthesis and , in particular , improved methods of surgical insertion and placement of a soft hydrogel prosthetic corneal device into the host cornea . the methods of the invention provide greatly improved rates of success for the implantation and retention of the device .