Glaucoma laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Rohan Bir Singh, M.B.B.S.[2]
Overview
Laboratory Findings
A comprehensive eye exam is necessary to determine whether a patient has glaucoma. Checking the intraocular pressure alone (tonometry) is not enough to diagnose glaucoma because eye pressure changes. Furthermore, pressure in the eye is normal in about 25% of people with glaucoma (normal-tension glaucoma). There are other problems that cause optic nerve damage.
- Gonioscopy (use of a special lens to see the outflow channels of the angle)
- Optic nerve imaging (photographs of the inside of the eye)
- Pupillary reflex response
- Retinal examination
- Slit lamp examination / Dilated eye exam
- Visual acuity
- Visual field measurement
Structural Tests
- Tonometry: measuring the intraocular pressure and comparing with both population norms and with subsequent measurements over time. The Goldmann Applanation Tonometer is one example.
- Fundoscopy: stereoscopically viewing the optic nerve head and the retina, looking for characteristic glaucomatous signs and for changes in appearance over time. One important observation is the optic nerve's "cup-disc ratio". Fundus photos (stereoscopic or mono) may be taken to aid the clinician. The 3Dx Digital stereoscopic camera is one example.
- Pachymetry: using a variety of modalities to measure the thickness of the cornea, as a thin cornea is a risk factor for glaucoma.[1][2][3] Corneal pachymetry can also be used to calibrate the measured intraocular pressure for the patient's corneal thickness, as a thicker cornea tends to yield higher intraocular pressure readings.[4][5] The Tomey SP3000 is one example.
- Scanning laser ophthalmoscopy: using a scanning laser to quantify the appearance of the optic nerve head. The Heidelberg Retinal Tomographer (HRT)] is one example.
- Scanning laser polarimetry: using polarised light to measure the thickness of the retinal nerve fiber layer. The GDx-VCC is one example.
- Optical coherence tomography: using interferometry to obtain cross-sectional views of the retina and optic nerve head and to measure the thickness of the retinal nerve fiber layer. The Stratus OCT is one example.
For the latter three the quantified results are then statistically compared to age-matched population norms, and to subsequent scans of the same patient over time.
Functional Tests
- Automated perimetry: Each area in the patient's visual field is psychometrically tested to see how bright a given spot in that field must be for the patient to detect it. Thus a map can be made of the patient's sensitivity over their visual field and statistically compared to age-matched population norms and to subsequent tests of the same patient over time. Obviously the reliance on patients' response and attention is a factor in itself, one disadvantage of such subjective testing. The Medmont M700 is an example of standard automated perimetry, using a white spot over a white background. Newer instruments such as the Humphrey Matrix FDT use frequency-doubling technology to assess the function of a smaller subset of retinal cells, revealing glaucomatous visual field damage somewhat earlier than with standard perimetry.[6][7][8][9][10]
- Visually-evoked potential: to analyse the electrical activity of the visual cortex, assessing the function of the visual system "upstream" from the measured areas on the visual cortex. This has the advantage of assessing visual function without relying on subjective patient input. The EPIC-4000 is one example.
References
- ↑ Herndon L, Weizer J, Stinnett S (2004) Central Corneal Thickness as a Risk Factor for Advanced Glaucoma Damage. Arch Ophthalmol 122(1):17-21
- ↑ Jonas J, Stroux A, Velten I, Juenemann A, Martus P, Budde W (2005) Central Corneal Thickness Correlated with Glaucoma Damage and Rate of Progression. Investigative Ophthalmology and Visual Science. 46:1269-1274
- ↑ Medeiros F, Sample P, Zangwill L, Bowd C, Aihara M, Weinreb R (2003) Corneal thickness as a risk factor for visual field loss in patients with preperimetric glaucomatous optic neuropathy. American Journal of Ophthalmology 136(5):805-813
- ↑ Doughty M, Zaman M (2000) Human corneal thickness and its impact on intraocular pressure measures: a review and meta-analysis approach. Surv Ophthalmol 44(5):367-408
- ↑ Shah S, Chatterjee A, Mathai M, Kelly S, Kwartz J, Henson D, McLeod D (1999) Relationship between corneal thickness and measured intraocular pressure in a general ophthalmology clinic. Ophthalmology 106(11):2154-60
- ↑ Ferreras A, Polo V, Larrosa J, Pablo L, Pajarin A, Pueyo V, Honrubia F (2007) Can frequency-doubling technology and short-wavelength automated perimetries detect visual field defects before standard automated perimetry in patients with preperimetric glaucoma? J Glaucoma 16(4):372-83
- ↑ Wadood A, Azuara-Blanco A, Aspinall P, Taguri A, King A (2002) Sensitivity and specificity of frequency-doubling technology, tendency-oriented perimetry, and Humphrey Swedish interactive threshold algorithm-fast perimetry in a glaucoma practice. Am J Ophthalmol 133(3):327-32
- ↑ Kalaboukhova L, Lindblom B (2003) Frequency doubling technology and high-pass resolution perimetry in glaucoma and ocular hypertension. Acta Ophthalmol Scand 81(3):247-52
- ↑ Akiko N, Kyoko M, Mikio N, Naoyuki T, Tomoko U, Hiroshi O, Kiichiro Y (2004) Ability of Frequency Doubling Technology to Detect Early Glaucomatous Visual Field Changes. Folia Ophthalmologica Japonica 55(1):22-26
- ↑ Cello K, Nelson-Quigg J, Johnson C (2000) Frequency doubling technology perimetry for detection of glaucomatous visual field loss. Am J Ophthalmol 129(3):314-22