Make an Appointment (978)-854-5090

How is vision measured? Know symptoms of low vision and treatment

By admin | Jun 23, 2017

The ability for us to see properly relies on many different components working together in harmony.  Our visual system works very similarly to a camera.  Light passes through the cornea which refracts the incoming light. The iris (the colored part of the eye) regulates the size of the pupil. The iris has the ability to shrink and enlarge thereby controlling how much or how little light enters the eye. Located behind the pupil is the lens which further focuses light by lengthening or shortening its width in order to focus light rays properly. All of these structures need to work in harmony so that light can be focused as sharply as possibly onto the retina.  The retina is like the film of the camera.  It captures the sharply focused light rays and converts them into electrical impulses.  These electrical impulses are then transmitted to the brain through a cable called the optic nerve.  The pathway to the brain is long, and any issues along this path can result to problems in vision.  Once the electrical signals get the proper region of the brain, it is “developed” and we get an image.

Vision Measured

Vision Measured_1

If there is a breakdown in any aspect of this complex visual pathway, it can result in a problem in how we see.  If the lens becomes cloudy, a normal aging condition called cataract, the light passes through a “dirty window” resulting in a blurry image.  If there is a problem with the retina, the film of the camera, blurry or distorted images can be produced.  If there is a problem with the optic nerve, the cable carrying the electrical impulses to the brain, glaucoma can result.  If a patient has a stroke that affects the region of the brain responsible for vision, visual problems can arise.


Low vision is a condition caused by a group of eye diseases that cannot be corrected or improved by eyeglasses, medicine, or surgery.  Irreversible damage has been done to some aspect of the visual pathway.  Example of eye diseases that can lead to low vision include diabetic retinopathy, glaucoma and macular degeneration. Visual acuity is a number that indicates the sharpness or clarity of vision. A person with a visual acuity of 20/70 or poorer is considered to have low vision.

There are many signs associated with low vision. If you are experiencing difficulties performing everyday tasks such as reading, driving, writing, shopping, or recognizing faces you may have low vision. Lights may appear dimmer than before and doing regular chores may become impossible. There are different types of low vision with some of the most common types being loss of central vision, loss of peripheral vision, night blindness, hazy and blurred vision.

Low vision is not a not a normal symptom of old age. If you are experiencing significant changes in your vision, you should consult with an eye doctor right away. Yearly eye exams by an ophthalmologist are extremely important in order to detect early onset eye disease.  If you are affected by low vision, your ophthalmologist will work with you to try to optimize your vision and your quality of life.  Here at Retina Consultants of Boston, we are committed to helping our patients preserve their sight, and helping them achieve the best quality of life possible.

In the interest of maintaining further transparency and providing a wide breadth of information to our patients and providers, this blog will serve as an educational and informative resource on interesting happenings within Retina Consultants of Boston and in the greater field of Ophthalmology.

Here at Retina Consultants of Boston, Dr. John J. Weiter and Dr. Namrata Nandakumar are on the forefront of diagnostic techniques, treatment and micro-surgical techniques for macular degeneration, diabetic retinopathy, retinal detachments, macular holes, and a number of other issues affecting the vitreous and retina. Check back here frequently for news and updates on our practice and all things retina!