Toxic anterior segment syndrome (TASS), an acute, noninfectious inflammation of the anterior segment of the eye, is a complication of anterior segment eye surgery, such as cataract extraction surgery. Various contaminants, usually from surgical equipment or supplies, have been implicated as causes of TASS [
TASS typically develops within 24 hours after surgery and is characterized by corneal edema and cellular reaction in the anterior chamber of the eye. Although most cases of TASS can be treated successfully with topical steroids, topical nonsteroidal anti-inflammatory agents, or both, the inflammatory response associated with TASS can cause serious damage to intraocular tissues, resulting in vision loss [
From October 2008 to November 2008, the Kangbuk Samsung Hospital Ophthalmology Surgical Center observed several patients who developed TASS after cataract surgery and who had been exposed to indocyanine green (ICG) dye for anterior capsular staining because of the presence of a mature senile cataract (Figure
Corneal edema, severe inflammation, and fibrous membrane formation in the anterior chamber ((a) Patient 1, (b) Patient 2, and (c) Patient 3).
This experimental study was approved by and conducted in compliance with IACUC protocol number 10-016-D1-N, 2010.12.16. It involved eight eyes of four male 2.5-month-old New Zealand white rabbits that weighed 2.5–3.0 kg. This was a preliminary study to evaluate the role of ICG with regard to postoperative inflammation, where we aimed to use as few rabbits as possible to evaluate the potential impact of ICG. Using the given study design and sample size, our aim was not to prove the effect statistically but rather to provide proof of principle.
ICG dye was used for anterior capsular staining in these rabbits, and the three physical variables of concentration, exposure time, and degree of dissolution were tested. There are several previous studies dealing with the safety and efficacy of ICG dye for capsular staining in cataract surgery [
The ICG dye was prepared by dissolving the commercially available product in aseptic distilled water (Diagnogreen, Daiichi Pharmaceutical, Tokyo, Japan). The control solution did not contain any ICG. According to previous studies [
In this study, three concentrations of ICG (0.25%, 0.50%, and 1.00%) were prepared by dissolving ICG powder in 1.0 mL distilled water (provided with the ICG powder), and then these distilled-water solutions were diluted with 4.0 mL balanced salt solution (BSS, Alcon, Fort Worth, USA) to the final concentration of 0.5% ICG solution. To achieve concentrations of 0.25 and 1.0% ICG solutions, 1.0 mL distilled water with 9.0 mL BSS and 0.5 mL distilled water with 2.0 mL BSS were mixed, respectively, with 25 mg ICG granules. The calculated osmolarity values for each solution were 277.73, 250.45, and 250.5 mOsm (0.25%, 0.50%, and 1.0%), respectively. The pH measurements (Istek’s Desktop pH meter, model 730P) of each solution at 37°C were
General anesthesia was induced by intramuscular injection of zolazepam tiletamine (10 mg/kg; Zoletil, Virbac, Carros, France) and xylazine hydrochloride (0.5 mg/kg; Rompun, Bayer Healthcare, Seoul, Korea), supplemented with topical anesthetic (Alcaine, Alcon-Couvreur NV, Puurs, Belgium). A wire lid speculum was inserted to separate the eyelids. Two clear corneal incisions were made using a 1.0 mm diamond blade. One incision was used for the injection of the ICG solution and BSS for capsular staining or anterior chamber irrigation, respectively. The second incision served as the exit point for the irrigation solution. After a clear corneal incision was performed, air was injected into the anterior chamber to displace the aqueous humor. Then, with a 26-gauge cannula, 0.1 mL ICG solution was instilled onto the anterior capsule for the scheduled time, and the anterior chamber was washed with BSS. The time of exposure to ICG was 10 seconds or 60 seconds.
Rabbit Number One (ICG presence or absence) is described as follows:
Right eye: 0.50% ICG dye prepared by vortexing for three minutes was administered for an exposure time of 60 seconds. Left eye (control): a mixture of distilled water and BSS without ICG was administered. Rabbit Number Two (difference in exposure time) is described as follows:
Right eye: 0.50% ICG dye vortexed for three minutes was administered for 60 seconds. Left eye: 0.50% ICG dye vortexed for three minutes was administered for 10 seconds. Rabbit Number Three (difference in degree of dissolution) is described as follows:
Right eye: 0.50% ICG dye vortexed for three minutes was administered for 60 seconds. Left eye: 0.50% ICG dye vortexed for 30 seconds was administered for 60 seconds. Rabbit Number Four (difference in ICG concentration) is described as follows:
Right eye: 0.25% ICG dye vortexed for three minutes was administered for 60 seconds. Left eye: 1.00% ICG dye vortexed for three minutes was administered for 60 seconds.
Anterior segment photography, prostaglandin E2 (PGE2) competitive enzyme-linked immunosorbent assays (ELISA), and scanning electron microscopy were used to evaluate the eyes. Inflammatory reactions such as corneal edema, fibrin formation, and conjunctival injection were measured in the anterior segment with photography using slit lamp biomicroscopy (BX 900, Haag-Streit International, Koeniz, Switzerland) preoperatively and at 30 minutes, 12 hours, and 24 hours postoperatively. Within the cyclooxygenase cascade, PGE2 plays a major part in mediating the classical signs of inflammation and pain. Aqueous PGE2 levels can therefore serve as an indicator of the relative level of inflammation [
“Fibrous membrane” [
Fibrous membrane in the anterior chamber was observed immediately after applying ICG to the right eye of Rabbit Number One (a). It was more pronounced at 12 hours after the injection and then disappeared within 24 hours. The control eye was clear at all times (b).
Compared to the ICG exposure time, fibrous membrane formation was more prominent in the right eye (a) of Rabbit Number Two that was exposed to ICG for a longer time than left eye (b).
The right eye injected with ICG, dissolved for 3 minutes (a), and the left eye injected with ICG, dissolved for only 30 seconds (b). After 24 hours, the anterior chambers of both eyes were clear.
A very severe inflammation for up to 24 hours was observed in the eye to which 1.00% ICG had been applied (b). There was no inflammation in the eye treated with 0.25% ICG (a).
The results of prostaglandin E2 ELISA analysis correlated well with those of anterior segment photography. The rabbit eyes exposed to ICG for a longer period of time (60 seconds), ICG dissolved for only a short time (30 seconds), or ICG with a high concentration (1.00%) resulted in high PGE2 levels. The most significant difference was observed between eyes treated with different concentrations of ICG (Figure
The PGE2 concentrations in aqueous humor. The rabbit eyes exposed to ICG for a longer period of time (60 seconds), ICG dissolved for only a short time (30 seconds), or a high concentration of ICG (1.00%) resulted in high PGE2 levels.
Residual ICG particles on the iris surface were observed using scanning electron microscopy. ICG granules were identified based on their presence and morphology compared to the control image. As there could not physiologically be electron dense round particles on the iris, these particles were characterized as ICG granules. Furthermore, the ICG granules were also completely different in size and shape when compared with inflammatory cells, fibers, and muscular structures. There were many ICG granules on the iris of the right eye of Rabbit Number One, ranging in size from 1 to 5
Residual ICG particles on the iris surface were observed using scanning electron microscopy. There were many ICG granules on the iris of the right eye of Rabbit Number One, ranging in size from 1 to 5
The right eye of Rabbit Number Two, which was exposed to ICG for 60 seconds, had slightly more granules (a) than the left eye (b).
The left eye of Rabbit Number Three treated with ICG dissolved for only 30 seconds had larger white granules (b) compared with the right eye, which was treated with ICG, that was vortexed for a longer time (a).
There were numerous granules in the left eye of Rabbit Number Four, which was treated with 1.00% ICG (b). In contrast, very few remnant ICG particles were observed in the right 0.25% ICG-treated eye of this rabbit (a).
There are several factors influencing anterior chamber inflammation during cataract surgery, such as insufficient mydriasis, elongated surgery time, excessive use of ultrasonic energy during phacoemulsification, iris incarceration into the corneal incisions, iris damage through phaconeedle, and irritating or toxic foreign materials. In this study we isolated and analyzed the role of ICG as a factor for inflammation in the anterior chamber.
Our results based on an animal model suggest that residual intraocular indocyanine green (ICG) dye can cause postoperative inflammation in the anterior segment. In this preliminary study to evaluate the role of ICG with regard to postoperative inflammation, the study design and sample size were optimized to harm as few rabbits as possible in order to provide proof of principle rather than prove a statistical effect.
Although toxic anterior segment syndrome was first described by Monson et al. [
The common causes of TASS, as described by the ASCRS task force team, include improper cleansing of surgical equipment, use of enzymatic cleaners, an inappropriate detergent concentration, and antibiotics or preservatives for antibiotics that are intraoperatively mixed with an irrigation solution [
Trypan blue is commercially available in liquid form, whereas ICG comes in powder form and needs to be dissolved in a solvent before use. In countries such as South Korea where there are legal issues surrounding the intraocular use of trypan blue and/or import difficulties, ICG is used for anterior capsular staining. Generally, a 0.5% ICG solution is used for anterior capsular staining [
In this study, anterior chamber inflammation was found to be severe, and scanning electron microscopy of the iris surface showed more residual ICG particles when the time of exposure was long (60 seconds) and when the dissolving time was short (30 seconds). The degree of inflammation was much more severe and there were more residual ICG particles on the iris surface when 1.00% ICG was used compared to those when 0.25% ICG was used. The concentration of PGE2 in the aqueous humor was measured to quantify the degree of anterior chamber inflammation. We found that the higher the degree of anterior chamber inflammation was, the higher the level of PGE2 was in the aqueous humor.
Based on these findings, we hypothesize that insoluble particles that remain in the ICG solution attached to the iris surface or to the anterior chamber angle during anterior capsular staining without being completely washed off can cause inflammation. Thus, if the formation of insoluble ICG particles can be minimized, inflammation caused by residual ICG particles could be reduced. The dissolution time, solution concentration, and solvent type all contribute to the formation of insoluble ICG particles. Generally, a mixed solution of distilled water and BSS is used to prepare ICG dye solution. Nishimura et al. [
A preliminary experiment was performed using different ICG concentrations and different ratios of the two solvents [distilled water and BSS], and we observed a difference in the amounts of insoluble particles that were formed using a light microscope. We found that the higher the ICG concentration and the proportion of BSS in the solvent, the greater the proportion of insoluble particles (data not shown). This is likely to be related to the saturability of the solution. Of the substances used, the one which is most similar to aqueous humor in composition is BSS. As BSS contains various ions and molecules, its upper limit of complete dissolution of ICG is 0.5%. If the ratio of distilled water is increased to achieve complete dissolution of ICG, however the pH and osmolality of the ICG dye solution could decrease, which would adversely affect the anterior segment structures. Thus, sufficient time is required to dissolve ICG in a mixed solution containing a higher ratio of BSS to distilled water in order to maintain the regular intraocular environment.
Parikh and Edelhauser [
The limitations of this study are as follows: we only used a small number of rabbits; the pupil was undilated when anterior capsular staining was performed, which increased the possibility of ICG particles remaining on the iris surface; the amount of insoluble ICG in the anterior chamber could not be quantitatively measured according to exposure time, dissolution time, or concentration. There might also be differences in the inflammatory reactions of humans and rabbits. The difference in osmolarity values could also affect the inflammatory reactions after exposure of ICG solution in the anterior chamber. Nevertheless, we demonstrated for the first time that ICG can cause intraocular inflammation. In addition, we showed that the concentration of ICG, time of exposure to ICG, and the degree of dissolution of ICG affected the severity of inflammation. Anterior segment photography, scanning electron microscopy, and aqueous PGE2 ELISA objectively showed that the greater the number of residual intraocular ICG particles was, the greater the severity of inflammation was.
These results show that, in the absence of trypan blue, ICG could also be used with caution as a capsular dye. In this case, special care should be taken to ensure a proper dissolution rate, lower concentration, and thorough cleansing of the ICG from the anterior chamber after staining the anterior capsule of the lens to avoid ICG granules from being captured within the meshwork-like structures of the iris surface which can otherwise cause significant anterior chamber inflammation. Chang et al. [
Further studies are required to investigate other substances that can be related to the occurrence of TASS.
The authors alone are responsible for the content and writing of the paper.
The authors report no competing interests.