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LETTERS
Pachy-bubble and diamond knife–assisted deep anterior lamellar keratoplasty Vajpayee et al.1 describe a technique that uses intraoperative ultrasonic pachymetry to create a diamond knife incision that reaches the deep stroma and allows manual lamellar dissection near Descemet membrane for subtotal stromal removal. No trephination is performed, and the whole cornea is cut 360 degrees along the trephination mark with scissors. The authors compare their technique with ours, the pachy-bubble,2 and state that the major advantage of their technique is that they do not perform trephination for corneal debulking. They state that there is a significant risk for corneal perforation during initial trephination. We would like to clarify that their technique is very similar to ours in conception, aiming at safely reaching the deep stroma to facilitate its removal, rather than injecting air with a needle through the trephination, as in the big-bubble technique.3 Superficial air injection is the main cause of unsuccessful big-bubble formation.4 In our pachy-bubble technique, we overcome this limitation by injecting air deep into the stroma with a deep anterior lamellar keratoplasty (DALK) cannula. This achieves air-bubble formation in about 90% of the cases. The pachymetry-guided incision described by Vajpayee et al. is exactly as was described in our technique, a 2.0 mm incision created with a calibrated diamond knife at the 12 o’clock position. The major differences between the 2 techniques are the following: (1) We calibrate the knife at a value of the thinnest corneal thickness at the incision site minus 60 mm (a 90% depth incision in the original paper), which is safer than the 30 mm in their paper. Using 50 mm, we have had 1 case of diamond-knife perforation.2 (2) We perform a superficial trephination to approximately 60% to 70% of corneal thickness. This is very safe and will greatly facilitate stromal removal with a more regular border than making the whole 360-degree incision with scissors. In more than 110 cases of pachy-bubble that I have performed, no case of perforation during trephination occurred. (3) We inject air with a DALK cannula through the diamond knife incision. There is no advantage in performing manual dissection aiming at partial stromal removal rather than injecting air to form the bubble for a clean and easier dissection plane for complete stromal removal. Manual dissection at the depth proposed by Vajpayee et al. certainly carries the risk for perforation. In addition, interface haze and
Figure 1. A: Biomicroscopic examination 1 year after DALK with manual stromal dissection shows central interface haze. B: Despite a residual stroma of only 38 mm seen on high-resolution optical coherence tomography, the corrected distance visual acuity was only 20/40. Three years after surgery, no improvement was observed despite low levels of astigmatism.
stromal irregularity are potential sources for decreased corrected visual acuity when residual stroma is left (Figure 1).5 Ramon Coral Ghanem, MD, PhD Santa Catarina, Brazil REFERENCES 1. Vajpayee RB, Maharana PK, Sharma N, Agarwal T, Jhanji V. Diamond knife–assisted deep anterior lamellar keratoplasty to manage keratoconus. J Cataract Refract Surg 2014; 40:276–282 2. Ghanem RC, Ghanem MA. Pachymetry-guided intrastromal air injection (“pachy-bubble”) for deep anterior lamellar keratoplasty. Cornea 2012; 31:1087–1091 3. Anwar M, Teichmann KD. Big-bubble technique to bare Descemet’s membrane in anterior lamellar keratoplasty. J Cataract Refract Surg 2002; 28:398–403 4. Scorcia V, Busin M, Lucisano A, Beltz J, Carta A, Scorcia G. Anterior segment optical coherence tomography–guided big-bubble technique. Ophthalmology 2013; 120:471–476 5. Ardjomand N, Hau S, McAlister JC, Bunce C, Galaretta D, Tuft SJ, Larkin DF. Quality of vision and graft thickness in deep anterior lamellar and penetrating corneal allografts. Am J Ophthalmol 2007; 143:228–235
J CATARACT REFRACT SURG - VOL 40, AUGUST 2014
LETTERS
Pachy-bubble and diamond knife–assisted deep anterior lamellar keratoplasty Vajpayee et al.1 describe a technique that uses intraoperative ultrasonic pachymetry to create a diamond knife incision that reaches the deep stroma and allows manual lamellar dissection near Descemet membrane for subtotal stromal removal. No trephination is performed, and the whole cornea is cut 360 degrees along the trephination mark with scissors. The authors compare their technique with ours, the pachy-bubble,2 and state that the major advantage of their technique is that they do not perform trephination for corneal debulking. They state that there is a significant risk for corneal perforation during initial trephination. We would like to clarify that their technique is very similar to ours in conception, aiming at safely reaching the deep stroma to facilitate its removal, rather than injecting air with a needle through the trephination, as in the big-bubble technique.3 Superficial air injection is the main cause of unsuccessful big-bubble formation.4 In our pachy-bubble technique, we overcome this limitation by injecting air deep into the stroma with a deep anterior lamellar keratoplasty (DALK) cannula. This achieves air-bubble formation in about 90% of the cases. The pachymetry-guided incision described by Vajpayee et al. is exactly as was described in our technique, a 2.0 mm incision created with a calibrated diamond knife at the 12 o’clock position. The major differences between the 2 techniques are the following: (1) We calibrate the knife at a value of the thinnest corneal thickness at the incision site minus 60 mm (a 90% depth incision in the original paper), which is safer than the 30 mm in their paper. Using 50 mm, we have had 1 case of diamond-knife perforation.2 (2) We perform a superficial trephination to approximately 60% to 70% of corneal thickness. This is very safe and will greatly facilitate stromal removal with a more regular border than making the whole 360-degree incision with scissors. In more than 110 cases of pachy-bubble that I have performed, no case of perforation during trephination occurred. (3) We inject air with a DALK cannula through the diamond knife incision. There is no advantage in performing manual dissection aiming at partial stromal removal rather than injecting air to form the bubble for a clean and easier dissection plane for complete stromal removal. Manual dissection at the depth proposed by Vajpayee et al. certainly carries the risk for perforation. In addition, interface haze and
Figure 1. A: Biomicroscopic examination 1 year after DALK with manual stromal dissection shows central interface haze. B: Despite a residual stroma of only 38 mm seen on high-resolution optical coherence tomography, the corrected distance visual acuity was only 20/40. Three years after surgery, no improvement was observed despite low levels of astigmatism.
stromal irregularity are potential sources for decreased corrected visual acuity when residual stroma is left (Figure 1).5 Ramon Coral Ghanem, MD, PhD Santa Catarina, Brazil REFERENCES 1. Vajpayee RB, Maharana PK, Sharma N, Agarwal T, Jhanji V. Diamond knife–assisted deep anterior lamellar keratoplasty to manage keratoconus. J Cataract Refract Surg 2014; 40:276–282 2. Ghanem RC, Ghanem MA. Pachymetry-guided intrastromal air injection (“pachy-bubble”) for deep anterior lamellar keratoplasty. Cornea 2012; 31:1087–1091 3. Anwar M, Teichmann KD. Big-bubble technique to bare Descemet’s membrane in anterior lamellar keratoplasty. J Cataract Refract Surg 2002; 28:398–403 4. Scorcia V, Busin M, Lucisano A, Beltz J, Carta A, Scorcia G. Anterior segment optical coherence tomography–guided big-bubble technique. Ophthalmology 2013; 120:471–476 5. Ardjomand N, Hau S, McAlister JC, Bunce C, Galaretta D, Tuft SJ, Larkin DF. Quality of vision and graft thickness in deep anterior lamellar and penetrating corneal allografts. Am J Ophthalmol 2007; 143:228–235
J CATARACT REFRACT SURG - VOL 40, AUGUST 2014
