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JOURNAL ABSTRACTS
Year : 2010  |  Volume : 58  |  Issue : 4  |  Page : 353-358

Management of keratoconus: A review


S7, R. P. Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India

Date of Web Publication7-Jun-2010

Correspondence Address:
Rajesh Sinha
S7, R. P. Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, Ansari Nagar, New Delhi
India
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Source of Support: None, Conflict of Interest: None


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How to cite this article:
Sinha R, Gupta N, Sharma N, Gupta R, Titiyal JS. Management of keratoconus: A review. Indian J Ophthalmol 2010;58:353-8

How to cite this URL:
Sinha R, Gupta N, Sharma N, Gupta R, Titiyal JS. Management of keratoconus: A review. Indian J Ophthalmol [serial online] 2010 [cited 2020 May 27];58:353-8. Available from: http://www.ijo.in/text.asp?2010/58/4/353/64146

Management of keratoconus is often complex and differs at different stages and state of progression of the disease. Special attention should be given to optimize visual outcome depending on the need of the patient. The various modalities available today can be broadly divided into nonsurgical and surgical. In early cases, spectacles may provide adequate visual correction but subsequently, contact lenses provide better correction due to presence of irregular astigmatism. Contact lenses are the main stay of nonsurgical management in moderate and advanced keratoconus. Corneal collagen cross- linking should be considered as a treatment modality in patients with progressive disease. Surgery is indicated for keratoconus when management with contact lenses fails. About 10 to 25% of keratoconus progresses to a condition where extreme thinning or scarring warrants a keratoplasty. In the present article, we have reviewed various management options that have been tried with variable success.


  Management Top


Comparison of current treatment options

Tan et al.
(Curr Opin Ophthalmol. 2007;18(4):284-9) observed that intrastromal corneal ring segments, recent developments in anterior lamellar keratoplasty enabling targeted replacement or augmentation of corneal stroma without replacement of endothelium, microkeratome or laser-assisted anterior lamellar surgery, and peripheral tectonic lamellar keratoplasty procedures are new forms of surgical alternatives to conventional penetrating keratoplasty (PK) for restoration of tectonic integrity in corneal ectasia.

Tan et al. (Trans Am Ophthalmol Soc.2006;104:212-20) described the results of intrastromal corneal ring segments (Intacs) and a new variation of lamellar keratoplasty, termed intralamellar keratoplasty (ILK), for the treatment of keratoconus: Mean uncorrected visual acuity (UCVA) and best corrected visual acuity (BCVA), and manifest and topographic astigmatism improved in both the procedures.

Crews et al. (CLAO J. 1994;20(3):194-7) described clinical management of 118 eyes with keratoconus in a 6 year retrospective study. Twenty-one eyes received glasses or required no correction. Rigid gas permeable (RGP) lenses, Dura-T style PMMA lenses, and specially designed gas permeable lenses were used to successfully fit 63 eyes. Twenty-eight eyes underwent PK, and an additional six eyes were PK candidates. Factors associated with the need for PK included BCVA of 20/40 or worse, average keratometry > 55D, and the presence of apical scarring.

Carney et al. (CLAO J. 1991;17(1):52-8) compared the visual performance of keratoconus patients whose vision had been corrected with one of the following: RGP lenses alone, PK, or epikeratoplasty. Despite similar BCVA, there were statistically significant differences in the visual responses for the three correction types, with the epikeratoplasty procedure providing the poorest results.

Contact lens

Abdalla et al.
(Cornea2010;29(1):5-8) discussed the initial results of fitting SynergEyes hybrid contact lenses (SynergEyes, Inc, Carlsbad, CA) for keratoconus (KC) and pellucid marginal degeneration (PMD). The most common indication for SynergEyes was RGP lens intolerance (50.8%). The success rate was 86.9%; most failures (8 eyes of 6 patients) discontinued the lens within the first 1-2 months because of discomfort (5 eyes) or unsatisfactory vision (3 eyes).

Yanai et al. (Eye Contact Lens. 2010;36(2):86-9) determined whether Aphex KC, a newly designed RGP contact lens (CL) with dual aspherical base curves, improves visual acuity and lens wear time in 24 patients with keratoconus. A total of 19 eyes (65.5%) had a BCVA of 0.2 logarithm of the minimum angle of resolution (logMAR) (20/29) or better with Aphex KC. The mean wear time was 12.6±3.2 hr/day with Aphex KC and 0.4 ±0.7 hr/day with a previously prescribed spherical RGP CL. The numbers of eyes wearing Aphex KC or the previously prescribed RGP CL for >12 hr/day were 26 and 0, respectively.

Schornack et al. (Eye Contact Lens. 2010;36(1):39-44) described the use of Jupiter scleral lenses (Medlens Innovations, Front Royal, VA; and Essilor Contact Lenses, Inc., Dallas, TX) in the management of keratoconus in 52 eyes of 32 patients. Thirty eyes (19 patients) were fitted successfully. The average number of lenses ordered per eye was 1.5. The fitting process required an average of 2.8 visits. Standard lenses were prescribed for 23 eyes, and custom designs were needed for 7 eyes. Median BCVA improved from 20/40 (mean, 20/76) before scleral lens fitting to 20/20 (mean, 20/30) after fitting. Follow-up ranged from 3 to 32 months.

Yamazaki et al. (Arq Bras Oftalmol. 2006;69(4):557-60) evaluated the fitting and use of a soft CL in 66 keratoconic patients (80 eyes). The main reasons for this special lens fitting were due to reduced tolerance and poor fitting pattern achieved with other lenses. The majority of eyes of patients using CL (91.25%) achieved visual acuity better than 20/40. The most frequent base curve was 7.6 mm (61%).

Edrington et al. (Optom Vis Sci. 2004;81(3):182-8) identified factors associated with rigid contact lens comfort in the CLEK Study. Measures of disease severity (steep keratometry and the first definite apical clearance lens) were not associated with lens comfort. There was no difference in self-reported contact lens comfort between patients fitted with apical touch vs. apical clearance. Patients with a peripheral clearance rating of "minimal unacceptable" were approximately half as likely to report good contact lens comfort compared with patients with "average" peripheral clearance.

Lee et al. (Eye Contact Lens2004;30(1):20-4) evaluated the clinical outcome and fitting characteristics with a multicurve lens for keratoconus in a Korean population. Three-point touch was applied in 59 eyes, and apical clearance was adopted in an eye with a persistent epithelial defect. Flatter lens was related to better visual acuity. The mean daily wearing time was 11.9 hours. Customization with the multicurve lens enabled patients with keratoconus to wear the CL comfortably.

Segal et al. (Cornea2003;22(4):308-10) described the vision-correcting and therapeutic benefits of gas-permeable scleral contact lenses (GP-ScCL) and reported marked subjective improvement in quality of life by 86% of patients, mainly due to improvement in their visual function and reduction in discomfort.

Betts et al. (Optom Vis Sci. 2002;79(8):493-501) studied the visual performance and comfort with the Rose K lens for keratoconus. There were no statistically significant changes in high- or low-contrast visual acuity with the Rose K lenses. There was statistically significant improvement in self-reported assessment of vision and self-reported assessment of comfort in the eyes with more advanced keratoconus. At the conclusion of the study, 72% of patients preferred the Rose K lenses over their habitual lenses, and 87% reported that they would continue wearing the Rose K lenses.

Lim et al. (Eye (Lond). 2002;16(1):54-9) observed that 16.4% of all patients attending the Contact Lens clinic had keratoconus. The mean age at referral was 28.6 years and the mean age of keratoconus during the study period was 34.9 years. The types of contact lenses used included PMMA lenses (2.7%), rigid gas permeable lenses (96.1%) of the spherical, elliptical and special cone lens designs, Keratosoft or Softperm lenses (0.8%) and scleral lenses (0.4%). Sixty four percent of eyes that had undergone PK required CL. They concluded that RGP CLs remain the mainstay treatment for advanced keratoconus.

Edrington et al. (Optom Vis Sci.1996;73(6):369-75) developed a standardized rigid CL fitting protocol for keratoconus. The initial trial lens's base curve was the average keratometric reading; sequentially steeper lenses were applied until definite apical clearance was observed.

Yeung et al. (Am Optom Assoc.1995;66(9):539-43) published their clinical experience with piggyback contact lens systems (PBCLS) on 16 keratoconic eyes. Vision and average lens wearing time were stable, if not improved, for the 16 patients when the data was compared to the patients' wear of RGP CL. Although two patients developed neovascularization and one patient developed giant papillary conjunctivitis (GPC), all pre-existing corneal complications resolved with PBCLS wear. No gross corneal edema was noted upon slit lamp observation.

Kok et al. (Cornea1993;12(1):60-4) published their results of 40 eyes in 26 patients who were consecutively fitted with a new aspheric combination lens. Thirty-five eyes (87.5%) showed no discomfort, acceptable wearing time, and visual acuity. Failures were found in five eyes (12.5%), which were caused by GPC (two eyes), severe keratoconus (one eye), difficulty in lens handling and lack of motivation (two eyes). The successful use of an aspheric piggyback combination lens in rigid lens-intolerant keratoconus may preclude early surgical therapy.

Dana et al. (Ophthalmology1992;99(8):1187-92) observed that the primary reasons for PK in keratoconus were, a BCVA of under 20/40 [despite good contact lens fit] (43%), contact lens intolerance (32%), frequent lens displacement (13%), and significant peripheral thinning of the cornea (12%).

Intacs

Coskunseven et al.
(J Refract Surg. 2010 Feb 25:1-4) described the visual and refractive outcomes in three eyes (two keratoconic patients) with previous intrastromal corneal ring segments (INTACS, Addition Technology Inc) that underwent adjuvant single KeraRing (Mediphacos) intrastromal corneal ring segment implantation. Six months following surgery, the UCVA improved from 20/100 and 20/200 to 20/32 and 20/40 in the right and left eyes, respectively, of patient 1, and from 20/400 to 20/50 in the treated right eye of patient 2. Keratometric measurements also improved.

PiAero et al. (Clin Experiment Ophthalmol. 2010;38(2):154-67) summarized all the scientific literature regarding the use of intracorneal ring segments (ICRS) in corneal ectatic disease and concluded that ICRS technology is a promising therapeutic option in avoiding or deferring the need of a corneal graft.

Titiyal et al. (Eur J Ophthalmol. 2010 Mar 23. [Epub ahead of print]) successfully performed deep anterior lamellar keratoplasty (DALK) with Intacs explantation in two patients with poor visual outcome with Intacs for KC. At 2 years follow-up, the grafts were clear in both patients, with a BCVA of 20/25.

Feldman et al. (J Cataract Refract Surg. 2010;36(2):332-5) reported the enhanced effect of double-stacked intrastromal corneal ring segments in a patient with poor visual acuity and contact lens intolerance due to advanced keratoconus. Postoperatively, both rings migrated inferiorly and overlapped each other in a double-stacked formation. This resulted in a dramatic central shift of the cone and flattening of the inferior paracentral cornea with significant improvement in vision.

Sansanayudh et al. (J Cataract Refract Surg.2010;36(1):110-3) reported the efficacy and safety of ICRS implantation using femtosecond laser in 10 eyes with advanced keratoconus. The mean UCVA and aberrations improved significantly at 6 months (P= 0.007), and there was no complication.

Kymionis et al. (Open Ophthalmol J. 2009;3:77-81) reviewed a case of early stage keratoconus after nine years of bilateral Intacs implantation and reported a significant improvement and postoperative stability in patient's visual acuity with absence of any long-term, sight-threatening complication.

Shetty et al. (Cornea2008;27(9):1022-9) evaluated the surgical outcomes of microthin INTACS implantation in 14 eyes with advanced KC. At 6 months, the UCVA improved from 0.05 ±0.08 to 0.16 ±0.11 (P < 0.05), and BCVA improved from 0.50 ± 0.23 to 0.67 ± 0.00 (P= 0.01). Younger age, male sex, and minimum central pachymetry of more than 400΅ seemed to be associated with better outcomes.

Ertan et al. (J Cataract Refract Surg. 2008;34(9):1521-6) evaluated the efficacy of intrastromal ring segment (Intacs, Addition Technology, Inc.) implantation and analyzed outcomes according to different keratoconus stages in 306 cases. At a mean follow-up of 10.39±5.04 months, BCVA improved in 71.6% of eyes and UCVA improved in 75.7% of eyes. The mean keratometry (K) decreased from 50.7 diopters (D) to 47.9 D (P<0.05). Intacs treatment with femtosecond laser was effective for management of keratoconus of all stages, however, there was less improvement in UCVA in severe keratoconus.

Kymionis et al. (Am J Ophthalmol. 2007;143(2):236-244) evaluated long-term follow-up of Intacs microthin prescription inserts in 17 eyes of keratoconus. No late postoperative complication occurred in any patient. At five years, the spherical equivalent (SE) error was statistically significantly reduced.

Zare et al. (J Cataract Refract Surg. 2007;33(11):1886-91) assessed the safety and efficacy of intracorneal ring segment in 30 keratoconic eyes. All patients were contact-lens intolerant. The mean UCVA improved from 0.60 ±0.31 preoperatively to 0.29 ± 0.20 at 6 months postoperatively (P<0.001) and the mean BCVA, from 0.25±0.16 to 0.13 ±0.14, respectively (P<0.001). The mean keratometry decreased from 49.84 ±3.58D to 47.90 ± 3.58D postoperatively (P<0.001). Three eyes had ring exposure, and 1 eye had bacterial keratitis and ring exposure.

Ertan et al. (J Cataract Refract Surg. 2006;32(12):2039-42) assessed the outcomes of Intacs implantation for keratoconus using the femtosecond laser in 118 eyes of 69 patients. Intacs were successfully implanted in all eyes. At the end of the first postoperative year, 81.3% of eyes had improved UCVA and 73.7% had improved BCVA. The mean keratometry decreased from 51.56D to 47.66D, and the mean refractive spherical equivalent decreased from -7.57 D to -3.72D.

Hellstedt et al. (J Refract Surg. 2005;21(3):236-46) reported that asymmetric Intacs placement improves BCVA and UCVA and reduces astigmatism in patients with mild to moderate keratoconus; however, the correction of astigmatism was unpredictable.

Siganos et al. (Am J Ophthalmol. 2003;135(1):64-70) studied the use of Intacs microthin prescription inserts for the management of keratoconus and reported improvement in UCVA and BCVA in majority.


  Collagen Cross linking Top


Standard technique

Mazzotta et al.
(Acta Ophthalmol. 2010 Apr 23. [Epub ahead of print]) investigated the correlations between corneal structural modifications assessed by in vivo corneal confocal microscopy with visual function after corneal collagen cross-linking (CXL) in 44 eyes with progressive keratoconus. Epithelial thinning associated with stromal oedema and keratocytes apoptosis explained initial tendency towards slightly reduced visual acuity (VA) and more glare one month postoperatively in 70% of eyes. There was a significant correlation between visual functions and morphological findings.

Goldich et al. (Cornea2010 Feb 15. [Epub ahead of print]) observed that CXL is a safe procedure that does not cause damage to the corneal endothelium and central retina. Comparative preoperative and postoperative results showed stable endothelial cell density (2730 cells/mm, 2793 cells/mm, and 2640 cells/mm, preoperatively, at month 6, and at month 12, respectively) and stable foveal thickness (203, 202, and 205 ΅, preoperatively, at month 6, and at month 12, respectively).

Stojanovic et al. (J Refract Surg. 2010;26(2):145-52) evaluated a combination of topography-guided custom ablation and CXL in a single procedure for the treatment of keratectasia. Mean UCVA increased from 20/1000 preoperatively to 20/125 at 12 months postoperatively. Mean astigmatism reduced from 5.40±2.13D to 2.70±1.44D, and keratometric asymmetry decreased from 6.38±1.02D to 2.76±0.73D and no progression of ectasia occurred during the observation period of 12 months.

Caporossi et al. (Am J Ophthalmol. 2010 Feb 5 [Epub ahead of print]) reported stability in 44 eyes after 48 months of minimum follow-up after CXL, while fellow eyes showed a mean progression of 1.5D in more than 65% after 24 months. There was a reduction of 2D in the mean K value, with reduction in coma aberration and improvement in VA.

Coskunseven et al. (J Cataract Refract Surg. 2009;35(12):2084-91) reported their results of combined ICRS implantation and CXL in progressive keratoconus. In this study, CXL was followed by ICRS implantation (Group 1) or ICRS implantation was followed by CXL (Group 2). The UCVA, BCVA and corneal parameters improved in both the groups, however there was greater improvement in Group 2.

Constantin et al. (Oftalmologia. 2009;53(2):88-91) observed an increase in corneal thickness, and reduction in keratometric values in keratoconus patients after CXL.

Coskunseven et al. (J Refract Surg. 2009;25(4):371-6) assessed the progression of keratoconus in patients treated with CXL. The worse eye was treated with collagen cross-linking, and the fellow eye served as the control. The group treated with CXL showed a mean decrease in spherical equivalent refraction and cylinder and an increase in UCVA and BCVA. The maximal curvature decreased by 1.57 ±1.14D, and no statistical difference was noted regarding central corneal thickness (P=0.06) and endothelial count (P= 0.07). They concluded that CXL appears to inhibit the progression of keratoconus.

Hafezi et al. (J Cataract Refract Surg. 2009;35(4):621-4) studied the effect of CXL in advanced keratoconus with thin cornea by preoperatively swelling thin corneas to a stromal thickness of at least 400΅ using hypoosmolar riboflavin solution in 20 patients with no complication.

Grewal et al. (J Cataract Refract Surg. 2009;35(3):425-32) used Scheimpflug imaging to illustrate their results on CXL. There were no significant differences (P > 0.05) in mean preoperative and postoperative values at 1 year in BCVA, SE, and cylinder vector.

Wittig-Silva et al. (J Refract Surg. 2008;24(7):S720-5) reported flattening of the steepest simulated keratometry (sim-K) value (K-max) by an average of 0.74D (P = 0.004) at 3 months, 0.92D (P = 0.002) at 6 months, and 1.45D (P = 0.002) at 12 months after CXL. In the control eyes, mean K-max steepened by 0.60D (P= 0.041) after 3 months, by 0.60D (P= 0.013) after 6 months, and by 1.28D (P ≤0.0001) after 12 months. Preliminary results of this study suggest a temporary stabilization of all treated eyes after CXL.

Raiskup-Wolf et al. (J Cataract Refract Surg. 2008;34(5):796-801) published their long term results of CXL in 272 patients with progressive keratoconus. The steepening decreased significantly by 2.68D in first year, 2.21D in second year, and 4.84D in third year. Two patients had continuous progression of keratoconus and required repeat CXL.

Transepithelial technique

Leccisotti et al.
(J Refract Surg. 2010 Feb 25:1-7) evaluated the clinical effects of transepithelial CXL on 51 keratoconic eyes pre-treated with substances enhancing epithelial permeability. Gentamicin, ethylenediaminetetraacetic acid and benzalkonium chloride were instilled for 3 hours. Riboflavin 0.1% in 20% dextran-T500 and oxybuprocaine were instilled for 30 minutes. Finally, UV-A irradiation to the central 7.5 mm of cornea was applied for 30 minutes, while riboflavin was instilled every 5 minutes. The mean BCVA improved by 0.036 logMAR after CXL and worsened by 0.039 logMAR in the control eyes (P<0.05). Mean refraction (SE) decreased by 0.35D (less myopic) after CXL and increased by 0.83D in control eyes (P<0.05). Mean sim-K decreased by 0.10D after CXL and increased by 0.88D in control eyes (P<0.05). A limited but favorable effect of trans-epithelial CXL was noted without complications.

Comparison of standard and modified procedure

Bakke et al.
(J Cataract Refract Surg. 2009;35(8):1363-6) compared the severity of postoperative pain and the rate of penetration of riboflavin between eyes treated by CXL using excimer laser superficial epithelial removal, programmed to 35΅ (Group 1), and mechanical full-thickness epithelial removal with a brush (Group 2). Postoperative pain was severe in 40.0% of patients in Group 1 and in no patient in Group 2 (P= 0.009) and moderate in 53.3% and 33.3%, respectively (P= ns).The mean time to riboflavin saturation was 43.7±10.8 minutes in Group 1 and 31.3±3.0 minutes in Group 2 (P = 0.001). Superficial epithelial removal using excimer laser resulted in more postoperative pain and the need for prolonged application of riboflavin to achieve corneal saturation.

Baiocchi et al. (J Cataract Refract Surg. 2009;35(5):893-9) evaluated the intrastromal concentrations of riboflavin in CXL with (standard) and without epithelium (transepithelial). The HPLC quantitative study showed that a theoretically safe and effective stromal riboflavin concentration of 15 ΅g/g was obtained only after epithelial removal and after at least 10 minutes of riboflavin application every 2 minutes.

Wollensak et al. (J Cataract Refract Surg. 2009;35(3):540-6) observed that CXL without epithelial debridement reduced the biomechanical effect by approximately one fifth compared with standard cross-linking, probably because of restricted and inhomogeneous stromal distribution of riboflavin. The cytotoxic damage was restricted to 200΅ stromal depth, which is an advantage over the standard method.

Laboratory studies

Ahearne et al.
(Br J Ophthalmol. 2008;92(2):268-71) studied the effect of CXL on the mechanical properties of collagen hydrogels and reported that UVA irradiation without riboflavin showed decreased mechanical integrity and strength. Cell viability was reduced with increased UVA exposure time.

Wollensak et al. (Cornea2004;23(5):503-7) studied the collagen fiber diameter in rabbit cornea after CXL and reported a significantly increased diameter by 12.2% (3.96 nm) in the anterior stroma, and by 4.6% (1.63nm) in the posterior stroma, compared with the control fellow eyes. This suggests that CXL effect is strongest in the anterior stroma because of rapid decrease in UVA irradiance across the corneal stroma as a result of riboflavin-enhanced UVA absorption.

Complications of CXL

Koller et al.
(J Cataract Refract Surg. 2009;35(8):1358-62) evaluated 117 eyes of 99 patients, approximately 90% of which completed 12-month follow-up. The complication rate (percentage of eyes losing 2 or more Snellen lines) was 2.9%. The failure rate of CXL (percentage of eyes with continued progression) was 7.6%. A high preoperative Kmax reading was a significant risk factor for failure. Sterile infiltrates were seen in 7.6% of eyes and central stromal scars, in 2.8%. Results indicated that a preoperative maximum K reading less than 58.0D may reduce the failure rate to less than 3%, and restricting patient age to younger than 35 years may reduce the complication rate to 1%..

Parez-Santonja et al. (J Cataract Refract Surg. 2009;35(6):1138-40) reported a case of Staphylococcus epidermidis keratitis following an uneventful CXL for keratoconus.

Sharma et al. (J Cataract Refract Surg. 2010;36(3):517-20) reported a case of Pseudomonas aeruginosa keratitis occurring one day after CXL for keratoconus. They attributed presence of epithelial defect, use of a soft bandage contact lens, and topical corticosteroids in the immediate postoperative period as the risk factors.

Kymionis et al. (J Cataract Refract Surg. 2007;33(11):1982-4) reported geographic epithelial keratitis and iritis following CXL without prior history of herpetic disease.

Toric intraocular lens

Navas et al.
(J Cataract Refract Surg. 2009;35(11):2024-7) described two cases of forme fruste keratoconus (FFKC) wherein toric intraocular lens (TIOL) implantation was done following cataract surgery. One year postoperatively, the UCVA was 20/25 in both cases, and no progression or IOL rotation was observed in either case.

Venter (J Refract Surg. 2009;25(9):759-64) observed that implantation of Artisan iris-fixated phakic intraocular lens (PIOL) in patients with stable keratoconus for correction of astigmatism and myopia is safe, predictable, and effective with minimal complications.

Kamiya et al. (J Refract Surg. 2008;24(8):840-2) implanted toric implantable Collamer lenses (toric ICL, STAAR Surgical) in two patients with high myopic astigmatism and stable keratoconus. Postoperatively, the manifest refraction in the two eyes was +0.50 -1.00 x 90 in case 1 and -0.25 -1.25 x 100. They concluded that toric ICL may be an alternative in managing eyes with stable keratoconus.

Coskunseven et al. (Am J Ophthalmol. 2007;144(3):387-389) evaluated the results of combined Intacs and posterior chamber toric ICL implantation at intervals between six and 10 months following Intacs in keratoconic patients with extreme myopia and irregular astigmatism. There was improvement in UCVA and BCVA with no intraoperative or postoperative complication. All eyes were emmetropic within 1D.

Budo et al. (J Refract Surg. 2005;21(3):218-22) also reported that Artisan toric PIOL may be an alternative for treating astigmatism and myopia in keratoconus patients with contact lens intolerance.


  Corneal Transplantation Top


Penetrating keratoplasty (PK)

Fukuoka et al.
(Cornea2010;Mar 17 Epub ahead of print) investigated long-term results of PK for keratoconus. With an average follow-up period of 15.3 ±9.7 years, 9.6% eyes experienced rejection and 4.0% eyes experienced graft failure. The average BCVA 10, 20, and 25 years after surgery was 1.54 ± 0.68, 0.06 ± 0.22, 0.03 ± 0.17, and 0.14 ± 0.42, respectively. The cumulative probability of graft survival at 10, 20, and 25 years after PK was 98.8%, 97.0%, and 93.2%, respectively.

Kymionis et al. (J Cataract Refract Surg. 2009;35(1):11-3) performed arcuate keratotomy [anterior arcuate side cut (400΅ thick, 6.5mm diameter)] using the keratoplasty software, with femtosecond laser in a 68-year-old woman with irregular astigmatism 28 years after PK for keratoconus. No intraoperative or postoperative adverse events were seen during the follow-up period. Six months after the procedure, the UCVA improved from 20/60 to 20/50 and mean manifest astigmatic correction decreased to 0.50D.

Wagoner et al. (Cornea2009;28(1):14-8) evaluated graft survival, postoperative complications, and visual outcome after PK for keratoconus in 464 eyes with (17.2%) or without (82.8%) a history of vernal keratoconjunctivitis (VKC). There were no statistically significant differences in Kaplan-Meier graft survival or complications between the 2 groups at any time interval. However, late-onset persistent epithelial defects were significantly more likely to occur in eyes with VKC (P= 0.04).

Wagoner et al. (Cornea2009;28(8):882-90) evaluated graft survival after PK for various indications and reported that 5-year survival probability was 96.1% for keratoconus, 71.1% for stromal scarring, 85.9% for stromal dystrophy, and 40.3% for corneal edema.

Bahar et al. (Am J Ophthalmol. 2008;146(6):905-12) compared the visual outcomes following DALK, penetrating keratoplasty (PK), and manual top-hat PK (TH-PK) in subjects undergoing corneal transplantation for keratoconus. The median BCVA at 12 month follow-up was 20/40 in DALK eyes and 20/30 in traditional PK and TH-PK eyes. DALK, PK, and TH-PK provide comparable visual outcomes in keratoconus patients. Although DALK and TH-PK induce more HOA, they speed up the time to suture removal and provide higher endothelial cell density at one year follow-up.

Jaycock et al. (Ophthalmology2008;115(2):268-75) used same-size donor and recipient trephines for PK in eyes with keratoconus. The mean SEs for the same-size and oversize donor trephine groups, respectively, were -1.45D and -1.41D at 1 year (P =0.6) and -1.74D and -2.19D at 2 years postoperatively (P = 0.3). They noted that use of same-size donor and recipient trephines did not reduce myopia and was associated with an increased risk of postoperative wound leaks.

Shoja et al. (Saudi Med J.2007;28(9):1389-92) in their study found that PK with 0.25 mm disparity had a better final VA and lesser myopic shift than those with 0.50 mm oversize in patients of keratoconus.

Gordon et al. (Am J Ophthalmol. 2006;142(6):923-30) identified baseline demographic and clinical factors associated with high likelihood of PK that included younger age, steeper keratometric values, worse VA, corneal scarring, poorer contact lens comfort, and poorer vision-related quality of life.

Lamellar corneal surgery

Chan et al.
(Cornea. 2010;29(3):290-5) reviewed patient outcomes after femtosecond laser-assisted mushroom configuration DALK and showed good morphological outcome with stepped corneal wounds. At 3 months, mean BCVA was 20/40.

Feizi et al. (Cornea2010;29(2):177-82) evaluated the visual and refractive outcomes after DALK using big-bubble technique in 129 eyes with keratoconus. In 3 eyes, the operation was converted to PK. Bared descemet's membrane (DM) was achieved in 103 eyes, whereas in 23 eyes pre-Descemet dissection was performed. DM perforation occurred in 5 eyes.

Shi et al. (Ophthalmology2010;117(2):226-31) performed a modified deep lamellar keratoplasty for advanced-stage keratoconus and reported similar efficacy to PK with lesser risk of immune rejection. Javadi et al. (Cornea2010 Feb 17Epub ahead of print) compared DALK using big-bubble technique to PK in patients with moderate to advanced keratoconus and reported comparable results.

Sarnicola et al. (Cornea2010;29(1):53-9) reported outcomes in 236 cases with Descemetic (dDALK) and predescemetic (pdDALK) DALK. There was no difference in VA between the two groups at an average follow-up of 30.4 months, although the eyes in dDALK group had faster visual recovery.

Javadi et al. (Cornea. 2009;28(10):1130-4) reported that relaxing incisions and suturing at the steep meridian followed by selective suture removal can effectively and predictably reduce post-DALK astigmatism in patients with keratoconus.

Jones et al. (Invest Ophthalmol Vis Sci. 2009;50(12):5625-9) compared DALK and PK in keratoconus and noted that the risk of early graft failure for DALK was almost twice that for PK (P= 0.02). Excluding these early failures, there was little difference between the 3-year graft survival. DALK recipients were less likely to achieve BCVA of 6/6 and were more likely to have -3D or worse myopia.

Han et al. (Am J Ophthalmol. 2009;148(5):744-751) compared outcomes after PK and two techniques of DALK in patients with keratoconus. DALK group had a significantly lower incidence of complications compared with PK cases, including allograft rejection and glaucoma.

Farid et al. (J Cataract Refract Surg. 2009 ;35(5):809-13) described a variation of big-bubble DALK using femtosecond laser zigzag incision. This technique allowed precise depth visualization for air-needle placement in the posterior stroma based on the lamellar and posterior laser cuts, thus minimizing the risk for perforation of DM. The matching donor and host tissue zigzag cut allowed more precise tissue apposition and greater surface area for healing. The angled anterior donor and host junction allows a smooth transition for improved visual outcomes.

Spadea et al. (J Cataract Refract Surg.2009;35(1):105-12) evaluated anatomical and functional results of excimer laser-assisted lamellar keratoplasty (ELLK) in 41 keratoconus patients. The UCVA and BCVA were significantly better at all follow-ups. The mean refractive astigmatism was 2.20D and mean manifest refraction (SE) was -1.18D. Complications included corneal melting that was treated with PK (1 case) and postoperative high refractive error requiring excimer laser photorefractive keratectomy.

Farias et al. (Cornea2008;27(9):1030-6) compared the efficacy of lyophilized corneas versus optisol corneas for DALK in patients with keratoconus. All variables improved similarly in both groups, except for UCVA in the sixth postoperative month, which was better in the lyophilized group.

Das et al. (Cornea2007;26(9):1156-7) reported a case of successful deep lamellar keratoplasty (DLK) in a patient with keratonous after healed hydrops.

Coullet et al. (J Refract Surg.2008;24(2):166-72) evaluated a new automated technique microkeratome-assisted additive stromal keratoplasty (MASK) for the management of keratoconus. The first step of the surgical procedure consisted of performing a nasal-hinged flap on the host cornea with a microkeratome. The second step consisted of extracting a stromal plano-powered disk from the donor's cornea using an artificial chamber. The 80΅ thick lamellar graft was punched with a 7.5-mm circular trephine and positioned beneath the flap. Corneal refractive surgery was scheduled for the end of the sixth postoperative month. At the end of surgery, mean corneal thickness was increased by 148.75΅. MASK appeared to be a safe surgical technique but cannot be considered as an alternative to PK or DLK in the management of keratoconus because of imprecise anatomic and refractive outcomes.

Coombes et al. (Br J Ophthalmol. 2001;85(7):788-91) reported the results of DLK in 44 eyes using lyophilised donor corneal tissue in keratoconus. Perforation of DM occurred in nine eyes (20%). A double anterior chamber was noted formed in five eyes, which resolved spontaneously in three eyes. The median corrected postoperative acuity was 6/9.

Epikeratoplasty and phototherapeutic keratectomy (PTK)

Ward et al.
(CLAO J. 1995;21(2):130-2) performed PTK in four cases of keratoconus with contact lens intolerance due to pain and raised, nodular scars. All patients resumed RGP contact lens wear 2 to 4 weeks after surgery. Visual acuities ranged from 20/40 to 20/70 before surgery and improved to 20/25 or better in all patients postoperatively. PTK flattened the central cornea by an average of 5.43D (range: 1.13-10.19 D); and refractive cylinder was reduced by an average of 4.00D (range: 3.25-5.25 D). Goosey et al. (Am J Ophthalmol. 1991;111(2):145-51) studied 47 eyes with keratoconus that were surgically corrected with either epikeratoplasty (N= 31) or PK (N= 16). The PK group had higher percentage of eyes with VA of 20/20 than the epikeratoplasty group (73% vs 24.1%). The PK group had 3.0D greater keratometric flattening.

Management of hydrops

Poyales-Galan et al.
(Arch Soc Esp Oftalmol.2009;84(10):533-6) successfully managed a case of hydrops occurring in the eye secondary to keratoconus by intracameral sulfur hexafluoride (SF6) gas.

Panda et al. (Cornea. 2007;26(9):1067-9) also reported successful use of SF6 gas in early resolution (4 weeks) of corneal edema caused by acute corneal hydrops secondary to keratoconus in 9 eyes in comparison to 9 eyes managed conservatively (12 weeks).

Wylegala et al. (Ophthalmology2006;113(4):561-4) performed amniotic membrane transplantation with cauterization in keratoconus complicated by persistent hydrops in 10 eyes of mentally retarded patients. Hydrops was successfully resolved in all eyes. The mean initial corneal protuberance (7.6±4.2 mm) resolved after 21.4±9.5 days in all eyes.

Sii et al. (Cornea2005;24(4):503-4) reported a case of a perforated acute hydrops in a mentally retarded patient that was successfully managed with intracameral SF6 gas and cyanoacrylate tissue adhesive, thus avoiding the need for an emergency tectonic keratoplasty. A follow-up examination at 1 month showed a formed anterior chamber with tissue adhesive in situ and no aqueous leak.




 

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