We would like to comment on the article by Chee and coauthors1 about postoperative inflammation after phacoemulsification and extracapsular cataract extraction (ECCE). The study results agree with those in previous studies,2–4 which indicate that the blood–aqueous barrier (BAB) reaction is reduced after phacoemulsification compared with ECCE. The flare in the anterior chamber was measured quantitatively with laser flare photometry and, as the authors point out, this method is preferable to subjective assessment of flare intensity, which may give inconsistent results. Laser flare photometry, which is a noninvasive procedure and easy to perform, provides an objective but indirect measure of the inflammatory response.
Direct measurement of the inflammatory reaction in the anterior chamber requires quantitative analysis of inflammatory mediators in the aqueous humor, such as prostaglandins and leukocytes.3 In the nonpigmented ciliary epithelium, inflammatory mediators such as prostaglandin E2 (PGE2) cause disruption of the BAB by breaking up the tight junctions.
The most sensitive technique to measure changes in BAB function is fluorophotometry.4 This can be performed in different ways, the most reliable method being computerized anterior chamber fluorophotometry after intravenous injection of fluorescein with determination of the diffusion coefficient for fluorescein leakage across the BAB.5,6 This method provides a physical value for the leakage of the small fluorescein molecules (molecular weight [MW] 376) through the BAB and is independent of aqueous flow. Laser flare photometry, on the other hand, measures the relative protein content in the anterior chamber, which is dependent on size and shape of the much larger protein molecules (MW about 50 000 or more), as well as on aqueous flow rate.
The postoperative BAB function is a good measure of surgical quality, and although fluorophotometry is a time-consuming technique requiring invasive procedures, it is more sensitive than laser flare photometry in measuring alterations in this function. This may explain why we, when using fluorophotometry, found ECCE to induce significantly more BAB breakdown than phacoemulsification even 3 months after surgery, while laser flare photometry indicated a difference only at 3 days.4
We have performed randomized controlled studies of the effects of incision size, intraocular lens (IOL) location, and capsulorhexis (CCC) size.7,8 Although the studies were performed in rabbits, the results indicate significantly less inflammation after a 5.2 mm incision than an 11.0 mm incision after capsular bag implantation versus ciliary sulcus implantation and after a 4.0 mm versus a 7.0 mm CCC. (A poly[methyl methacrylate] IOL with a 5.0 mm optic was implanted in all eyes.) The small incision induced less release of PGE2 and white blood cells (WBCs) into the aqueous humor, and the WBC counts (and after-cataract formation) were lower after IOL implantation in the capsular bag. Reduced inflammatory response with a small CCC may be due to better isolation of the IOL from the posterior surface of the iris and less exposure of the IOL to the aqueous humor.
Carl-Gustaf Laurell MD, PhD
Charlotta Zetterström MD, PhD
1. Chee SP, Ti SE, Sivakumar M, Tan DTH. Postoperative inflammation: extracapsular cataract extraction versus phacoemulsification. J Cataract Refract Surg 1999; 25:1280-1285
2. Pande MV, Spalton DJ, Kerr-Muir MG, Marshall J. Postoperative inflammatory response to phacoemulsification and extracapsular cataract surgery: aqueous flare and cells. J Cataract Refract Surg 1996; 22:770-774
3. Laurell C-G, Wickström K, Zetterström C, Lundgren B. Inflammatory response after endocapsular phacoemulsification or conventional extracapsular lens extraction in the rabbit eye. Acta Ophthalmol Scand 1997; 75:401-404
4. Laurell G-C, Zetterström C, Philipson B, Syrén-Nordquist S. Randomized study of the blood-aqueous barrier reaction after phacoemulsification and extracapsular cataract extraction. Acta Ophthalmol Scand 1998; 76:573-578
5. van Best J, Kappelhof JP, Laterveer L, Oosterhuis JA. Blood-aqueous barrier permeability versus age by fluorophotometry. Curr Eye Res 1987; 6:855-863
6. van Best J, del Castillo JB, Diestelhorst M, et al. Diffusion coefficient through the blood-aqueous barrier using a standard protocol. Br J Ophthalmol 1996; 80:356-362
7. Laurell C-G, Zetterström C, Lundgren B, et al. Inflammatory response in the rabbit after phacoemulsification and intraocular lens implantation using a 5.2 or 11.0 mm incision. J Cataract Refract Surg 1997; 23:126-131
8. Laurell C-G, Zetterström C, Lundgren B. Phacoemulsification and lens implantation in rabbit eyes: capsular bag versus ciliary sulcus implantation and 4.0 versus 7.0 mm capsulorhexis. J Cataract Refract Surg 1998; 24:230-236