Now a days many Optometrist must be coming across various cases in which there is no scope for improvement in visual acuity with surgical/medical intervention. The condition of vision loss may have arisen due to an eye disease, some developmental anomaly or injury. At this stage, the patient is extremely dejected and it is incumbent on the doctor to provide a solution for the patient’s problems. You can rehabilitate the patient by prescribing the correct low vision aid.
• Based on our experience at SOHAM LOW VISION AIDS CENTRE is a brief outline for setting up of a mini low vision practice. By doing these few key things, you can address the problems of your patients who have mild to moderate vision loss (upto 2/60, CF 2Mt vision) and help them lead a more independent life. For patients with vision less than 2/60, it is advisable to refer them to a centre for the Rehabilitation of the Blind.
• In low vision practice, it is important to understand that about 70% of the patients need devices for near i.e. reading or writing work. The devices prescribed should be based on the visual requirement of the patients.
• The Snellen distance charts are not very suitable for recording vision of patients with low vision, since they are calibrated for a distance of 6 meters and have very few letters at lower acuity, e.g. in a Snellen chart there is only one letter for 6/60 acuity. Hence special low vision charts should be used which are made specifically to be used at a distance of less than 6 m and have more letters at lower acuity. Snellen charts may suffice for patients with vision upto 6/24. Low contrast charts help in determining the role of illumination.
• Amsler charting, peripheral field assessment, colour vision assessment, binocularity assessment and glare testing can yield useful information for the management of the problems encountered by the patient.
• The devices for near vision are Hi-power Spectacles, Hand held Magnifiers, Illuminated Stand Magnifiers, CCTVs, talking devices, softwares to convert text to speech, etc.
• It is important to explain to the patient that high power glasses have to be held close to the eyes. The exact distance will be 100 divided by the power. So for a +10.0 addition , the reading distance will be 100/10=10 cm and so on. A more practical approach will be to ask the patient to keep bringing the reading chart closer to the eye till the print becomes clear.
• The addition can be prescribed either in glasses or a Hand held Magnifier of equivalent power can be tried. For an addition of more than 4 dioptres, base in prisms have to be prescribed in glasses. Binocular vision is possible for additions upto +8.0 dioptres of addition only. All patients who need an add of more than 8.0 dioptres will be functionally monocular readers. Most of the low vision patients will fall in this category. Hence such patients who are functionally monocular should not be given prisms to converge. Hi-power glasses should not be prescribed as bifocals.
• For patients having a large disparity between the vision of two eyes, should be corrected only in the better eye, the fellow eye may be kept plano, occluded or can even be given a regular add, whatever is subjectively acceptable. For patients having same vision in both eyes but who need an add of more than 8.0 D, the add should be prescribed in the dominant eye only.
• Stand Magnifiers with Illumination are always more effective and practical while prescribing high magnifications. The main advantage of Stand Magnifiers is that no focusing is required. Special visions can also be used for writing.
• As a guideline, for patients who require an add upto 10 dioptres, Spectacles can be prescribed, between 10 to 24 dioptres hand held magnifiers are more suitable. For patients who need an add between 20 to 36 dioptres, Illuminated stand magnifiers should be prescribed and for still higher adds, CCTVs are the only solution. CCTVs can provide reasonable improvement for patients with vision as low as CF one metre.
• When choosing a hand held or stand magnifiers one should keep in mind that magnifiers being manufactured locally have small diameters and are useful only for powers upto 10.0 dioptres (3.5x). Beyond that one should use illuminated ASPHERIC magnifiers, which can provide distortion free vision. Resources (COIL, UK) www.coil.co.uk, Carl Zeiss (Germany).
• Distance vision devices are basically telescopic spectacles, for patients who have difficulty in Watching television, spotting bus numbers, shop names, recognizing faces, Copying from black board etc, which involve the stationary use of vision. It is not advisable to move about with a telescopic device, since they have a small field of view. They can be focused from distance to intermediate to near. The main hindrance though, in the use of telescopic devices is that they are aesthetically not acceptable, since they look bulky. They are however indispensable for many patients and should be discussed as an available option for distance vision. The newer generation of telescopes like those made by Ocutech, USA(www.ocutech.com) are very discrete. The most commonly used magnifications for telescopic devices are 2.5x, 4.0x and 6x. While prescribing telescopes one should strike a balance between good acuity and wide field.
• Prisms can be prescribed for patients who have field constrictions. This requires extreme precision. It is only recommended for patients who understand the utility of relative improvement, its importance in safe mobility and have a strong motivation. Field expanders are more useful for patients with visual acuity 6/24 or better.
Proper illumination is the most important non-optical low vision device.
There are other aspects of low vision practice, which are more challenging and need more time like-
1) Field Expanders for peripheral vision loss
2) Eccentric viewing
3) Teaching daily living skills
4) Bioptic telescopic devices
5) Braille (profound vision loss)
We are manufacturing, importing and exporting various types of low vision devices. All the above mentioned low vision devices are available with us. These low vision devices are being manufactured in technical collaboration with CTP COIL, U.K. We can also supply trial kits for patient assessment.
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