PHYSIOLOGICAL OPTICS (SET 1)

PHYSIOLOGICAL OPTICS (P. O)

Visual science that deals with the study of the structures of the eye and their functions as affected by the behavior of light.

4 BEHAVIORS OF LIGHT

1. REFRACTION

2. ABSORPTION

3. REFLECTION

4. DISPERSION

4 THEORIES OF LIGHT

1. CORPUSCULAR/EMISSION THEORY

2. UNDULATORY/WAVE THEORY

3. ELECTROMAGNETIC THEORY

4. QUANTUM THEORY

Who corporate the Corpuscular theory?

ISAAC NEWTON (1642-1727)

Who corporate the Undulatory Theory?

CHRISTIAN HUYGENS (1629-1695)

What is the other term for Corpuscular Theory?

Emission Theory

What is the other term for Undulatory Theory?

Wave Theory

Who corporate the Electromagnetic Theory?

JAMES MAXWELL (1873)

Who corporate the Quantum Theory?

MAX PLANCK

PROCESS OF SEEING

1. PHYSICAL PROCESS

2. PHYSIOLOGICAL PROCESS

3. NEUROMUSCULAR PROCESS

4. PSYCHOLOGICAL PROCESS

PHYSICAL PROCESS

impinging of an incident of light upon the eye and its transmission through the various medias.

PHYSIOLOGICAL PROCESS

transformation of the radiant energy in/at the neural epithelium of the retina into some other form of energy capable of stimulating the receptor cells.

NEUROMUSCULAR PROCESS

generation of a nerve impulse in the retina and its transmission by a chain of neurons to the central nervous system.

PSYCHOLOGICAL PROCESS

the creation of a psychological process in the brain cells and constitutes the ‘real seeing’.

Optical System

Combination of two or more than two lenses having common principal axis.

Human Eye

considered as an optical system.

Cardinal Points

Physically measurable parameters for the position of the optical elements.

—> 2 principal points (P, P’)

—> 2 principal focus (F, F’)

—> 2 nodal points (N, N’)

Principal Points

Point of intersection of the principal plane with the optical axis.

Principal Points

Where the principal plane intersect the optic axis.

Principal Points

They are conjugate pair (object and image of each other).

Principal Points

In the eye, P and P’ are separated by 0.3 mm.

Principal Focus

It is the focus of parallel rays of light after refraction by a lens or after reflection by a curve mirror.

1st principal focus

a point where rays of light originate.

2nd principal focus

a point where rays of light intersect after refraction (in front, behind or on the retina)

Nodal Points

These are points on the crystalline lens.

Nodal Points

These are points in the lens on the principal axis from which objects and images appear under the same angle.

Nodal Points

The place where the chief ray passes undeviated through the lens (also true for thin lenses).

Optical Center

The place where an undeviated ray crosses the optic axis.

Optical Center

In reality, the nodal points represent the apparent position of the optical center

Dioptric Components

Curvature

Thickness

Axial length

Refractive index

Curvature of the Anterior Surface of the Cornea without accommodation?

7.7 mm

Curvature of the Anterior Surface of the Cornea with accommodation?

7.7 mm

Curvature of the Anterior Surface of the Lens without accommodation?

10 mm

Curvature of the Anterior Surface of the Lens with accommodation?

5.3mm

Curvature of the Posterior Surface of the Lens without accommodation?

6 mm

Curvature of the Posterior Surface of the Lens with accommodation?

5.3 mm

Thickness of the cornea without accommodation?

0.5mm

Thickness of the cornea with accommodation?

0.5mm

Thickness of the lens without accommodation?

3.6mm

Thickness of the lens with accommodation?

4.0mm

Refractive Index of Air without accommodation?

1.00

Refractive Index of Air

1.00

Refractive Index of Cornea

1.37

Refractive Index of Aqueous Humor

1.33

Refractive Index of Lens Cortex

1.38

Refractive Index of Lens Core

1.40

Refractive Index of Lens Nucleus

1.42

Refractive Index of Vitreous Humor

1.33

Normal axial length

24 mm (23.5 mm)

Planes of Reference

1. Face Plane

2. Listing’s Plane

3. Median Plane

4. Frontal Plane

5. Transverse Plane

6. Plane of Regard

7. Equatorial Plane

Face Plane

It is the frontal plane found to be tangential to the chin and super ciliary ridges

Listing’s Plane

It is a frontal plane that contains the center of rotation of both eyes.

Base Line

a line that connects the center of rotation of both eyes.

Median Plane

a plane that divides the head into right and left halves.

Frontal Plane

a plane that divides the head into anterior and posterior halves.

Transverse Plane

a plane that divides the head into upper and lower part.

Plane of Regard

it is the plane that includes the baseline and object of regard.

Equatorial Plane

it is a frontal plane perpendicular to the plane of regard that contains the baseline.

Reference Axes

1. X Axis / Transverse Axis

2. AP Axis / Y Axis / Sagittal Axis

3. Z Axis / Vertical Axis

4. Fixation Axis

5. Geometrical / Anatomical Axis

6. Optical Axis

7. Pupillary Axis

8. Visual Axis

9. Line of Sight

X Axis / Transverse Axis

It is a horizontal line of intersection of frontal and transverse plane (side by side)

X Axis / Transverse Axis

A horizontal line passing through the center of rotation of the eye and lying in the Listing’s plane

AP Axis / Y Axis / Sagittal Axis

It is a horizontal line of intersection of median and transverse plane (front to back)

AP Axis / Y Axis / Sagittal Axis

A line passing through the anterior and posterior poles and the center of rotation of the eye.

Fixation Axis

It is the line joining the object of regard to the center of rotation of the eye (14 mm behind the cornea)

Geometrical / Anatomical Axis

It is the line passing the anterior and posterior poles of the eye

Optical Axis

It is a line joining the optical centers of the refractive surfaces of the eye

Optical Axis

The line normal to the surfaces of the lens along which light will pass undeviated

Pupillary Axis

It is the line passing through the center of the entrance pupil of the eye and the poles of the cornea.

Pupillary Axis

Clinical counterpart of optical axis

Visual Axis

It is the line joining the object of regard to the foveola passing through the nodal points

Line of Sight

From the fixation point to the center of the entrance pupil and then from the exit pupil to the fovea.

Line of Sight

Clinical counterpart of the visual axis

Angles of Reference

1. Angle Gamma

2. Angle Alpha

3. Angle Lambda

4. Angle Kappa

Angle Gamma

The angle formed between the fixation axis and the optical axis at the eye’s center of rotation (C).

Angle Alpha

The angle formed between the optical and visual axis at the nodal point

Angle Alpha

In the average eye, the optical axis is displaced temporally (about 5 degrees) and down (1.5 degrees) with respect to the visual axis

Angle Lambda

The angle formed between the pupillary axis and line of sight at the center of the entrance pupil

Angle Lambda

The clinical counterpart of angle alpha; angle estimated during the Hirschberg Test

Angle Kappa

The angle formed between the pupillary axis and the visual axis.

Stimulus

refers to anything that can provoke a response.

Stimulus

Anything capable of exciting a sensory receptor cell.

Adequate Stimulus

It refers to a stimulus of sufficient intensity and of appropriate nature to provoke a response in a given receptor

Receptor

any structure that is capable of reacting when stimulated

Light stimulus

the adequate stimulus for the eye

Strength of Stimulus

1. Subthreshold/Subliminal

2. Threshold/Liminal

3. Suprathreshold

Subthreshold/Subliminal

Weak stimulus

Cannot create a response

Not enough

Threshold/Liminal

Minimum stimulus

Can create a response

Enough

Suprathreshold

Above minimum

Greater response

More than enough

FACTORS AFFECTING THRESHOLD

1. STATE OF THE EYE

2. NATURE OF LIGHT

3. RECIPROCAL RELATION DURATION OF EXPOSURE AND SENSITIVITY TO LIGHT

4. RETINAL AREA STIMULATED

5. SIZE OF RETINAL AREA STIMULATED

6. SIZE OF PUPIL

7. BINOCULAR SUMMATION

Dark Adapted Eye

lesser threshold intensity

Light Adapted Eye

greater threshold intensity

Green Light

lowest threshold for dark adapted eye

Yellow Light

lowest threshold for light adapted eye

Longer light intensity

longer time of stimulation

Shorter light intensity

shorter time of stimulation

Central Retinal Region

higher threshold

Peripheral Retinal Region

lesser threshold

Smaller Retinal Area

greater threshold

Bigger Retinal Area

lesser threshold

Smaller Pupil

less light enters the eye