Refractive outcome of phacovitrectomy

LETTERS

is whether the follow-up will reveal long-term side effects and complications affecting the cornea or underlying tissue. It is common knowledge that riboflavin has a double role in corneal collagen crosslinking. Riboflavin induces the cross links but, at the same time, it accumulates in the anterior chamber, protecting the eye from the UVA irradiation.2 Another way of providing the maximum protective effect to tissues predisposed to the harmful action of UVA irradiation might be the use of isoptocarpine, a slowly hydrolyzed muscarinic agonist used as a miotic. The miosis provoked probably minimizes the amount of UVA irradiation absorbed by the crystalline lens and the retina. Adding the use of isoptocarpine drops during patient preparation for surgery (1 drop 10 minutes before the beginning of the procedure) requires zero time but might provide a significant advantage in the long-term outcome of this procedure. George D. Kymionis, MD, PhD Dimitra M. Portaliou, MD Heraklion, Crete, Greece

2009

ultrasound biomicroscopy demonstrated movement of the capsular-fixated intraocular lens (IOL) during accommodation. In 1985, Spencer Thornton, MD, was the first ophthalmologist to demonstrate this phenomenon. He presented his initial observations at the Hawaiian Ophthalmological Society meeting (‘‘An IOL That Gives Accommodation?’’ Ocular Surgery News, May 1, 1985, pages 1,45; S.P. Thornton, MD, ‘‘Accommodating IOLs [letter],’’ Ocular Surgery News, October 1, 1985, pages 3–4). Thornton’s work was subsequently published in a peer-reviewed journal.2 Robert H. Osher, MD Cincinnati, Ohio, USA REFERENCES 1. Marchini G, Pedrotti E, Modesti M, Visentin S, Tosi R. Anterior segment changes during accommodation in eyes with a monofocal intraocular lens: high-frequency ultrasound study. J Cataract Refract Surg 2008; 33:949–956 2. Thornton SP. Lens implantation with restored accommodation. Curr Canad Ophthalmic Pract 1986; 4:60,62,82

REFERENCES 1. Hayes S, O’Brart DP, Lamdin LS, Doutch J, Samaras K, Marshall J, Meek KM. Effect of complete epithelial debridement before riboflavin–ultraviolet-A corneal collagen crosslinking therapy. J Cataract Refract Surg 2008; 34:657–661 2. Wollensak G. Crosslinking treatment of progressive keratoconus: new hope. Curr Opin Ophthalmol 2006; 17:356–360

REPLY: We thank Kymionis and Portaliou for their kind comments about our recent article and also for their interesting suggestion about the preoperative use of isoptocarpine drops to minimize the exposure of the retina and lens to UVA irradiation during corneal cross-linkage therapy. Based on current treatment protocols with complete epithelial debridement, adequate time for riboflavin 0.1% corneal stromal absorption, and homogeneous UV irradiance of 3 mW/cm2, the work of Spoerl et al.1 indicates that the radiant exposures achieved at the lens and retina are considerably less than their respective UV damage thresholds. However, any therapeutic modality that further reduces radiant exposure to these tissues merits further investigation.dDavid P. O’Brart, MD, Sally Hayes, PhD REFERENCE 1. Spoerl E, Mrochen M, Sliney D, Trokel S, Seiler T. Safety of UVA– riboflavin cross-linking of the cornea. Cornea 2007; 26:385–389

Initial report of IOL-induced accommodation I noted one important omission in the extensive bibliography of the article by Marchini et al.1 in which

REPLY: We agree with Osher, but even if we had known that Thornton was the first ophthalmologist to demonstrate anterior movement of a 3-piece loop IOL using A-scan biometry, we would not have found the original article. That is because Thornton’s important work was published in a journal that was not indexed in the medical indexes. We think it would have been incorrect to include an article that we could not read.dGiorgio Marchini, PhD, Emilio Pedrotti, MD, Silvia Visentin, MD

Refractive outcome of phacovitrectomy The refractive results of phacovitrectomy are increasingly important, and the paper by Patel et al.1 adds useful data and demonstrates that the accuracy of the refractive outcome of phacovitrectomy for macular hole is comparable to that of phacoemulsification alone. The authors found a mean postoperative prediction error (PPE) of 0.39 diopters (D) with the combined procedure and postulated that this small myopic shift may be secondary to anterior displacement of the intraocular lens (IOL) by intravitreal gas pressure. However, Patel et al. used historical control data from Murphy et al.,2 who also found a small myopic PPE of 0.32 D in their series of solitary uncomplicated phacoemulsification surgeries. The question arises as to whether the myopic shift Patel et al. observed is unique to the phacovitrectomy procedure, the precise surgical technique and IOL used, or the indication of macular hole surgery only.

J CATARACT REFRACT SURG - VOL 34, DECEMBER 2008

2010

LETTERS

Sridhar Manvikar, FRCS David Steel, FRCOphth Dimitri Pimenidis, FRCOphth Sunderland, United Kingdom

Table 1. Summary of refractive outcomes.

Procedure Phacovitrectomy overall Phacovitrectomy for macular holes with C3F8 tamponade Phacovitrectomy with no tamponade agent Phacovitrectomy for indications other than macular hole and C3F8 or SF6 tamponade Control phacoemulsification alone

Number of Patients

Mean PPE G SD

95 29

0.38 G 0.87 0.41G 0.67

24

0.37 G 0.81

17

0.30 G 0.63

97

C0.26 G 0.82

PPE Z postoperative prediction error

We performed an audit of the refractive results of phacovitrectomy for a range of indications performed by a single surgeon (D.H.W.S.) using a standardized technique in 2004. The SRK/T formula was used and the ultrasound axial length measurement. Patients were excluded if a scleral buckle was used, silicone oil was inserted, the IOL was not positioned in the capsular bag, or the macula was detached preoperatively. The mean PPE was 0.38 D. We analyzed the refractive results in 3 subgroups: (1) Patients having vitrectomy for macular hole with C3F8 gas tamponade. (n Z 29); (2) patients having vitrectomy for conditions in which no gas tamponade was used (eg, macular pucker) (n Z 24); (3) patients having vitrectomy for conditions other than macular hole in which the macula was clinically normal and gas tamponade was required (eg, macula on retinal detachment) (n Z 17). We found no significant difference in refractive outcomes between these 3 groups (Table 1). We then compared the results with those in a series of uneventful phacoemulsification alone using the same IOL and surgical technique. In this group, the mean PPE was C0.26 D. The refractive accuracy was very similar between the groups and similar to that found by Patel et al. In conclusion, we also found a small myopic overcorrection with phacovitrectomy surgery, which was not affected by the use of gas or the indication for surgery. Kovacs et al.3 recently correlated the myopic shift observed after phacovitrectomy for macular epiretinal membrane with the degree of macular thickening preoperatively. They concluded that the observed myopic shift was due to erroneous IOL calculation resulting from underestimation of the axial length because of a thicker macula. This is probably also responsible for at least some of the myopic shift observed with phacovitrectomy for other conditions, including macular hole with an elevated retinal cuff around the hole.

REFERENCES 1. Patel D, Rahman R, Kumarasamy M. Accuracy of intraocular lens power estimation in eyes having phacovitrectomy for macular holes. J Cataract Refract Surg 2007; 33:1760–1762 2. Murphy C, Tuft SJ, Minassian DC. Refractive error and visual outcome after cataract extraction. J Cataract Refract Surg 2002; 28:62–66 3. Kova´cs I, Ferencz M, Nemes J, Somfai G, Salacz G, Re´csa´n Z. Intraocular lens power calculation for combined cataract surgery, vitrectomy and peeling of epiretinal membranes for macular oedema. Acta Ophthalmol Scand 2007; 85:88–91

Risk factors for ectasia after LASIK In their letter1 about my 2007 article,2 Mohammadpour and Jabbavand asked whether the assumed risk factors for developing ectasia, in and of themselves, increased the risk in a population of eyes that had been screened for topographic abnormalities. Before the 1998 article by Seiler et al.,3 keratoconus was considered a contraindication to laser vision correction. As corneal and refractive surgeons, we were aware of the topographic appearance of keratoconus eyes well before that date.4 I screened potential laser refractive patients for the then accepted signs of keratoconus and, subsequently, forme fruste keratoconus.5 Of the 3 eyes (2 patients) in my series that developed ectasia, 1 patient had keratoconus in 1 eye, but I did not see that topography before surgery because of a computer printer error; only the fellow-eye topography was available and that was normal. I now have 8 years of follow-up for that particular patient and the uninvolved fellow eye did not develop ectasia. One issue in reviewing retrospective cases is that our diagnostic and surgical skills, as well as our screening criteria, are constantly evolving. What I might have approved for surgery in 1996, would certainly not meet the same approval criteria in 2008. For example, I previously used 250 mm of residual stromal bed thickness (RSBT) as a cut-off and if I felt I could not safely leave an eye with more than that thickness, I would perform photorefractive keratectomy (PRK). I have subsequently increased my minimal RSBT to more than 300 mm. In the second patient with bilateral ectasia, who was operated on in 2000, there was a 10-degree skewing of the radial axis; based on today’s criteria, this would have accounted for a 3-point score in the Randleman system and the patient would definitely have been eliminated as a laser in situ keratomileusis

J CATARACT REFRACT SURG - VOL 34, DECEMBER 2008