I got my new glasses and am feeling uncomfortable… high and low. The optometrist explained to me that the prescription has changed and I will take some time to adjust. Why?
How and what we see is a complex interaction between the eye and the brain. The cornea and the lens focus the light rays on the retina, and the retinal neurons transmit this information via the optic nerve to the visual cortex of the brain. Problems with vision arise when the images we see are not focused directly on the retina and thus we need spectacles lenses in front of the eye to redirect the direction of the light rays. Nearsighted people need convex lenses to focus the light properly on the retina, farsighted people need convex lenses, and people with astigmatism need toric lenses. In addition to this, presbyopes (people over 40 usually) need bifocal lenses.
Light rays pass through optic nerves to the brain where the signal is decoded and translated into vision. This is a really complex occurrence and even small changes to the norm have the potential to cause significant discomfort and problems, depending on 1) the amount of change and 2) the sensitivity of the patient. For example, a finger is cut with a piece of glass; one person may just put a band-aid on it and go about their everyday life, and another person will be distracted by the pain all day. When you get your eyes tested, the primary objective of the optometrist is to give you the best vision possible. However, to achieve this, there may be a significant change in the prescription. Some people can adapt to this change with no problem, and some people experience eye strain, headaches, or ‘pulling.’ This does not mean that the prescription is wrong, just that the brain is having a hard time adjusting to the change. People who have problems adapting to change should accept that they may need up to three weeks before they feel comfortable with their new glasses.
I have astigmatism and it has increased. Is this causing the distortion I’m feeling, and will I get used to it?
Astigmatism is a condition where the curvature of the cornea, the front surface of the eye, is irregular. The first surface of the eye that the light from an image hits is the cornea, and it is curved or spherical (round like a tennis ball. This requires a spectacle correction that has a different strength in 2 meridians, 90 degrees apart. Sometimes, the prescription changes in one of the 2 directions only, and this will cause problems with adaptation more than if both had changed. Imagine looking at a circle: if it is magnified more one way than the other, the retinal image will not be a circle, but an oval. In another common-sense judgment the brain gets it wrong – how can an object known to be round look oval? It would if it was tilted… imagine looking down on a coffee cup – circle. Look at the cup at an angle and we would see an oval. So the brain can introduce a tilt to things which can’t be true but feel so. Desks and floors may slope and door frames may appear distorted.
Glasses help us to see. But while doing so, they may also cause slight changes in a person’s visual perception. Normally these changes only cause a slight feeling of uneasiness for a period of a few hours to several days. Your optometrist will advise you as to the extent of the change in your prescription and possible problems getting used to the new glasses.
This article concludes our weekly question and answer column in the Weekend Magazine. For information pertaining to eyes and eye care please do not hesitate to contact any of the members of the Guyana Association of Optometrists, Drs José and Johan Da Silva tel # 226-1082, Dr Dionne Fries tel # 227- 0749, Dr Michele Ming tel # 225-4395 and Dr Karen Persram tel # 225-0605.
