Eye Anatomy: Lens (True or False)

TRUE

suspensory ligaments

Yes, but gradually become yellow when turn 30

avascular

135 mg to 255mg

10 mm in diameter and 4mm thick by the 2nd decade

Capsule , epithelium, fibres

type 4 collagen

Mold the lens during accomodation

Yes and continue to increase throughout life

thickest @ anterior mid-periph portion of lens (pre-equator)
thinnest @ posterior pole

its the thickest BM in entire body & is comprised of type 4 collagen

anterior region of cuboidal cells that differentiate into lens fiber cells by losing their nucleus

Site of lens metabolism

Bow region

Nucleus

Cortex

Basal laminate of non-pigmented epithelium from pars plicata and pars plana of ciliary body

Ability of lens to change its curvature to focus both far and near

Ciliary muscle contract
Suspension ligament relax
Lens rounder/thicker
Refraction increase to focus on macula
Can see near object better

the transparent layer forming the front of the eye.
Convex outside, concave inside
Resembles small watch glass

Elliptical

Circle (11.7mm)

Refracts light into the eye
Protect intraocular contents

0.5 mm /0.52 mm central, 0.67 peripheral

1.3 cm

8mm

+43.1 D

1.367

Epithelium
Bowman membrane
Stroma
Descemet membrane
Endothelium

non-keratinized stratified squamous

Ectoderm

Basal
Wing
Surface cells

Mesenchyme

Delineates the junction between limbus and anterior cornea

Keratocytes

neural crest and mesenchyme

Endothelium

Neural crest cells

Is a single layer of hexagonal, cuboidal cells attached posterior aspect of Descemet'membrane

Corneal oedema and loss of corneal transparency

avascular except anterior ciliary cells invade its periphery

V1 via anterior ciliary nerves
-Lose their myelin sheath (free- nerve endings)

tricarboxylic acid (TCA) cycle (More so in endo than the epithelium)
anaerobic glycolysis
hexose monophosphate (HMP) shunt (35%-65% in mainly epi and endo)

Dehydrated and trasnparent

Endothelium pump

Water to draws into cornea

Water from going out

Cornea function is lost
Pseudophakic bullous keratopathy

Ciliary muscle contraction
Pupillary contraction
Convergence

Contraction of Both medial rectus with relaxation of both lateral rectus hence resulting the adduction of both eyes

-Improve the depth of focus
-Divergent rays scatter off the periphery of cornea hence do not fall on fovea (blurred distant rays)

thick lens, shorten focal length, increase refractive power

No

accommodates without reacting to light

Pupil to react to near object (near reflex present) even though light reflex was absent

Cortical area (frontal and occipital)

pupil does not react to light; does constrict with accommodation

Lesion gives:
*Perinaud's syndrome
a) paralysis of upward gaze
b) loss of pupillary/light reflex (pretectal nucleus)

the gradual loss of power to focus on near objects due to the aging process (far-sighted ness)
-hardening of lens, decreased muscle tension, loss of accomodation

Transient blurred vision when adjusting between distance and near
Worse in dim light
Mopes find it easier to read without distance glasses

A condition in which the lens of the eye becomes opaque or cloudy and making vision difficult. It is usually a slow gradual loss of vision in the affected eye. They are common in elderly but may also be caused by some drugs like corticosteroids.

Bilateral

Central gray opacity. Opaque gray surrounded by black background as it forms in the center of lens nucleus. Through ophthalmoscope, it looks like a black center against the red reflex. Begins after 40 and develops slowly, gradually obstructing vision.

Normal ageing
Myopic shift
Nucleus become more opaque
Need more light when read

Star-Shaped opacity. Cortical cataract shows asymmetric, radial, white spokes with black center. Through ophthalmoscope, black spokes are evident against the red reflux. Forms in outer cortex of lens, progressing faster than nuclear cataract.

Asymptomatic
Start from periphery
Vacuoles and cleft
Spoke-like lesion

Most troubling
this type of cataract begins at the back of the lens
DM, Steroid
Glare/Halo
Difficult to read

cataract is a lens opacity that distorts the image. with aging, lens gradually lose water and increases in density.
increased density= drying and compression of lens
**overtime transparency of the lens are lost

Soluble protein-> insoluble protein clouding the lens

Gradual, painless vision blurring
Double vision
Glare

-reduced visual acuity
-diminished red reflex
-changes in lens appearance
-changes in refractive error
-NORMAL PUPILLARY REFLEX

LENS EXTRACTION (PHaCOEMULSION, EXTRACAPSULAR, INTRACAPSULAR)
INTRAOCULAR LENS IMPLANT

Amblyopia (Lazy eyes)

Local

use of high-frequency sound waves to break up cataract, which is then removed by suction with needle (sutureless)

excision of the anterior segment of the lens capsule along with the lens, allowing for the insertion of an intraocular lens implant

Larger incision - Where the entire capsule is removed.

Curvature of cornea
Length of eyeball

-Posterior capsule rupture
-Iris prolapse and bleeding
-Suprachoroidal haemorrhage

-Endoopthalmitis (emergency due to patient's own flora and contaminated instrument)
-Cystoid macula oedema
-Retinal detachment
-Glaucoma
-Post op astigmatism

Steroid
Antibiotics
No strenuous lifting
Bending head forward
Visual correction

condition in which the center of the retina gradually loses its ability to discern fine details; leading cause of irreversible visual impairment in older adults.
Central vision is lost

Smoky haziness

Spots or dark strings floating in your vision (floaters)

tunnel vision

Retinal detachment, myopia

See floaters (cobwebs, squiggly lines, hair-like structures)

Bulging eye disease
Double vision
eyes do not close all the way when sleeping

drooping

sharpness of vision

3/60

distance patient is standing/score they get

presenting visual acuity worse than 6/12 to 6/18

presenting visual acuity worse than 6/18 to 6/60

presenting visual acuity worse than 6/60 to 3/60

worse than n6 at 40 cm

Ishihara chart -moderate to severe red-green deficiency
Farnsworth D-15 test

Due to the absence of M-cones (green)
Green looks like red

lack the red catching pigment.
Red looks like green

An individual who suffers from color blindness that is due to the absence of S-cones. Cannot differentiate between blue from green and yellow from red(blue-yellow Deficiency)

Confrontation test
Perimetry

6/12 in at least one eye
120 degree along horizontal median and 20 degree above and below the horizontal midline

6/12 in both eyes
120 degree along horizontal median and 20 degree above and below the horizontal midline

Fixation assessment
VOR -prolonged nystagmus
-Blink response (to bright flash of light)

Optokinetic nystagmus
Preferential looking
VOP

Cardiff test
Kay's picture
Sheridan -Gardner (not suitable for deaf mute, unable to interact with traditional letters)

Blurred vision, vision loss TUNNEL VISION

When eye is looking straight ahead

Positions in which one muscle is acting

Pair of muscles that work together to move both eyes in the same direction

Downward movement

Upward movement

Adduction

Intorsion

depress and adduct the cornea; extorsion (laterally rotate the eye)

intorsion(rotate the eye towards nose), depression, abduction

extorsion, elevation, adduction

superomedial deviation

Mydriasis, ptosis, down and out deviation of ipsilateral eye
- Nerve compression more likely to cause mydriasis since parasympathetic fibers situation on periphery of oculomotor nerve

medial deviation
Cannot move eye past midline

contralateral frontal eye field in the frontal lobe and the superior colliculus