Intrascleral concentration vs depth profile of mitomycin-C after episcleral application: impact of irrigation

Wound Healing Modulation in Glaucoma Filtration Surgery-Conventional Practices and New Perspectives: The Role of Antifibrotic Agents (Part I)

Glaucoma filtration surgery is regularly performed for the treatment of glaucoma and trabeculectomy is often regarded as the ‘gold standard' glaucoma operation. The biggest risk of failure of the operation is bleb scarring. The advent of anti-fibrotic agents, such as mitomycin C (MMC) and 5-fluorouracil (5FU) has vastly prolonged the longevity of the bleb, but concerns remain regarding the potential increase in postoperative complications. More selective therapeutic targets have therefore been explored. One of these is vascular endothelial growth factor (VEGF) inhibition. Vascular endothelial growth factor inhi bition has a role not only in sub conjunctival angiogenesis inhi bition but also it has direct anti-fibrotic properties. Newer phar macological compounds and materials have also been developed in recent years in attempt to modulate the wound healing in different ways after glaucoma surgery. These include physical barriers to scarring and vehicles for sustained release of pharmacological agents, and early promising results have been demonstrated. This two-part review will provide a discussion of the application of anti-fibrotic agents in glaucoma filtration surgery and evaluate the newer agents that have been developed.

How to cite this article: Fan Gaskin JC, Nguyen DQ, Ang GS, O'Connor J, Crowston JG. Wound Healing Modulation in Glaucoma Filtration Surgery–Conventional Practices and New Pers pectives: The Role of Antifibrotic Agents (Part I). J Curr Glaucoma Pract 2014;8(2):37-45.

Effect of different application depths of mitomycin-C in deep sclerectomy with collagen implant: a randomized controlled trial

PURPOSE

To evaluate effects of mitomycin-C (MMC) in deep sclerectomy with collagen implant applied under the superficial scleral flap or under the deep scleral flap.

METHODS

Twenty-five patients with primary or secondary open-angle glaucoma and at high risk for postoperative cicatrization underwent deep sclerectomy and were randomly distributed to the two treatment arms. In the superficial MMC group (S-MMC), MMC was applied under the superficial scleral flap using a soaked sponge for 60 s; in the deep MMC group (D-MMC), MMC was applied under the deep scleral flap for 60 s before entering the Schlemm's canal. In both groups, remaining MMC was irrigated with 40 mL balanced salt solution. Patients were followed up for up to 2 years. The volume of filtering blebs was studied with ultrasound biomicroscopy at the last follow-up visit.

RESULTS

Mean preoperative intraocular pressure (IOP) was 20.5 +/- 8.9 mmHg for D-MMC and 21.6 +/- 6.6 mmHg for S-MMC eyes (P = 0.67). The mean postoperative IOP was 5.3 +/- 3.3 mmHg (D-MMC) and 6.9 +/- 4.8 mmHg (S-MMC) at day 1 (P = 0.22) and 11.4 +/- 6.3 mmHg (D-MMC) versus 11.3 +/- 4.6 mmHg (S-MMC) at last follow up (P = 0. 54). The mean number of medications per patient was reduced from 2.5 +/- 0.5 to 0.4 +/- 0.5 (D-MMC) (P < 0.001) and from 2.5 +/- 0.9 to 0.3 +/- 0.4 (S-MMC) (P < 0.001). Ultrasound biomicroscopy at 24 months showed mean intrascleral space volume of 1.97 +/- 0.35 mm3 (D-MMC) and 5.68 +/-0.42 mm3 (S-MMC) (P < 0.05).

CONCLUSION

No significant difference in efficacy and safety was found between the two groups at a mean of 19.2 months of follow up. Deep scleral application of MMC, however, seems to produce significantly smaller intrascleral blebs.

Focal corneal decompensation after filtering surgery with mitomycin C

PURPOSE

To report a case with focal corneal decompensation after filtering surgery with inadvertent inadequate irrigation of mitomycin C (MMC).

METHODS

Case report and review of literature.

RESULTS

A 25-year-old man first referred with the complaint of photophobia. His ocular examinations revealed diffuse keratic precipitates and many iris nodules in both eyes. The primary diagnosis was idiopathic bilateral granulomatous anterior uveitis. The intraocular pressure (IOP) gradually increased in the left eye and was not controlled with a prescription of topical antiglaucoma medications. As the disease progressed, the left eye underwent filtering surgery with MMC 0.02%. The postoperative period was uneventful, and the anterior chamber was deep after surgery. The IOP was controlled without medications; however; the inferior third of the cornea was edematous because of severe endothelial dysfunction.

CONCLUSIONS

Inadequate irrigation of MMC during filtering surgery can cause focal corneal decompensation.

[Wound healing modulation in glaucoma surgery]

The wound healing response is one of the major determinants of filtering surgery success. Over the last two decades, antifibrotic agents, 5-fluorouracil (5-FU) and mitomycin C (MMC), have modified the prognosis of filtering surgery, particularly in patients at high risk for failure. Nevertheless, these agents are associated with severe complications. In order to maximize their benefits and minimize the rate of complications, the use of these powerful treatments has to be carefully evaluated in relation to patient risk factors for scarring. The choice of an antifibrotic agent, mode, dose and duration of application should be made with complete knowledge of the different effects of these treatments and adapted for each patient after an exhaustive preoperative evaluation.

Intraocular lens opacification after nonpenetrating glaucoma surgery with mitomycin-C

A 58-year-old woman had successful phacoemulsification with intraocular lens (IOL) implantation in January 2001. Two years later, nonpenetrating glaucoma surgery with mitomycin-C (MMC) 0.02% was performed for uncontrolled glaucoma. Two months later, opacification of the anterior IOL surface was observed. The IOL was removed and a hydrophobic acrylic AcrySof IOL (Alcon) implanted. The opacified IOL was studied by flame atomic absorption spectrometry, which showed the presence of calcium carbonate. A new IOL of the same model was placed in an aqueous solution with calcium carbonate and basic pH, and the same opacification developed. We hypothesize that the change in aqueous humor pH after glaucoma surgery and the characteristics of the IOL precipitated deposition of calcium.

Presence of mitomycin-C in the anterior chamber after photorefractive keratectomy

PURPOSE

To assess the presence of mitomycin-C (MMC) in hen aqueous humor after photorefractive keratectomy (PRK).

SETTING

Instituto Universitario de Oftalmobiología Aplicada, Faculty of Medicine, University of Valladolid, and Department of Analytical Chemistry, Faculty of Sciences, University of Valladolid, Valladolid, Spain.

METHODS

Mitomycin-C 0.02% was applied topically for 2 minutes to a right hen's eye after PRK (Group A) and to the left eye with intact epithelium (Group B). At different time points (10, 30, 60, 360, and 720 minutes), aqueous humor was extracted and high-performance liquid chromatography was performed to detect and quantify MMC levels.

RESULTS

The mean maximum drug concentration of MMC measured in the aqueous humor was 187.250 microg/L +/- 4.349 (SD) in Group A and 93.000 +/- 4.899 microg/L in Group B, both detected 10 minutes after topical application. Statistically significant differences were found between Groups A and B at 10, 30, and 60 minutes, with decreasing MMC levels in both groups but a higher concentration in Group A. After 360 minutes, MMC levels were undetectable in Group B and after 720 minutes in Group A.

CONCLUSIONS

Mitomycin-C was detectable in the aqueous humor of the hen eye after topical application in PRK-treated eyes and in eyes with intact epithelium. The presence of MMC is of concern as it may lead to ocular toxicity in the long term.

Effect of mitomycin C on ciliary body and intraocular pressure with various application depths: an experimental study

BACKGROUND

To evaluate the effects of mitomycin C (MMC) on intraocular pressure (IOP) and ciliary body via transmission electron microscopy when applied under conjunctiva or different depths of sclera, without performing any filtering surgery.

METHODS

Thirty-six eyes of 36 New Zealand albino rabbits were used in this study. MMC was prepared in a concentration of 0.4 mg/mL and 0.05 cc (20 microg) was soaked in preprepared sterile surgical sponges. Six groups each consisting of six eyes were formed and IOP was measured preoperatively. Group 1 was the control group: the superior conjunctiva was opened and only irrigated with balanced salt solution (BSS). In group 2, MMC soaked sponges were applied under the conjunctiva. In groups 3 and 4, a scleral flap of approximately 1/3 scleral thickness was prepared and in groups 5 and 6, and a scleral flap of approximately 2/3 scleral thickness was prepared, all with a standard size of 4 x 4 mm. MMC soaked sponges were applied under these areas for 5 min in eyes in groups 3 and 5 followed by an irrigation of the relevant areas with 10 cc BSS, whereas only irrigation with BSS was done in groups 4 and 6 as control groups. No filtering procedure was performed in any of the eyes. Eyes were enucleated on the 30th day following measurement of IOP and the ciliary body regions were evaluated using transmission electron microscopy. Kruskal-Wallis test was used for the statistical assessment of IOP between groups.

RESULTS

The deep scleral flap group (group 5) showed statistically significantly more IOP reduction than both the superficial scleral flap group (group 3; P = 0.004) and the subconjunctival group (group 2; P = 0.002) on postoperative day 30. Electron microscopic evaluation of the surgical groups revealed a wide range of different histopathological effects due to different MMC application methods. The histopathological changes were more evident in the group 5, where MMC was applied under deep scleral flap.

CONCLUSIONS

Subscleral application of MMC seems to provide greater IOP decrease than subconjunctival application, possibly caused by a more significant ciliary body toxicity. This may be the beginning of a non-penetrating, easy to perform and safe method to decrease IOP in glaucoma patients, which the authors call 'toxic ciliary ablation surgery'. However, the long-term results and complications must be assessed with further studies.

Comparison of Amniotic Membrane Graft Alone or Combined With Intraoperative Mitomycin C to Prevent Recurrence After Excision of Recurrent Pterygia

PURPOSE

Without effective adjunctive therapy, the recurrence rate after excision of recurrent pterygia is high. In an effort to determine a way to better reduce the recurrence of pterygia, we compared the efficacy and safety of amniotic membrane graft (AMG) alone and AMG combined with intraoperative mitomycin C after excision of recurrent pterygia.

METHODS

Patients with recurrent pterygia were randomly assigned to receive excision of pterygia followed by AMG alone or AMG combined with intraoperative 0.025% mitomycin C for 3 minutes (AMG-mitomycin C). Patients who could be followed up for more than 12 months were entered for data analysis. Conjunctival (potential) and corneal (true) recurrence of pterygia and other complications were recorded.

RESULTS

The group receiving AMG alone was made up of 48 eyes in 48 patients, and the group receiving AMG-mitomycin C consisted of 47 eyes in 46 patients. No significant difference was found in age distribution, sex distribution, or duration of follow-up between the 2 groups. Regarding the recurrence rates of each group, 6 conjunctival (12.5%) and 6 corneal (12.5%) recurrences developed in the AMG group, and 4 conjunctival (8.5%) and 6 corneal (12.8%) recurrences developed in the AMG-mitomycin C group. No significant difference was found in the conjunctival and corneal recurrence rate between the 2 groups (P=0.623 and 0.966, respectively; log rank test), and no major complications developed in either group.

CONCLUSIONS

AMG alone can be considered an effective alternative adjunctive treatment of recurrent pterygia. The addition of intraoperative mitomycin C did not further reduce the recurrence rate.

Modifying subsceral fluid pressure in an experimental model of mitomycin-C diffusion

BACKGROUND

Episcleral application of mitomycin-C (MMC) during glaucoma filtration surgery hinders the post-operative wound healing. Diffusion through the sclera might result in a toxic effect on the ciliary body resulting in reduced aqueous humor production leading to post-operative hypotony. We developed an experimental model to investigate the influence of intraocular pressure on the diffusion of MMC through the sclera and in subscleral compartments.

METHODS

Scleral quadrants of 10 human donor eyes were mounted on PMMA tubes filled with saline imitating the intraocular volume. By height variation of a coupled infusion line different intraocular pressures were simulated (0, 8, 23 and 80 mmHg). Additionally the model included a subscleral sponge to mimic the compartment of the ciliary body. The episcleral sides of the scleral quadrants were exposed for 1 min to sponges soaked with 200 microg ml(-1) MMC. An 8-mm-diameter scleral disk was punched out with a trephine and horizontally dissected with a kryotome. The MMC concentrations of scleral layers, epi-and subscleral sponges and the fluid within the tubes were analysed by means of high-performance liquid chromatography.

RESULTS

The MMC concentration gradually declined from the episcleral sponge (165 microg ml(-1)) to the superficial (3.3 microg ml(-1)) and deep scleral layers (1.2 microg ml(-1)), and to the subscleral sponge (0.2 microg ml(-1)). We were able to detect very small concentrations of MMC in the fluid within the PMMA tubes (0.01 microg ml(-1)).

CONCLUSION

We developed a new experimental in vitro model for investigating transscleral MMC diffusion. The different simulated intraocular pressures had no effect on the concentration gradient through the investigated compartments of our model.

Impact of Mitomycin-C application time on the scleral Mitomycin-C concentration

The aim of this study was to determine the effect of varying the application time of Mitomycin-C (MMC) on the scleral concentration of MMC. The sclerae of 14 human donor eyes were used for this study. The episcleral sides of the 4 scleral quadrants of each donor eye were exposed for 0.5, 1, 3 and 5 min to round, 8 mm-diameter sponges soaked with 50 microl of 0.2 mg/ml MMC. After 40-ml irrigation with saline, a central 8-mm diameter scleral disk was punched out, homogenized and analyzed with high performance liquid chromatography (HPLC). The scleral MMC concentrations (microg/g) after 0.5, 1, 3 and 5 min application times were 6.40 (+/-3.38), 9.02 (+/-2.40), 12.31 (+/-3.37), and 13.97 (+/-3.83). The differences of scleral MMC concentration in paired t-tests were statistically significant comparing 0.5 with 1 and 1 with 5 min application. However the effect was relatively small within the range of usual application times (1 to 5 min), and 64% of the MMC was delivered to the sclera within the first min.

In vitro diffusion of mitomycin-C into human sclera after episcleral application: impact of diffusion time

The purpose of this study was to investigate the impact of different diffusion times of mitomycin-C (MMC) on the intrascleral concentration vs depth profile of MMC in an experimental model. Scleral quadrants of eight human donor eyes were exposed to sponges soaked with MMC for an application time of 1 min. After irrigation with 40 ml saline, we allowed further diffusion of MMC in the sclera for 1, 5, 14 and 29 min until the specimens were further processed. A central 8 mm diameter scleral disk was horizontally dissected with a kryotome at -20 degrees C. MMC concentrations of six layers of 140 microm thickness were analysed by means of high-performance liquid chromatography. The MMC concentrations (microg g(-1)) of layer 1 were: 13.45+/- 5.9 (mean +/- S.D. at 2 min diffusion time), 7.6+/-2.5 (6 min diffusion), 5.6+/-3.1 (15 min diffusion) and 3.6+/-1.7 (30 min diffusion). The corresponding MMC concentrations of layer 6 were: 0.61+/-0.48, 1.47 +/-0.66, 1.83+/-0.42 and 2.98+/-0.97 microg g(-1). The superficial concentration of intrascleral MMC decreased with increasing diffusion time, the deep concentrations increased. After 30 min of diffusion time, equal concentrations of MMC were found in all layers. Even with current low-dose application regimens of MMC the concentrations in the inner side of the sclera rapidly increase beyond the limits of the therapeutic range. Owing to this fast diffusion of MMC, the only means of reducing ciliary body concentrations of MMC is to reduce the dose.

Intrascleral concentration vs depth profile of mitomycin-C after episcleral application: impact of applied concentration and volume of mitomycin-C solution

The purpose of this study was to investigate the impact of different concentrations and volumes of Mitomycin-C (MMC) on the intrascleral concentration vs depth profile of MMC in an experimental model. The episcleral sides of scleral quadrants of human donor eyes were exposed for 1 min to sponges (corneal light shield, Merocel Corp.) soaked with MMC. After irrigation with 40 ml saline a central 8 mm diameter scleral disk was horizontally dissected with a cryotome. MMC concentrations of six layers of 140 microns thickness were analysed by means of high-performance liquid chromatography. In Experiment 1 (11 eyes) the sponges were soaked with 50 microliters of 10, 100 and 200 micrograms ml-1 MMC solutions. In Experiment 2 (12 eyes) the sponges were soaked with 10, 30, 50 and 80 microliters of a 200 micrograms ml-1 isotonic MMC solution. In Experiment 1 the MMC concentrations (microgram g-1) of layer 1 were 0.35 (+/- 0.20; 10 micrograms ml-1 group) and 9.22 (+/- 2.92; 200 micrograms ml-1 group). In Experiment 2 the MMC concentrations were 2.57 (+/- 1.17; 10 microliters group), 7.35 (+/- 2.49; 30 microliters group) and 11.67 (+/- 3.25; 80 microliters group). The scleral MMC concentrations were significantly influenced by the applied concentrations (layers 1-5) and by the applied volumes (all layers) of MMC solution. The intrascleral MMC concentration increased linearly with increasing concentration and not linearly with increasing volume of the applied MMC solution. To achieve more predictable scleral concentrations of MMC after trabeculectomy with MMC it seems advisable to control both the concentration and the volume of the MMC solution used to soak the sponge.