Why does my vision change?

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Have you ever wondered why your vision changes from year-to-year or month-to-month or even day-to-day?  The term “vision” includes a wide spectrum of visual skills, and for this article, we will concentrate on two inter-related aspects – eyesight and prescription.  The references for this information are listed at the end of the article for your review.

According to research studies and clinical observation, the following can cause temporary or longer-lasting changes in a person’s visual acuity and/or prescription.  Not everyone who experiences one or more of the following will experience a vision change, but vision changes have been observed in enough of these situations to be aware of its potential effects:

  1. Diurnal changes in corneal curvature
  2. Menstrual cycle
  3. Stress hormones
  4. Diabetes
  5. Cataracts
  6. Medications
  7. Dry Eyes
  8. Pregnancy
  9. Increasing axial length
  10. Muscle spasms

The curve of the cornea changes during the day.  Clinical studies show that a person’s cornea can change as much 0.83 diopters.  This would effectively mean that how you see out of the same pair of glasses could go from 20/20 to approximately 20/40 just from normal daily changes in your corneal shape.  To help you better understand how this works, think about LASIK.  This refractive surgery procedure changes your prescription by permanently altering the shape of your cornea through lasers.  If you flatten the cornea, then you would change the prescription a certain way.  Alternatively, if you steepen the cornea, you would change the prescription another way.  Similarly, normal changes in corneal shape during the day can alter your prescription and how you see.

Changes in the cornea have also been observed during the menstrual cycle.  Clinical studies reveal that the curvature of the cornea steepens in the early phase while flattening during ovulation.   The thickness of the cornea changes too during the menstrual cycle.  The cornea thickens at ovulation and then thins out afterwards.  Changes in curvature, as discussed earlier, and changes in thickness will affect your prescription and acuity.  This is why some people may notice variations in acuity and prescription on a monthly basis even though they are wearing the same prescription.

Stress can affect many aspects of a person’s health including his/her vision.  In response to stress, your body releases many different hormones including cortisols, catecholamines, vasopressin, gonadotropins and potentially more.  A number of these hormones will affect the function and physiology of your eyes and visual system.  That discussion would be too detailed for this forum, but this is what it effectively means: If you’ve been stressed out all day and then visit the doctor, your prescription may be different once your stress has subsided and vice versa.

Changes in blood sugar levels can cause changes in vision and prescription.  Sugar can be trapped in the crystalline lens of the eye thereby causing it to swell.  This swelling will change a person’s prescription.  Alternatively, when a person’s sugar levels decrease, the crystalline lens will release the trapped sugars.  The prescription again will change because the shape of the crystalline lens has changed.  So, if you have diabetes, you can expect to occasionally experience changes in visual acuity and prescription as your blood sugar levels fluctuate.

Cataracts alter how light passes through the front of your eye to the back.  This pathway change will affect your prescription in different ways depending on what type of cataract(s) that you have.

Medications can change a person’s prescription in one of three ways: 1) spasm of the muscle located towards the front of the eye called the ciliary muscle, 2) retention of fluid in the crystalline lens or 3) swelling of the ciliary processes towards the front of the eye.  The list of medications that can cause changes to your prescription and visual acuity is too lengthy to list in this forum.

Dry eyes can cause changes in prescription and/or fluctuations in visual acuity because of this condition’s effect on the front surface of the eye.  The cornea plays an important role in focusing light to the proper place in the back of the eye.  As a matter of fact, the cornea accounts for 65-75 percent of the eye’s prescription.  Consequently, changes to the cornea due to dry eye can have a profound effect on visual acuity and/or prescription.

Changes in prescription seen in pregnancy can be temporary or long-lasting.  The hormones that are released during pregnancy can change corneal thickness, corneal curvature, how the crystalline lens transmits light to the back of the eye and how the front eye muscles focus light.  Some women experience changes in myopia (nearsightedness), hyperopia (farsightedness) or astigmatism.  There has even been a published case in which one woman experienced an increase in myopia during the first trimester only to experience a swing to hyperopia in her second and third trimester.

The length of the eyeball is known as axial length.  Increasing axial length is a common reason for changes in prescription seen in children up to the age of twenty-two years.  Clinical studies seem to indicate that multiple factors working in concert result in changes to axial length rather than just one component being the culprit.  Every one millimeter change equates to a three diopter change in prescription.

Spasms of the ciliary muscle will change the shape of the crystalline lens.  This change in shape will result in changes in prescription and visual acuity.  These spasms can be temporary or longer-lasting in different individuals.  Different medications as well as inefficient focusing visual systems can cause these spasms of the ciliary muscle.  This can cause transient changes in how you see through your glasses or contacts, or it can cause your prescription to change from one doctor visit to another.

For more information, please contact Dr. Edward Fong and Bright Eye Care & Vision Development.



  1. Ranabir S and Reetu K. Stress and hormones. Indian J Endocrinol Metab. 2011 Jan-Mar; 15(1): 18–22.
  2. Omoti AE, Waziri-Erameh JM, Okeigbemen VW. A review of the changes in the ophthalmic and visual system in pregnancy. Afr J Reprod Health. 2008 Dec;12(3):185-96.
  3. Ekpenyong BN, Aruotu NA, Uzodike EB, Njoku CG. Clinical Investigations and Management of Refractive Changes in Pregnancy: A Case Report. Afr J Reprod Health. 2015 Dec;19(4):107-17.
  4. Sunness JS. The pregnant woman’s eye. Surv Ophthalmol. 1988 Jan-Feb;32(4):219-38.
  5. Eisner A, Burke SN, Toomey MD. Visual sensitivity across the menstrual cycle. Vis Neurosci. 2004 Jul-Aug;21(4):513-31.
  6. Oliver KM, Walsh G, Tomlinson A, McFadyen A, Hemenger RP. Effect of the menstrual cycle on corneal curvature. Ophthalmic Physiol Opt. 1996 Nov;16(6):467-73.
  7. Kiely PM, Carney LG, Smith G. Menstrual cycle variations of corneal topography and thickness. Am J Optom Physiol Opt. 1983 Oct;60(10):822-9.
  8. Soni PS. Effects of oral contraceptive steroids on the thickness of human cornea. Am J Optom Physiol Opt. 1980 Nov;57(11):825-34.
  9. K Pesudovs, D B Elliott. Refractive error changes in cortical, nuclear, and posterior subcapsular cataracts. Br J Ophthalmol 2003;87:964–967.
  10. Handa T, Mukuno K, Niida T, Uozato H, Tanaka S, Shimizu K. Diurnal variation of human corneal curvature in young adults. J Refract Surg. 2002 Jan-Feb;18(1):58-62.
  11. Read SA, Collins MJ. Diurnal variation of corneal shape and thickness. Optom Vis Sci. 2009 Mar;86(3):170-80.
  12. Yasuda A, Yamaguchi T, Ohkoshi K. Changes in corneal curvature in accommodation. J Cataract Refract Surg. 2003 Jul;29(7):1297-301.
  13. Benjamin, WJ. Borish’s clinical refraction 2nd edition. Butterworth-Heinemann, 2007. Print.

Medical Disclaimer. The information on this site is not intended or implied to be a substitute for professional medical advice, diagnosis or treatment. All content, including text, graphics, images and information, contained on or available through this website is for general information purposes only.



Diabetes, Fish and Your Eyes


Recent research indicates that eating two weekly servings of oily fish may help prevent or delay diabetes in the eyes and lower heart disease risk in people age 55 years and older who have been diagnosed with type 2 diabetes.

For more information, please contact Bright Eye Care & Vision Development.

What causes your eyes to become red after swimming in a pool?

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The answer to the question, “What causes your eyes to become red after swimming in a pool?” is…

Urine. According to the Center for Disease Control (CDC), urine combines with the chlorine to create an irritant that causes the redness in your eyes. Believe it or not, 64% of Americans admit to urinating in the pool. Over the past two decades, Recreational Water Illnesses (RWI) associated with swimming have increased substantially per the CDC. Crypto, short for a parasite named cryptosporidium, illnesses have increased 200% from 2004 to 2008.

Please swim safely – don’t wear contacts while swimming in pools or lakes, do wear swim goggles while swimming, and please, use the restroom in the restroom when needed.

How do you get my child’s prescription?

How to determine child's prescription glasses Bright Eye Care Vision Development

Children’s eyes are different than those of adults. For example, if the eye doctor reports that the parent is seeing only 20/60, then there is justifiable concern. On the other hand, if the doctor says that the parent’s 2-year old is seeing 20/60, then that would be expected depending on other findings. So, another common question among parents is how the prescription for a young child is determined especially if he can not read or even talk. Fortunately, child-specific techniques will accurately determine a young child’s prescription even if he can not read or talk.

For more information, please contact Bright Eye Care & Vision Development.

What glasses are best for my young child?

How to pick children's glasses

One of the common concerns for children’s glasses is whether the glasses will fit properly. Because kids’ faces are not just miniature grown-up faces, many frames will slide off or become misaligned easily. An ill-fitting pair of glasses can adversely affect vision and even breathing patterns because of the shape of children’s noses. Since a child’s nose and cheeks change as he grows, a pair of glasses will need to be able to change with him for the proper fit and performance. A common misconception amongst parents is that they should order a pair of frames that are a little bigger so that the child can grow into it. However, this will only add to the poor fit because the larger size will cause the glasses to slip and misalign easily. A child needs a child-specific pair of frames rather than a down-sized adult frame. We have the solution with custom-fit frames for your child.

For more information, please contact Bright Eye Care & Vision Development.

Color Deficiency & School

Color Deficiency and School_Bright Eye Care & Vision Development

Imagine your teacher telling you to use the orange crayon to color the square, the yellow crayon to color the diamond, the red crayon to color the circle and the yellow crayon to color the rectangle. For most students, those instructions would be a run-of-the-mill activity. For some, however, it can be confusing because to them red, green, yellow and orange are just different names for what appears to be the same color. Reading litmus paper in science class would be an adventure for these students. Deciphering graphs may be more difficult than it could be. Color, which is often used to improve learning, may actually interfere with learning for students with a color deficiency.

For more information, please contact Bright Eye Care & Vision Development.

Color Deficiency & Sunglasses

Color Deficiency & Sunglasses_Bright Eye Care & Vision Development

People with color deficiency have difficulties detecting and recognizing traffic signal lights. Sunglass tints can make this worse. Correctly recognizing the traffic signal or taking significantly longer to correctly identify the signal are the main difficulties associated with specific sunglass tints and people with color deficiency.

For more information, please contact Bright Eye Care & Vision Development.