The glaucomatous eye
The pressure is on...
The pressure is on...
In the twenty first century glaucoma is understood as a loss of vision due to abnormally high intra-ocular pressure (IOP), which can take chronic or acute forms and as a condition which need not be, and most normally is not, associated with any other ocular disease.
The three tests of ophthalmoscopy, perimetry and tonometry permit routine screening for glaucoma, a procedure that is considered worthwhile because of the existence of effective means to control the condition via drops, tablets or in some cases surgical intervention. In the past the very nature of glaucoma was misunderstood and its occurrence often mistaken for, or confused with, associated conditions. The absence of a ‘cure’ and the risks inherent in forms of investigation involving contact with the eye discouraged developments in testing until a relatively late stage in ophthalmic history.
What was Glaucoma thought to be?
The earliest reference to glaucoma occurs in one of the Aphorisms contained within the so-called Hippocratic Books. Glaukosis meaning ‘to turn a diluted blue’, is reported as a disease of old age in which the pupil discolours. Historians now interpret this word as simply meaning ‘cataract’. Rufus (fl.98-115 AD) wrote about cataracts and mentioned how earlier authors had felt glaucoma and hypochyma (cataract) to be the same, but that later authors had distinguished them: Hypochyma in which there was an outpouring of crystalline fluid, which gelled and thus became surgically removable was a curable condition. Glaucoma, defined as a disease of this crystalline fluid, causing it to turn light blue, was incurable. As a disease of the crystalline lens, which was believed to be the seat of human vision (rather than the retina), it was felt that the visual loss was irreversible and this represented pretty much the last word on glaucoma in the West for several centuries.
Elsewhere in the world the Arabs demonstrated some awareness of Glaukosis, but very little of what we today call glaucoma. Tabarì, writing The Book about the Hippocratic Treatments in the second half of the tenth century, described chronic inflammatory glaucoma as one of four diseases of the retina. He also mentioned that many physicians wrongly believed eye pain to indicate brain disease. Shams Al-Dìn, who died in Egypt in 1348 described in The Discovery of Impurities in Ocular Diseases no fewer than 153 conditions, one of which was ‘Ocular Migraine’ [shaqì-qat al-‘ayn] also called ‘headache of the pupil’ [sudà‘al-hadaqah]. He said the cause was a substance retained in the blood vessels of the retina. This combined with opacification of the ocular fluids. Sometimes a cataract might develop and the pupil might dilate. It was treatable with purges, cleansing, and dropping a combination of egg white and milk into the eye. ‘Sometimes narcotics are necessary’.
For a more clear understanding of glaucoma the historian must look to the eighteenth century debate within the French Académie des Sciences as to the theory of cataract. Mery could pose the question in 1707: Are glaucoma and cataract two different diseases? (By ‘glaucoma’ he would have been thinking of opacification). Brisseau, one of the leading advocates of the ‘new cataract’ theory, realised that true glaucoma affects the vitreous (whilst the crystalline lens only appears to be affected). He developed his argument following experiments on an eyeball that had been sent to him preserved in alcohol.
St. Yves writing in 1722 (Traité des Maladies des Yeux Ch. XVI ‘Du Glaucome’) produced perhaps the first satisfying description of ocular hypertension. To him glaucoma was a ‘spurious cataract’ in which the patient sees a fog then loses vision and experiences pupillary dilation. The condition occasionally began with pain and there was a risk of the other eye following. St. Yves recommended enucleation as a means to protect the second eye.
Thomas Woolhouse was an English scientist who followed the exiled James II to Paris. He claimed to have ‘kept the great secret to himself how to differentiate infallibly between a curable cataract and an incurable glaucoma’. In later years he divulged the secret a little bit, describing, for example, how when looking through a cardboard pinhole a cataract patient would see moving threads whereas the patient in the early stages of glaucoma would see a series of bright unmoving circles.
In the early nineteenth century medical writers still seem to have been a bit confused. Glaucoma was identified as either a phenomenon of a paralysed retina or of the choroid. In 1813 the Viennese professor Joseph Beer wrote in Die Lehre von den Augenkrankheiten the first description of glaucoma by a true practising ophthalmologist, as opposed to a mere cataract surgeon. Beer described an inflammatory glaucoma with dilation of the pupil which he had observed using a loupe. This enabled him to discern a sea-green opacification of the interior of the eye and a dull cornea ‘as we see it in the dead’. This is the first complete description such as was possible in pre-ophthalmoscope days. Beer also promoted a treatment involving the excision of part of the iris to prevent pupillary occlusion. The subject was then also well summarised by Antoine Pierre Demours whose Précis théorique et pratique sur les maladies des yeux, published very shortly afterwards, in 1821, defined glaucoma as a disease of advanced age, of irritable nervous systems and of gouty or rheumatic patients. Demours noted that, within six months, the eye that could read fine print would be unable to see sunlight.
In 1830 MacKenzie of Glasgow was the first to suggest relief of the retina by puncturing the sclera and choroid using a broad iris knife to drain the liquefied vitreous fluid. He opposed enucleation but did advocate removal of the crystalline lens as reducing the green colour and improving the patient’s vision.
By the mid nineteenth century glaucoma was properly understood (by a limited but influential number of people) as a condition caused by a rise in IOP, which might result in spontaneous arterial pulsation. The short-lived Albrecht von Graefe, the Berlin ophthalmologist, first promoted his idea that glaucoma could be cured (as opposed to its effect on vision merely being tempered) by iridectomy. Sir William Bowman was one of the first to appreciate this and was the first to perform it in England in May 1857. Of note here is the significance of the recent invention of the ophthalmoscope (1852) and Bowman’s enthusiasm for it. The Moorfields surgeon J. W. Hulke, an assistant to Bowman, was another who wrote about both the ophthalmoscope (producing the first English monograph on the subject) and glaucoma.
Observation of the optic disc, via ophthalmoscopy, and the prospect of a surgical ‘cure’ by iridectomy encouraged those who sought more effective means to test for glaucoma. This led to the development of a specific instrument, the tonometer.