Contrast Sensitivity: The Forgotten Part of Vision

D.Sivaganesh, B. Optom Student

Elite School of Optometry (ESO), Chennai, India

 

While standard eye exams focus on visual acuity, which measures how sharply the eye can see high-contrast details, vision in real life is not just about sharpness. It is also about how well we can detect objects when the contrast between the object and its background is low, for example, seeing a faded sign in dim light. This ability is measured by contrast sensitivity, a fundamental visual function that is often neglected but equally important.

What is Contrast Sensitivity?

Contrast Sensitivity (CS) is the ability of the visual system to detect small differences in luminance between an object and its background. The relationship between CS and spatial frequency is called the CS function, which typically shows peak sensitivity at intermediate spatial frequencies and reduced sensitivity across very low and higher frequencies. ⁽¹⁾

Why Contrast Sensitivity Matters?

Many day-to-day tasks require good CS, such as:

• Driving at night or in foggy environments.
• Recognising faces or objects against a similar background.
• Navigating across uneven ground in dim light.
• Reading low contrast prints. ⁽¹⁾

In these situations, CS often predicts real-world visual performance better than visual acuity, highlighting its importance in functional vision.

Contrast Sensitivity in Eye diseases

Glaucoma: Various studies show that CS loss correlates with the visual field damage and reduces quality of life, and it can be reduced even when the visual acuity is not reduced much. This makes CS useful in diagnosis and monitoring in cases of glaucoma. ⁽²⁾

Cataracts and Lens Changes: Mainly Cortical and Posterior Subcapsular Cataracts, cause light scattering, reducing image quality and CS significantly before acuity is lost. ⁽³⁾

Retinal diseases: Diseases like Diabetic Retinopathy, Age-Related Macular Degeneration, Retinal Vein Occlusion and other ischemic or macular disorders can lead to reduced CS, affecting day-to-day activities despite standard acuity preserved. ⁽⁴⁾

Neuro-Ophthalmic conditions: In conditions like optic neuritis and multiple sclerosis, CS can be significantly reduced across frequencies, which provides additional information about visual pathway functions. ⁽⁵⁾

Measuring Contrast Sensitivity 

Commonly used test includes: ⁽¹⁾

• Pelli-Robson chart: Letters remain the same size, but the contrast decreases across the lines.
• Bailey-Lovie Chart: Logarithmic progression of the size with constant contrast
• CSV -1000: Test CS at multiple spatial frequencies for a detailed profile.

 

Figure 1: This image shows the tools for measuring CS.

Image Courtesy: https://www.aph.org/product/contrast-sensitivity-kit/

 

Indications

So, CS should be prioritised when:

• A patient reports “Blurred vision” despite normal visual acuity.
• Patient complaint of vision problems in night driving or difficulty in fog or dim lights.
• Monitoring progression and functional vision in Glaucoma, Retinal diseases and Neuro-ophthalmic conditions. ⁽¹⁾

 

Conclusion

CS is a fundamental parameter of functional vision, along with visual acuity, it provides a comprehensive understanding of the functional vision of the patient. Incorporating CS testing into indicated conditions can facilitate early deficit detection, guided rehabilitation, and enhance the quality of life.

 

References

1. Owsley, C. (2003). Contrast sensitivity. Ophthalmology Clinics of North America, 16(2), 171-177.
2. Pang, R., Peng, J., Cao, K., Sun, Y., Pei, X. T., Yang, D., … & Wang, N. (2024). Association between contrast sensitivity function and structural damage in primary open-angle glaucoma. British Journal of Ophthalmology, 108(6), 801-806.
3. Shandiz, J. H., Derakhshan, A., Daneshyar, A., Azimi, A., Moghaddam, H. O., Yekta, A. A., … & Esmaily, H. (2011). Effect of cataract type and severity on visual acuity and contrast sensitivity. Journal of ophthalmic & vision research, 6(1), 26.
4. Wolkstein, M., Atkin, A., & Bodis-Wollner, I. (1980). Contrast sensitivity in retinal disease. Ophthalmology, 87(11), 1140-1149.
5. Sanders, E. A. C. M., Volkers, A. C. W., Van der Poel, J. C., & Lith, G. V. (1984). Spatial contrast sensitivity function in optic neuritis. Neuro-ophthalmology, 4(4), 255-259.

 

 

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About the Author

 D.Sivaganesh

 Optom Student

Elite School of Optometry (ESO), Chennai, India