Ophthalmology Optics & The Eye

• Geometric optics is the study of light and images, using geometric principles.
• Physical optics emphasizes the wave nature of light.
• Quantum optics emphasizes the particle nature of light and how it interacts with matter.
• Geometric optics uses linear rays to show how light travels.

Ophthalmology Optics Components

• Physical optics studies on how light travels and the electromagnetic spectrum.
• Geometric optics studies how light rays behave when they interact with surfaces and different materials.
• Physiologic optics studies the mechanisms, psychology, and physiology behind vision.

The Eye

• This is an optical system that enables organisms to perceive their environment through sight
• It's a complex sensory organ for vision.
• The eye detects, processes light, and converts it into electrical signals for the brain to make images.
• Key parts include the cornea, lens, retina, iris, and optic nerve, all working together to focus light and send visual data to the brain.

Optical System of the Eye Defined

• It's a set of structures in the eye that work together to focus light and create clear images on the retina including the cornea, lens, aqueous humor, vitreous humor, and pupil.
• These components work to refract or bend the light effectively, ensuring it focuses correctly on the retina.
• The retina converts the focused light into electrical signals and sends them to the brain, enabling vision.

Lens Functionality: Eye Vs Camera/Telescopes

• Eye: The eye has a natural lens that focuses incoming light onto the retina.
• Optical systems such as cameras and telescopes have lenses that focus light onto a sensor (like film or sensors in cameras).

Light Regulation: Eye Vs Camera

• Eye: The iris regulates the amount of light that enters by adjusting the size of the pupil.
• Optical Systems: Cameras use an aperture to control the amount of light entering, subsequently controlling exposure.

Focusing Mechanism: Eye Vs Camera/Telescopes

• Eye: Ciliary muscles change the shape of the lens to focus on objects at varying distances in a process called accommodation.
• Optical Systems: Lenses are adjusted to focus on subjects at various distances, either manually or automatically.

Image Formation: Eye Vs Camera

• Eye: Light rays go through the cornea, and lens and converge by making an inverted image on the retina for the brain to read.
• Optical Systems: Light goes through a lens and creates an inverted image on film or a digital sensor.

Sensing Light: Eye Vs Camera

• Eye: The retina containing photoreceptor cells (rods and cones) acts as a sensor by detecting light and color, relaying signals to the brain.
• Optical Systems: A sensor, like film or a digital CCD/CMOS sensor, detects light intensity and color to form an image.

Field of View: Eye Vs Camera/Telescopes

• Eye: A wide field of view is determined by the shape of the cornea and the position of the lens.
• Optical Systems: The focal length of the lens and the sensor or image plane size determines the field of view.

Aberrations: Eye Vs Optical Systems

• Eye: Optical aberrations like myopia, hyperopia, and astigmatism can impact the focusing of light in the human eye.
• Optical Systems: Lenses can have aberrations like chromatic or spherical aberration, impacting image quality.

Protective Features: Eye Vs Optical Systems

• Eye: Features like the eyelid, eyelashes, and cornea shield and focus light.
• Optical Systems: Lens covers and hoods protect lenses from damage and stray light.

Camera Shutter vs Pupil of the Eye

• A diaphragm controls the amount of light that gets through the lens, in cameras it is the shutter at the pupil of the the eye.

Protection: Eye Vs Camera

• Eyelids protect the eye from foreign bodies and dust.
• The body cap protects the glass mount or lens from dust and foreign bodies.

Camera Lens Mount vs Cornea

• The most important function in the human eye is the cornea.
• The cornea is the transparent, refracting part of the eye.
• The cornea helps in refraction of light into the eye.
• A glass lens mount acts as the first transparent medium which does the same function.

Aperture & Pupil Compared

• After light passes through the cornea, it then reaches the pupil.
• The pupil regulates how much light needs to enter the retina by varying its size.
• The same task is performed by the aperture in cameras.
• The pupil is controlled by the iris similar to how the pupil size is controlled by the iris.
• The size of the pupil gets smaller to control the amount of light getting in when there's high light intensity
• The work of allowing maximum light to enter occurs when the pupil increases in size and is the same work is done by the shutter in camera.

Crystalline Lens Focusing

• The image distance is fixed in human eye .
• The focal length is adjusted for a clear picture when the object distance changes.
• Ciliary muscles and zonules change the lens's shape through accommodation.

Camera Lens Focusing

• Basic camera lenses has a fixed focal length.
• Moving the lens adjusts the image distance when the object distance changes.

Retina Compared To Photo-Film

• Passing light through lens focuses light on photoreceptors
• Photo receptors are in both eyes and cameras
• The human retina has rod & cone cells.
• Rods enable vision in low light or scotopic conditions.
• Cones enable color vision for higher spatial acuity or photopic conditions.
• Camera film contains a few chemical coatings that capture image formation.
• A flash enhances both day and night photography using typically silver compound coatings.
• Phosphor coatings are used for low light conditions instead of flash.
• Coatings can extend sensitivity from the visible light into the ultraviolet and infrared spectrums.

Image Formation

• Human eyes contain a convex lens and concave mirror to form a real and inverted image.
• Photoreceptor cells send information to the brain via an optic nerve.
• The occipital part of the brain decodes it to give an erect image.

Camera Variations

• Analog cameras form real and inverted negative images on 35mm film.
• Digital cameras use CCD arrays to make images and charged-coupled devices work like the optic nerve to form an electrical signal.

The Human Eye

• The human eye has different parts that work together to create sight.
• The eye acts as a camera with a lens, and the retina, and a light tissue which acts as photographic film.
• A healthy eye forms a real, inverted image on the retina.
• In a first step, the human eye gathers light from the object.
• Next, electrical impulses move from the eye through the optic nerve to the brain to interpret light signals as an image.