Background information
Accommodation is the ability of the eye to adjust its optical power to keep an object in focus as the object moves various distances from the eye. As the object is brought closer to the eye there will be a point where it cannot focus on the object any longer. This distance is referred to as the near point. In textbooks, you will see that it is explained that the closest you can bring the object and still see in sharp focus is related to the elasticity of the lens and this changes with age. We would therefore expect that with ageing, there would be changes in the near point. In this simulation you will be investigating the effects aging has on accommodation and the near point.
To demonstrate accommodation and the effects of aging on the near point, this simulation depicts a photo being held in front of someone's face. In this simulation you can adjust the person's age (the box below the eye) and the distance at which the photo is held from their eyes (the box below the slider).
You can use the near point values to calculate the amplitude of accommodation using the equation:
Amplitude of accommodation = 1 รท (near point distance in m)
Once you have collected all of the data you should be able to describe the relationship between aging and the near point. Before beginning the simulation what do you hypothesise the relationship will be? After you have finished the simulation: did the data you collected support your hypothesis?
Visual accommodation simulation
Procedure:
- Start with the Age set to 10 years, and the Photo distance set to 105cm.
- Slowly drag the slider to move the image towards the eyeball.
- Find the shortest distance at which the photo remains in focus - this is the near point. Record your data on a sheet.
- Systematically increase the age in steps of 5 years (up to 60 years), resetting the distance slider to 105cm, then repeating steps 2 and 3 to find the near point for each age.
Amplitude of accommodation: 8.333 [1/m]
Measure your accommodation amplitude
Take a book or printed document and look at it at arms length. Start bringing it closer to your eyes until the print becomes blurry. Measure the distance between your eyes and the paper when the print is just starting to become illegible. This is your near point.
Enter your age and near point to compare your accommodation amplitude to the average data:
| Age (years) | |
| Near point (cm) |
NOTE: If you wear glasses or contacts, your accommodation amplitude may be different with and without your correction. Try measuring both ways to find out!
Test your understanding