Does Your Glasses Prescription Change Often? Could It Be Keratoconus?
A glasses prescription change is natural in childhood. However, frequent change between ages 20 and 40, especially rising astigmatism, can be the first sign of keratoconus.
A glasses prescription change is natural in childhood and adolescence. Myopia can also increase until the early 20s. However, your prescription should stay stable between ages 20 and 40. If your glasses change often, your astigmatism rises, and you still cannot see clearly with new glasses, think of keratoconus. The diagnosis is made with corneal mapping (topography). If keratoconus is found early, cross-linking treatment can stop its progression.
Until what age does a glasses prescription change?
In childhood, the eye grows, so a glasses prescription change is expected. Myopia can usually increase until the early 20s. After the eye stops growing, your prescription should stay stable between about ages 20 and 40. In your 40s, near vision starts to decline. This is a different kind of change.
“Your glasses prescription should be stable between ages 20 and 40. If your prescription, especially your astigmatism, changes often at these ages, it may be keratoconus. You must have a topography test.”
— Prof. Dr. Fırat Helvacıoğlu, from the video
Does your glasses prescription change often?
Prof. Dr. Fırat Helvacıoğlu explains what a frequently changing glasses prescription may indicate.
Which kinds of glasses prescription change are warning signs?
- Changing glasses every year or even more often as an adult
- A rise in the amount of astigmatism, or a change in its angle (axis)
- Vision that is still not fully clear with new glasses
- Double or ghosted vision in one eye, and scatter of light around lights
- Frequent eye rubbing or allergic eye itching
However, a frequent change can also have other causes. For example, uncontrolled blood sugar can swell the lens and change the prescription temporarily. In older age, cataract shifts the prescription toward myopia. An eye examination finds the correct cause.
The cornea behind a frequent glasses prescription change
In keratoconus, the cornea thins and bulges forward in a cone shape. This causes a constantly changing astigmatism that glasses cannot fully correct. The diagnosis is made with corneal mapping.
- Normal corneaA cornea with a smooth dome shape bends light evenly. Therefore, the prescription stays stable in adulthood.
- KeratoconusAs the cornea thins and steepens, irregular astigmatism increases. Glasses change often, but vision does not become fully clear.
- TopographyOn the corneal map, steepening usually appears in warm colors in the lower area. It shows the disease at an early stage.
What is keratoconus?
Keratoconus is a disease in which the cornea gradually thins and bulges forward in a cone shape. It usually starts in adolescence or young adulthood. It mostly affects both eyes to different degrees.
A national study in the Netherlands found keratoconus in about 1 in 375 people. This rate is 5–10 times higher than earlier estimates. The average age at diagnosis was 28. Eye rubbing, allergy and a family history of keratoconus are counted among the risk factors.
How is it diagnosed?
Early keratoconus can be missed in a standard glasses measurement. The most important test for diagnosis is corneal topography and tomography. It maps the front and back surfaces of the cornea and measures its thickness. The test takes a few minutes and does not touch the eye.
Laser eye surgery is not performed on an eye with suspected keratoconus, because it may speed up the disease. For this reason, we always examine the corneal map before laser surgery.
Why early diagnosis matters, and treatment
In keratoconus treatment, the first aim is to stop the disease from progressing. Then we aim to improve the quality of vision:
| Treatment | Aim |
|---|---|
| Cross-linking (CXL) | To strengthen the cornea and stop progression |
| Combined CXL + surface laser | To smooth the corneal surface and strengthen it in the same session |
| Corneal ring | To flatten a marked cone shape |
| Special contact lenses | To provide clear vision on an irregular cornea |
We shared the long-term results of a hybrid treatment at ESCRS congresses. In this treatment, we smooth the corneal surface with a personalized laser profile and apply cross-linking in the same session. I described this approach with a patient example in the congress presentation article. For all options, you can see the keratoconus page.
Frequently asked questions
It can be normal in childhood and until the early 20s. However, between ages 20 and 40, a prescription that changes every year needs an examination and a corneal map, especially if astigmatism is rising.
Keratoconus usually does not cause complete blindness. However, if untreated, it can reduce the quality of vision markedly. With early diagnosis and cross-linking, we can stop progression in most patients.
In the early stage, you can see well with glasses. As the disease progresses, irregular astigmatism increases. Then special contact lenses or surgical treatments may be needed.
Classic laser eye surgery is not performed, because it may speed up keratoconus. However, in suitable patients, special surface treatments combined with cross-linking can be an option.
Frequent and hard eye rubbing is considered an important risk factor for keratoconus. If you have itching, treat the allergy instead of rubbing.
Related pages
References
- Godefrooij DA, de Wit GA, Uiterwaal CS, Imhof SM, Wisse RP. Age-specific incidence and prevalence of keratoconus: a nationwide registration study. Am J Ophthalmol. 2017;175:169-172. doi:10.1016/j.ajo.2016.12.015
- Gomes JAP, Tan D, Rapuano CJ, et al. Global consensus on keratoconus and ectatic diseases. Cornea. 2015;34(4):359-369. doi:10.1097/ICO.0000000000000408
- Sunay E, Helvacıoğlu F, Kaya Ünsal S, Kavalcıoğlu Ö, Bulut E. Long-term outcomes of keratoconus management with corneal wavefront-guided normalisation combined with corneal cross-linking stabilisation. 37th ESCRS Congress, Paris, September 2019 (paper).
This article is for patient information only and does not replace an examination or medical evaluation. The treatment that suits you is decided after an eye examination and measurements. Publication date: 25 September 2026.
Contact Prof. Dr. Fırat Helvacıoğlu with your questions
Prof. Dr. Fırat Helvacıoğlu · Veni Vidi Eye Clinic, Bağdat Cad. No: 257, Caddebostan – Kadıköy / Istanbul