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an 82-year - old woman experienced an abrupt decrease in visual acuity with associated pain in the left eye for seven days . the visual acuity was fc 30 cm with correction at initial visit .
slit - lamp examination showed a 4  4 mm - sized corneal ulceration with severe stromal thinning that bulged anteriorly from the base of the ulceration near the inferior paracentral area ( fig .
1 ) . we used a sterile fluorescein dye to paint the suspected thinning area of perforation , applying gentle pressure from above or below the thinning of the cornea .
there was no visualization of retinal details through the pupil due to severe cortical opacity and nucleosclerosis .
corneal thickness was measured by pachymetry , while the evaluation of endothelial cell counts and shapes was performed by specular microscopy .
a lamellar dissection was created at a thickness of 400 m and a diameter of 9.0 mm with femtosecond laser ( intralase , intralase corporation , irvine , california , usa ) .
a blunt spatula was used to separate the overlying corneal tissue along the plane of dissection .
the anterior lamellar flap was immersed in optisol gs solution and was stored at -70 in a freezing system , while the posterior lamella flap was used as the descemet - stripping endothelial keratoplasty in the bullous keratopathy patient . after four weeks of storage ,
afterwards , the epithelium , bowman 's layer , and anterior stromal tissue of the recipient around the impending perforation area were carefully peeled away using a crescent blade ; the irregular margin of the keratectomy bed was trimmed with vannas scissors .
the donor tissue was cut in the same size , attached to the recipient wound , and sutured into the host bed using running 10 - 0 nylon sutures and two interrupted sutures as an adjustable slip knot ( fig .
the corneal graft was covered with a temporary amniotic membrane patch to reduce the pain and corneal haze ( fig .
six months after surgery , the cornea remained transparent and approximately 470 m in the thinnest area ( fig . 2c and 2d ) .
there were no complications , such as suture - related infection , corneal haze or scars , graft rejection , recurrent corneal ulcer , and postoperative rise of intraocular pressure .
moist chamber storage at 4 which was first described by filatov   in 1935 , is safe for up to 48 hours .
the use of tissue culture media such as k - sol , corneal storage media , dexsol and optisol can prolong the length of storage up to 12 days . since the successful cryopreservation of spermatozoa in ringer 's solution containing 40% glycerol , many human tissues or cells
cryopreservation of the corneal tissue has a long history ; however , most studies have focused on the cryoprotection of endothelial cells . to protect the living endothelial cells from freezing damage ,
many cryoprotectants such as glycerol , dimethyl sulphoxide ( dmso ) , and dextran   were used .
the transplantation of cryopreserved human corneas used with cryoprotectants has been limitedly successful in both the short- and long - term . however , with the introduction of short - term storage at 4 in optisol gs solution , cryopreservation failed to gain wide acceptance owing to its technically demanding nature , costliness , and variable clinical and experimental results achieved . on the other hand , in the field of surgery
the surgical techniques used in lamellar keratoplasty have been improved with dalk and descemet membrane endothelial keratoplasty .
cryopreserved tissues are used for lamellar keratoplasty , and most of them were treated with dmso or glycerol in the past .
some trials used lyophilized , that is , frozen and dried , tissue . with the advance of lamellar keratoplasty ,
precut buttons using the femtosecond laser and microkeratome , corneal tissue storage techniques and media have increasingly gained much interest . to minimize waste of donor tissue ,
the preservation and recycling of leftover cornea seem reasonable in countries where there is a shortage in donor cornea tissues .
we preformed tectonic dalk on cryopreserved cornea at -70. the cornea was dissected using a femtosecond laser and was dipped in optisol gs solution for four weeks .
however , the study on epikeratophakia lenticule reveal that neither fresh nor lyophilized tissue elicits immune reactions in non - vascularized corneas of immune recipients or in non - immune recipients .
this means that immunogenicity does not matter when the tissue is implanted into the avascular pocket .
it is difficult to expect that the keratocytes would survive under the condition of -70 without a proper concentration of cryoprotectant .
it was reported that the survival rate of keratocytes frozen in preservation media at -40 without cryoprotectant were 0 - 0.1% .
the distribution of the tissue does not matter in countries where there is a shortage in donor tissue , because the ophthalmology department can easily consume cryopreserved lamellar tissue in its own eye bank .
our cryopreserved grafts immersed for four weeks in optisol gs solution showed a significant freshly thawed cornea state until the end of surgery .
optisol gs contains 1% dextran , but it may not be able to protect keratocytes from freezing damage .
the recent report on small - diameter penetrating keratoplasty in eccentric corneal perforation with glycine - cryopreserved tissue seems to be effective .
the tectonic dalk , which is used in the case of still - intact descemet 's membrane , does not require endothelial cells .
establishing the safety of dalk for larger grafts in order to use this technique for keratoconus patients is necessary . in this case
, we experienced that simple cryopreserved cornea in optisol gs solution can be valuable substitutes in emergency tectonic lamellar keratoplasty of a small avascular area , such as in impending perforation .
however , more study about the safety regarding the potential structural damage or change would be necessary prior to the recommendation for such use .
we report a case of tectonic corneal transplantation for impending corneal perforation to preserve anatomic integrity using cryopreserved donor tissue . 
 an 82-year - old woman exhibiting impending corneal perforation suffered from moderate ocular pain in the left eye for one week . 
 after abnormal tissues around the impending perforation area were carefully peeled away using a crescent blade and vannas scissors , the patient received tectonic deep anterior lamellar keratoplasty using a cryopreserved cornea stored in optisol gs solution at -70 for four weeks . at six months after surgery 
 , the cornea remained transparent and restored the normal corneal thickness . 
 there were no complications such as corneal haze or scars , graft rejection , recurrent corneal ulcer , and postoperative rise of intraocular pressure . 
 cryopreserved donor lamellar tissue is an effective substitute in emergency tectonic lamellar keratoplasty , such as impending corneal perforation and severe necrotic corneal keratitis .