Glaucoma Diagnosis – The Role of Optic Nerve Examination

European Ophthalmic Review, 2007:15-7 DOI:
Received: January 17, 2011 Accepted January 17, 2011 Citation European Ophthalmic Review, 2007:15-7 DOI:

Glaucoma is a chronic progressive disease that, left untreated, can lead to blindness. Glaucoma represents a range of conditions in which the flow of aqueous humour in the eye is blocked, causing an increase in intraocular pressure (IOP). An impaired blood flow to the optic disc may also cause glaucoma, even without an abnormally high IOP. Even with careful monitoring and lowering of IOP, approximately 25% of patients lose their sight.1 Consequently, glaucoma is the second most common cause of blindness worldwide.

The global prevalence of glaucoma was estimated to be 67 million in 2001.2 Approximately 13% of these were estimated to be in Europe, of which half were undiagnosed and untreated. The most prevalent type of glaucoma, primary open-angle glaucoma (POAG), has subtle symptoms early in its course and, consequently, often remains undetected. Late diagnosis of glaucoma significantly increases the cost of treatment and raises the risk of visual impairment.3 Historically, an increased level of IOP was presumed to be the most accurate means of diagnosis; however, it is now recognised that high IOP is a risk factor for glaucoma, but is not an accurate diagnostic. Therefore, there is a need for an accurate diagnosis system.

Glaucoma Diagnosis – The ‘Gold Standard’ Tests
In glaucoma, structural changes usually occur first and are followed by functional deficits. There are three well-established ‘gold standard’ tests used by ophthalmologists to diagnose glaucoma: IOP measurements, visual field tests and (stereoscopic) assessments of the optic nerve. Together, these methods provide information on both structural and functional defects.

Intraocular Pressure
A gradual increase in IOP has long been recognised as the major risk factor for glaucoma, and the lowering of IOP serves to impede progression of optic nerve damage. Therefore, IOP measurements are usually documented over time.4 The Goldmann applanation tonometer is the standard device used by physicians to detect alterations in IOP. The device can accurately measure IOP in the eye with a small deviation of 0.5mmHg.5

Although the device is fairly accurate, the measurement of IOP is not always a precise indication of glaucoma. Individually, IOP is highly variable, and even low IOP cannot be ruled out for risk of glaucoma. Additionally, IOP does not indicate the extent of damage or, indeed, that damage has actually been done to the optic nerve. Thus, in the diagnosis of glaucoma this variable can be used only alongside other evidence for a positive outcome.

Peripheral vision is usually the first to deteriorate in glaucoma; hence, tests of the visual field have been used to diagnose the disease. Perimetry is a systematic measurement of light sensitivity in the visual field by the detection of targets presented on a defined background. The standard diagnostic tool for visual field examination is the computerised field analyser. Responses are statistically analysed and compared with a database of normal responses. Even with this comparison it is challenging to state definitively whether a patient has glaucoma. Previously, for detecting any progression the test results were judged by comparing print-outs from visual field tests, which was time-consuming and often inaccurate. Today, new software provides ophthalmologists with automated visual-field-progression analysis; however, it may take three examinations before an accurate baseline is obtained. Also, long-term fluctuations in the field tests can often occur, thus the accuracy of this method of diagnosis is still in question.

  1. Leydhecker W, Graner E, Long-term studies of visual field changes by means of computerised perimetry in eyes with glaucomatous field defects after normalisation of the intraocular pressure, Int Ophthalmol, 1989;13:113–17.
  2. Michelson G, Groh MJ, Screening models for glaucoma, Curr Opin Ophthalmol, 2001;12:105–11.
  3. Traverso CE, Walt JG, Kelly SP, et al., Direct cost of glaucoma and severity of the disease; a multinational long-term study of resource utilization in Europe, Br J Ophthalmol, 2005;89;1245–9.
  4. The Advanced Glaucoma Intervention Study (AGIS); The AGIS Investigators, The relationship between control of intraocular pressure and visual field deterioration, Am J Ophthalmol, 2000;130(4):429–40.
  5. Sandhu SS, Chattopadhyay S, Birch MK, et al., Frequency of Goldmann applanation tonometer calibration error checks, J Glaucoma, 2005;14(3):215–18.
  6. Reus NJ, de Graaf M, Lemij HG, Accuracy of GDx VCC, HRT I and clinical assessment of stereoscopic optic nerve head photographs for diagnosing glaucoma, Br J Ophthalmol, 2007;91(3):313–18.
  7. Reus NJ, Lemij HG, European Optic Disc Assessment Trial (EODAT) group, Assessment of stereoscopic optic disc photographs in glaucoma by European ophthalmologists, Invest Ophthalmol Vis Sci, 2007;48:E-Abstract 1970.
  8. Sommer A, Katz J, Quigley HA, et al., Clinically detectable nerve fiber atrophy precedes the onset of glaucomatous field loss, Arch Ophthal, 1991;109:77–83.
  9. Colen TP, Lemij HG, Motion artifacts in scanning laser polarimetry, Opthalmology, 2002;109:1568–72.
  10. Greenfield D, Knighton RW, Huang X, Effect of corneal polarization axis on assessment of retinal nerve fiber layer thickness by scanning laser polarimetry, Am J Ophthalmol, 2000;129:715–22.
  11. Knighton RW, Huang X, Linear birefringence of the central human cornea, Invest Ophthalmol Vis Sci, 2002;43:82–6.
  12. Weinreb RN, Bowd C, Zangwill LM, Glaucoma detection using scanning laser polarimetry with variable corneal polarization compensation, Arch Ophthalmol, 2003;121(2):218–24.
  13. Medeiros FA, Zangwill LM, Bowd C, et al., Fourier analysis of scanning laser polarimetry measurements with variable corneal compensation in glaucoma, Invest Ophthalmol Vis Sci, 2003;44: 2606–12.
  14. Shuman H, Murray J, DiLullo C, Confocal microscopy: an overview, Biotechniques, 1989;7:154–63.
  15. Chauhan BC, McCormick TA, Nicolela MT, et al., Optic disc and visual field changes in a prospective longitudinal study of patients with glaucoma, Arch Ophthalmol, 2001;119:1492–9.
  16. Huang D, Swanson EA, Lin CP, et al., Optical coherence tomography, Science, 1991;254(5035):1178–81.
  17. 17. Schuman JS, Hee MR, Arya AV, Optical coherence tomography: a new tool for glaucoma diagnosis, Curr Opin Ophthalmol, 1995;6(2):89–95.
  18. Sihota R, Sony P, Gupta V, Diagnostic capability of optical coherence tomography in evaluating the degree of glaucomatous retinal nerve fibre damage, Invest Ophthalmol Vis Sci, 2006;47(5):2006–10.
  19. Schuman JS, Pedut-Kloizman T, Hertzmark E, et al., Reproducibility of nerve fiber layer thickness measurements using optical coherence tomography, Ophthalmology, 1996; 103(11):1889–98.
  20. Medeiros FA, Zangwill LM, Bowd C, et al., Comparison of the GDx VCC scanning laser polarimeter, HRT II confocal scanning laser ophthalmoscope, and stratus OCT optical coherence tomograph for the detection of glaucoma, Arch Opth, 2004; 122:827–37.
  21. Deleón-Ortega JE, Arthur SN, McGwin G Jr, et al., Discrimination between glaucomatous and nonglaucomatous eyes using quantitative imaging devices and subjective optic nerve head assessment, Invest Opth Vis Sci, 2006;47:3374–81.