This document provides an overview of the anatomy and physiology of the human eye. It describes the external structures like the eyelids and tear film and their protective functions. The internal structures discussed include the cornea, iris, pupil, crystalline lens, vitreous humor, retina, choroid and sclera. It explains how light enters the eye and is focused on the retina by these structures. The document also discusses the role of photoreceptors, optic nerve and visual cortex in vision and color perception.

1. JAINULL ABEDIN
SR.OPTOMETRIST
ODISHA
CONTACT
#09437902254

2. INTRODUCTION
BEFORE WE EXPLORE VISUAL CONDITIONS AND
THE PHYSIOLOGY INVOLVED WITH VISION , IT IS
IMPORTANT THAT YOU HAVE A BASIC
UNDERSTANDING OF:
• EXTERNAL STRUCTURE OF THE EYE
• MAIN ELEMENTS OF THE EYE
• SOME COMMON TERMINOLOGY ASSOCIATED
WITH THESE STRUCTURES

3. THE EXTERNAL STRUCTURE OF
THE EYE
IS AS IMPORTANT AS THE EYE ITSELF

4. ORBIT
THE EYE IS SITUATED
IN THE CAVITY OF
SKULL: KNOW AS THE
ORBIT, IT PROVIDES
THE PROTECTION TO
THE POSTERIOR
SEGMENT OF THE EYE
GLOBE

5. EYELIDS
• THE ANTERIOR SEGMENT OF THE EYE IS UNDER THE
EYELIDS
• A THIN FOLD OF SKIN WHICH COVERS AND
PROTECTS FROM DUST AND FOREIGN DEBRIS AS
WELL AS FROM SWEATING
• THE BLINKING FUNCTION OF EYELID IS TO
REGULARLY SPREAD THE TEARS ON THE EYE
SURFACE TO KEEP IT MOST, CREATING THE TEAR
FILM
• THE TEAR FILM PLAYS AN IMPORTANT ROLE IN THE
EYE’S HEALTH AND FUNCTION:
• DRY EYES ARE CONNECTED TO EYESTRAIN AND CAN
IMPACT ON VISION.
• THE USE OF CONTACT LENSES IS ALSO POSSIBLE
ONLY IF THE EYES HAVE HEALTHY TEAR FILM.

6. LET’S
CONTINUE
WITH THE
MAIN
ELEMENTS OF
HUMAN EYE

7. CORNEA
• THE CORNEA IS THE CLEAR,
TRANSPARENT STRUCTURE AT
THE FRONT OF THE GLOBE AND
SERVES AS THE PRIMARY
REFRACTIVE SURFACE OF THE EYE
• THE CORNEA TRANSMITS AND
FOCUSES LIGHT INTO THE EYE
• FOR CONTACT LENS FITTING, THE
CONTACT LENSES HAVE TO
MATCH WITH THE CURVATURE OF
THE CORNEA

8. IRIS
• THIS IS THE COLORED PART
OF THE EYE
• WHEN WE SAY SOMEONE
HAS BLUE, GREEN OR
BROWN EYES, WE REFER TO
THE IRIS
• THE IRIS HELPS REGULATE
THE AMOUNT OF LIGHT
THAT ENTERS THE EYE
THROUGH PUPIL

9. PUPIL
• THE PUPIL IS THE DARK CENTER IN THE
MIDDLE OF THE EYE IT APPEARS BLACK
BECAUSE MOST LIGHT ENTERING THE
EYE GETS ABSORBED BY TISSUES
• CONTROLLED BY THE IRIS, THE PUPIL
CAN CHANGE ITS SZE TO ALLOW MORE
OR LESS LIGHT TO ENTER THE EYE.. IN
THE BRIGHT LIGHT / DAY THE PUPIL
GETS SMALL TO CONTROL LIGHT TO
ENTER
• CONTROLLED BY THE IRIS, THE PUPIL
CAN CHANGE ITS SIZE TO ALLOW MORE
OR LESS LIGHT TO ENTER THE EYE. AT
DIM LIGHT / NIGHT IT INCREASES ITS
SIZE TO COLLECT AS MUCH LIGHT AS
POSSIBLE

10. SIZE OF PUPIL IN
DAY
SIZE OF PUPIL IN DIM LIGHT

11. CRYSTALLINE
LENS
• THE CRYSTALLINE LENS IS LOCATED
INSIDE THE GLOBE JUST BEHIND THE IRIS
• THIS TRANSPARENT STRUCTURE FOCUSES
LIGHT RAYS ONTO THE RETINA
• THE CRYSTALLINE LENS ADJUSTS BY
CHANGING THE SHAPE TO HELP US FOCUS
AT DIFFERENT DISTANCES BY THE
PROCESS OF ACCOMMODATION

12. VITREOUS HUMOR
• THE VITREOUS HUMOR IS THE
TRANSPARENT, JELLY LIKE
SUBSTANCE THAT FILLS ABOUT 2/3
OF THE SPACE WITHIN THE EYE.
LOCATED BETWEEN THE
CRYSTALLINE LENS AND THE RETINA
• IT MAINTAINS THE SPHERICAL SHAPE
OF THE EYE

13. DEPOSITS WITHIN THE VITREOUS HUMOR
• HAVE YOU EVER NOTICED SMALL, ALMOST
TRANSPARENT SPOTS OR THREADS FLOATING SOWLY
BEFORE YOUR EYES (THEY ARE ESPECIALLY VISIBLE
AGAINST BLUE SKY)
• DO YOU KNOW WHAT THEY ARE???
# THESE FLOATERS ARE DEPOSITS WITHIN THE
VITREOUS HUMOR CAUSED BY DEGENERATIVE
PROCESSES. MOST FLOATERS ARE CHANGELESS AND
CAN PERSIST DURING THE WHOLE LIFETIME.
• DID YOU KNOW?ALTHOUGH THEY FLOATERS ARE
QUITE COMMON AND DO NOT CAUSE PROBLEMS TO
MOST PEOPLE, THEY ARE OFTEN REPORTED TO EYE

14. RETINA
• THE RETINA IS THE NERVE LAYER
THAT LINES IN THE BACK OF THE EYE
• THE RETINA SENSE THE LIGHT
FOCUSED BY THE CORNEA AND THE
CRYSTALLINE LENS AND CRATES
IMPULSES THAT ARE SENT THROUGH
THE OPTIC NERVE TO THE BRAIN
# LET'S TAKE A CLOSER LOOK AT THE
MAIN ELEMENTS OF THE RETINA

15. PHOTORECEPTORS
• THE RETINA CONTAINS MILLIONS
OF LIGHT RECEPTORS ALSO
KNOWN AS PHOTORECEPTORS
• THERE IS ONE SMALL SPACE WHERE
THE OPTIC NERVE ENTERS THE EYE,
THAT HAS NO PHOTORECEPTORS.
THIS IS COMMONLY REFERRED TO
AS OUR BLIND SPOT.

16. MACULA AND FOVEA
• THE MACULA IS AN AREA OF THE
RETINA, APPROXIMATELY 55 MM IN
DIAMETER, WITH THE FOVEA IN THE
CENTER
• THE MACULA HAS THE HIGHEST
DENSITY OF PHOTORECEPTORS AND S
FREE OF MAJOR BLOOD VESSELS
• THE FOVEA IN THE CENTER OF THE
MACULA RESPONSIBLE FOR SHARP
DETAILED VISION
# EG WHEN DOING ACTIVITIES SUCH AS
READINGWATCHING TV OR DRIVING A
CAR

17. CONJUNCTIVA
• A MEMBRANE THE CONJUNCTIVA,
COVERS THE SCLERA AND LINES
INSIDE OF THE EYELIDS
• THE CONJUNCTIVA IS HIGHL
VASCULARISED WITH MANY MICRO
VESSELS EASILY VISIBLE.
• WHEN IRRITATED IT GIVES TO THE
SCLERA A PINK OR BLOODY RED
APPEARANCE
• SOMETIMES IT ACT AS A BARRIER OF
FOREIGN PARTICLES TO ENTER

18. CHOROID AND
SCLERA
• THE CHOROID PROVIDES OXYGEN AND
NOURISHMENT TO THE RETINA
• THE SCLERA IS ALSO KNOWN AS THE
WHITE PART OF THE EYE AND IS THE
PROTECTIVE OUTER LAYER OF THE EYE
• IN HUMANS THE WHOLE SCLERA IS
WHITE CONTRASTING WITH THE
COLORED IRIS

19. CILIARY BODY AND
ZONULES
• JUST BEHIND THE IRIS IS THE CILIARY
BODY ATTACHED WITH TINY FIBERS
CALLED ZONULES
• THE CRYSTALLINE LENS SUSPENDED
BY THE ZONULES
• THE MAIN FUNCTION OF THE CILIARY
BODY AND THE ZONULES IS TO
CONTROL FOCUSING AT VARIOUS
DISTANCES
( A PROCESS
CALLED"ACCOMMODATION )

20. CILIARY BODY AND
ZONULES: FOCUSING
# WHAT DO YOU THINK HOW IS THE
FOCUS CONTROLLED
• THE FOCUS O CONTROLLED BY
CHANGING THE SHAPE OF THE
CRYSTALLINE LENS
OR
• THE FOCUS CONTROLLED BY MOVING
THE CRYSTALLINE LENS

21. • WHEN THE CILIARY BODY CONTRACT THE ZONULES RELAX- THE LENS GETS ROUND IN
SHAPE THICKERS AND ALLOWS US TO FOCUS ON NEAR OBJECTS
• THE OPPOSITE HAPPENS WHEN WE LOOK AT A DISTANT OBJECT. THE CILIARY BODY
RELAXES, CAUSING THE ZONULES TO CONTRACT AND THE LENS BECOMES FLATTER SO
WE CAN SEE CLEARLY
• DID YOU KNOW? WITH AGE, CILLARY BODY AND CRYSTALLINE LENS LOSES ELASTICITY.
THAT’S MAKES IT HARDER FOR US TO FOCUS ON NEAR WORK WITHOUT THE HELP OF
GLASSES CALLED PRESBYOPIA
I
N D

22. THE ANATOMY OF
THE EYE EYE
MUSCLES
AND
THEIR FUNCTION
RELATING TO
VISION

23. ONLY A SMALL PART OF RETINA=THE FOVEA=PROVIDES SHARPE VISION, OUR EYES
HAVE TO MOVE TO FOLLOW A TARGET
• THE MOVEMENT OF EACH EYE IS CONTROLLED BY SIX TINY MUSCLES
• FOUR OF THEM CONTROL THE MOVEMENT TO ALLOW US TO LOOK UP DOWN, LEFT
AND RIGHT
• THE REMAINING TWO MUSCLES ALLOW THE EYE TO ROTATE IN AND OUT

24. EYE MUSCLES AND THEIR FUNCTION
CONVERGENCE AND ACCOMMODATION
• THREE THINGS HAPPENS WHEN WE FOCUS ON AN OBJECT
• THE MUSCLES PLAY AN IMPORTANT ROLE IN FOCUSING AT DIFFERENT
DISTANCES
• DID YOU KNOW??? THE COORDINATED INWARD MOVEMENT OF BOTH EYES IS
CALLED CONVERGENCE

25. • IN ORDER TO SEE CLEARLY AT DIFFERENT DISTANCES THE THREE ACTIONS
FROM THE PREVIOUS SLIDE MUST HAPPEN SIMULTANEOUSLY. FOR EXAMPLE, TO
SEE CLEARLY UP CLOSE, THE EYES MUST ROTATE IN AND DOWN, THE
PUPIL.CONSTRICTS AND THE LENS BECOMES THICKERLET'S BRING THE BOOK
CLOSER TO SEE HOW THE EYES ROTATE TO KEEP THE FOCUS
Did you know?Pupils constrict to improve depth of field
facilitating near vision Reading difficulties, headaches,
difficulty with concentrating can be symptoms of binocular
vision disturbance.

26. YOU CAN SEE THIS ROTATION HAPPENING BY CHANGING THE DISTANCE OF THE
OBJECT

31. • YOU HAVE LEARNED
ABOUT THE MAJOR
STRUCTURES OF THE EYE
• HOW LIGHT PASSES
THROUGH CORNEA, PUPIL,
LENS AND VITREOUS
HUMOR TO THE RETINA
BUT HOW DOES THAT
LIGHT CREATES AN
IMAGE IN OUR BRAIN?

32. PHOTORECEPTORS
• REMEMBER THOSE
PHOTORECEPTORS ON THE
RETINA?
• THERE ARE ACTUALLY TWO
TYPES OF PHOTORECEPTORS
THEY ARE RODS AND CONES
• LET'S LEARN MORE ABOUT
THESE TYPES

33. RODS
• THE RODS, WHICH ARE HIGHLY
SENSITIVE TO LIGHT ARE RESPONSIBLE
FOR BLACK AND WHITE VISION
• RODS FUNCTION BEST IN DIM LIGHT/
NIGHT VISION
• DISTRIBUTED IN ALL BUT IN THE
CENTRAL AREAS OF THE RETINA ARE
ABSENT
• VISION WITH RODS ALONES
RELATIVELY POOR

34. CONES
• THE CONES IN CONTRAST. GIVE US
THE ABILITY TO SEE COLORS BUT ARE
LESS SENSITIVE TO LIGHT
• CONES PERFORM BEST IN LIGHT/ DAY
VISION
• HUMANS USUALLY HAVE THREE
KINDS OF CONES
• SOME HAVE DIFFERENT RESPONSE TO
THE WAVE LENGTH OF LIGHT AND
OTHERS ARE SPECIALIZED IN THE
PERCEPTION OF THREE BASIC COLORS
REDGREENBLUE

35. SO AS WE KNOW THAT THE RODS HAVE
HIGHER SENSITIVITY TO THE LIGHT THAN THE
CONES
• THE ENTIRE RETINA CONTAINS 7 MILLION
CONES AND ABOUT 100 MILLION RODS
• THERE ARE NO RODS PRESENT IN THE
CENTRAL AREA OF THE RETINA ONLY CONES
• THE SIGNALS RECEIVED FROM THE THREE
CONE TYPES.-SHORT, MEDIUM AND LONG
WHICH ALLOWS THE BRAIN TO PERCEIVE A
CONTINUOUS RANGE OF COLORS

36. BY MIXING ONLY THREE BASIC COLORS ITS POSSIBLE TO CREATE THE
PERCEPTION OF ANY COLOR. THIS CAN BE DONE IN TWO WAYS
SUBTRACTIVE
• MIXING IN CONTRAST SUBTRACTIVE MUNG WORKS BY
SUBTRACTING THREE OTHER COLORS - CYAN,
MAGENTA, AND YELLOW - FROM WHITE IMAGINE A
WHITE CANVAS WHERE THESE COLORS ARE DRAWN
ON TOP OF EACH OTHER
ADDITIVES
• ADDITIVE MIXING MEANS THE INDIVIDUAL INTENSITIES
OF RED GREEN AND BLUE ARE ADDED UP TO THE
RESULTING COLOR
• OUR BRAIN USES ADDITIVE COLOR MIXING TO CREATE
ANY COLOR FROM THE INTENSITIES OF RED GREEN
BLUE LIGHT

37. WHEN THE CONES AND RODS
HAVE CONVERTED THE
INCOMING LIGHT INTO A
SIGNAL , THEN THESE
SIGNALS HAVE TO BE
TRANSMITTED TO THE BRAIN
IN ORDER TO VERIFY ANY
OBJECT
• THIS IS THE TASK OF THE
OPTIC NERVE.
• EACH EYE HAS ITS OWN
OPTIC NERVE WITH MORE
THAN A MILLION NERVE
FIBERS
OPTIC NERVES

38. OPTIC CHIASM
• BOTH OPTIC NERVES CROSSED OVER TO THE OPPOSITE SIDE OF THE BRAIN. IN
ORDER TO IMPROVE BINOCULAR VISION
• THE PLACE WHERE THEY PARTIALLY CROSS IS CALLED OPTIC CHIASM IT IS
LOCATED AT THE BOTTOM OF THE BRAIN
• IN HUMANS, ABOUT 50% OF OPTICAL NERVE FIBERS ARE CROSSED.FROM THERE,
THE VISUAL INFORMATION IS TRANSMITTED INTO THE BRAIN, WHERE IT IS
PROCESSED BY THE VISUAL CORTEX.

39. VISUAL FIELDS
VISUAL FIELDS ARE A MEASURE OF THE AREA
FROM WHICH WE ARE ABLE TO PERCEIVE
VISUAL DATA WHEN LOOKING STRAIGHT
AHEAD , THE AREA IS MEASURED FROM TWO
MERIDIANS
• VERTICAL
• HORIZONTAL
LETS HAVE A CLOSER LOOK AT THESE
MERIDIANS

40. VERTICAL MERIDIAN
• THE HUMAN VISUAL FIELD
EXTENDS TO ABOUT 60
DEGREES NASALLY TO 100
DEGREES TEMPORAL
VERTICAL MERIDIAN - BOTH
EYES
• A VISUAL FIELD IS PUT
TOGETHER BY THE BRAIN
WITH INPUT FROM BOTH
EYES. AS A RESULT THE
FIELD INCREASES TO 200
DEGREES
HORIZONTAL MERIDIAN
• OUTSION EXTENDS ABOUT
60 DEGREES ABOVE AND
75 DEGREES BELOW THE
HORIZONTAL MERIDIAN.

41. VISUAL FIELDS PERCEPTION
BOTH SIDES
YOU CAN SEE HOW LIGHT HITS
DIFFERENT PARTS OF OUR RETINA
• INFORMATION FROM THE RIGHT SIDE
REACHES TO THE LEFT SIDE OF THE
RETINA IN BOTH EYES AND VICE
VERSA
• LIKEWISE THE BRAIN INTERPRETATION
OF THE SIGNALS FIXES THE
PERCEPTION AND ABLE TO SEE THE
RIGHT POSITION OF OBJECTS
SURROUNDING US.
• RETINAL DISEASE CAN BE DETECTED
BY THE REDUCTION OF THE VISUAL
FIELD, AND IT'S IMPORTANT TO
MEASURE THE VISUAL FIELD FOR
DIAGNOSIS AND PREVENTION

42. Right
Side
Left Side

43. BY COMBINING THE INFORMATION OF THE
VISUAL FIELDS
TWO MAJOR BENEFITS ARE THE RESULT
INCREASED FIELD OF VISION
• WE HAVE AN INCREASED FIELD OF
VISION
• THAT IS TO SAY, WE SEE MUCH MORE
THAN JUST THE OBJECTS DIRECTLY IN
FRONT OF US.
DEPTH PERCEPTION
• BINOCULAR VISION PROVIDES US
WITH DEPTH PERCEPTION IN THE
AREA WHERE THE USUAL FIELDS OF
THE RIGHT AND LEFT EYE ARE
OVERLAPPING

44. HOPE WE HAVE LEARNED SOME ESSENTIALS
ABOUT THE ANATOMY AND PHYSIOLOGY OF
THE EYE
AND
I HOPE THAT YOU FIND THIS INFORMATION
HELPFUL IN YOUR CONTINUING QUEST
KNOWLEDGE IN THE WORLD OF OPTOMETRY
THANK YOU FOR YOUR ATTENDANCE AND I
LOOK FORWARD TO SEE YOU ALL SOON
AGAIN

45. THANKS
JAINULL ABEDIN
SR.OPTOMETRIST
ODISHA
CONTACT #09437902254