Prevention of retrobulbar hemorrhageafter sub-Tenon anesthesia

In their recent article, 1 Subbiah et al. noted thata rigid sub-Tenon cannula caused complications suchas a retrobulbar hemorrhage, albeit rarely. The authorsconcluded that a ‘‘soft cannula’’ could be an ideal alter-native for sub-Tenon injection in high-risk patients.

We reported the same thing in our Sandwell tech-nique,2 in which the soft plastic sheath of a Venflonwas used to deliver the local anesthetic agent in thesub-Tenon space. This prevents injury to blood vesselsin a highly vascular region during an essentially blindprocedure. It is probably because our report was pub-lished in April 2007 that Subbiah et al. overlooked thisvery effective technique that addresses the point raisedin the article.

In our practice, we have found that the ultrashortversion3 is not as effective as the Venflon sheath, as itoften does not deliver the anesthetic agent to the actualretrobulbar region. Since our report, we have used thistechnique in all cases and have had no complications.

Yajati K. Ghosh, FRCSEdAmanda Van Vuuren, FRCA

Shashi P. Aggarwal, FRCOphthDinesh Dubash, FRCA

Birmingham, United Kingdom

REFERENCES1. Subbiah S, McGimpsey S, Best RM. Retrobulbar hemorrhage

after sub-Tenon’s anesthesia. J Cataract Refract Surg 2007;

33:1651–1652

2. Ghosh YK, Van Vuuren A, Aggarwal SP, Dubash D. The Sand-

well technique of sub-Tenon’s infiltration anesthesia for cataract

surgery and other ophthalmic procedures. J Cataract Refract

Surg 2007; 33:750–751

3. McNeela BJ, Kumar CM. Sub-Tenon’s block with an ultrashort

cannula. J Cataract Refract Surg 2004; 30:858–862

347LETTERS

Central corneal thickness and applanationtonometry

The excellent work by Salvi et al.1 addresses theimportant issue of central corneal thickness (CCT)changes after phacoemulsification. They confirm thatCCT increases in the immediate postoperative period.

An earlier study by Kohlhass et al.2 concludes thata 1mmHg correction should bemade in themeasuredintraocular pressure (IOP) for every 25 mm deviationfrom a CCT of 550 mm. Based on this formula, Salviet al. suggest that the IOP is overestimated by app-roximately 3 mm Hg in the immediate postoperativeperiod and by at least 1 mm Hg on the first day afterphacoemulsification. Kohlhass et al. looked at corneaswith different physiological thicknesses, while Salviet al. studied eyes with corneal edema.

Hamilton et al.3 report that a small increase in cor-neal hydration resulted in an overestimation of IOPby Goldmann applanation tonometry in human eyes,whereas Kaufman4 observed that Goldmann applana-tion tonometry usually underestimates the IOP in eyeswith moderate corneal epithelial edema. Simon et al.5

demonstrate an inverse relationship between cornealhydration and IOP measured with applanation to-nometry. Whitacre and Stein6 conclude that cornealepithelial and probably stromal edema result in a sub-stantial underestimation of the IOP in human eyes.The relationship between CCT increased by edemaand applanation-measured IOP is clearly differentfrom the relationship between physiological CCTand applanation-measured IOP. In our opinion, Kohl-hass et al.’s formula should not be directly applied tocorneas that are thicker because of edema.

Yuqiang Huang, MBBSClement C.Y. Tham, FRCS, FCOphth

Mingzhi Zhang, MDHong Kong, China

Self-repositioned IOL in a vitrectomized eyeI would like to address some important issues raised

by Mansouri’s report of a self-repositioned intraocularlens (IOL) in a vitrectomized eye.1

First, it is not clear when the radial tear at the9:30 o’clock position occurred. I question whether itoccurred during placement of a foldable single-pieceplate-haptic acrylic IOL such as the Acri.Smart 48 S(Acri.Tech). The tear might have occurred duringcapsulorhexis or phacoemulsification or there mighthave been a preexisting posterior capsule defect thatoccurred during the previous pars plana vitrectomy.Consulting the retinal surgeon and/or carefully study-ing the surgical notes might reveal posterior capsuleinjuries during vitreoretinal surgery. If there are

REFERENCES1. Salvi SM, Soong TK, Kumar BV, Hawksworth NR. Central

corneal thickness changes after phacoemulsification cataract

surgery. J Cataract Refract Surg 2007; 33:1426–1428

2. Kohlhass M, Boehm AG, Spoerl E, et al. Effect of central corneal

thickness, corneal curvature, and axial length on applanation

tonometry. Arch Ophthalmol 2006; 124:471–476

3. Hamilton KE, Pye DC, Hali A, et al. The effect of contact lens

induced corneal edema on Goldmann applanation tonometry

measurements. J Glaucoma 2007; 16:153–158

4. Kaufman HE. Pressure measurement: which tonometer? Invest

Ophthalmol 1972; 11:80–85. Available at: http://www.iovs.org/

cgi/reprint/11/2/80. Accessed December 4, 2007

5. Simon G, Small RH, Ren Q, Parel J-M. Effect of corneal hydration

on Goldmann applanation tonometry and corneal topography.

Refract Corneal Surg 1993; 9:110–117

6. Whitacre MM, Stein R. Sources of error with use of Goldmann-

type tonometers. Surv Ophthalmol 1993; 38:1–30

J CATARACT REFRACT SURG - VOL 34, MARCH 2008