In The Optics of Vision – Part 9, we learned about the function of the crystalline lens. But as I pointed out towards the end of the lesson, the crystalline lens gradually stops functioning. This results in the condition we’re going to discuss in this lesson called Presbyopia.
This being the last lesson of The Optics of Vision course, it will continue to build off of everything taught so far. I strongly recommend making sure that you have read every previous lesson before reading this one.
- THE OPTICS OF VISION – LESSON 1: UNDERSTANDING LIGHT
- THE OPTICS OF VISION – LESSON 2: INTRODUCTION TO LENSES
- THE OPTICS OF VISION – LESSON 3: LENS POWER
- THE OPTICS OF VISION – LESSON 4: BASIC EYE ANATOMY
- THE OPTICS OF VISION – LESSON 5: BASIC EYE OPTICS
- THE OPTICS OF VISION – LESSON 6: EMMETROPIA & MYOPIA
- THE OPTICS OF VISION – LESSON 7: HYPEROPIA
- THE OPTICS OF VISION – LESSON 8: ASTIGMATISM
- THE OPTICS OF VISION – LESSON 9: THE CRYSTALLINE LENS
The Crystalline Lens & Accommodation
Recall from Lesson 9 that crystalline lens allows us to see clearly up close by automatically adjusting its curvature to give just the right amount of focusing power for the distance the eye is looking at.
Quick Accommodation Recap
Looking in the distance (further than 6m/20ft)
- The crystalline lens is at rest (as flat as possible)
- Takes no effort
Looking at intermediate distances (~1m/40”)
- The crystalline lens ‘accommodates’ (gets more curved)
- Requires minimal effort
Looking at near distances (~30cm/12”)
- The crystalline lens accommodates even more (gets even more curved)
- Requires significant effort
Looking at extremely near distances (~15cm/6”)
- The crystalline lens maximally accommodates (gets as curved as it can)
- Requires maximal effort
Takeaway: Without accommodation, we cannot see clearly up close.
Requirements for Accommodation
Functioning accommodation requires 2 things:
- A flexible crystalline lens
- Functioning ciliary muscles (the mucles that act on the crystalline lens)
For the vast majority of people, the crystalline lens is very flexible and the ciliary muscles are very strong in the first 4 decades of life (~ age 0 to 40 yrs). During this time, accommodation works so well that most of us don’t even know its happening – and thus take it for granted.
After the age of 40, the crystalline lens becomes stiff to the point that the ciliary muscles can no longer flex it. That’s when accommodation begins to fail. This is what is called presbyopia.
What is Presbyopia?
Presbyopia begins when accommodation starts to become sluggish due to changes in the crystalline lens and ciliary muscle. When presbyopia kicks in, our vision up close becomes blurry. It’s often noticed for the first time when attempting to make out small print up close such as the kind found of medicine bottles. From there, it gradually gets worse year after year until eventually, nothing within a couple of arm lengths is clear.
Who Does Presbyopia Affect?
When Does Presbyopia Start?
What Are The Symptoms of Presbyopia?
What is the Treatment for Presbyopia?
Can You Reverse Presbyopia Naturally?
Can You Reverse Presbyopia With Medication?
Can Presbyopia be Reversed Surgically?
Presbyopia is the inability of our eyes to focus on near objects due to the loss of accommodation. It’s a normal age-related change and will happen to everybody once they enter their 40’s. The best treatment for presbyopia depends on many factors such as your underlying distance prescription, occupation, lifestyle, etc.
If you’ve read through lessons 1-10 and you understand the material presented, you now know a lot about the eyes, optics, and how vision works. Congratulations on making it through! It really shows your dedication to becoming successful in the eye care industry.
With all of this knowledge in the bank, the next step of your training is to take The Lost Contact’s course on Optical Dispensing. I’ll see you there!