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Glaucoma Clinical Optic Disc Evaluation Clinical Optic Disc Evaluation in Glaucoma A l e x a n d r e S C R e i s , 1,2 A n d r e w T o r e n 3 a n d M a r c e l o T N i c o l e l a 4 1. Research Fellow, Department of Ophthalmology and Visual Sciences, Dalhousie University, Halifax, Nova Scotia, Canada; 2. Research Fellow, Department of Ophthalmology, University of Sao Paulo, Brazil; 3. Resident; 4. Associate Professor, Department of Ophthalmology and Visual Sciences, Dalhousie University, Halifax, Nova Scotia, Canada Abstract Examination of the optic nerve head (ONH) is essential for the diagnosis of glaucoma and assessment of its progression. Slit-lamp biomicroscopy with a handheld lens is the best method of ONH examination since it provides good stereopsis and magnification. ONH stereo photographs are complementary and may identify findings missed on slit-lamp examination. As a result of its subjective nature, a standardised approach should be utilised for clinical ONH evalaution, including an assessment of ONH size and careful evaluation of the neuroretinal rim contour, the presence of retinal nerve fibre layer (RNFL) defects and optic disc haemorrhages. Other aspects, such as peripapillary chorioretinal atrophy, vessel alterations and asymmetry between fellow eyes, might help differentiate normal from glaucomatous eyes. Progressive changes in the appearance of the ONH or RNFL are best identified with optic disc photographs or automated devices. The findings of clinical ONH evaluation are of greater value when corroborated with other aspects of clinical examination and clinical test. Keywords Optic disc, open-angle glaucoma, ophthalmoscopy, stereo photography, retinal nerve fibre layer, clinical examination, optic disc haemorrhage Disclosure: The authors have no conflicts of interest to declare Received: 15 October 2011 Accepted: 7 March 2012 Citation: European Ophthalmic Review, 2012;6(2):92–7 Correspondence: Marcelo T Nicolela, Department of Ophthalmology and Visual Sciences, Dalhousie University, 1276 South Park Street, Room 2035, Halifax, NS, Canada, B3H 2Y9. E: nicolela@dal.ca The detection of structural damage to the optic nerve head (ONH) is central to the diagnosis of glaucoma and is extremely important for monitoring patients at risk of glaucoma or with established disease. Glaucoma, by definition, is an optic neuropathy and therefore specific attention must be directed to the examination of the optic nerve. The ONH is the site at which the dropout of retinal ganglion cells is identified most easily with current clinical techniques and is postulated as the primary site for damage in glaucoma. 1–3 Careful evaluation of the ONH and peripapillary tissues can usually identify early glaucomatous damage before detectable visual field loss occurs. 4,5 The main difficulties in the clinical assessment of the ONH relate to its inherent subjectivity, and to the overlapping spectrum and large diversity in the appearance of normal and diseased discs. Early progressive glaucomatous changes in the ONH are subtle and may be missed without careful serial examinations of the individual’s optic disc. Additionally, there is currently no quick, simple, inexpensive, specific, sensitive and objective method of ONH analysis by which glaucoma is reliably diagnosed and progression detected. Clinicians should be aware that optic disc evaluation requires not only an understanding of the normal disc appearance and the pathological process of glaucoma, but also training and clinical experience. It is essential to associate the findings of the ONH evaluation with those of the clinical history, clinical examination (such as refractive error, presence of afferent pupillary defect and intraocular pressure [IOP]) and visual field tests. This review article highlights the most relevant aspects of clinical ONH evaluation: the relevant anatomy, examination 92 techniques and clinical signs linked to glaucomatous damage and their relevance to patient care. The Normal Optic Nerve Head The ONH, or optic disc, is the location where the axons from the retinal ganglion cells converge to exit the eye through the scleral canal. Besides axons, the ONH consists of blood vessels, glia and connective tissue. The size of the scleral canal governs the size of the ONH: eyes with small canals have small optic discs (commonly seen in high hyperopia) and those with large canals have large discs (commonly seen in high myopia). Jonas et al. measured the size of the scleral canal in 107 enucleated human donor eyes. 6 They found a high inter-individual variability with an average area of 2.59 mm 2 , ranging from 0.68 to 4.42 mm 2 . The edges of the scleral canal define the optic disc margin, which is clinically visible as a whitish circular band at the edge of the optic disc. The ONH is usually vertically oval, with an average dimension of 1.92 ± 0.29 mm (0.96–2.91 mm) vertically, and 1.76 ± 0.31 mm (0.91–2.61 mm) horizontally, and a surface area of 2.69 ± 0.70 mm 2 (0.80–5.54 mm 2 ). 6 Jonas and Papastathopoulos proposed that in routine practice, the clinician need not measure the exact numerical value of the disc size, but instead use a quick, crude estimate of whether the size of the disc in question is of average size, smaller than average or larger than average (Figure 1). 7 The optic cup is a central pale depression in the ONH not occupied by neural tissue. The pale colour of the cup is a result of exposure of the lamina cribrosa and loss of glial tissue. There is a physiological relationship between optic disc size and cup size, so that large optic © TOUCH BRIEFINGS 2012