Reply: Seven year follow-up of combined cataract extraction and viscocanalostomy

LETTERS

7. Carassa RG, Bettin P, Brancato R. Viscocanalostomy vs. trabeculectomy [letter]. Ophthalmology 2002; 109:410 8. Drolsum L. Conversion from trabeculectomy to deep sclerectomy; prospective study of the first 44 cases. J Cataract Refract Surg 2003; 29:1378–1384

REPLY: Faulkner is in error when he says ‘‘they pointed out that it does not work as well post-argon laser trabeculoplasty, but works well post-selective laser trabeculoplasty.’’ What we said was that a possible explanation for varying success rates between surgeons might be that as argon laser trabeculoplasty (ALT) causes thermal scarring and damage to the trabecular meshwork, this may limit the success of viscocanalostomy in eyes that have had ALT. As our eyes had not had ALT, we speculated this might be one reason for our good results. We also commented that it has been shown that selective laser trabeculoplasty does not cause this thermal damage to the trabecular meshwork, but we did not comment on its influence on results because as yet there are no data on the success of viscocanalostomy in eyes that have had this procedure. In the second paragraph, Faulkner implied that we considered the presence of the ‘‘scleral lake’’ the ‘‘method of action.’’ We did not make this assertion. Fulkner then describes his success with the procedure, which he calls a modified viscocanalostomy. However, what he describes is a penetrating procedure using an OVD injected into the canal of Schlemm to create a viscotrabeculotomy. We have no experience with this procedure and therefore cannot comment on its effectiveness or safety. However, Stegmann has told us that in the long process of developing viscocanalostomy, creating a viscotrabeculotomy was a technique he tried but abandoned in favor of the technique of viscocanalostomy described in his paper.1dManijeh S. Wishart, MD, FRCS, FRCOphth

REFERENCE 1. Stegmann R, Pienaar A, Miller D. Viscocanalostomy for openangle glaucoma in black African patients. J Cataract Refract Surg 1999; 25:316–322

Corneal ectasia after photorefractive keratectomy Randleman et al.1 referred to my lecture entitled ‘‘PRK in Latent Keratoconus, High Myopia, and After RK’’ presented at the ASCRS Symposium on Cataract, IOL and Refractive Surgery, San Diego, California, USA, May 2004. The relevant paragraphs were published, and the writer states, ‘‘In a series of 93 eyesd65

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with latent keratoconus, 14 with frank keratoconus, and 14 with thin corneasdAmoils and his colleagues achieved at least 20/40 UCVA in 96% of eyes. Seventy-six percent achieved at least 20/30 UCVA, 65% at least 20/25 and 43% at least 20/20. And 100% of eyes, which had one to seven years of follow up, had a BSCVA of 20/40 or better’’ (M. Young, ‘‘Contraindications for LASIK No Problem for PRK,’’ EyeWorld, May 2004, pages). The corneal topographies in this article clearly illustrate inferior bulging only. However, case 1 in Randleman et al.’s paper clearly illustrates the extreme danger of performing photorefractive keratectomy (PRK) in the central form of early keratoconus. The cardinal biomechanical reason that PRK, with only central ablation of Bowman’s membrane and anterior stroma, protects against the development of inferior ectasia does not apply in this case. The hammock-supporting effect of an intact Bowman’s membrane and intact anterior stroma offer no protection to the rapid development of central keratectasia when the central anterior tissue has been ablated by the excimer laser. Rapid ectasia occurred in case 1, as is seen in cases of ultrathick flaps after laser in situ keratomileusis with very thin residual posterior stromal beds. The rapid progress of the ectasia was exacerbated by the use of strong steroid drops, which further weakened the central corneal stroma and, probably, raised the intraocular pressure. I have not heard or seen reports of the rarer central variety of keratoconus treated with PRK. I have not performed PRK in this type of central keratoconus. To date, I have performed PRK in 26 eyes with manifest inferior keratoconus, of which 14 cases were presented at the 2004 ASCRS Symposium on Cataract, IOL and Refractive Surgery. The article published in May 2004 does not mention PRK in eyes treated for central keratoconus under the area to be ablated with the excimer laser. It is important not to perform PRK in eyes with obvious keratoconus that can be corrected to 20/20 with spectacles and do not require hard contact lenses. Photorefractive keratectomy for any case of early keratoconus must be done unilaterally with at least 3 monthly intervals between eyes to assess the efficacy of the procedure. Early keratoconic patients must be warned that PRK may not be effective or improve the visual acuity substantially without the use of hard contact lenses. Also, the possibility that a penetrating keratoplasty (PKP) may be required following PRK must be discussed. Photorefractive keratectomy for keratoconus must be performed only to obviate the need for hard contact lenses. Photorefractive keratectomy often gives good results in obviating or postponing the need for PKP in the common inferior variety of early keratoconus

J CATARACT REFRACT SURG - VOL 33, JUNE 2007