Critical Study of the Aetiology and Pathogenesis of Infantile Glaucoma The WritePass Journal

Critical Study of the Aetiology and Pathogenesis of Infantile Glaucoma Introduction Critical Study of the Aetiology and Pathogenesis of Infantile Glaucoma IntroductionEpidemiology of Primary Infantile Glaucoma Signs, Symptoms and Consequences of Primary Infantile GlaucomaPathology, Pathogeneses and Causes of Primary Infantile GlaucomaOptic Cup Asymmetry in Primary Infantile Glaucoma Secondary infantile glaucomaReferencesRelated Introduction The incidence of glaucoma in the young population is incomparable to the incidence in the adult population, as it is very rare in infants, nevertheless it can significantly affect a child’s life, as vision is vital for a young child. Signs and symptoms of infantile glaucoma can commonly be overlooked and this can cause a delay to the treatment process. The underlying causes of infantile glaucoma have been agreed upon by most authors, however the exact mechanism by which the structures in the young eye are affected are debatable. As well as primary infantile glaucoma, young children can also be affected by secondary infantile glaucoma, which again can significantly impact a young child’s life. This paper looks at the classifications, epidemiology, signs, symptoms, aetiology and pathogenesis of primary infantile glaucoma, as well as touching upon the causes of secondary infantile glaucoma. ‘Glaucoma is an Optic neuropathy with characteristic appearances of the optic disc and specific pattern of visual field defects that is associated frequently but not variably with raised intra-ocular pressure (IOP)’ (Kanski, 2003). The ciliary processes of the eye produce aqueous humor; this is then drained by the trabecular meshwork; Figure 1. A balance of this production and drainage maintains a normal IOP. The aqueous humor produced flows into the posterior chamber, then through the pupil and into the anterior chamber. The trabecular meshwork drains the aqueous humor through Schlemm’s canal. Open angle glaucoma occurs when there is a decrease in the outflow of aqueous through the trabecular meshwork, and angle closure glaucoma occurs when the iris adheres to the lens leading to a build-up of aqueous humor in the posterior chamber   (Kanski, 2003). In addition to open and closed angle glaucoma there are other types of glaucoma which are classified in Figure 2. There are several classifications of congenital and infantile glaucomas, the most accepted and simplified version is presented in figure 3. Primary infantile glaucoma is defined as ‘the result of isolated abnormal development of the anterior chamber angle structures’ (Myron Yanoff, 2009) Secondary infantile glaucomas are ‘associated with a variety of ocular and systemic syndromes and with surgical aphakia’ (Myron Yanoff, 2009). Primary congenital glaucoma is present at birth however it is not always recognised at this stage and sometimes it is diagnosed later during infancy or in early childhood. To minimise problematic visual development, recognition of primary congenital glaucoma must be as early as possible followed by respective treatment or therapy, allowing the child to lead a ‘normal’ life (A.Armstrong, 2008). Glaucoma in infants and young children is relatively rare and in some cases asymptomatic (Kanski, 2003). And so, if an increase in IOP is not detected at an early stage then there is a greater risk of blindness (Robert N. Shaffer, 1970). Some cases of glaucoma in infants are only recognised and diagnosed after several months or years at which stage sometimes significant glaucomatous damage has already occurred (Robert N. Shaffer, 1970). Most cases will present bilaterally nevertheless this does not rule out the fact that it can sometimes present unilaterally   (Robert N. Shaffer, 1970). Epidemiology of Primary Infantile Glaucoma Primary infantile glaucoma is extremely rare and occurs in one out of 10,000 births (MillerSJ, 1966). It accounts for 0.01% to 0.04% of cases of total blindness (A.Armstrong, 2008) (Vincent P Deluise, 1983) In the Irish childhood population primary open angle glaucoma is the cause of blindness for 4% of the population. (Morin JD, 1974) The majority of cases in the US and Europe present with bilateral primary infantile glaucoma; 65%-80% (Moller, 1977). It is also well-known that it occurs greater in males compared to females with a ratio of 3:2 respectively (Vincent P Deluise, 1983). This is proven by a study with 125 infants from Westerlund, 76 of whom were male i.e. nearly 61% were males (Vincent P Deluise, 1983). On the other hand in Japan, this is no longer true and the ratio is actually reversed (Vincent P Deluise, 1983). In another study based in Japan out of 46 children with primary infantile glaucoma 63% were actually female (Vincent P Deluise, 1983). In the majority of cases the development of primary infantile glaucoma is found to sporadic, and so it is non-familial and nonhereditary, but approximately 10% of cases are familial, transmitted to the child via autosomal recessive inheritance (Vincent P Deluise, 1983). Signs, Symptoms and Consequences of Primary Infantile Glaucoma Children are commonly referred to the Ophthalmologist due to clinical evidence of corneal oedema. Primary infantile glaucoma is commonly misdiagnosed, hence causing a delay in the correct diagnosis, as it may initially show symptoms similar to conjunctivitis such as a ‘red eye’ (Becker B, 1965). There will also be evidence of the classic triage; epiphora, blepharospasm and photophobia. (Becker B, 1965). Further examination will reveal megalocornea (enlarged corneal diameter), buphthalmos (enlarged globe), Haab’s striae (breaks in Descemet’s membrane) and optic nerve head changes (Becker B, 1965). Buphthalmos; figure 4, or ocular enlargement, occurs in primary infantile glaucoma because the globe of neonates is still distensible (Vincent P Deluise, 1983). Collagen of the cornea and scleral have not hardened enough, so expansion of the fibrils occurs due to an increase in IOP (Vincent P Deluise, 1983). This therefore causes stretching to occur in several structures of the infant eye; such as the cornea, the anterior chamber angle, the sclera, the optic nerve, scleral canal and the lamina cribrosa (Becker B, 1965). This explains why ocular enlargement due to glaucoma does not occur in adults, as the globe is no longer distensible and collagen fibres of the cornea are sclera are hardened hence expansion doesn’t occur in adults. It is agreed that delayed therapy of infants with glaucoma, will result in a poor visual outcome for the infant, which could have been prevented or at least minimised. To understand why some infants had more advanced glaucoma than others; a study with 24 infants and children was conducted (David J. Seidman MD1, 3 March 1986). Their signs and symptoms were noted. The parents of the infant were asked to indicate whether they had noticed either epiphora or photophobia and only 32% said their infant had these symptoms. A small 21% of infants presented with only signs of glaucoma, noticed by the parents but no symptoms. And finally the majority of infants, 90%, actually did have signs when presenting to the physician. It has been noted that signs of infantile glaucoma are more difficult to notice when it is bilateral, as in all 3 cases where the physicians failed several times to refer the infant to an ophthalmologist the glaucoma was in fact bilateral   (David J. Seidman MD1, 3 March 1 986). A normal value for the corneal diameter of a neonate is approximately 10mm, an increase to 12mm or greater, along with expansion of the corneal-scleral junction, is usually due to increased IOP (Kwitko, 1973). Enlargement of the cornea due to an increase in IOP is most likely to occur up to the age of three (Scheie, 1955) after which the sclera may become deformed up to age ten (Mann, 1957). Breaks occur in the endothelium and Descemet’s membrane due to the increase in IOP which also causes stretching in these layers (Vincent P Deluise, 1983).   ‘Haab’s striae form as endothelial cells lay down new basements membrane (Descemet’s membrane) and hyaline ridges develop. Breaks in Descemet’s membrane from increased IOP rarely occur after age three’ (Vincent P Deluise, 1983).   Increased IOP also causes slow expansion of the sclera of the neonate. A ‘bluish’ scleral appearance is seen due to thinning of the sclera, causing the choro id to be more apparent (Vincent P Deluise, 1983). As the neonate becomes older and growth occurs the expansion of the sclera no longer occurs due to a build-up of extracellular connective tissue (Vincent P Deluise, 1983). Even if the IOP decreases back to a value within normal the globe does not usually return to normal size (Vincent P Deluise, 1983). Studies have shown that myopia and astigmatism are the consequence of an increase in the axial length of the globe, figure 5 (Robin AL, 1979). Robin et al also found that ‘In contrast to adult eyes, the scleral canal in children apparently enlarges with high IOP. Thus, disk cup size increase in children could occur from neural tissue loss, from scleral canal enlargement, or from a combination of the two processes’ (Robin AL, 1979). ‘Myopic astigmatism and anisometropia are particularly common in cases of unilateral or asymmetric primary infantile glaucoma’ (Vincent P Deluise, 1983).   A study carried out by Broughton and Parks found that all of their patients with unilateral primary infantile glaucoma had anisometropia; on the affected side an average difference of 4.93D of myopia was found (Broughton WL, 1981 May). Optic nerve changes which occur in adults with glaucoma are very different to the optic nerve changes which occur in children with glaucoma. At first Becker Shaffer initially thought that cupping in primary infantile glaucoma was a process which was gradual however it was soon discovered that optic nerve changes in primary infantile glaucoma could also occur early and rapidly (Becker B, 1965). In adults with optic nerve changes which occur due to an increase in IOP the change is very unlikely to be reversible, however in infants optic nerve cupping which occurs due to an increase in IOP can be reversed once the IOP is returned back to normal (Vincent P Deluise, 1983). The most accepted and most reasonable hypothesis which aims to explain why cupping is reversible in neonates is based on the fact that the connective tissue of the lamina cribrosa is not matured (Quigley, 1977 Sep). However there are cases when even though the pressure has decreased back to normal the Optic nerve head damage does not reverse, this is due to one of two reasons. Firstly it is possible that some of the stretching is permanent ‘with remoulding of the connective tissue’   (Vincent P Deluise, 1983). Secondly it could be due to ‘a loss of glial and axons’ (Vincent P Deluise, 1983).   ‘Adult optic nerve heads with their dense connective tissue investments are more resistant to remoulding, indicating that cupping is caused by permanent loss of glia and axons’ (Vincent P Deluise, 1983). Pathology, Pathogeneses and Causes of Primary Infantile Glaucoma The explanation for the increase in IOP in primary infantile glaucoma has been described using Barkan’s membrane theory. This theory is based on the fact that the anterior chamber angle is covered by a thin and imperforate membrane, which inhibits aqueous outflow, which in turn leads to raised IOP (Vincent P Deluise, 1983). According to the theory, this raised IOP is treated by goniotomy when the surface tissue of this membrane is detached, and so â€Å"the peripheral iris falls posteriorly,† subsequently there is aqueous outflow and a decrease in IOP (Vincent P Deluise, 1983). Worst also agreed with the Barkan membrane theory, â€Å"†¦in congenital glaucoma the chamber angle is filled with a band of persistent mesodermal tissue (persistent uveal meshwork or persistent pectinate ligament). This tissue completely covers the fetal corneoscleral system, but is not the cause of the obstruction to aqueous outflow in its own right. It is the presence of an imperforate surface layer on this persistent mesodermal tissue, which is the only cause of obstructed outflow. This surface membrane, Barkans membrane, is probably an endothelial surface, which normally breaks apart, but which persists in congenital glaucoma† (Worst, April 1968). There is no well supported histopathologic evidence to support Barkan’s membrane theory, despite this Worst still believes that the theory along with its concepts are valid, he says â€Å"though histopathologic proof of this structure is almost completely lacking†¦this has little influence on the probability th at this concept is valid† (Worst, April 1968). So if Barkan’s membrane theory has insufficient evidence to explain the cause of an increase in IOP in congenital glaucoma, then what is the alternative? There is some histopathologic evidence which aims to explain in detail the anterior chamber angle and its histopathology in infants with primary infantile glaucoma see Figure 6 (Vincent P Deluise, 1983). Anderson thoroughly researched the development of the trabecular meshwork in infantile glaucoma. He said that earlier thoughts were that â€Å"the anterior chamber recess deepens by atrophy of the rarified tissue that in the earlier stage separated the trabecular meshwork and ciliary body.† He then confirmed that later thoughts highlighted the function of cleavage into the loose tissue, as there was no proof of atrophy (D.R.Anderson, 1981). These views may have seemed correct at the time however, evidence has proven that cleavage or atrophy are not the only explanations of the process of development. Both cleavage and atrophy would cause the uveal tract to become fragmented from the shell of the cornea and sclera as well as the tissue of the trabeculae (Fig 7A) (D.R.Anderson, 1981). This would result in extension of the ciliary muscle to the peripheral iris and on the posterior surface of the peripheral iris would be the ciliary processes (D.R.Anderson, 1981). However this does not actually occur, in fact the ciliary muscle and the ciliary processes continue to adhere to the envelope of the cornea and sclera although compared to their earlier position they do become depressed (Fig 7B) (D.R.Anderson, 1981). Anderson found that there is an overlay of the ciliary muscle in particular the ciliary processes over the trabecular meshwork; however they are subsequently depressed behind the scleral spur (D.R.Anderson, 1981). He found that â€Å"This repositioning can be explained only by a posterior sliding of the uveal tissues in relation to the cornea and sclera, presumably due to a differential growth rate of the various tissue elements† (D.R.Anderson, 1981). He concluded that this course of repositioning was not simply due to the â€Å"sliding of the uveal tract along the inner side of the sclera. There is also a repositioning of the various layers within the uveal tract in relation to one another: initially the innermost muscle fibers have a position relatively more anterior than the outermost fibers† (D.R.Anderson, 1981) Anderson also found that compared to the ciliary muscle the ciliary processes are at first a lot more frontward, as time passes both become level behind the scleral spur and meshwork (D.R.Anderson, 1981). So, far it has been established that primary infantile glaucoma occurs because the anterior chamber does not develop normally. At what stage of development do these changes or lack of changes occur? It has been noted that at week twelve of development â€Å"a wedge shaped mass of mesenchyme can be identified at the anterior chamber angle i.e. at the junction of the papillary membrane and the lateral margins of the cornea. Within this wedge shaped portion of the tissue there is a row of small capillaries, which are lined with mesoderm-derived vascular endothelial cells† (A.Armstrong, 2008). At the beginning of the fifth month â€Å"early trabeculae are apparent separated by intervening spaces† (A.Armstrong, 2008) subsequently the capillaries fuse to form the canal of Schlemm, this is continuous with the collector channels as well as the scleral vessels (A.Armstrong, 2008). â€Å"The meshwork becomes specialised into inner uveal trabeculae, numerous intermediate layers of lamellar corneoscleral trabeculae, and a more loosely organised cribriform meshwork† (A.Armstrong, 2008). The inner surface of the meshwork is lined with cuboidal cells, perforations of these cells occur onwards from 15 weeks (A.Armstrong, 2008). Communication between the meshwork and the anterior chamber occur via these cuboidal cells (A.Armstrong, 2008). Between the sixth and ninth month development of the anterior chamber occurs (A.Armstrong, 2008). It presents â€Å"as a chink in the mesoderm between the iris root and the developing trabeculum. If the mesoderm does not entirely regres s in this region, an impervious layer may remain bridging the angle between the iris and the cornea and which impedes access of aqueous to the trabecular meshwork† (A.Armstrong, 2008). Figure 8: Comparision of optic cup asymmetry in normal infants with unilateral glaucoma infants. Taken from (Richardson, April 1968) Optic Cup Asymmetry in Primary Infantile Glaucoma It has been established that chronic open angle glaucoma is found to be bilateral and symmetrical to a certain extent, however some meticulous studies may find that there is somewhat of asymmetry in the cupping of the optic discs (Richardson, April 1968). Nevertheless the asymmetry of the discs can be used to diagnose early signs of glaucoma (Richardson, April 1968). Although optic disc cupping is assessed in infantile glaucoma it is not used as prominently compared to chronic open angle glaucoma (Richardson, April 1968). One of the reasons for this is due to the obvious fact that it is not as easy to conduct ophthalmoscopy in infants especially with added factors such as hazy corneas, miotic pupils (Richardson KT, 1966). It is also a common misconception that cupping in the optic nerve occurs at a very late stage and so it is no longer relevant to aid diagnosis (Richardson, April 1968). The opposite is actually true, as changes to the optic disc in infantile glaucoma occur relatively early on, hence valuable factor to aid prognosis (Shaffer.RN, 1967). To emphasise the importance of asymmetry of optic discs in infantile glaucoma compared to chronic glaucoma, the following study was conducted by Kenneth Richardson. Normal newborn infants, 96 hours old or less, were randomly chosen and their optic discs were assessed. Out of 468 it was found that only 11 infants had optic cup asymmetry, 2.3%; figure 8 (Richardson, April 1968). Similarly Snydacker found that out a random 500 adults only 15 had any sign of asymmetry, 3% (SyndackerD, 1964). Going back to the infants it was found that only 3 out of the 11 actually had marked asymmetry between their optic cups i.e. only 0.6%; figure 8 (Richardson, April 1968). A very different but much predicted result was found when Shaffer conducted a slightly different study (Shaffer.RN, 1967). 27 infants with unilateral glaucoma were assessed and it was found that 89% or 24 out of 27 had marked asymmetry; figure 8 (Shaffer.RN, 1967). In other infantile glaucoma studies Schaffer also found that 61% (52/85) patients had optic cups with a disc diameter greater than 1/3 in comparison to 2.6%(26/936) normal newborns who had optic cups with a disc diameter greater than 1/3 (Shaffer.RN, 1967). The above data provides vital evidence supporting the views that optic disc assessment in newborn infants is extremely important and any asymmetry in optic cupping is very significant as ‘normal’ infants are expected and likely to have symmetrical optic cups. Hence any asymmetry of cupping could be indicative of congenital glaucoma. Also it can be said that optic cupping assessment is of more importance in congenital glaucomas â€Å"since these cases are prone to follow a more asymmetrical course than adult glaucomas† (Richardson, April 1968). In order chronic glaucoma in order to be able to determine whether cupping is physiological or pathological the disc appearance must be tracked over many years. Whereas in newborns the cupping is expected to be symmetrical at birth therefore any asymmetry should be and can be picked up at birth (Richardson, April 1968). Secondary infantile glaucoma There are several causes of secondary infantile glaucoma, the most important is ocular trauma and this is due to the fact that ocular trauma is common in young infants. Blunt trauma to the eye causes compression of the globe which in turn leads to a temporary increase in IOP. When a blunt object hits the eye its cause indentation of the cornea, this then forces the aqueous humor â€Å"laterally against the anterior chambers angle structures and backwards against the iris and lens† (Robert N. Shaffer, 1970). Thereafter â€Å"in the anterior segment the iris sphincter ruptures† (Robert N. Shaffer, 1970) the ciliary body could become separated from the scleral spur or it may just be split or torn (Robert N. Shaffer, 1970). Likewise the trabecular meshwork may become ruptured, consequently leading to glaucoma (Robert N. Shaffer, 1970). Traumatic iritis is another cause of secondary glaucoma. Blunt ocular trauma can cause inflammatory cells and increase in proteins in the aqueous humor, in the early stages. These cells along with the protein molecules then cause obstruction of the trabecular meshwork. (Robert N. Shaffer, 1970) Oedema of the trabecular meshwork will also lead to resistance in the outflow of the aqueous. Even though there is an increase in the resistance of outflow, the IOP will remain within a normal range and in some cases it may actually be lower than normal because the blow will have caused depression of the ciliary body along with hyposecretion (Robert N. Shaffer, 1970). Anterior chamber haemorrhage (hyphema) occurs due to trauma or injury to the eye. Small haemorrhages are unlikely to clot, however large haemorrhages may fill the anterior chamber and cause compression of the meshwork which in turn leads to an acute increase in IOP (Robert N. Shaffer, 1970). Another cause of secondary glaucoma is recession of the anterior chamber angle. â€Å"A significant percentage of traumatic hyphemas results from a longitudinal cleavage of the ciliary body† (Robert N. Shaffer, 1970). A chain of damage reactions which occur to the trabecular meshwork following this will decrease the outflow and lead to glaucoma. Contusion cataract can be caused by blunt trauma. â€Å"If the cataract intumesces, a phacogenic pupillary block glaucoma may result. If the cataract becomes hypermature the lens cortex which is liquefied may leak into the anterior chamber†¦Ã¢â‚¬ , (Robert N. Shaffer, 1970) a macrophage response occurs and these cells then cause an increase in IOP as they block access of the aqueous to the trabecular meshwork. (Robert N. Shaffer, 1970) This is known as phacolytic glaucoma. Dislocation of the lens most likely occurs due to trauma, and if the lens after dislocation ends up in the anterior chamber then pupillary block glaucoma is l ikely (Robert N. Shaffer, 1970). Secondary glaucoma is usually the result of a laceration to the globe. A blunt blow, by a child’s fist, is often very serious as the smaller size of the fist does not allow the orbit to provide protection and the blow lands straight on the eye (Robert N. Shaffer, 1970). Intra-ocular foreign bodies can also cause glaucoma; particles which contain iron will oxidise and can be toxic to structures within the eye such as the trabecular meshwork (Robert N. Shaffer, 1970). Severe iritis can lead to glaucoma, and transient or chronic glaucoma can result from inflammation of the trabecular meshwork with increased resistance to outflow (Robert N. Shaffer, 1970).   Inflammation of the cornea can also cause secondary glaucoma, due to further inflammation of the meshwork leading to obstruction of the aqueous outflow (Robert N. Shaffer, 1970). It is well-known that glaucoma can be induced by steroids. An increase in IOP can be induced by prolonged use of topical steroids, in susceptible individuals. Ocular tumours uncommon in children, however if one is present it can sometimes lead to secondary glaucoma (Robert N. Shaffer, 1970). Retinoblastoma, a well-known and common tumour found in the young can also cause glaucoma. The tumour will invade the anterior chamber angle structures; iris and trabecular meshwork. There is a very strong link between prenatal rubella infection and glaucoma and it is now well agreed upon that prenatal rubella can in fact cause glaucoma. It is estimated that rubella infantile glaucoma occurs in 2-4% of children with congenital rubella syndrome (Robert N. Shaffer, 1970). It usually presents in the first six months of life and the symptoms are identical to those of primary congenital glaucoma; an enlarged oedematous cornea which is cloudy, a deep anterior chamber and the classic high IOP (Robert N. Shaffer, 1970). Clinically it is found to be almost impossible to distinguish rubella infantile glaucoma from primary congenital glaucoma (Robert N. Shaffer, 1970). In conclusion, it has been determined that although rare conditions both primary and secondary infantile glaucoma can significantly affect the life of a child. Hence examination of the optic discs at birth is vital to ensure that any asymmetry of optic cups is detected and the possibility of the newborn developing glaucoma is known immediately, as it has been proven that infants with glaucoma are significantly more likely to show asymmetry of optic cupping compared to ‘normal’ infants. If the glaucoma is not detected at birth it is vital that healthcare professionals are able to recognise the signs and symptoms of infantile glaucoma so it can be treated before any significant damage has occurred, as it has been proven that the majority of children present with all or some of the signs and symptoms of glaucoma yet they are either overlooked by the parents or misdiagnosed by clinicians. In relation to the pathogenesis of infantile glaucoma significant evidence or lack of has proven that Worst along with Barkan’s Membrane theory are no longer valid. Vital histopathologic evidence undermines the theory; in fact Anderson has provided substantial evidence to prove that repositioning, sliding, cleavage and atrophy play a significant role in the development of primary infantile glaucoma. Along with the histopathologic evidence it can be concluded that Anderson’s findings can be accepted. References A. Edward Maumenee, M. (1962). 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