recently , the femtosecond solid - state laser   was successfully used in several corneal surgical procedures .
the technology consists of an infrared nd : glass laser beam focused at the desired corneal depth to induce optical breakdown ( called photodisruption ) without thermal or shockwave damage to the surrounding tissue , which particularly improves the reproducibility and outcomes of lamellar surgery [ 24 ] .
the femtosecond laser technology facilitates flap creation in laser in situ keratomileusis , the creation of arcuate incisions and channels for intracorneal rings , and the preparation of donor and host tissue for the anterior , posterior , and penetrating keratoplasty ( pk ) .
different surgical approaches have been proposed for deep anterior lamellar keratoplasty ( dalk ) [ 59 ] , but the the big - bubble technique introduced by anwar and teichmann   in which air is injected into the deep stroma in an attempt to achieve a large air bubble between the descemet 's membrane and the stroma to facilitate pre - descemet 's plane dissection , probably at the moment results as the more common .
we proposed a variant of the big - bubble technique in dalk assisted by femtosecond laser which we have called intrabubble   in whom the laser allows a pre - descemet 's plane lamellar dissection to a predefined corneal depth and the creation of a channel in the posterior stroma of the recipient , 50   above the corneal thinnest point , into which a smooth cannula for air injection can be introduced .   in this paper , we report the 12-month follow - up results after big - bubble dalk assisted by femtosecond laser .
thirty - five eyes of 35 patients ( mean age  23  6  ( sd ) years ) affected by keratoconus were enrolled in the study .
corneal trephination was performed using the intralase 60  khz femtosecond laser ( abbott medical optics , inc . )
loaded with the intralase enabled keratoplasty ( iek ) computer program that provides the creation of corneal lamellae of different shapes ( mushroom , zigzag , christmas tree , etc . ) .
the intralase requires placement of a suction ring and an applanation lens . after obtaining a proper vacuum seal
, we applied the applanation lens to provide a uniform reference plane for the laser .
we used the same laser settings to achieve mushroom incisions for both recipient and donor .
the donor cornea was removed from optisol ( bausch & lomb ) storage , mounted on an artificial anterior chamber ( coronet patient artificial anterior chamber , network medical products , ltd . ) , and then treated under the 60  khz femtosecond laser .
the laser treatment was planned in three consecutive steps as previously described by buzzonetti et al .  
the intralase performs an anterior side cut ( 30 angled , 25  arc length , and 6.0  mm diameter ) 50   above the thinnest corneal site as measured by sirius scheimpflug camera ( cso , firenze , italy ) .
a recipient lamellar cut 7.5  mm in diameter ( figure 3 ) is created by the intralase using a target thickness of 100   above the thinnest corneal site . a mushroom lamella ( anterior diameter of 8.0  mm and posterior diameter of 7.0  mm )
is created by the intralase using the same target thickness of the lamellar cut ( 100   above the thinnest corneal site ) because the lamellar cut depth has to correspond to the bottom side depth of the mushroom lamella .  
the recipient lamella was then removed , a fogla - pointed dissector ( bausch & lomb storz ophthalmic ) was used to prolong the stromal channel created by the laser , too short to achieve the complete insertion of the cannula for air injection ; then a fogla 27 gauge air injection cannula ( bausch & lomb storz ophthalmic ) , attached to a 5  ml syringe filled with air , was inserted into the residual stroma and slightly advanced into the channel .
air was then forcefully injected into the stroma to achieve the formation of a big - bubble ( figure 4 ) .
the surgery was then completed as the conventional big - bubble procedure : a peripheral paracentesis was performed , allowing some aqueous to escape to lower the intraocular pressure , and a small air bubble was injected into the anterior chamber to check the baring of descemet 's membrane . then a 15 disposable knife was used to perforate the bubble and an ophthalmic viscosurgical device was injected to refill the space and protect the descemet 's membrane .
the residual stroma was excised using corneal scissors and the smooth transparent descemet 's membrane appeared .
finally , the donor lamella , previously prepared by femtosecond laser , after the endothelium , was removed by sponge , was fitted into place , and sutured using 16 interrupted 100 monofilament nylon sutures .
the followup is 12 months , and sutures were removed by the 10th postoperative month in all patients .
the following data were evaluated : best corrected visual acuity ( bcva ) , spherical equivalent and , by sirius scheimpflug camera ( cso , firenze , italy ) , keratometric astigmatism .
all procedures were completed as dalk except 2 converted to pk because an inadvertent intraoperative macroperforation occurred . in 3 patients the bubble
was not achieved , but the dalk was completed anyway by layer - by - layer stromal dissection .
twelve months after surgery mean postoperative bcva was 0.8 ( range : 0.5 to 1.0 ) , mean spherical equivalent was 3.5  1.7  d ( range : 0.25 to 1.50  d ) , and mean keratometric astigmatism was 4.8  3.1  d ( range : 3.0 to 6.50  d ) .
the dalk , alternative to pk in cases of a healthy endothelium , is the first choice for many surgeons that appreciate the advantages of extraocular surgery , the associated good visual outcome , and the absence of endothelial rejection due to the preservation of the recipient endothelium .
however , technical difficulties , protracted operating times and the risk of corneal intraoperative perforation limit dalk 's success .   like conventional big - bubble dalk , the intrabubble technique decreases the risk of immune rejection
. however , the creation of a channel for smooth air injection in the intrabubble technique significantly reduces the risk of inadvertent perforation , the main complication of dalk .
moreover , the use of the femtosecond laser , allowing the maintenance of a predefined corneal depth very close to the endothelium , provides a good percentage of success in achieving the bubble ( 82% ) .
in fact it has been reported   that if the needle is not advanced deep enough in the stroma , more difficult is the baring of descemet 's membrane . in last months we were evaluating the application of the big - bubble dalk assisted by femtosecond laser to the pediatric patients . also if the number of patients treated until now is less and the followup is short , our early findings suggest that the intrabubble technique could be applied also to the children in the attempt to decrease the high rejection percentage ( the reported   prognosis for graft survival after pediatric pk is of approximately 50% at 1 year ) and improve the refractive outcome because in my experience the residual astigmatism results are effectively lower after the keratoplasty is assisted by femtosecond laser , probably because of the lamellae geometry that provides a better surface contact between donor and recipient . in conclusion
we believe that intrabubble could help to standardise the big bubble technique in dalk , reducing the learning curve for surgeons who approach the big - bubble technique as well as the risk of intraoperative complications , especially perforation which is the real risk with this procedure , and allowing good refractive outcomes for the good alignment of donor and recipient mushroom configuration , both in adults and children .
 
 purpose . to report the 12-month follow - up after big - bubble deep anterior lamellar keratoplasty ( dalk ) assisted by femtosecond laser that we have called intrabubble 
 . 
 methods . a 60  khz intralase femtosecond laser ( abbott medical optics ) 
 firstly created a 30 angled intrastromal channel to insert the air injection cannula , 50   above the thinnest corneal site measured by sirius scheimpflug camera ( cso , firenze , italy ) , then performed a full lamellar cut 100   above the thinnest corneal point , and from the same corneal depth , created a mushroom incision . 
 the lamella was removed , and the smooth cannula of fogla was inserted into the stromal channel and air was injected to achieve a big bubble . 
 the follow up is 12 months , and sutures were removed by the 10th postoperative month in all patients . 
 best corrected visual acuity ( bcva ) , spherical equivalent and , by sirius scheimpflug camera ( cso , firenze , italy ) keratometric astigmatism were evaluated . 
 results . 
 all procedures were completed as dalk except 2 converted to pk because an inadvertent intraoperative macroperforation occurred . 
 mean postoperative bcva was 0.8 , mean spherical equivalent was -3.5  1.7  d , and mean keratometric astigmatism was 4.8  3.1  d. 
 conclusion . 
 the femtosecond laser could standardize the big - bubble technique in dalk , reducing the risk of intraoperative complications and allowing good refractive outcomes . 
1. Introduction
2. Materials and Methods
3. Results
4. Discussion