Automated perimetry is the current gold standard to diagnose and manage glaucoma. The main aim of this book is to help the ophthalmologist to understand the basic fundamentals of automated static perimetry, to select the most appropriate test to the clinical condition one is dealing with, to understand the visual field printouts and to interpret the printouts without much difficulty so that one should be able:
- To identify a field defect.
- To decide whether the field defect is due to glaucoma.
- To set target intraocular pressure (IOP).
- To make a reasonable decision whether the defect is progressive or not.
REASONS FOR COMPUTERIZED PERIMETRY
- Reproducible testing conditions.
- Data-storage capability: Results can be compared overtime and analyzed using expert system software.
- More sensitive testing. Many researchers claim static perimetry to be superior to kinetic perimetry to identify defects.
- Easy operation and menu-driven software make automated perimetry easy to learn and to use.
- Requires little technician training for reliable results.
HISTORY
1970: The original octopus perimeter was first introduced. It never gained popularity due to its very large room size and high expense.
1982: Humphrey field analyzer was first displayed at American Academy of Ophthalmology.
1983: August-Michael Patella showed its first clinical trial.
1984: February-started production and became very popular because of its small size and affordable price.
ROLE OF VISUAL FIELDS IN THE FIELD OF OPHTHALMOLOGY
Every ophthalmologist in his/her daily practice requires visual fields mainly for two purposes:
- To diagnose various clinical conditions:
- Ocular conditions—glaucoma and optic nerve disorders
- Central nervous system (CNS) conditions—optic nerve pathway disorders, CNS tumors and occipital lobe disorders)
- To manage glaucoma.
Role of Visual Fields in Making a Diagnosis
The loss of retinal sensitivity will present in three forms: Localized form, uniform generalized form and irregular generalized form with a definite pattern of the field defect, from which we diagnose various conditions. So, we must know the pattern of the field defect even when it is masked by generalized depression due to cataract, media opacities, uncorrected refractive error, optic atrophy, etc. to diagnose various conditions.
The pattern of field defect in glaucoma: It depends on the stage of glaucoma. Visual fields are required to diagnose glaucoma at an early stage. In early stage it can present as nasal step, Seidel scotoma, irregular loss of sensitivity on either side of horizontal axis and isolated scotomas either in the arcuate nerve fiber zone or within 10° circle area around fixation.
The pattern of the field defect due to cataract: Mostly it is a uniform generalized field defect. Occasionally, it may present with irregular generalized field defect with more loss of sensitivity at the center. This type of field defect is usually seen in dense central lenticular opacities.
The pattern of the field defect due to optic nerve disorders:
- Optic neuritis—generalized depression, central scotomas.
- Anterior ischemic optic neuropathy—altitudinal field defects.
The pattern of the field defect due to tumor pressing the central binasal fibers of optic chiasma: Bitemporal hemianopia.
The pattern of the field defect due to occipital lobe infarcts: Homonymous hemianopia. The most important role of visual field is to tell us the pattern of the field defect through which we can diagnose various conditions.
Role of Visual Fields in the Management of Glaucoma
In established cases of glaucoma we need to know the details of the field defect regarding its location, extent, depth, direction of progression of the field defect and the foveal status. The target IOP will be decided on these factors. In advanced cases of glaucoma, we need to know the details of sensitivity around fixation point to explain the prognosis to the patient. Our aim in the management of glaucoma is to arrest progression of the field defect due to glaucoma. Hence we require a base line visual field and the follow-up fields preferably on a single sheet so that the comparison of the fields becomes easy. With this background the single field analysis printout and the overview printout have been developed.