**15. Goldman applanation tonometry**

depends of abnormal resistance to aqueous outflow caused by anatomic or functional

Not until the 1890s did open-angle glaucoma become well proved and accepted in theories.

Thanks to gonioscopy, started recognition of a type or types of glaucoma without obstruc‐

In the first edition of the Graefe-SaemischHandbook of Ophthalmology (1877), Saemisch lists the following ocular diseases as frequently giving rise to secondary glaucoma: cicatri‐ cial ecstasies of the cornea, circular or total adhesions of the iris to the lens, iritis serosa, trau‐ matic cataract, dislocations of the lens, intraocular tumours, hemorrhagic retinal processes (referring mainly, if not exclusively, to occlusions of the central retinal vein), and sclerectasia pastries (which probably referred to glaucoma in eyes with malignant myopia). Congenital

William Bowman introduced digital estimation of the ocular tension at the annual meeting of the British Medical Association in 1862. Estimation of the ocular tension by palpation be‐ came one of the ophthalmologist's special skills, and some ophthalmologists developed so

The early beginning of instrumental tonometry, apparently made by von Graefe, who men‐ tions preliminary trials of mechanical tonometers in a letter to Donders dated December 24, 1862. Unfortunately, none of these instruments, however, reached the drawing board stage.

The real beginning and the first tonometers actually produced and tested on human eyes were developed in Donders' clinic in Utrecht between 1863 and 1868. They were instruments for use on the sclera. The scleral curvature at the site of tonometer application was deter‐ mined first; it then served as a reference plane for the measurement of the depth of the in‐

Impression tonometry had its drawbacks. The principal flaw was that the indentation, by displacing a significant amount of intraocular fluid, changes the pressure which is intended to measure; this was clearly expressed for the first time by AdoIf Weber in 1867. Weber was official inventor of the first applanation tonometer, which was intended to give a tension reading with only minimal fluid displacement. Despite its theoretic superiority, this instru‐ ment did not gain wide acceptance, because recognition of the point of perfect applanation without indentation proved to be difficult. Lately, the principles of applanation tonometry were explored by Maklakoff in 1885. andImbert and Fick, father and son, a few years later. It

hydrophthalmos was at the time also classified with the secondary glaucomas.

much confidence in it that they viewed instrumental tonometry with suspicion.

changes within the outflow channels.

tion of the angle by the iris.

284 Glaucoma - Basic and Clinical Aspects

**13. Secondary glaucomas**

**14. Tonometry**

dentation.

The technology to estimate intraocular pressure (IOP) has evolved tremendously since Sir William Bowman emphasized the importance of ocular tension measurements in 1826. In an address delivered at the annual meeting of the British Medical Association, Sir William un‐ derscored the critical role that digital estimation of ocular tension played in his practice. In his address, Sir William stated that "it is now my constant practice, where defective vision is complained of, to ascertain almost at the first instant the state of tension in the eye...It is easy enough to estimate the tension of the eye, though there is a right and a wrong way of doing even so simple a thing... With medical men, the touch is already an educated sense, and a very little practice should suffice to apply it successfully to the eye."[44]

Soon afterwards, digital tonometry became an essential clinical skill necessary to master by all ophthalmologists. When mechanical tonometry was first introduced in the late 1800s, many ophthalmologists felt so confident with their ability to estimate IOP by palpation that they viewed the new technology as inferior. Isador Schnabel, in an address to the Vienna Ophthalmological Society in 1908, was noted to state that although he did not object in prin‐ ciple to mechanical tonometry, he expected "…very little from this test since digital tonome‐ try by an expert is a much more accurate test".[45]

**16. Perimetry**

step [46].

Modern diagnostic of glaucoma is unimaginable without perimetry. The merit for meas‐ urements of peripheral vision for the diagnosis and follow-up of ocular disease, as many other things in ophthalmology, is attributed to Albert von Graefe. With a primitive campimeter—a sheet of paper with radial rows of dots which served as stimuli—he was probably the first (1856) to plot paracentral field defects in chronic glaucoma and to use them in the evaluation of surgical results. Similar to von Graefe's device, Haffmanns from Donder's clinic discovered the greater frequency in glaucoma simplex of serious in‐ volvement of the upper half of the field, which gave rise to an easily detectable nasal

The History of Detecting Glaucomatous Changes in the Optic Disc

http://dx.doi.org/10.5772/52470

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In 1857.Förster introduced the first perimeter, which placed accent on large targets, such as the 10/330, which permitted only very gross measurements. The observations of that time did suggest partial reversibility of field defects if the pressure was lowered substan‐ tially by an iridectomy or sclerotomy. 1889. was a very important year for a develop‐ ment of techniques most appropriate for glaucoma. Bjerrum presented 2-meter screen, the 2-meter test distance, and the 2- to 5-ram white test objects. He discovered the rela‐ tive or absolute scotomas, circling the point of fixation and including the blind spot, which became the hallmark of chronic glaucoma. Conceptually, it means the beginning

Further major step was the occurrence of small scotomas in the zone from 12° to 20° from the point of fixation, in early glaucomas, presented by Peter [47]. These scotomas, in the be‐ ginning were not connected with the blind spot, but they reached it later via expansion.

The construction of smaller isopters, another early glaucoma characteristic, presented in 1920s, was clearly established with Bjerrum's technique. Bjerrum's technique also confirmed the regression of early glaucomatous defects following normalization of pressure document‐ ed by instrumental tonometry. The close relationship between pressure and field of vision was demonstrated further by Samojloff's observations [48]of temporary enlargement of the blind spot concurrent with osmotically induced pressure elevations. By stereocampimetry with minute targets, Evans was able to detect a gross form of parallelism between diurnal

Also in 1920s was noticed that among patients with glaucomatous defects close to the point of fixation (late stages of glaucoma optic neuropathy), a surgical procedure, partic‐ ularly iridectomy, could have an untoward effect and lead to further rapid shrinkage of the visual field. The incrimination of the iridectomy referred originally to the period when the alternative, the sclerotomy, had proved relatively free of unfavourable effects on the visual field. Subsequent experience with filtering operations temporarily led to the distinction between two classes of glaucoma operations: 1) the less risky: cyclodialy‐

sis and sclerotomy and 2) the riskier: iridectomy, sclerectomy, and trephination.

of the nerve fibre bundle theory of the glaucomatous optic nerve disease.

pressure fluctuations and the size of paracentralscotomas[49].

Although Grafe is credited with the first attempts to create instruments that mechanically measured IOP in the early 1860s, his proposed instruments were neither designed nor built. Rather, it was Donders who designed the first instrument capable of estimating IOP – albeit not accurately – with mechanical tonometry in the mid 1860s. The principle behind Dond‐ ers's instrument was to displace intraocular fluid by contact with the sclera. The ophthal‐ mologist first measured the curvature of the sclera at the site of contact, and then used this measurement as a reference plane to measure the depth of indentation. Smith and Lazerat refined this technology in the 1880s, and the discovery of cocaine by Carl Koller in 1884 led the way to corneal impression tonometry soon thereafter. With the aid of a powerful corneal anesthetic agent, corneal tonometry became the definitive choice of IOP measurements be‐ cause it offered a well – defined and uniform site of impression when compared with the sclera.

Impression tonometry's major shortcoming was that it displaced so much fluid upon contact with the eye that the measured readings were highly variable and mostly inaccurate. What was needed was a way to displace a minimal amount of fluid to record IOP. This break‐ through came when Adolf Weber designed the first applanation tonometer in 1867, which gave a highly defined applanation point without indentation. After two decades of skepti‐ cism, the value of applanation tonometry was re-discovered when Alexei Maklakoff and others introduced new versions of applanationtonometers. In early 20th century, there were about 15 models of tonometers in use. In fact, Maklakoff's 1892 model is the basis of appla‐ nation tonometry today. However, digital tonometry still remained the gold standard among most ophthalmologists in the early 1900s.

The first clinically useful mechanical tonometer was designed and introduced by Hjalmar‐ Schiotz in the early 1900s. The instrument was simple, easy to use, and highly precise. It was quickly accepted and became the new gold standard beginning the 1910s. Innovations in calibration led to its increased use, and a tremendous amount of knowledge about the nor‐ mal and glaucomatous eye was quickly acquired. An adjustment for ocular rigidity was in‐ troduced by Goldmann in the 1950s, which led to the development of Goldmannapplanationtonometers. The Goldmanntonometers displace such little fluid that variations in ocular rigidity are mostly negligible. The electronic and non – contact tonome‐ ters used today rely heavily on the principles and instrumentation first introduced by Ma‐ klakoff, Schiotz and Goldmann.

Today, for the most part, digital tonometry has been replaced by sophisticated technologies to estimate IOP. Today's instruments are incredibly accurate and easy to use. Yet, there is sometimes no good substitute for digital tonometry. For example, some ophthalmologists may prefer digital tonometry when estimating IOP in patients with keratoprostheses. In these situations, fingers that have mastered Sir William's art are highly desirable. In fact, it is said that the famous Dr. Claus Dohlman, Harvard professor of Ophthalmology at the Mas‐ sachusetts Eye and Ear Infirmary, remains as accurate in measuring IOP with his fingers as any ophthalmologist using the high-tech tonometers of today!
