MACHO 3

Eye Department KCMC Newsletter

Issue 1 Volume 2 Serial 3                                                                          30^th March 2012

The Role of Visual Field Analysis in Glaucoma                                     William Makupa

Primary Open Angle Glaucoma is defined as optic neuropathy with visual field defects whereby increased intra-ocular pressure is the main risk factor. Therefore by definition it is a disease of the optic nerve, where gradually the axons connecting the eyeball to the brain get destroyed by increased pressure of the aqueous humour. Loss of axons, seen clinically as excavation (cupping) of the optic disc results in visual field defects, this is because the areas represented by the destroyed axons are not transmitting impulses to the brain anymore.

The cause of increased intra-ocular pressure is a complex one, has to do with deficient drainage of the trabecular meshwork. There is a strong genetical component to developing Primary Open Angle Glaucoma. In case of Secondary Open Angle Glaucoma the causes for clogging up of the trabecular meshwork are usually obvious clinically, be it exfoliation, pigment, red blood cells (usually related to injury) or lens proteins.

Clinically a glaucoma patient might have difficulty in expressing the symptoms, some of the patients will vaguely describe the advanced visual field loss as visual disturbance. It is very important for the eye healthcare cadre to understand that glaucoma is an asymptomatic eye disease. The first tell tale sign is either increased intra-ocular pressure or cupped disc, depending on the skills and knowledge of the examiner. Intra-ocular pressure is not measured routinely in set ups relying on Schiøtz tonometer. Disc assessment using a direct ophthalmoscope needs skill and versatility and should be a routine examination by all eye healthcare cadres. The severity of glaucoma in our setting is graded by the extent of disc excavation, 0.3 cupping is considered healthy and 0.9 cupping is considered severe. Optic disc cupping evaluation is a subjective matter at best of times, hence the role of visual field analysis.

Since February 2009, the Eye Department KCMC had a Carl Zeiss Humphrey Visual Field Analyser Model 740i. This equipment is an automated visual field analyser, which is easy to administer and gives accurate perimetric readings. Before acquiring it we were relying on a manual Goldman perimeter that had broken down, it took a long time to administer, relied on optometrists who were always busy with other tasks and could not accurately plot scotomata.

After the excitement of this new equipment had died down, we got to the task of training one of our medical attendants to be the Visual Field Technician, this was done successfully. Within three months Howard Kitonka was administering the perimetric test as well as any other perimetrist. To make it accessible the test cost only Sh 10,000/= and there is a waiver for those too poor to pay.  Ideally every glaucoma patient should have the test done once a year, to determine whether the disease has been arrested by the treatment offered or it is progressing nevertheless. Also it enables the clinicians to decide whether the glaucoma damage is too advanced to risk filtration surgery so as to opt for other kinds of treatment. Lastly it is an essential tool for neurologists to locate central nervous system lesions.

Going back to the definition of glaucoma, visual field defects are the most accurate clinical signs of the disease, their progression correlates with diseases progression and finally in cases of normal tension glaucoma, visual field defects may be the only clinical sign confirming the diagnosis.  

Visual Field Assessment at KCMC.

          Eye Health Care Services available at KCMC are:

1. Optical services, complete with refraction, prescription and making of eye glasses for both adults and children
2. Complete ophthalmolgical consult, with paraclinical diagnostic tools such as: automated refraction, keratometry, pachymetry, cornea topography,  ophthalmic ultrasound, automated perimetry, fundus colour photography, fundus flourescein angiography and optical coherence tomography.
3. Comprehensive ocular surgical services, biometry is performed in each cataract patient to calculate the power of intraocular lens to be implanted with the aim of achieving best possible outcome.
4. Ocular pharmacy stocked to cater for basic and necessary ocular therapeutics
5. Rehabilitative services for the visually impaired are available with a range of low vision devices.
6. The Eye Department in collaboration with its partners (CBM and EACO), conducts Day Eye Diseases Screening Outreaches within Kilimanjaro Region  every week to screen the population for sight threatening conditions and transports to hospital all those who need intervention. Also Week-Long Eye Surgical Outreaches (Surgical Outreach or Surgical Safari) are conducted to places too far from KCMC but the need for care exists.     

Editor: W. Makupa, Eye Department KCMC, P.O.Box 3010 Moshi – Tanzania

Tel: +255 784 332 667 Fax: +255 27 275 4381 Email: makupauw@yahoo.com