**4. Pathomechanism**

and a relative pupillary block forms with progressive shallowing of the central and cir‐ cumferential anterior chamber, narrowing, and gradual angle closing [29]. However this is not the only angle closing mechanism in this pathology. Peripheral iridectomy, which eliminates pupillary block, does not prevent progressive overfilling of the choroidal bed, which may cause further angle closure. If the aqueous humour is directed to the vitreous cavity instead of the posterior chamber, symptoms of malignant glaucoma will occur [30]. Thus, in a genetically conditioned microphthalmos, glaucoma with a complex iris and cil‐

The occurrence of malignant glaucoma in the pathology that is the microphthalmos may not only be connected to abnormal anatomical relationships but also to incorrect histolog‐ ical structure of the sclera. The sclera in a microphthalmos is thicker relative to physiolog‐ ical conditions and its collagen fibers are more disorganized [31]. Trelstad et al. stated, that in a microphthalmos, collagen fibers of the intercellular substance in the connective tissue of the sclera have a normal thickness, but the collagen fibers are longer, less organ‐ ized, and more interwoven [32]. Yue et al. stated that a greater heightened level of fibro‐ nectin, and speculated that a change in the glycosaminoglycan metabolism may influence the contraction of collagen fibers and lead to thickening of the sclera. The authors believe, that an incorrect glycosaminoglycan metabolism may cause a decrease in the elasticity of the sclera, which hampers normal development of the eye [33]. Based on known measure‐ ments of the thickness of the sclera, increased thickness of the tissues, including the reti‐ na, choroid, and sclera in echographic measurements was considered to be a value above 1.7 mm [34]. The increased thickness of the sclera in hyperopic eyes and its simultaneous‐ ly lower surface area decrease transscleral protein transport, what, in consequence, causes choroidal expansion [22]. According to Quigley et al., a similar situation occurs in many eyes that do not achieve such small sizes, and malignant glaucoma can occur in eyes of correct sizes as well as in small eyes, but all cases would have dramatic choroidal expan‐ sion or vitreous flow abnormality [22]. In the case of a nanophthalmos, a tendency to‐ ward spontaneous or postoperative uveal effusion was also observed [21]. Quigley et al. observed that in eyes with extremely small sizes, displacement of the lens to the front oc‐ curs, caused by choroidal expansion [22]. Furthermore, the increased pressure in the vor‐ tex veins occurring in a microphthalmos as well as disrupted transscleral protein transport and increased oncotic pressure of the vitreous body may be linked to an in‐

One of the more important factors predisposing the occurrence of malignant glaucoma is al‐ so partial or total closing of the filtration angle at the time of the surgery, especially if the malignant glaucoma occurred in the second eye [3]. However, IOP has no direct correlation to the risk of occurrence of malignant glaucoma. In Simmons's studies, the IOP level during the operation was not correlated with the probability of development of malignant glauco‐ ma after surgery [3]. Moreover, it should be pointed out, that in the case of malignant glau‐ coma in one eye, the fellow eye exhibits a predisposition for occurrence of a malignant

iary block may be expected [20].

424 Glaucoma - Basic and Clinical Aspects

creased risk of development of malignant glaucoma [21,22].

process [6].

The causes of malignant glaucoma are complex and there are several theories on the subject of factors that may have an influence on its development. As of now, the pathophysiological mechanism of malignant glaucoma is not yet fully understood. There is no certainty as to what structures or biochemical processes lead to the development of malignant glaucoma, and its cause seems to be conditioned by many factors.

An anterior rotation of the ciliary body processes, leading to ciliolenticular touch and cil‐ iary block, has been suggested [25]. Forward displacement of a relatively large lens, which then blocks communication between the posterior and anterior chamber, as well as outlets from the eye, is the essential anatomical feature of malignant glaucoma [35]. Congestion of the uveal tract may play a part in pushing the lens into its forward posi‐ tion and holding it there [35]. In addition, in certain cases, the lens capsule and zonules may constitute a place of resistance for the flow of aqueous humour to the front [36]. The aqueous humour produced to the posterior chamber is directed to the back instead of to the anterior chamber [5], causing anterior displacement of the lens-iris diaphragm. Furthermore, swelling of the ciliary processes caused by inflammation or miotics can cause critical narrowing of an already anatomically narrow space between the lens equa‐ tor and the ciliary body and relative block of forward aqueous flow [18]. Abnormal cho‐ roidal circulation may also lead to accumulation of blood and swelling of the ciliary processes. Moreover, Epstein and coauthors hypothesized that there is decreased perme‐ ability of the vitreous body or the anterior hyaloid to anterior flow of aqueous humour into the anterior chamber in malignant glaucoma [37].

Probably, there are eyes with predispositions for malignant glaucoma, in which there is a pathology of connective tissue related to a predominance of intercellular substance, mainly comprised of glycosaminoglycans. Glycosaminoglycans produced by fibroblasts of patho‐ logical connective tissue accumulate in the vitreous of such eyes with malignant glaucoma. Glycosaminoglycans, together with proteins gathered in the vitreous body because of im‐ paired transscleral outflow, are responsible for the increase of oncotic pressure and accumu‐ lation of water. Moreover, high viscosity caused by mucopolysaccharides content makes the flow from the posterior to the anterior chamber more difficult. Glycosaminoglycans may al‐ so be a cause of iridocorneal angle damage.

The coexistence of anatomical and physiological predispositions and changes in IOP in the anterior chamber during surgery, activates a specific pump mechanism caused by move‐ ments of the lens-iris diaphragm, which may have an influence on the development of ma‐ lignant glaucoma. The malignant process can have various dynamics with clinical manifestation occurring directly after surgery, when exciting factors cannot be compensated in the closed system of the eyeball. On the other hand, the occurrence of malignant glauco‐ ma symptoms may be delayed if a relative equilibrium between the volume of the produced fluid and the outflow from the eyeball is reached.
