Intraocular pressure (IOP) is one of the most important factors associated with the development of glaucoma. The IOP depends on the amount of aqueous humor in the eye ball. Therefore, the limbal tissue where aqueous humor leaves the eye is a crucial part determining not only the IOP, but also the development and treatment of glaucoma. In this review, I describe the pathogenesis, diagnosis and treatment of glaucoma.
I. Trabecular meshwork cells and the extracellular matrix (ECM)
1. Corticosteroid and trabecular meshwork
We examined the trabecular meshwork obtained at trabeculectomy from eyes with corticosteroid-induced glaucoma both histologically and immunohistochemically. The studies showed the accumulation of amorphous substances with heparan sulfate proteoglycans and type IV collagens. An experiment using cultured human trabecular meshwork cells (TMCs) made it clear that dexamethasone activated RhoA/ROCK signaling through the transcription factor, Twist, which led to reconstruction of the cytoskeleton in TMC. Simvastatin, a type of statin, blocked this activation by dexamethasone. These studies may indicate that there is either accumulation of ECM in the trabecular meshwork or reconstruction of the cytoskeleton in TMCs, and this might be involved in the pathogenesis of corticosteroid-induced glaucoma.
2. Oxidative stress and TMC
We examined the anti-oxidative stress activity of cultured human TMCs using a Western blot analysis, MMT assay and siRNA study, and found that TMCs possessed anti-oxidative enzymes such as peroxiredoxin (PRDX) 1 and histone deacetylase Sirt1. Timolol induced the expression of PRDX 2 through the activation of the Foxo3a transcription factor. Quercetin, a flavonoid, activated the Nrf2/NRF1 transcription pathway to upregulate PRDX3 and 5. Tafluprost activated the c-myc/Sirt1 transcription pathway. All three substances were shown to protect TMCs from oxidative stress.
3. Metalloproteinase and the ECM in the trabecular meshwork
Matrigel invasion assay revealed that the cultured TMCs originating from a glaucomatous eye had higher invasion activity than that from a normal eye. By a Western blot analysis, TMCs were confirmed to express matrix metalloproteinase (MMP)-2, MMP-9 and RECK. Timolol downregulated RECK and upregulated MMP-9, which might be the reason why TMCs from the glaucomatous eye showed higher invasion activity, since the eyes had been treated with topical timolol.
II. Congenital microcoria and glaucoma
We followed up a family with congenital microcoria for more than 30 years. The family consisted of 22 members, including seven with microcoria in three generations. Four of five members, who were more than 20 years old and had microcoria, developed late onset developmental glaucoma. This finding led us to conclude that congenital microcoria was frequently accompanied by late onset developmental glaucoma. We performed a DNA linkage analysis of 16 members and an exome sequencing analysis in two members of this family with microcoria in order to disclose the causative gene. The analyses suggested that UNC13B on chromosome 9 could be a causative gene for congenital microcoria, but we were not able to confirm this possibility.
III. The difference in IOP values obtained using three different types of tonometers
We evaluated the effects of the corneal properties on the IOP values measured by a non-contact tonometer (NCT) or Goldmann applanation tonometer (GAT). The study revealed that the values measured by either tonometer had a significant positive correlation with the central corneal thickness (CCT). The difference of IOP readings between NCT and GAT showed a significant positive correlation with CCT. The IOP values measured by GAT showed a significant negative correlation with the corneal curvatures, while those measured by NCT did not. The values measured by dynamic contour tonometer (DCT), in contrast, were not affected by CCT. The IOP of the right eye of 500 Japanese adults who lived in Kyushu was 17.0±3.1 mmHg (average±S.D.) by DCT.
IV. Glaucoma surgery using adjunctive substances
1. Trabeculectomy using FocalSeal^® (FS)
FS is a type of hydrogel sealant which hardens following blue-green illumination. We performed trabeculectomy on rabbit eyes to examine the usefulness of FS for maintaining the filtration bleb. Before closing the conjunctival wound, a hardened FS was placed on the sclera covering the scleral flap. Compared with control eyes treated without FS, those treated with the FS exhibited lower IOPs and maintained larger filtration blebs by ultrasound biomicroscopy for four weeks after the operation. The morphologically reactive proliferation in the area of the operation was also lower in the eyes with FS than in those without FS. These findings indicate that FS is a useful substance for glaucoma filtration surgery.
2. Repairing filtration bleb leakage with FS
We successfully generated a rabbit model of filtration bleb leakage by perforating the bleb wall with a 24 gauge needle one week after trabeculectomy. We occluded the conjunctival hole with FS. One week after treatment, there was no bleb leakage, while the control eyes without the treatment exhibited leakage. At that time, the penetrating wound was morphologically covered by conjunctival epithelium, which suggests the usefulness of FS for repairing filtration bleb leakage.
3. Reconstruction of trabeculectomy blebs using an amniotic membrane-wrapped silicone sponge
Eight eyes that had undergone two or more surgeries for refractory glaucoma were treated by reconstruction of a trabeculectomy bleb using amniotic membrane-wrapped silicone sponges. In six out of the eight eyes, the IOPs stayed controlled under 20 mmHg for more than six months. In the six successful eyes, bleb needling was performed twice in two eyes and amniotic membrane patch covering for early aqueous leakage was needed in one. This study indicates that reconstruction of a nonfunctional trabeculectomy bleb using a silicone sponge wrapped with amniotic membrane can be a useful strategy for treating refractory glaucoma.
Nippon Ganka Gakkai Zasshi (J Jpn Ophthalmol Soc) 118: 189-215, 2014.