ARTICLE
Diamond knife–assisted deep anterior lamellar keratoplasty to manage keratoconus Rasik B. Vajpayee, MS, FRCS(Ed), FRANZCO, Prafulla K. Maharana, MD, Namrata Sharma, MD, Tushar Agarwal, MD, Vishal Jhanji, MD
PURPOSE: To evaluate the outcomes of a new surgical technique, diamond knife–assisted deep anterior lamellar keratoplasty (DALK), and compare its visual and refractive results with bigbubble DALK in cases of keratoconus. SETTING: Tertiary eyecare hospital. DESIGN: Comparative case series. METHODS: The visual and surgical outcomes of diamond knife–assisted DALK were compared with those of successful big-bubble DALK. RESULTS: Diamond knife–assisted DALK was performed in 19 eyes and big-bubble DALK, in 11 eyes. All surgeries were completed successfully. No intraoperative or postoperative complications occurred with diamond knife–assisted DALK. Six months after diamond knife–assisted DALK, the mean corrected distance visual acuity (CDVA) improved significantly from 1.87 logMAR G 0.22 (SD) to 0.23 G 0.06 logMAR, the mean keratometry improved from 65.99 G 8.86 diopters (D) to 45.13 G 1.16 D, and the mean keratometric cylinder improved from 7.99 G 3.81 D to 2.87 G 0.59 D (all PZ.005). Postoperatively, the mean refractive astigmatism was 2.55 G 0.49 D and the mean spherical equivalent was 1.97 G 0.56 D. The mean logMAR CDVA (P Z .06), postoperative keratometry (PZ.64), refractive cylinder (PZ.63), and endothelial cell loss (PZ.11) were comparable between diamond knife–assisted DALK and big-bubble DALK. CONCLUSIONS: Diamond knife–assisted DALK was effective and predictable as a surgical technique for management of keratoconus cases. This technique has the potential to offer visual and refractive outcomes comparable to those of big-bubble DALK. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2014; 40:276–282 Q 2013 ASCRS and ESCRS Online Video
Deep anterior lamellar keratoplasty (DALK) is currently the most popular technique for sparing the corneal endothelium in the management of cases with corneal pathology anterior to Descemet membrane, including keratoconus, stromal scars, and stromal dystrophies.1–4 The benefits of DALK over full-thickness keratoplasty are that it is an extraocular procedure, there is no risk for endothelial rejection, and it offers better wound integrity.5,6 An optimum visual outcome after DALK may depend on the residual thickness of the recipient stromal bed.7 In a comparative study between DALK and penetrating keratoplasty (PKP), Ardjomand et al.7 found that eyes with a recipient corneal bed thickness of less than 20 mm 276
Q 2013 ASCRS and ESCRS Published by Elsevier Inc.
had visual acuities similar to those in eyes with PKP, whereas those with a residual stromal bed (RSB) thickness of more than 80 mm had significantly reduced visual acuity. To perform DALK, the recipient bed dissection can be performed manually with a lamellar dissector or using a microkeratome or femtosecond laser. Other methods of DALK use air injection, hydrodelamination, or injection of an ophthalmic viscosurgical device (OVD).5,6 Among the described techniques of DALK, the most popular are the Anwar big-bubble technique and the Melles technique.8 The major limitation of bigbubble DALK is its steep learning curve and the risk for intraoperative perforation. The risk for perforation 0886-3350/$ - see front matter http://dx.doi.org/10.1016/j.jcrs.2013.07.047
DIAMOND KNIFE–ASSISTED DALK FOR MANAGEMENT OF KERATOCONUS
is higher in cases with advanced keratoconus and extreme corneal thinning (!250 mm).9 Also, it is often difficult to perform this surgery in the presence of a corneal scar due to resolved hydrops.10 We describe a new technique of DALK for the management of keratoconus that is easy to perform, provides visual outcomes comparable to those of big-bubble DALK, and can be performed in cases of extreme corneal thinning or corneal scars. PATIENTS AND METHODS Eyes of consecutive patients with advanced keratoconus had diamond knife–assisted DALK. All patients were intolerant to contact lenses and had a corrected distance visual acuity (CDVA) of worse than 1 logMAR. All patients provided informed consent. The Human Research Ethics Committee, Royal Victorian Eye and Ear Hospital, approved the conduct of the study. The study adhered to the tenets of the Declaration of Helsinki. All surgeries were performed by the same experienced surgeon (R.B.V).
Surgical Technique Host Preparation The surgeries were performed under peribulbar or general anesthesia. The center of the host cornea was marked first. Then, a circular mark (7.5 to 8.5 mm in diameter) was made with a disposable trephine blade (Madhu Instruments) whose edges had been stained with gentian violet (Figure 1, A). Intraoperative ultrasonic pachymetry (Micropach, model 200PC, Sonomed) was performed on this corneal mark between the 11 o'clock and 1 o'clock positions (Figure 1, B). A diamond knife set at a depth of 30 mm less than the intraoperative pachymetry reading was used to make a 2.0 mm incision at the 11 to 12 o'clock position (Figure 1, C). Medium, curved, fineblade scissors (Cindy Scissors, Bausch & Lomb) were then used to extend the incision on either side circumferentially for 360 (Figure 1, D). An open centripetal lamellar dissection was performed using lamellar dissectors (Figure 1, E). The central stromal disk was then excised, leaving a thin RSB. Donor Preparation The donor corneoscleral button was placed endothelial side up on a wet polytetrafluoroethylene (Teflon) block. The donor button was punched from the endothelial side and was oversized by 0.25 mm. The
Submitted: May 17, 2013. Final revision submitted: July 20, 2013. Accepted: July 24, 2013. From Dr. Rajendra Prasad Centre for Ophthalmic Sciences (Vajpayee, Maharana, Sharma, Agarwal), All India Institute of Medical Sciences, New Delhi, India; the Centre for Eye Research Australia (Vajpayee, Jhanji), University of Melbourne, Australia; the Department of Ophthalmology and Visual Sciences (Jhanji), Chinese University of Hong Kong, Hong Kong. Corresponding author: Rasik B. Vajpayee, MS, FRCS(Ed), FRANZCO, Cornea, Cataract & Refractive Surgery Services, Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi 110029, India. E-mail: [email protected].
277
Descemet membrane of the donor lenticule was stripped after staining with 0.1 mL of trypan blue 0.06% (Visiblue, Shah & Shah). The donor lenticule was placed on the host bed and sutured using 10-0 monofilament nylon (Figure 1, F) (Video, available at http://jcrsjournal.org). Postoperatively, all patients received prednisolone acetate 1% eyedrops 4 times a day, moxifloxacin hydrochloride 0.5% eyedrops 3 times a day, and preservative-free artificial tears 4 times a day. The antibiotic eyedrops were continued for 2 months, and the topical corticosteroid eyedrops were tapered over 4 months. Postoperatively, all patients were seen every week for 1 month, every month for 6 months, and every 6 months thereafter. At each follow-up visit, a complete ocular examination was performed. The examination included visual acuity, manual keratometry, refraction (from 1 month onward), slitlamp biomicroscopy, anterior segment optical coherence tomography (AS-OCT) (Visante, Carl Zeiss Meditec AG), and Scheimpflug imaging (Pentacam, Oculus, Inc.). Residual host thickness measurements were obtained from the center of the cornea in all cases. The readings were obtained after the measuring tool (caliper) was positioned at the corneal center. One reading was used in each case. The parameters recorded were uncorrected distance visual acuity (UDVA), CDVA, keratometry, refraction, intraocular pressure, residual host bed thickness using AS-OCT, and endothelial cell counts (SP-2000P, Topcon Corp.). Selective suture removal was performed for suture-related events or to control astigmatism.
Comparison and Statistical Analysis The outcomes of diamond knife–assisted DALK were compared with those in another cohort that had Descemet membrane–baring, big-bubble DALK using the Anwar technique in the previous year by the same surgeon (R.B.V.). Only successful cases with no intraoperative perforations were included in the analysis. The postoperative UDVA, CDVA, keratometry, astigmatism, and endothelial cell loss between the 2 surgical techniques were compared. Postoperative 6-month data were used for analysis. The Wilcoxon rank-sum test was used for statistical analysis.
RESULTS Nineteen eyes of 19 patients (12 men [63.2%]) had diamond knife–assisted DALK (Tables 1 and 2). Of the 19 cases, 3 had healed hydrops and 1 had resolved keratitis. The mean thinnest corneal pachymetry was 250 G 60.37 mm. In all patients having diamond knife–assisted DALK, there was a significant improvement from preoperatively to 6 months postoperatively in the following mean values (Tables 1 to 3): CDVA, average keratometry, and keratometric cylinder (all PZ.005). The mean postoperative spherical equivalent was 1.97 G 0.56 D. The mean residual host bed thickness was 45.42 G 14.79 mm (Figures 2 to 4). No intraoperative perforations occurred in any case. One case had stromal graft rejection that was
J CATARACT REFRACT SURG - VOL 40, FEBRUARY 2014
278
DIAMOND KNIFE–ASSISTED DALK FOR MANAGEMENT OF KERATOCONUS
Figure 1. Intraoperative steps of diamond knife–assisted DALK. A: Marking the cornea with a manual corneal trephine. B: Intraoperative pachymetry at the 11 to 12 o'clock position. C: Incision made with a diamond knife. D: Initial incision enlarged with the help of curved scissors. E: Lamellar dissection performed to remove the anterior stroma. F: Donor cornea sutured to the host bed.
successfully treated with a course of intensive topical corticosteroids. Table 2 shows a comparison of parameters between diamond knife–assisted DALK and big-bubble DALK (11 cases) 6 month postoperatively. There were significant differences in preoperative keratometry, pachymetry, and the mean CDVA between the 2 groups, suggesting that the diamond knife–assisted DALK group had more severe cases of keratoconus than the big-bubble DALK group. Postoperatively, the mean geometric logMAR UDVA, CDVA, postoperative keratometry, refractive cylinder, and endothelial cell loss in the 2 groups were comparable. DISCUSSION The recent American Academy of Ophthalmology Technology assessment report10 found that the visual
and refractive outcomes after DALK and PKP are comparable if the residual bed thickness in DALK cases is between 25 mm and 65 mm. Similarly a study by Ardjomand et al.7 found that when the RSB thickness was less than 80 mm, the chances of obtaining good visual outcomes increased significantly. Using the diamond knife–assisted DALK technique, the mean RSB thickness in our study was 45.42 G 14.79 mm. A CDVA of better than 20/40 was achieved in all cases in our study, which is comparable to results in other studies of DALK using different techniques.1 Deep anterior lamellar keratoplasty using the big-bubble technique proposed by Anwar and Teichmann4 involves injection of air into the deep stroma after partial trephination of the host cornea to allow safer dissection by creating a cleavage plane between Descemet membrane and the posterior corneal stroma.
J CATARACT REFRACT SURG - VOL 40, FEBRUARY 2014
279
DIAMOND KNIFE–ASSISTED DALK FOR MANAGEMENT OF KERATOCONUS
Table 1. Preoperative and postoperative parameters of patients who had diamond knife–assisted DALK. Preoperative Age (Y)/Sex 26/M 20/M 20/M 18/M 10/M 13/F 37/F 23/F 35/M 25/M 19/F 29/M 18/M 28/F 16/F 22/M 18/F 21/M 15/M
Postoperative
CDVA (LogMAR)
Pachymetry (mm)
K (D)
K Cyl (D)
UDVA (LogMAR)
CDVA (LogMAR)
K (D)
K Cyl (D)
Pachymetry (mm)
RHT (mm)
2.079 1.778 2.079 1.477 1.778 1.778 1.778 2.079 2.079 1.778 1.778 1.778 2.079 2.079 2.079 1.477 2.079 2.079 1.477
222 234 202 302 202 262 211 295 197 169 422 260 306 177 265 211 311 268 234
60.32 59.48 71.20 59.38 58.85 41.70 79.50 76.80 73.75 72.40 62.50 67.50 70.15 70.65 73.40 59.20 62.25 62.25 72.60
4.82 6.27 4.20 6.31 4.70 13.80 6.90 6.60 11.10 12.40 7.40 0.40 12.50 13.50 4.20 6.40 8.50 8.60 13.40
0.477 0.477 0.477 0.602 0.477 0.477 0.602 0.602 0.477 0.602 0.477 0.477 0.602 0.477 0.602 0.477 0.477 0.477 0.602
0.301 0.176 0.301 0.301 0.176 0.176 0.176 0.176 0.301 0.176 0.301 0.301 0.176 0.176 0.301 0.176 0.301 0.176 0.301
47.75 43.00 45.00 44.30 45.75 45.75 46.56 44.67 45.44 46.05 44.95 46.58 45.85 44.68 43.60 44.35 43.70 44.40 45.24
4.2 2.4 2.2 2.8 2.5 3.1 2.8 3.2 3.1 3.2 2.2 3.1 2.6 2.1 2.3 3.7 2.2 3.8 3.1
591 588 540 556 566 578 560 544 598 556 599 560 542 560 558 559 579 568 588
37 25 27 40 62 55 32 30 62 46 78 49 27 50 36 47 62 39 59
CDVA Z corrected distance visual acuity; K Z average keratometry; K Cyl Z keratometric cylinder; pachymetry Z corneal thickness; RHT Z residual host thickness; UDVA Z uncorrected distance visual acuity
The certainty of baring Descemet membrane is highest with this technique provided the air is in the correct plane. The major limitations of this technique are the failure to achieve a successful big bubble at all times and a high risk for perforation. The risk for Descemet
membrane perforation in cases of big-bubble DALK ranges from 4% to 20%, while that of successful bigbubble formation is 56% to 80%.11 Despite successful big-bubble formation, the rate of conversion of DALK to PKP is between 0% and 4% and the chances
Table 2. Comparison of parameters between diamond knife–assisted DALK and big-bubble DALK 6 month postoperatively. Mean G SD Parameter Preoperative Age (y) Average K (D) Mean pachymetry (mm) Mean CDVA (logMAR) Mean cone diameter (mm) Postoperative UDVA (logMAR) CDVA (logMAR) Average K (D) Mean cylinder (D) Endothelial loss (%)
Diamond Knife–Assisted DALK (n Z 19)
Big-Bubble DALK (n Z 11)
P Value
21.73 G 6.99 65.99 G 8.86 310.78 G 68.86 1.87 G 0.22 4.78 G 0.85
19.7 G 6.2 55.32 G 6.51 381.7 G 28.43 0.82 G 0.65 4.25 G 0.92
.438 .001 .003 .0001 .1214
0.52 G 0.06 0.23 G 0.06 45.13 G 1.16 2.55 G 0.49 8.14 G 3.74
0.51 G 0.08 0.17 G 0.10 44.86 G 2.025 2.81 G 2.39 12.95 G 12.17
.648 .065 .643 .635 .117
CDVA Z corrected distance visual acuity; DALK Z deep anterior lamellar keratoplasty; K Z keratometry; UDVA Z uncorrected distance visual acuity
J CATARACT REFRACT SURG - VOL 40, FEBRUARY 2014
280
DIAMOND KNIFE–ASSISTED DALK FOR MANAGEMENT OF KERATOCONUS
Table 3. Comparison of preoperative and postoperative characteristics of patients who had diamond knife–assisted DALK. Parameter
Preoperative
Postoperative
UDVA 1.83 G 0.22 0.523 G 0.061 CDVA 1.87 G 0.22 0.235 G 0.064 Keratometry (D) 65.99 G 8.86 45.13 G 1.16 Keratometric 7.99 G 3.81 2.87 G 0.59 cylinder (D) Pachymetry (mm) 310.78 G 68.86 567.89 G 18.42
P Value .005 .005 .005 .005 .005
CDVA Z corrected distance visual acuity; UDVA Z uncorrected distance visual acuity
of achieving a CDVA of better than 20/40 ranges from 78% to 92%, even when the surgery is performed by experienced surgeons.11 Another popular DALK technique is the Melles technique,12 which involves injection of air into the anterior chamber initially to highlight the air-to-endothelium interface. This is followed by injection of an OVD into deep corneal stroma using the interface as a guide to achieve the plane of Descemet membrane exposure. This technique of DALK for keratoconus yields visual, refractive, aberrometry, and biomechanical outcomes comparable to those of the big-bubble technique.8 However, the closed method of lamellar dissection in this technique potentially increases the chances of perforation. In comparison, our technique uses intraoperative ultrasonic pachymetry to create an accurate diamond knife incision that reaches a depth just above Descemet membrane. A properly calibrated diamond knife can provide an incision depth as accurate as within G10 mm.13 The average thickness of Descemet membrane is approximately 13 mm14; thus, by setting the diamond knife at a depth of 30 mm less than the intraoperative pachymetry, a minimum safety margin of approximately 17 mm stroma is left, which
reduces the chance of perforating Descemet membrane. After the initial dissection, the rest of the lamellar dissection is performed using an open technique of dissection under direct visualization. We achieved a near Descemet membrane level of dissection in all our cases without perforation of the Descemet membrane. Four cases in our study had a residual host thickness of more than 60 mm. This may be attributed to a slight variation in the cutting depth of the diamond knife.15 It is also possible that the initial stromal dissection was superficial in these cases. Nevertheless, all our diamond knife–assisted DALK cases achieved a visual acuity of better than 20/40. Rama et al.16 also report the use of a manual dissection technique for DALK. Ghanem and Ghanem17 describe a surgical technique of intrastromal injection of air to bare Descemet membrane during DALK. After initial trephination, a 2.0 mm incision is created with a diamond knife between the 11 o'clock and 1 o'clock positions. An air bubble is injected through this incision using a cannula; this is followed by stromal dissection. The major difference is that in our technique, we do not perform trephination for corneal debulking. The corneal thickness may not be the same in all areas of trephination, and there is a risk for corneal perforation during initial trephination. A major advantage of our technique is that the exact depth can be reached through a 2.0 mm incision created with a diamond knife; the incision is large enough to allow the use of scissors for creating a nice edge along the mark of trephination. This allows us to complete the entire dissection as a single step rather than performing initial debulking. Sarnicola et al.18 report comparable visual outcomes after pre-descemetic and descemetic DALK. The authors found a difference of 18 mm between the mean corneal thickness after pre-descemetic (DALK with residual stroma) and descemetic DALK (big-bubble DALK). Likewise, the mean residual host thickness
Figure 2. A: Preoperative slitlamp photograph of a case of keratoconus. B: Postoperative slitlamp photograph after diamond knife–assisted DALK. C: Postoperative AC-OCT.
J CATARACT REFRACT SURG - VOL 40, FEBRUARY 2014
DIAMOND KNIFE–ASSISTED DALK FOR MANAGEMENT OF KERATOCONUS
281
Figure 3. A: Preoperative slitlamp photograph of a case of keratoconus with healed hydrops. B: Postoperative slitlamp photograph after diamond knife–assisted DALK. C: Postoperative AS-OCT.
was 45.42 G 14.79 mm in our case series. Considering that Descemet membrane thickness is approximately 10 to 15 mm, the amount of residual corneal stroma in diamond knife–assisted DALK cases was approximately 30 mm. In cases of corneal scarring near Descemet membrane due to healed hydrops or healed keratitis, the big-bubble technique is usually not successful.8 In our series, DALK could be performed successfully in 3 cases of healed hydrops and in 1 case with a corneal scar due to Pseudomonas keratitis that developed after corneal collagen crosslinking for keratoconus. In advanced keratoconus, when the corneal thickness is less than 250 mm, the risk for Descemet membrane perforation is high with the big-bubble technique.9 The mean thinnest corneal pachymetry in our study was 250 G 60.37 mm, and almost half our cases (47.3%) had a corneal thickness of less than 250 mm. Although we did not encounter cases of Descemet membrane perforation, we believe that this could happen. In such an event, the remaining dissection may be performed carefully, leaving stromal support at the site of microperforation. Conversion
to full-thickness keratoplasty cannot be avoided in cases with large or macroperforation intraoperatively. Also, we believe that diamond knife–assisted DALK would be difficult to perform in cases with extensive peripheral corneal thinning due to the perceived difficulties in making the initial incision with a diamond knife. We compared our cases with the best-case scenario in Descemet membrane–baring big-bubble DALK; that is, cases in which successful and uneventful surgery had been performed. We did not find a significant difference in the visual or refractive outcomes, confirming findings in previous studies7,10,16 and highlighting that it is not necessary to bare Descemet membrane in DALK to achieve an optimum visual outcome. The major limitation of our study is the small sample. Nevertheless, our technique of diamond knife–assisted DALK was predictable and provided visual outcomes comparable to those of other popular techniques of DALK. We believe this technique is economical, is easy to learn, and allows DALK to be performed even in cases in which other DALK techniques carry a higher risk for failure.
Figure 4. A: Preoperative slitlamp photograph of a case of healed keratitis. B: Postoperative slitlamp photograph after diamond knife–assisted DALK. C: Postoperative AS-OCT.
J CATARACT REFRACT SURG - VOL 40, FEBRUARY 2014
282
DIAMOND KNIFE–ASSISTED DALK FOR MANAGEMENT OF KERATOCONUS
WHAT WAS KNOWN Removal of all corneal stroma is necessary to achieve good visual outcomes after DALK.
7.
Good visual outcomes can be achieved by baring Descemet membrane using the big-bubble DALK technique
8.
WHAT THIS PAPER ADDS
9.
The diamond knife–assisted DALK technique leaves a very thin layer of corneal stroma over Descemet membrane. The visual outcomes were comparable to those of big-bubble DALK. Diamond knife–assisted DALK is a safe and easily reproducible technique of anterior lamellar corneal transplantation.
10.
11.
12.
REFERENCES 1. Shimmura S, Tsubota K. Deep anterior lamellar keratoplasty. Curr Opin Ophthalmol 2006; 17:349–355 2. Kawashima M, Kawakita T, Den S, Shimmura S, Tsubota K, Shimazaki J. Comparison of deep lamellar keratoplasty and penetrating keratoplasty for lattice and macular corneal dystrophies. Am J Ophthalmol 2006; 142:304–309 3. Vajpayee RB, Tyagi J, Sharma N, Kumar N, Jhanji V, Titiyal JS. Deep anterior lamellar keratoplasty by big-bubble technique for treatment corneal stromal opacities. Am J Ophthalmol 2007; 143:954–957 4. Anwar M, Teichmann KD. Big-bubble technique to bare Descemet’s membrane in anterior lamellar keratoplasty. J Cataract Refract Surg 2002; 28:398–403 5. Jhanji V, Sharma N, Vajpayee RB. Management of keratoconus: current scenario. Br J Ophthalmol 2011; 95:1044–1050 6. Karimian F, Feizi S. Deep anterior lamellar keratoplasty: indications, surgical techniques and complications. Middle East Afr J Ophthalmol 2010; 17:28–37. Available at: http://www.ncbi.
13.
14. 15. 16.
17.
18.
nlm.nih.gov/pmc/articles/PMC2880371/?reportZprintable. Accessed September 11, 2013 Ardjomand N, Hau S, McAlister JC, Bunce C, Galaretta D, Tuft SJ, Larkin DFP. Quality of vision and graft thickness in deep anterior lamellar and penetrating corneal allografts. Am J Ophthalmol 2007; 143:228–235 Baradaran-Rafii A, Eslani M, Sadoughi M-M, Esfandiari H, Karimian F. Anwar versus Melles deep anterior lamellar keratoplasty for keratoconus; a prospective randomized clinical trial. Ophthalmology 2013; 120:252–259 Michieletto P, Balestrazzi A, Balestrazzi A, Mazzotta C, Occhipinti I, Rossi T. Factors predicting unsuccessful big bubble deep lamellar anterior keratoplasty. Ophthalmologica 2006; 220:379–382 Reinhart WJ, Musch DC, Jacobs DS, Lee WB, Kaufman SC, Shtein RM. Deep anterior lamellar keratoplasty as an alternative to penetrating keratoplasty; a report by the American Academy of Ophthalmology (Ophthalmic Technology Assessment). Ophthalmology 2011; 118:209–218 Kubaloglu A, Sari ES, Unal M, Koytak A, Kurnaz E, Cinar Y, €rk Y. Long-term results of deep anterior lamellar keratoOzertu plasty for the treatment of keratoconus. Am J Ophthalmol 2011; 151:760–767 Melles GRJ, Lander F, Rietveld FJR, Remeijer L, Beekhuis WH, Binder PS. A new surgical technique for deep stromal, anterior lamellar keratoplasty. Br J Ophthalmol 1999; 83:327–333. Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1722959/ pdf/v083p00327.pdf. Accessed September 11, 2013 Neumann AC, McCarty GR, Copello B, Mastel D. Enhanced accuracy is necessary for refractive surgery instrumentation. J Cataract Refract Surg 1989; 15:220–226 DelMonte DW, Kim T. Anatomy and physiology of the cornea. J Cataract Refract Surg 2011; 37:588–598 Unterman SR, Rowsey JJ. Diamond knife corneal incisions. Ophthalmic Surg 1984; 15:199–202 M, Rama P, Knutsson KA, Razzoli G, Matuska S, Vigano Paganoni G. Deep anterior lamellar keratoplasty using an original manual technique. Br J Ophthalmol 2013; 97:23–27 Ghanem RC, Ghanem MA. Pachymetry-guided intrastromal air injection (“pachy-bubble”) for deep anterior lamellar keratoplasty. Cornea 2012; 31:1087–1091 Sarnicola V, Toro P, Gentile D, Hannush SB. Descemtic DALK and predescemetic DALK: outcomes in 236 cases of keratoconus. Cornea 2010; 29:53–59
J CATARACT REFRACT SURG - VOL 40, FEBRUARY 2014
Diamond knife–assisted deep anterior lamellar keratoplasty to manage keratoconus Rasik B. Vajpayee, MS, FRCS(Ed), FRANZCO, Prafulla K. Maharana, MD, Namrata Sharma, MD, Tushar Agarwal, MD, Vishal Jhanji, MD
PURPOSE: To evaluate the outcomes of a new surgical technique, diamond knife–assisted deep anterior lamellar keratoplasty (DALK), and compare its visual and refractive results with bigbubble DALK in cases of keratoconus. SETTING: Tertiary eyecare hospital. DESIGN: Comparative case series. METHODS: The visual and surgical outcomes of diamond knife–assisted DALK were compared with those of successful big-bubble DALK. RESULTS: Diamond knife–assisted DALK was performed in 19 eyes and big-bubble DALK, in 11 eyes. All surgeries were completed successfully. No intraoperative or postoperative complications occurred with diamond knife–assisted DALK. Six months after diamond knife–assisted DALK, the mean corrected distance visual acuity (CDVA) improved significantly from 1.87 logMAR G 0.22 (SD) to 0.23 G 0.06 logMAR, the mean keratometry improved from 65.99 G 8.86 diopters (D) to 45.13 G 1.16 D, and the mean keratometric cylinder improved from 7.99 G 3.81 D to 2.87 G 0.59 D (all PZ.005). Postoperatively, the mean refractive astigmatism was 2.55 G 0.49 D and the mean spherical equivalent was 1.97 G 0.56 D. The mean logMAR CDVA (P Z .06), postoperative keratometry (PZ.64), refractive cylinder (PZ.63), and endothelial cell loss (PZ.11) were comparable between diamond knife–assisted DALK and big-bubble DALK. CONCLUSIONS: Diamond knife–assisted DALK was effective and predictable as a surgical technique for management of keratoconus cases. This technique has the potential to offer visual and refractive outcomes comparable to those of big-bubble DALK. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2014; 40:276–282 Q 2013 ASCRS and ESCRS Online Video
Deep anterior lamellar keratoplasty (DALK) is currently the most popular technique for sparing the corneal endothelium in the management of cases with corneal pathology anterior to Descemet membrane, including keratoconus, stromal scars, and stromal dystrophies.1–4 The benefits of DALK over full-thickness keratoplasty are that it is an extraocular procedure, there is no risk for endothelial rejection, and it offers better wound integrity.5,6 An optimum visual outcome after DALK may depend on the residual thickness of the recipient stromal bed.7 In a comparative study between DALK and penetrating keratoplasty (PKP), Ardjomand et al.7 found that eyes with a recipient corneal bed thickness of less than 20 mm 276
Q 2013 ASCRS and ESCRS Published by Elsevier Inc.
had visual acuities similar to those in eyes with PKP, whereas those with a residual stromal bed (RSB) thickness of more than 80 mm had significantly reduced visual acuity. To perform DALK, the recipient bed dissection can be performed manually with a lamellar dissector or using a microkeratome or femtosecond laser. Other methods of DALK use air injection, hydrodelamination, or injection of an ophthalmic viscosurgical device (OVD).5,6 Among the described techniques of DALK, the most popular are the Anwar big-bubble technique and the Melles technique.8 The major limitation of bigbubble DALK is its steep learning curve and the risk for intraoperative perforation. The risk for perforation 0886-3350/$ - see front matter http://dx.doi.org/10.1016/j.jcrs.2013.07.047
DIAMOND KNIFE–ASSISTED DALK FOR MANAGEMENT OF KERATOCONUS
is higher in cases with advanced keratoconus and extreme corneal thinning (!250 mm).9 Also, it is often difficult to perform this surgery in the presence of a corneal scar due to resolved hydrops.10 We describe a new technique of DALK for the management of keratoconus that is easy to perform, provides visual outcomes comparable to those of big-bubble DALK, and can be performed in cases of extreme corneal thinning or corneal scars. PATIENTS AND METHODS Eyes of consecutive patients with advanced keratoconus had diamond knife–assisted DALK. All patients were intolerant to contact lenses and had a corrected distance visual acuity (CDVA) of worse than 1 logMAR. All patients provided informed consent. The Human Research Ethics Committee, Royal Victorian Eye and Ear Hospital, approved the conduct of the study. The study adhered to the tenets of the Declaration of Helsinki. All surgeries were performed by the same experienced surgeon (R.B.V).
Surgical Technique Host Preparation The surgeries were performed under peribulbar or general anesthesia. The center of the host cornea was marked first. Then, a circular mark (7.5 to 8.5 mm in diameter) was made with a disposable trephine blade (Madhu Instruments) whose edges had been stained with gentian violet (Figure 1, A). Intraoperative ultrasonic pachymetry (Micropach, model 200PC, Sonomed) was performed on this corneal mark between the 11 o'clock and 1 o'clock positions (Figure 1, B). A diamond knife set at a depth of 30 mm less than the intraoperative pachymetry reading was used to make a 2.0 mm incision at the 11 to 12 o'clock position (Figure 1, C). Medium, curved, fineblade scissors (Cindy Scissors, Bausch & Lomb) were then used to extend the incision on either side circumferentially for 360 (Figure 1, D). An open centripetal lamellar dissection was performed using lamellar dissectors (Figure 1, E). The central stromal disk was then excised, leaving a thin RSB. Donor Preparation The donor corneoscleral button was placed endothelial side up on a wet polytetrafluoroethylene (Teflon) block. The donor button was punched from the endothelial side and was oversized by 0.25 mm. The
Submitted: May 17, 2013. Final revision submitted: July 20, 2013. Accepted: July 24, 2013. From Dr. Rajendra Prasad Centre for Ophthalmic Sciences (Vajpayee, Maharana, Sharma, Agarwal), All India Institute of Medical Sciences, New Delhi, India; the Centre for Eye Research Australia (Vajpayee, Jhanji), University of Melbourne, Australia; the Department of Ophthalmology and Visual Sciences (Jhanji), Chinese University of Hong Kong, Hong Kong. Corresponding author: Rasik B. Vajpayee, MS, FRCS(Ed), FRANZCO, Cornea, Cataract & Refractive Surgery Services, Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi 110029, India. E-mail: [email protected].
277
Descemet membrane of the donor lenticule was stripped after staining with 0.1 mL of trypan blue 0.06% (Visiblue, Shah & Shah). The donor lenticule was placed on the host bed and sutured using 10-0 monofilament nylon (Figure 1, F) (Video, available at http://jcrsjournal.org). Postoperatively, all patients received prednisolone acetate 1% eyedrops 4 times a day, moxifloxacin hydrochloride 0.5% eyedrops 3 times a day, and preservative-free artificial tears 4 times a day. The antibiotic eyedrops were continued for 2 months, and the topical corticosteroid eyedrops were tapered over 4 months. Postoperatively, all patients were seen every week for 1 month, every month for 6 months, and every 6 months thereafter. At each follow-up visit, a complete ocular examination was performed. The examination included visual acuity, manual keratometry, refraction (from 1 month onward), slitlamp biomicroscopy, anterior segment optical coherence tomography (AS-OCT) (Visante, Carl Zeiss Meditec AG), and Scheimpflug imaging (Pentacam, Oculus, Inc.). Residual host thickness measurements were obtained from the center of the cornea in all cases. The readings were obtained after the measuring tool (caliper) was positioned at the corneal center. One reading was used in each case. The parameters recorded were uncorrected distance visual acuity (UDVA), CDVA, keratometry, refraction, intraocular pressure, residual host bed thickness using AS-OCT, and endothelial cell counts (SP-2000P, Topcon Corp.). Selective suture removal was performed for suture-related events or to control astigmatism.
Comparison and Statistical Analysis The outcomes of diamond knife–assisted DALK were compared with those in another cohort that had Descemet membrane–baring, big-bubble DALK using the Anwar technique in the previous year by the same surgeon (R.B.V.). Only successful cases with no intraoperative perforations were included in the analysis. The postoperative UDVA, CDVA, keratometry, astigmatism, and endothelial cell loss between the 2 surgical techniques were compared. Postoperative 6-month data were used for analysis. The Wilcoxon rank-sum test was used for statistical analysis.
RESULTS Nineteen eyes of 19 patients (12 men [63.2%]) had diamond knife–assisted DALK (Tables 1 and 2). Of the 19 cases, 3 had healed hydrops and 1 had resolved keratitis. The mean thinnest corneal pachymetry was 250 G 60.37 mm. In all patients having diamond knife–assisted DALK, there was a significant improvement from preoperatively to 6 months postoperatively in the following mean values (Tables 1 to 3): CDVA, average keratometry, and keratometric cylinder (all PZ.005). The mean postoperative spherical equivalent was 1.97 G 0.56 D. The mean residual host bed thickness was 45.42 G 14.79 mm (Figures 2 to 4). No intraoperative perforations occurred in any case. One case had stromal graft rejection that was
J CATARACT REFRACT SURG - VOL 40, FEBRUARY 2014
278
DIAMOND KNIFE–ASSISTED DALK FOR MANAGEMENT OF KERATOCONUS
Figure 1. Intraoperative steps of diamond knife–assisted DALK. A: Marking the cornea with a manual corneal trephine. B: Intraoperative pachymetry at the 11 to 12 o'clock position. C: Incision made with a diamond knife. D: Initial incision enlarged with the help of curved scissors. E: Lamellar dissection performed to remove the anterior stroma. F: Donor cornea sutured to the host bed.
successfully treated with a course of intensive topical corticosteroids. Table 2 shows a comparison of parameters between diamond knife–assisted DALK and big-bubble DALK (11 cases) 6 month postoperatively. There were significant differences in preoperative keratometry, pachymetry, and the mean CDVA between the 2 groups, suggesting that the diamond knife–assisted DALK group had more severe cases of keratoconus than the big-bubble DALK group. Postoperatively, the mean geometric logMAR UDVA, CDVA, postoperative keratometry, refractive cylinder, and endothelial cell loss in the 2 groups were comparable. DISCUSSION The recent American Academy of Ophthalmology Technology assessment report10 found that the visual
and refractive outcomes after DALK and PKP are comparable if the residual bed thickness in DALK cases is between 25 mm and 65 mm. Similarly a study by Ardjomand et al.7 found that when the RSB thickness was less than 80 mm, the chances of obtaining good visual outcomes increased significantly. Using the diamond knife–assisted DALK technique, the mean RSB thickness in our study was 45.42 G 14.79 mm. A CDVA of better than 20/40 was achieved in all cases in our study, which is comparable to results in other studies of DALK using different techniques.1 Deep anterior lamellar keratoplasty using the big-bubble technique proposed by Anwar and Teichmann4 involves injection of air into the deep stroma after partial trephination of the host cornea to allow safer dissection by creating a cleavage plane between Descemet membrane and the posterior corneal stroma.
J CATARACT REFRACT SURG - VOL 40, FEBRUARY 2014
279
DIAMOND KNIFE–ASSISTED DALK FOR MANAGEMENT OF KERATOCONUS
Table 1. Preoperative and postoperative parameters of patients who had diamond knife–assisted DALK. Preoperative Age (Y)/Sex 26/M 20/M 20/M 18/M 10/M 13/F 37/F 23/F 35/M 25/M 19/F 29/M 18/M 28/F 16/F 22/M 18/F 21/M 15/M
Postoperative
CDVA (LogMAR)
Pachymetry (mm)
K (D)
K Cyl (D)
UDVA (LogMAR)
CDVA (LogMAR)
K (D)
K Cyl (D)
Pachymetry (mm)
RHT (mm)
2.079 1.778 2.079 1.477 1.778 1.778 1.778 2.079 2.079 1.778 1.778 1.778 2.079 2.079 2.079 1.477 2.079 2.079 1.477
222 234 202 302 202 262 211 295 197 169 422 260 306 177 265 211 311 268 234
60.32 59.48 71.20 59.38 58.85 41.70 79.50 76.80 73.75 72.40 62.50 67.50 70.15 70.65 73.40 59.20 62.25 62.25 72.60
4.82 6.27 4.20 6.31 4.70 13.80 6.90 6.60 11.10 12.40 7.40 0.40 12.50 13.50 4.20 6.40 8.50 8.60 13.40
0.477 0.477 0.477 0.602 0.477 0.477 0.602 0.602 0.477 0.602 0.477 0.477 0.602 0.477 0.602 0.477 0.477 0.477 0.602
0.301 0.176 0.301 0.301 0.176 0.176 0.176 0.176 0.301 0.176 0.301 0.301 0.176 0.176 0.301 0.176 0.301 0.176 0.301
47.75 43.00 45.00 44.30 45.75 45.75 46.56 44.67 45.44 46.05 44.95 46.58 45.85 44.68 43.60 44.35 43.70 44.40 45.24
4.2 2.4 2.2 2.8 2.5 3.1 2.8 3.2 3.1 3.2 2.2 3.1 2.6 2.1 2.3 3.7 2.2 3.8 3.1
591 588 540 556 566 578 560 544 598 556 599 560 542 560 558 559 579 568 588
37 25 27 40 62 55 32 30 62 46 78 49 27 50 36 47 62 39 59
CDVA Z corrected distance visual acuity; K Z average keratometry; K Cyl Z keratometric cylinder; pachymetry Z corneal thickness; RHT Z residual host thickness; UDVA Z uncorrected distance visual acuity
The certainty of baring Descemet membrane is highest with this technique provided the air is in the correct plane. The major limitations of this technique are the failure to achieve a successful big bubble at all times and a high risk for perforation. The risk for Descemet
membrane perforation in cases of big-bubble DALK ranges from 4% to 20%, while that of successful bigbubble formation is 56% to 80%.11 Despite successful big-bubble formation, the rate of conversion of DALK to PKP is between 0% and 4% and the chances
Table 2. Comparison of parameters between diamond knife–assisted DALK and big-bubble DALK 6 month postoperatively. Mean G SD Parameter Preoperative Age (y) Average K (D) Mean pachymetry (mm) Mean CDVA (logMAR) Mean cone diameter (mm) Postoperative UDVA (logMAR) CDVA (logMAR) Average K (D) Mean cylinder (D) Endothelial loss (%)
Diamond Knife–Assisted DALK (n Z 19)
Big-Bubble DALK (n Z 11)
P Value
21.73 G 6.99 65.99 G 8.86 310.78 G 68.86 1.87 G 0.22 4.78 G 0.85
19.7 G 6.2 55.32 G 6.51 381.7 G 28.43 0.82 G 0.65 4.25 G 0.92
.438 .001 .003 .0001 .1214
0.52 G 0.06 0.23 G 0.06 45.13 G 1.16 2.55 G 0.49 8.14 G 3.74
0.51 G 0.08 0.17 G 0.10 44.86 G 2.025 2.81 G 2.39 12.95 G 12.17
.648 .065 .643 .635 .117
CDVA Z corrected distance visual acuity; DALK Z deep anterior lamellar keratoplasty; K Z keratometry; UDVA Z uncorrected distance visual acuity
J CATARACT REFRACT SURG - VOL 40, FEBRUARY 2014
280
DIAMOND KNIFE–ASSISTED DALK FOR MANAGEMENT OF KERATOCONUS
Table 3. Comparison of preoperative and postoperative characteristics of patients who had diamond knife–assisted DALK. Parameter
Preoperative
Postoperative
UDVA 1.83 G 0.22 0.523 G 0.061 CDVA 1.87 G 0.22 0.235 G 0.064 Keratometry (D) 65.99 G 8.86 45.13 G 1.16 Keratometric 7.99 G 3.81 2.87 G 0.59 cylinder (D) Pachymetry (mm) 310.78 G 68.86 567.89 G 18.42
P Value .005 .005 .005 .005 .005
CDVA Z corrected distance visual acuity; UDVA Z uncorrected distance visual acuity
of achieving a CDVA of better than 20/40 ranges from 78% to 92%, even when the surgery is performed by experienced surgeons.11 Another popular DALK technique is the Melles technique,12 which involves injection of air into the anterior chamber initially to highlight the air-to-endothelium interface. This is followed by injection of an OVD into deep corneal stroma using the interface as a guide to achieve the plane of Descemet membrane exposure. This technique of DALK for keratoconus yields visual, refractive, aberrometry, and biomechanical outcomes comparable to those of the big-bubble technique.8 However, the closed method of lamellar dissection in this technique potentially increases the chances of perforation. In comparison, our technique uses intraoperative ultrasonic pachymetry to create an accurate diamond knife incision that reaches a depth just above Descemet membrane. A properly calibrated diamond knife can provide an incision depth as accurate as within G10 mm.13 The average thickness of Descemet membrane is approximately 13 mm14; thus, by setting the diamond knife at a depth of 30 mm less than the intraoperative pachymetry, a minimum safety margin of approximately 17 mm stroma is left, which
reduces the chance of perforating Descemet membrane. After the initial dissection, the rest of the lamellar dissection is performed using an open technique of dissection under direct visualization. We achieved a near Descemet membrane level of dissection in all our cases without perforation of the Descemet membrane. Four cases in our study had a residual host thickness of more than 60 mm. This may be attributed to a slight variation in the cutting depth of the diamond knife.15 It is also possible that the initial stromal dissection was superficial in these cases. Nevertheless, all our diamond knife–assisted DALK cases achieved a visual acuity of better than 20/40. Rama et al.16 also report the use of a manual dissection technique for DALK. Ghanem and Ghanem17 describe a surgical technique of intrastromal injection of air to bare Descemet membrane during DALK. After initial trephination, a 2.0 mm incision is created with a diamond knife between the 11 o'clock and 1 o'clock positions. An air bubble is injected through this incision using a cannula; this is followed by stromal dissection. The major difference is that in our technique, we do not perform trephination for corneal debulking. The corneal thickness may not be the same in all areas of trephination, and there is a risk for corneal perforation during initial trephination. A major advantage of our technique is that the exact depth can be reached through a 2.0 mm incision created with a diamond knife; the incision is large enough to allow the use of scissors for creating a nice edge along the mark of trephination. This allows us to complete the entire dissection as a single step rather than performing initial debulking. Sarnicola et al.18 report comparable visual outcomes after pre-descemetic and descemetic DALK. The authors found a difference of 18 mm between the mean corneal thickness after pre-descemetic (DALK with residual stroma) and descemetic DALK (big-bubble DALK). Likewise, the mean residual host thickness
Figure 2. A: Preoperative slitlamp photograph of a case of keratoconus. B: Postoperative slitlamp photograph after diamond knife–assisted DALK. C: Postoperative AC-OCT.
J CATARACT REFRACT SURG - VOL 40, FEBRUARY 2014
DIAMOND KNIFE–ASSISTED DALK FOR MANAGEMENT OF KERATOCONUS
281
Figure 3. A: Preoperative slitlamp photograph of a case of keratoconus with healed hydrops. B: Postoperative slitlamp photograph after diamond knife–assisted DALK. C: Postoperative AS-OCT.
was 45.42 G 14.79 mm in our case series. Considering that Descemet membrane thickness is approximately 10 to 15 mm, the amount of residual corneal stroma in diamond knife–assisted DALK cases was approximately 30 mm. In cases of corneal scarring near Descemet membrane due to healed hydrops or healed keratitis, the big-bubble technique is usually not successful.8 In our series, DALK could be performed successfully in 3 cases of healed hydrops and in 1 case with a corneal scar due to Pseudomonas keratitis that developed after corneal collagen crosslinking for keratoconus. In advanced keratoconus, when the corneal thickness is less than 250 mm, the risk for Descemet membrane perforation is high with the big-bubble technique.9 The mean thinnest corneal pachymetry in our study was 250 G 60.37 mm, and almost half our cases (47.3%) had a corneal thickness of less than 250 mm. Although we did not encounter cases of Descemet membrane perforation, we believe that this could happen. In such an event, the remaining dissection may be performed carefully, leaving stromal support at the site of microperforation. Conversion
to full-thickness keratoplasty cannot be avoided in cases with large or macroperforation intraoperatively. Also, we believe that diamond knife–assisted DALK would be difficult to perform in cases with extensive peripheral corneal thinning due to the perceived difficulties in making the initial incision with a diamond knife. We compared our cases with the best-case scenario in Descemet membrane–baring big-bubble DALK; that is, cases in which successful and uneventful surgery had been performed. We did not find a significant difference in the visual or refractive outcomes, confirming findings in previous studies7,10,16 and highlighting that it is not necessary to bare Descemet membrane in DALK to achieve an optimum visual outcome. The major limitation of our study is the small sample. Nevertheless, our technique of diamond knife–assisted DALK was predictable and provided visual outcomes comparable to those of other popular techniques of DALK. We believe this technique is economical, is easy to learn, and allows DALK to be performed even in cases in which other DALK techniques carry a higher risk for failure.
Figure 4. A: Preoperative slitlamp photograph of a case of healed keratitis. B: Postoperative slitlamp photograph after diamond knife–assisted DALK. C: Postoperative AS-OCT.
J CATARACT REFRACT SURG - VOL 40, FEBRUARY 2014
282
DIAMOND KNIFE–ASSISTED DALK FOR MANAGEMENT OF KERATOCONUS
WHAT WAS KNOWN Removal of all corneal stroma is necessary to achieve good visual outcomes after DALK.
7.
Good visual outcomes can be achieved by baring Descemet membrane using the big-bubble DALK technique
8.
WHAT THIS PAPER ADDS
9.
The diamond knife–assisted DALK technique leaves a very thin layer of corneal stroma over Descemet membrane. The visual outcomes were comparable to those of big-bubble DALK. Diamond knife–assisted DALK is a safe and easily reproducible technique of anterior lamellar corneal transplantation.
10.
11.
12.
REFERENCES 1. Shimmura S, Tsubota K. Deep anterior lamellar keratoplasty. Curr Opin Ophthalmol 2006; 17:349–355 2. Kawashima M, Kawakita T, Den S, Shimmura S, Tsubota K, Shimazaki J. Comparison of deep lamellar keratoplasty and penetrating keratoplasty for lattice and macular corneal dystrophies. Am J Ophthalmol 2006; 142:304–309 3. Vajpayee RB, Tyagi J, Sharma N, Kumar N, Jhanji V, Titiyal JS. Deep anterior lamellar keratoplasty by big-bubble technique for treatment corneal stromal opacities. Am J Ophthalmol 2007; 143:954–957 4. Anwar M, Teichmann KD. Big-bubble technique to bare Descemet’s membrane in anterior lamellar keratoplasty. J Cataract Refract Surg 2002; 28:398–403 5. Jhanji V, Sharma N, Vajpayee RB. Management of keratoconus: current scenario. Br J Ophthalmol 2011; 95:1044–1050 6. Karimian F, Feizi S. Deep anterior lamellar keratoplasty: indications, surgical techniques and complications. Middle East Afr J Ophthalmol 2010; 17:28–37. Available at: http://www.ncbi.
13.
14. 15. 16.
17.
18.
nlm.nih.gov/pmc/articles/PMC2880371/?reportZprintable. Accessed September 11, 2013 Ardjomand N, Hau S, McAlister JC, Bunce C, Galaretta D, Tuft SJ, Larkin DFP. Quality of vision and graft thickness in deep anterior lamellar and penetrating corneal allografts. Am J Ophthalmol 2007; 143:228–235 Baradaran-Rafii A, Eslani M, Sadoughi M-M, Esfandiari H, Karimian F. Anwar versus Melles deep anterior lamellar keratoplasty for keratoconus; a prospective randomized clinical trial. Ophthalmology 2013; 120:252–259 Michieletto P, Balestrazzi A, Balestrazzi A, Mazzotta C, Occhipinti I, Rossi T. Factors predicting unsuccessful big bubble deep lamellar anterior keratoplasty. Ophthalmologica 2006; 220:379–382 Reinhart WJ, Musch DC, Jacobs DS, Lee WB, Kaufman SC, Shtein RM. Deep anterior lamellar keratoplasty as an alternative to penetrating keratoplasty; a report by the American Academy of Ophthalmology (Ophthalmic Technology Assessment). Ophthalmology 2011; 118:209–218 Kubaloglu A, Sari ES, Unal M, Koytak A, Kurnaz E, Cinar Y, €rk Y. Long-term results of deep anterior lamellar keratoOzertu plasty for the treatment of keratoconus. Am J Ophthalmol 2011; 151:760–767 Melles GRJ, Lander F, Rietveld FJR, Remeijer L, Beekhuis WH, Binder PS. A new surgical technique for deep stromal, anterior lamellar keratoplasty. Br J Ophthalmol 1999; 83:327–333. Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1722959/ pdf/v083p00327.pdf. Accessed September 11, 2013 Neumann AC, McCarty GR, Copello B, Mastel D. Enhanced accuracy is necessary for refractive surgery instrumentation. J Cataract Refract Surg 1989; 15:220–226 DelMonte DW, Kim T. Anatomy and physiology of the cornea. J Cataract Refract Surg 2011; 37:588–598 Unterman SR, Rowsey JJ. Diamond knife corneal incisions. Ophthalmic Surg 1984; 15:199–202 M, Rama P, Knutsson KA, Razzoli G, Matuska S, Vigano Paganoni G. Deep anterior lamellar keratoplasty using an original manual technique. Br J Ophthalmol 2013; 97:23–27 Ghanem RC, Ghanem MA. Pachymetry-guided intrastromal air injection (“pachy-bubble”) for deep anterior lamellar keratoplasty. Cornea 2012; 31:1087–1091 Sarnicola V, Toro P, Gentile D, Hannush SB. Descemtic DALK and predescemetic DALK: outcomes in 236 cases of keratoconus. Cornea 2010; 29:53–59
J CATARACT REFRACT SURG - VOL 40, FEBRUARY 2014
