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Contact us at firstname.lastname@example.org Chapter 18 Malignant Glaucoma Marek Rękas and Karolina Krix-Jachym Additional information is available at the end of the chapter http://dx.doi.org/10.5772/53979
1. Introduction Malignant glaucoma was described for the first time and named so by Albrecht von Graefe in 1869 . It is characterized by normal or increased IOP (intraocular pressure) associated with axial shallowing of the entire anterior chamber in the presence of a patent peripheral iridotomy [2,3]. The pathology is based on the existence of a block for normal flow of aque‐ ous humour, which results in the accumulation of aqueous at an improper location in the eyeball . The proposed mechanism involves a misdirection of aqueous humour passing posteriorly into or behind the vitreous gel . This is a dynamic process, and if untreated, causes loss of vision. Local hypotensive treatment does not cause normalization of IOP, and conventional glaucoma surgery proves to be ineffective .
1.1. Classification Classification includes phakic, aphakic, and pseudophakic malignant glaucoma. Aphakic malignant glaucoma is the onset of symptoms after a cataract surgery or the persistence of symptoms after treatment of phakic malignant glaucoma through the cataract extraction .
“Non-phakic malignant glaucoma” is a general term used for both types: aphakic and pseu‐ dophakic malignant glaucoma . The term malignant-like glaucoma was proposed for cases with a known cause of forward displacement of the lens along with the frontal surface of the vitreous body other than the “trapping” of humour inside of the vitreous body . There also exists a classification of malignant glaucoma into that occurring after surgical interven‐ tion and without such intervention .
The not fully known etiology of the process creates difficulties in the standardization of no‐ menclature. Certain authors suggest that the malignant glaucoma group should exclude cas‐ es in which e.g. pupillary block or choroidal detachment has been stated . Others believe that using this term to encompass a broader spectrum of eye diseases will create a better un‐ © 2013 Rękas and Krix-Jachym; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
422 Glaucoma - Basic and Clinical Aspects derstanding of the pathophysiology and the relationship between pathologies with similar clinical pictures .
According to literature, malignant glaucoma develops in 2% to 4% of patients with a his‐ tory of acute or chronic angle-closure glaucoma that have undergone filtration surgery . In own material, consisting of a total of 1689 penetrating and non-penetrating opera‐ tions, performed as glaucoma surgery alone or combined with cataracts, malignant glau‐ coma occurred in 1.3% of all eyes after surgery. After penetrating surgery this complication was noted in 2.3% of eyes. It was also observed after laser iridotomy , phacoemulsification of cataract , posterior capsulotomy using a Nd-YAG laser (Neody‐ mium-yttrium-aluminum-garnet laser) , cyclophotocoagulation , after implantation of large-sized IOLs (intraocular lens) , after local application of miotics , after suturol‐ ysis , and even in eyes that did not undergo surgical procedures . Cases of malig‐ nant glaucoma have also been described in eyes in which glaucoma had not been established earlier .
Malignant glaucoma occurs significantly more frequently after penetrating surgery than in the case of non-penetrating surgery, after just the glaucoma surgery than after treatment combined with phacoemulsification, as well as in eyes with narrow angle glaucoma. It was stated with greater frequency among women, which may be related to the lesser dimensions of the anterior segment of the eyeball in this group of patients . This complication can take place at various times after the operation, sometimes immediately, and sometimes after one year has passed or even after a longer period of time .
2. Anatomical basis
It is considered that incorrect anatomical relationships lead to disruptions in the direction of aqueous humour flow [4,19]. The place of increased resistance may be located at the level of the iris-lens, ciliary-lens, iris-hyaloid, and ciliary-hyaloid block [4,20]. Structures that are
particularly related to the development of malignant glaucoma and its clinical picture:
Sclera – a thick sclera may lead to partial stenosis of the vortex veins, impairing normal ve‐ nous outflow and causing overfilling of the choroid , as stated in eyes with malignant glaucoma . Opening of the anterior chamber during surgery, which causes lowering of IOP, together with possible movements of the irido-lenticular diaphragm can trigger a ma‐ lignant glaucoma mechanism in such eyes.
Choroid – the choroid has a lobular structure with a tendency for accumulation of blood and thickening when outflow is impaired. Secondary, ciliary body and iris rotate to the front in patients with malignant glaucoma , closing access to the filtration angle from the back.
Vitreous body – Slit-lamp examination of the vitreous may reveal optically clear areas with‐ in the vitreous body – reservoirs of aqueous humour trapped in its gel structure , which may be confirmed on ultrasound . In aphakic eyes, the anterior surface of the vitreous body may directly adhere to the ciliary processes .
The anterior and posterior chambers and their relationship – total obliteration of the posteri‐ or chamber by the vitreous and a highly resistant hyaloid membrane may be observed in aphakic and pseudophakic eyes .
3. Predisposing factors
The anatomic and functional differences of predisposed eyes seem to be a significant factor for determining the occurrence of malignant glaucoma. The following predisposing factors have been described, among others: axial hyperopia , nanophthalmos , disorders of anatomical proportions in the anterior chamber .
Figure 1. Normal eye, relative anterior microphthalmos and nanophthalmos.
It is considered that malignant glaucoma is related to a special eye anatomy (small eye phenotype). Lynch et al. stated that it occurs more frequently in small eyes with an ana‐ tomically narrow iridocorneal angle . Many nanophthalmic and RAM eyes have nar‐ row angles with crowded structures in the anterior chambers. Typically, the lens is of normal or increased thickness, leading to a high lens:eye ratio and this crowding results in a shallow anterior segment that predisposes to angle-closure glaucoma . In micro‐ phthalmos, due to small eye size, the increase in the size of the lens with age is critical, 424 Glaucoma - Basic and Clinical Aspects and a relative pupillary block forms with progressive shallowing of the central and cir‐ cumferential anterior chamber, narrowing, and gradual angle closing . 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 .
Thus, in a genetically conditioned microphthalmos, glaucoma with a complex iris and cil‐ iary block may be expected .
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 . 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 . 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 . 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 . 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 . 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 . In the case of a nanophthalmos, a tendency to‐ ward spontaneous or postoperative uveal effusion was also observed . Quigley et al.
observed that in eyes with extremely small sizes, displacement of the lens to the front oc‐ curs, caused by choroidal expansion . 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‐ creased risk of development of malignant glaucoma [21,22].
4. Pathomechanism 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 . 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 .
Congestion of the uveal tract may play a part in pushing the lens into its forward posi‐ tion and holding it there . 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 .
The aqueous humour produced to the posterior chamber is directed to the back instead of to the anterior chamber , 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 . 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 .
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.
426 Glaucoma - Basic and Clinical Aspects
5. Objective symptoms
Myopic shift in refraction related to the anterior dislocation of the iris-lens diaphragm with secondary improvement of near vision .