Ocular Pressure in Physics
September 25, 2013
Physics Tutorial
Tonometry for Intra-Ocular Pressure
In the linear non-elastic collision of the rod with the eyelid, there are 4 notable forces in action (Figure 1).
1. The force (or pressure) of the rod (rod/size of rod) exerted is equal and opposite to the force (or pressure) the cornea re-exerting pressure on the rod.
2. The force (or pressure) required to applanate a constant area of a cornea is equal and opposite to the force (or pressure) of the rebound on the rod exerted by the flattening of the constant area of the cornea
In the Newton’s cradle example, when one ball is pulled away and released, the ball as well as the balls in the middle of the cradle come to a complete stop. The ball on the opposite end acquires almost all of the velocity of the first ball. Tonometry can be thought of in a similar manner. The rod is the first ball that exerts an initial velocity on the eyelid (the balls in the middle of the cradle example), but the eyelid does not move. The velocity is transferred to the cornea (final ball) where it bends (ball moves backwards) and then bends in the opposite direction (ball moves back towards middle balls), transferring the velocity back to the rod, where the captured pressure is measured. The tonometer knows the pressure it exerted on the eye, so it compares the initial pressure exerted on the eye to the pressure received. Not all of the pressure exerted initially will be captured again. This change in momentum is the impulse. After the cornea has rebounded after being flattened, it won’t come to a complete stop, it will vibrate back and forth. This loss in momentum captured by the tonometer can be accounted for using the following method:
1. m1iv1i + m2iv2i = m1Fv1f + m1fv2f (momentum in number one) m1= mass rod , m2=mass cornea, v1i= velocity rod hitting eye, v2i= 0, v1f= o, v2f= velocity of flattening
2. m1iv1i + m2iv2i = m1Fv1f + m1fv2f (momentum in number 2) m1= mass rod , m2=mass cornea,
Physics Tutorial
Tonometry for Intra-Ocular Pressure
In the linear non-elastic collision of the rod with the eyelid, there are 4 notable forces in action (Figure 1).
1. The force (or pressure) of the rod (rod/size of rod) exerted is equal and opposite to the force (or pressure) the cornea re-exerting pressure on the rod.
2. The force (or pressure) required to applanate a constant area of a cornea is equal and opposite to the force (or pressure) of the rebound on the rod exerted by the flattening of the constant area of the cornea
In the Newton’s cradle example, when one ball is pulled away and released, the ball as well as the balls in the middle of the cradle come to a complete stop. The ball on the opposite end acquires almost all of the velocity of the first ball. Tonometry can be thought of in a similar manner. The rod is the first ball that exerts an initial velocity on the eyelid (the balls in the middle of the cradle example), but the eyelid does not move. The velocity is transferred to the cornea (final ball) where it bends (ball moves backwards) and then bends in the opposite direction (ball moves back towards middle balls), transferring the velocity back to the rod, where the captured pressure is measured. The tonometer knows the pressure it exerted on the eye, so it compares the initial pressure exerted on the eye to the pressure received. Not all of the pressure exerted initially will be captured again. This change in momentum is the impulse. After the cornea has rebounded after being flattened, it won’t come to a complete stop, it will vibrate back and forth. This loss in momentum captured by the tonometer can be accounted for using the following method:
1. m1iv1i + m2iv2i = m1Fv1f + m1fv2f (momentum in number one) m1= mass rod , m2=mass cornea, v1i= velocity rod hitting eye, v2i= 0, v1f= o, v2f= velocity of flattening
2. m1iv1i + m2iv2i = m1Fv1f + m1fv2f (momentum in number 2) m1= mass rod , m2=mass cornea,