Sometimes distance vision blurs only at night, or a new eye test suddenly shows a higher minus number. This does not always mean your eyes have become more short-sighted. The eye can focus too close in dim light, the focusing muscle can go into spasm after long near work, and blood sugar, some medicines and early cataract can all change the number. Finding the real cause avoids glasses that are too strong.
| Cause | Who gets it | What it feels like |
|---|---|---|
| Night myopia | Young adults, drivers | Clear in daylight, but road signs and lights look blurred at night |
| Focusing spasm (pseudomyopia) | Students and screen users | Distance blur after long reading or mobile use, headaches, vision that comes and goes |
| Machine (autorefractor) reading too strong | Children and young adults | The computer test shows more minus than you really need |
| Blood sugar changes | New or poorly controlled diabetes | Vision and number change over days or weeks |
| Some medicines | For example topiramate (for migraine, epilepsy or weight loss) and some sulfa drugs | Sudden blur in both eyes, sometimes with eye pain or headache |
| Early cataract | Usually over 55 | Distance blur, glare, sometimes reading becomes easier without glasses |
See an eye doctor the same day if
Not always. A machine reading, focusing spasm, sugar levels or early cataract can make the number look higher. A full test, sometimes with drops, gives the true number.
Only if a dim-light test shows you need it. Many people simply need their full correct number and clean anti-reflection lenses.
No. Any tint reduces the light reaching your eyes at night.
Long near work can cause temporary focusing spasm. Regular breaks and outdoor time help, and children should have their eyes checked regularly.
Related: Understanding Myopia, Cataract, Computer Vision Syndrome.
This leaflet gives general information and does not replace advice from your own eye doctor. Reviewed by Dr. Dhaval Patel, MD (Ophthalmology, AIIMS New Delhi), November 2026.
Sadbhaav Eye & Dental Clinic, Motera, Ahmedabad. Dr. Dhaval Patel, MD (AIIMS New Delhi). Monday to Saturday, 10 am to 1 pm and 5 pm to 8 pm. For a serious eye injury outside clinic hours, go to the nearest eye hospital or emergency department.
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