Katarzyna Pikulska
Medical University of Warsaw
GLAUCOMA
Etiology
Factors involved in the etiology of retinal ganglion cell death and thus in the etiology of glaucomatous optic neuropathy can be grouped as below:
Primary insults
1. Raised intraocular pressure (Mechanical theory). Raised intraocular pressure causes mechanical stretch on the lamina cribrosa leading to axonal deformation and ischaemia by altering capillary blood flow. As a result of this, neurotrophins (growth factors) are not able to reach the retinal ganglion cell bodies in sufficient amount needed for their survival.
2. Pressure independent factors (Vascular insufficiency theory). Factors affecting vascular perfusion of optic nerve head in the absence of raised IOP have been implicated in the glaucomatous optic neuropathy in patients with normal tension glaucoma (NTG). However, these may be the additional factors in cases of raised IOP as well. These factors include:
- Failure of autoregulatory mechanism of blood flow. The retina and optic nerve share a peculiar mechanism of autoregulation of blood flow with rest of the central nervous system. Once the autoregulatory mechanisms are compromised, blood flow may not be adequate beyond some critical range of IOP (which may be raised or in normal range).
- Vasospasm is another mechanism affecting vascular perfusion of optic nerve head. This hypothesis gets credence from the convincing association between NTG and vasospastic disorders (migranous headache and Raynaud's phenomenon).
- Systemic hypotension particularly nocturnal dips in patients with night time administration of antihypertensive drugs has been implicated for low vascular perfusion of optic nerve head resulting in NTG.
- Other factors such as acute blood loss and abnormal coagulability profile have also been associated with NTG.
Secondary insults (Excitotoxicity theory)
Neuronal degeneration is believed to be driven by toxic factors such as glutamate (excitatory toxin), oxygen free radicals, or nitric oxide which are released when RGCs undergo death due to primary insults. In this way the secondary insult leads to continued damage mediated apoptosis, even after the primary insult has been controlled.
PRIMARY DEVELOPMENTAL/CONGENITAL GLAUCOMA
Characteristical signs
1. Photophobia, blepharospasm, lacrimation and eye rubbing often occur together. These are thought to be caused by irritation of corneal nerves, which occurs as a result of the elevated IOP. Photophobia is usually the initial sign, but is not enough by itself to arouse suspicion in most cases.
2. Corneal signs. Corneal signs include its oedema, enlargement and Descemet's breaks.
- Corneal oedema. It is frequently the first sign which arouses suspicion. At first it is epithelial, but later there is stromal involvement and permanent opacities may occur.
- Corneal enlargement. It occurs along with enlargement of globe-buphthalmos , especially when the onset is before the age of 3 years. Normal infant cornea measures 10.5 mm. A diameter of more than 13 mm confirms enlargement. Prognosis is usually poor in infants with corneal diameter of more than 16 mm.
- Tears and breaks in Descemet's membrane (Haab's striae). These occur because Descemet's membrane is less elastic than the corneal stroma. Tears are usually peripheral and concentric with the limbus.
3. Sclera becomes thin and appears blue due to underlying uveal tissue.
4. Anterior chamber becomes deep.
5. Iris may show iridodonesis and atrophic patches in late stage.
6. Lens becomes flat due to stretching of zonules and may even subluxate.
7. Optic disc may show variable cupping and atrophy especially after third year.
8. IOP is raised which is neither marked nor acute.
9. Axial myopia may occur because of increase in axial length which may give rise to anisometropic amblyopia.
Work-up
A complete examination under general anaesthesia should be performed on each child suspected of having congenital glaucoma. The examination should include following:
1. Measurement of IOP with Schiotz or preferably
hand held Perkin's applanation tonometer since
scleral rigidity is very low in children.
2. Measurement of corneal diameter by callipers.
3. Ophthalmoscopy to evalute optic disc.
4. Gonioscopic examination of angle of anterior chamber reveals trabeculodysgenesis with either flat or concave iris insertion as described in pathogenesis.
Differential diagnose
It is to be considered for different presenting signs
as follows:
1. Cloudy cornea. In unilateral cases the commonest cause is trauma with rupture of Descemet's membrane (forceps injury). In bilateral cases causes may be trauma, mucopolysaccharidosis, interstitial keratitis and corneal endothelial dystrophy.
2. Large cornea due to buphthalmos should be differentiated from megalocornea.
3. Lacrimation in an infant is usually considered to be due to congenital nasolacrimal duct blockage and thus early diagnosis of congenital glaucoma may be missed.
4. Photophobia may be due to keratitis or uveitis.
5. Raised IOP in infants may also be associated with retinoblastoma, retinopathy of prematurity, persistent primary hyperplastic vitreous, traumatic glaucoma and secondary congenital glaucoma seen in rubella, aniridia and Sturge-Weber syndrome.
Treatment
Treatment of congenital glaucoma is primarily surgical. However, IOP must be lowered by use of hyperosmotic agents, acetazolamide and betablockers till surgery is taken up. Miotics are of no use in such cases.
Surgical procedures for congenital glaucoma
1. Goniotomy In this procedure a Barkan's goniotomy knife is passed through the limbus on the temporal side. Under gonioscopic control the knife is passed across the anterior chamber to the nasal part of the angle. An incision is made in the angle approximately midway between root of the iris and Schwalbe's ring through approximately 75°. The knife is then withdrawn. Although the procedure may have to be repeated, the eventual success rate is about 85 percent.
2. Trabeculotomy. This is useful when corneal clouding prevents visualization of the angle or in cases where goniotomy has failed. In this, canal of Schlemm is exposed at about 12 O'clock position by a vertical scleral incision after making a conjunctival flap and partial thickness scleral flap. The lower prong of Harm's trabeculotome is passed along the Schlemm's canal on one side and the upper prong is used as a guide. Then the trabeculotome is rotated so as to break the inner wall over one quarter of the canal. This is then repeated on the other side. The main difficulty in this operation is localization of the Schlemm's canal.
3. Combined trabeculotomy and trabeculectomy is now-a-days the preferred surgery with better results.
PRIMARY OPEN ANGLE GLAUCOMA
Etiology
Etiopathogenesis of POAG is not known exactly. Some of the known facts are as follows:
Predisposing and risk factors. These include the following:
1. Heredity. POAG has a polygenic inheritance. The approximate risk of getting disease is 10% in the siblings, and 4% in the offspring of patients with POAG.
2. Age. The risk increases with increasing age. The POAG is more commonly seen in elderly between 5th and 7th decades.
3. Race. POAG is significantly more common, develops earlier and is more severe in black people than in white.
4. Myopes are more predisposed than the normals.
5. Diabetics have a higher prevalence of POAG than non-diabetics.
6. Cigarette smoking is also thought to increase its risk.
7. High blood pressure is not the cause of rise in IOP, however the prevalence of POAG is more in hypertensives than the normotensives.
8. Thyrotoxicosis is also not the cause of rise in IOP, but the prevalence of POAG is more in patients suffering from Graves' ophthalmic disease than the normals.
Pathogenesis of rise in IOP. It is certain that rise in IOP occurs due to decrease in the aqueous outflow facility due to increased resistance to aqueous outflow caused by age-related thickening and sclerosis of the trabeculae and an absence of giant vacuoles in the cells lining the canal of Schlemm. However, the cause of these changes is uncertain.
Corticosteroid responsiveness. Patients with POAG and their offspring and sibilings are more likely to respond to six weeks topical steroid therapy with a significant rise of IOP
Characteristical signs
1. The disease is insidious and usually asymptomatic, until it has caused a significant
loss of visual field. Therefore, periodic eye examination is required after middle age.
2. Patients may experience mild headache and eyeache.
3. Occasionally, an observant patient may notice a defect in the visual field.
4. Reading and close work often present increasing difficulties owing to accommodative failure due to constant pressure on the ciliary muscle and its nerve supply. Therefore, patients usually complain of frequent changes in presbyopic glasses.
5. Patients develop delayed dark adaptation, a disability which becomes increasingly disturbing in the later stages.
Work-up
1. Anterior segment signs. Ocular examination including slit-lamp biomicroscopy may reveal normal anterior segment. In late stages pupil reflex becomes sluggish and cornea may show slight haze.
2. Intraocular pressure changes. In the initial stages the IOP may not be raised permanently, but there is an exaggeration of the normal diurnal variation.
Therefore, repeated observations of IOP (every 3-4 hour), for 24 hours is required during this stage (Diurnal variation test).
3. Optic disc changes. Optic disc changes, usually observed on routine fundus examination, provide an important clue for suspecting POAG. These are typically progressive, asymmetric and present a variety of characteristic clinical patterns. It is essential, therefore, to record the appearance of the nerve head in such a way that will accurately reveal subtle glaucomatous changes over the course of follow-up evaluation.
4. Visual field defects. Visual field defects usually run parallel to the changes at the optic nerve head and continue to progress if IOP is not controlled. These can be described as early and late field defects.
INVESTIGATIONS
1. Tonometry. Applanation tonometry should be preferred over Schiotz tonometry (see page 479).
2. Diurnal variation test is especially useful in detection of early cases
3. Gonioscopy. It reveals a wide open angle of anterior chamber. Its primary importance in POAG is to rule out other forms of glaucoma. For details
4. Documentation of optic disc changes is of utmost importance
5. Slit-lamp examination of anterior segment to rule out causes of secondary open angle glaucoma.
6. Perimetry to detect the visual field defects.
7. Nerve fibre layer analyzer (NFLA) is a recently introduced device which helps in detecting the glaucomatous damage to the retinal nerve fibres before the appearance of actual visual field changes and/or optic disc changes.
8. Provocative tests are required in border-line cases. The test commonly performed is water drinking test. Other provocative tests not frequently performed include combined water drinking and tonography, bulbar pressure test, prescoline test and caffeine test.
Differential diagnose
Elevated episcleral venous pressure/carotid cavernous fistula.
Iridocorneal endothelial (ICE) syndrome.
Uveitis-glaucoma-hyphema (UGH) syndrome
Angle recession refers to a tear between the circular and longitudinal fibers of the ciliary body. Cyclodialysis is defined as a detachment of the ciliary body from its insertion at the scleral spur. Iridodialysis is separation of the iris root from its attachment to the anterior ciliary body. By comparison, iridoschisis refers to splitting of layers of iris stroma. All of these conditions are sequelae of blunt ocular trauma, and any of these conditions may coexist
Treatment
1. Identification of target pressure.)
2. Single drug therapy. One topically instilled antiglaucoma drug should be chosen after due consideration to the patient's personal and medical factors. If the initial drug chosen is ineffective or intolerable, it should be replaced by the drug of second choice.
3. Combination therapy. If one drug is not sufficient to control IOP then a combination therapy with two or more drugs should be tried.
4. Monitoring of therapy by disc changes and field changes and tonometry is most essential on regular follow-up. In the event of progress of glaucomatous damage the target pressure is reset at a lower level.
Drugs: Topical beta-blockers, Pilocarpine, Latanoprost, Dorzolamide, Adrenergic drugs.
Surgical therapy is also possible.
Follow up
Nonglaucomatous comorbidity in eyes with angle recession increases the risk of vision loss. Traumatic insults to the cornea, iris, lens, vitreous, retina, or optic nerve may contribute to vision-threatening sequelae.
Traumatic cataract often accompanies angle recession. Gonioscopy should always be performed when a patient with a unilateral cataract is evaluated, even when his or her history is negative for trauma.
After surgical management, the risk of complications is higher with a traumatic cataract than with a senile cataract. Intraoperative complications include the following:
- Zonular dialysis
- Vitreous loss
- Intraocular hemorrhage
- Inadequate posterior intraocular lens (IOL) support: Zonular injury is a common finding in such cases. When zonular defects are small, placement of the IOL into the capsular bag usually can be achieved without further complication. Placement of an anterior-chamber IOL is not preferred in eyes with even minimal angle recession, and it is fully contraindicated when the angle is recessed more than 180°.
Postoperative complications
- IOP elevation
- Inflammation
- IOL malposition
- Pupil capture
- Intraocular hemorrhage
-Glare
- Monocular diplopia: Symptoms may result from iris abnormalities.
SECONDARY GLAUCOMA
Depending upon the causative primary disease, secondary glaucomas are named as follows:
1. Lens-induced (phacogenic) glaucomas.
2. Inflammatory glaucoma (glaucoma due to
intraocular inflammation).
3. Pigmentary glaucoma.
4. Neovascular glaucoma.
5. Glaucomas associated with irido-corneal
endothelial syndromes.
6. Pseudoexfoliative glaucoma.
7. Glaucomas associated with intraocular
haemorrhage.
8. Steroid-induced glaucoma.
9. Traumatic glaucoma.
10. Glaucoma-in-aphakia.
11. Glaucoma associated with intraocular tumours.
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