Can eyes adapt to defocus?

By: Kristian GalanMentors: Frances Rucker

& Olufunke Adeusi

Introduction

• The goal for this experiment is to see if the eye adapts to defocus.

• Adaptation is when the eye changes its sensitivity to maintain good vision.

Vocabulary

• Choroid~ thin vascular layer between the sclera and the retina. It supplies blood to the retina and conducts arteries and nerves to other structures in the eye

• Retina~ the nerve layer that lines the back of the eye. It senses light and creates impulses that travel through the optic nerve to the brain

Vocabulary (cont’d)

• Defocus~ when images aren’t focused directly on the retina

• Lens~ used to correct defocused images. In this experiment we are inducing defocus with lenses.

• Hypermetropia~ when an image is focused behind the retina

• Myopia~ when an image is focused in front of the retina

Equipment/tools

• White Leghorn chicks• + and - lenses(+6, -6.5)• Ultrasound• Refractometer

(Refraction)• Anesthetics

Movie

Procedure• Measurements of the chicks

eyes are taken before exposing the chicks to the lenses, using both ultrasound and refraction

• A negative lens was put on the chick’s right eye for 2 days to create a state of hypermetropia

• The lens was taken off 4 times a day for 15 minutes each time to prevent the eye growing to compensate for the hypermetropia

• On the third day we measured the eyes again. We then put positive lenses on both eyes of the chick to create a state of myopia for four hours. After that the eyes were measured again.

Results

-200

-100

0

100

200 Δ choroid thickness

Results (cont’d)

• The choroid in the control eye did not thicken as much as the choroid in the experimental eye.

• The choroid response in the experimental eye was more sensitive to plus lens defocus.

• The eye appears to adapt to having the minus lens on.

Further experiments

• Because we have only tried this with the minus lens, we plan to do the same experiment using positive lens first followed by a minus lens.

References

• http://www.crypticscriber.com/dump/eye.gif

• http://www.dblink.org/images/et-fig9.JPG

• http://www.Medterms.com

Acknowledgements

• Dr. Frances Rucker

• Olufunke Adeusi

• CCNY

• Dr. Sat

• Harlem Children Society