LIVING WITH GLAUCOMA Volume 29, Number 1

Transcription

1 LIVING WITH GLAUCOMA Volume 29, Number 1 Fall 2014 DECODING THE VISUAL FIELD AND OTHER GLAUCOMA CONCERNS Dr. Daniel Laroche opened his address on September 20, 2014 at the Glaucoma Support group by complimenting the members on learning as much as they can about glaucoma in order to better handle this disease. He also referred to the educational videos available for purchase on the net produced by the American Academy of Ophthalmology and other organizations. Actually, we have scheduled such a video for one of our workshops. Dr. Laroche added that he provides I- Pads in his waiting room that inform patients about glaucoma and various eye diseases and their associated problems. Instruction on daily activities as instilling eyedrops are is also included. The videos run not more than 5 to 10 minutes. Assessing the visual field arouses anticipatory dread in many glaucoma patients. Not because it is called a test, although some of us shudder at the word test but because the results tell us whether glaucoma has progressed. I only know of one person who enjoyed the visual field. My husband with 20/ This newsletter is published by The Glaucoma Support and Education Group in participation with The Glaucoma Foundation 1

2 vision was tested for a retinal problem. He found it to be an interesting game. Glaucoma, of course, is no game. It is optic neuropathy characterized by optic nerve excavation called cupping. Most often it is associated with elevated pressure. As well, it can also be associated with decreased blood flow to the optic nerve. Preventing visual field loss in glaucoma patients is treated by lowering the intraocular pressure and by preserving good blood flow to the eye. The visual field was described by Traquair over a hundred years ago who called it an island of vision surrounded by a sea of blindness. Vision is limited to a window in front of the eye, a precious feature of the body that we need to try to preserve especially when glaucoma enters into the equation. Each eye, when intact, possesses 60 degrees above 60 degrees nasally 75 degrees below and 110 degrees wide from temporally. PERIMETRY: This is another name for a visual field. It involves a critical assessment of the visual field. There are generally two types of instruments used for this purpose. One, that is automated, the Humphrey Visual Field test is called a static test. The target is stationary and increases in light intensity from below threshold until you perceive it. To take the test you enter a darkened room, sit down and place your chin on a chin rest located in the outer center of a half dome. A series of lights are projected on the screen. This test is familiar to people who have glaucoma. Another option is the Goldmann Visual Field. This is called a kinetic test and it is administered by a technician who can ask you questions about whether or not you see the stimulus as it is bought in from the outside the field and is brought closer to the center until you indicate that see it. 2

3 Everyone s visual field possesses a blind spot that s located 15 degrees of central fixation. It is the place where the optic nerve inserts into the eye. On a visual field test this blind spot registers as a black spot. TAKING THE TEST: It is very important to be rested and focused for the test and position yourself properly. You will be sitting in the chair for at least a half hour and you will want to be as comfortable as possible. The technician administering the test who also should be present while you re taking it will see to it that you are sitting properly and are comfortable with the chin rest. If you become fatigued the technician can stop the test to give you a few moments rest, or on some machines, you can hold down the buzzer and it will stop the test for a few moments. You need to refrain from searching for the stimulus for that will make the test invalid that is described as fixation losses. Generally, the technician can see this action and corrects your lapse. Your untested eye should have a patch covering it to prevent interference with the eye being tested. The reading correction needs to be centrally placed and conform to your prescription. These are all important features to make sure your visual field reflects your best possible vision. Early glaucoma s visual field changes can present in different ways such as a generalized depression in the visual field, a slow concentric contraction of the visual field, an enlargement of the blind spot, a paracentral scotoma next to the area of central vision, (a rare challenging condition), or a nasal step. Some glaucomatous visual fields have an arcuate scotoma, an arc-shaped blind spot in the visual field caused by nerve fiber 3

4 layer damage in the retina. Temporal Islands and Central Islands indicate advanced glaucoma. Optic nerve damage precedes visual field loss. So in addition to learning the health of your visual field, you want to know about the health of your optic nerve. Here is where it is important to ask your ophthalmologist for an explanation of your condition. Other tests are available to measure vision loss. These consist of color vision, contrast sensitivity, electro- physiological assessment, frequency doubling perimetry, but the gold standard is the Humphrey Visual Field. Results of a visual field test are entered into a normative database and compared with a standard comprised of similar age individuals. The Humphrey uses a white- on- white screen, but other forms exist such as blue on yellow. The latter actually is best to help pick up earlier vision loss. When you initially take a visual field, your initial one may not be fully reliable but upon repeated tests your score improves. This is attributed to a learning curve, confirmed by studies. Repeated visual fields will be necessary to establish a baseline and to determine whether or not there is progression. The mean intraocular pressure in the general normal population registers 15mmHg. The mean intraocular pressure of a person with glaucoma charts about 18. But these are general readings. For those with advanced glaucoma doctors now attempt to bring pressures closer to 12. But each individual is treated uniquely. Corneal thickness may also help determine 4

5 what the pressure should be. People with thinner corneas may need a lower intraocular pressure. In examining a patient s eye the doctor checks to rule out other causes of visual field loss such as a retinal detachment. It is possible to examine the optic nerve in the doctor s office. Examination of the rim will reveal whether it is thin, a cause for concern or thick signifying health of the nerve. The nerve contains sets of fibers. The inferior fibers control the superior visual field, and the superior fibers control the inferior visual field. Basically your doctor assesses the entire condition of the nerve when the eye is dilated. THE Visual field PRINTOUT The printout identifies the patient s name and the date of the test and it contains information about the condition of your eye. When you look at the printout you want to be able to know which eye you re looking at. The blind spot on the right side is the right eye. The blind spot on the left side is the left eye. Initially, your doctor decides on the format that is best for you. There are three available options for the display on the screen. Generally, for glaucoma patients the setting is 24-2; If your doctor wishes to expand the range to a larger visual field, the setting can be increased to 30-2; for a central focused visual field where there is a great deal of peripheral depression, the setting can be reduced to The stimulus size, refraction, pupil width are also noted. Refraction may need to be performed to determine the lens needed for your visual field test. The size of your pupil also makes a difference in performance. There is a class of medications such as pilocarpine that constricts the pupil. Should this be so, your pupil will be 5

6 smaller than average and your doctor may then use a medication to dilate the pupil before the test is administered. The pupil should be at least 3 or 4 millimeters in width in order to do a valid test. If it is impossible to expand your pupil, the test results of the visual field will be depressed. Conditions such as a cataract can worsen the visual field. A large cataract will affect your performance on the Humphrey. A stroke can also affect the visual field. This is why your glaucoma doctor and your general practitioner should be in touch with each other for physical limitations may skew the results of the visual field. Test Reliability. Should you be confused about what you re seeing and randomly press the button in the hope that you ll hit some of the targets, the machine will out you and the test will be designated as unreliable. This doesn t mean that you re unreliable but it does mean that taking the test presents problems for you. There are a number of terms to describe your performance and the condition of your eye. False positive indicates an unreliable test. The machine retests a previously observed location using a much brighter stimulus. If you do not respond, perhaps because of fatigue or you just plain don t see it, the machine will register this as a False Positive. False Negative you do not respond to a stimulus that you should be able to see. With worsening vision the number of false negatives increases. Fixation loss: This is an important part of the visual field test. You must be able to fixate on the center dot. When you deviate and your eye starts to wander around, what you see 6

7 becomes invalid. It is tempting to search for the stimulus. Resist it for you may then need to repeat the test. You re instructed to look straight at the center dot. If your eye searches for the stimulus the machine will pick that up and register it as a fixation loss. MD stands for Mean Deviation: Essentially this is an overview. The numbers listed represent how many decibels your vision deviates from the norm. It is also an indicator of whether your vision is stable or progressing. There are a number of other terms that designate features in the visual field including but not limited to: A nasal step, paracentral defect, superior altitudinal defect is the loss of all or part of the superior half or the inferior half of the visual field. Superior Arcuate Defects- - arc shaped defects in the superior part of the eye. LIMITATIONS OF AUTOMATED PERIMETRY: Some patients just cannot do a visual field for a number of reasons. They may have a form of dementia and concentration is Impossible. Some patients spend well over 30 minutes on each eye. Extended time can lead to worsening of the field by about 4 decibels. Other difficulties include high fixation losses, false positives and false negatives. Should the losses be over 10 percent, the resulting visual field will not be counted as reliable. Assessment in this case needs to be re- evaluated.. RATE OF PROGRESSION: The machine also identifies rates of progression. Naturally, we hope that progression will be slow and we want to keep it that way. Should a patient s progression 7

8 move quickly, the doctor will do everything possible to maintain vision during the patient s lifetime. Visual Field Index, VFI. A normal visual field is scored at 100; a blind visual field is scored 0%. Your visual field index is scored along this spectrum. The GPA, the Glaucoma Progression Analysis is based on the analysis of standard deviation whereas the Visual Field Index can complement this. Visual Evoked Potential VFP and Pattern ERG are new technologies. They look at the visual pathway comprising the eyeball, the retinal ganglion cells and the visual center in the brain. It can pick up glaucoma earlier before visual field loss and unlike the Humphrey does not require patient participation. BLOOD FLOW: Certainly it would be good to be able to measure blood pressure to the eye, but, unfortunately, this technology is not commercially available. Again expense is an issue. Nevertheless, by reducing the eye pressure, blood flow to the eye is improved. The machines equipped to measure blood flow comprise part of laboratory equipment. COMPOSITION OF THE OPTIC NERVE: The optic nerve is composed of a variety of cells that include retinal ganglion cells, bipolar cells and other cells that contribute to your vision. The optic nerve is still being explored by scientists. It is one of the most sensitive and complicated features of the human body. We do know that glaucoma impacts on the retinal ganglion cells and that the optic nerve is a conduit of signals to the visual cortex that controls what you see. BLOOD PRESSURE AND EYE PRESSURE: There have been many studies exploring the relationship. The latest consensus 8

9 reveals that high blood pressure doesn t contribute as much to glaucoma but low blood pressure does. On the other hand uncontrolled high blood pressures can cause vascular events such as vein occlusions that can adversely affect the eye. Bottom line- - blood pressure should be neither too low nor too high. It should range in the neighborhood of 120/80. Diastolic pressure below 60 is too low. RECORD KEEPING: You are entitled to a copy of your records from your doctor. Should you switch doctors, you can save time by handing over copies to your new doctor. A NOTE ABOUT YOUR SLEEPING POSITION. Some patients sleep on an eye and/or a fist. This position can drive eye pressure as high as 50. If someone is sleeping on their eye they should protect it with a shield. Also sleeping at a 45% angle reduces night time pressure elevation that may occur from certain sleeping positions. In summary, through the use of new types of electronic devices that are objective and that will become more and more readily available for diagnosis of function the state of glaucoma treatment and prevention of loss will be enhanced. In the meantime your eye pressure and visual fields are still the tools that your doctor will be using to assess progression Furthermore,, research is ongoing to find more effective treatment and screening of glaucoma conditions. And as we all know medications and surgery still remain the means for vision preservation. 9

10 Your job is to be compliant following your doctor s orders. Diet is important. Salads, vegetables especially the deep green vegetables, fruit in moderation. If your appetite is poor, or you re sick or have other conditions, supplement with vitamins. Regular exercise is very important especially walking. What could be easier? We want to thank Dr. Laroche for his detailed and thoughtful lecture, and we want to especially thank him for responding to the concerns of the group present at this meeting. Please note: The contents of this newsletter are for informational purposes only. The content is not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. ====================================================== Editor: Edith Marks Associate Editor: Janice Ewenstein Production/Mailing: Ann Bially, Linda Flood, Susan Genis, Elaine Paris, Grace Pellicano, Robin Smith, and other glaucoma patient volunteers. 10