2. Outline
A. Anatomy of the lens
I. Structure of the lens
II. Sutures
III. Lens characteristics
B. Physiology of the lens
I. Transport of ions
II. pH of the lens
III. Amino acid and sugar transport
C. Embryogenesis of the lens
D. Functions of the lens
I. Light transmission
II. Accommodation of the lens
E. Abnormalities of the lens
I. Congenital
II. Cataracts
4. Lens
Biconvex, transparent, non-innervated and non-vascularized
structure
Anterior surface less convex than posterior surface
The equator in perpendicular to the anteroposterior axis
Lens is 3.5 mm away from the cornea
5. I. Structure of the lens
3 compartments:
Capsule
Elastic membrane
Capsule is permeable
Constantly reproduced :
basal membrane of the lens epithelium anteriorly
basal membrane of elongating fiber cells posteriorly
Thickest near the equator
Thinnest region is at the posterior surface
8. Distribution and reproductive capacity of
EP cells:
At the central zone, high concentration but low
reproductivity
At the pregerminative zone, rare reproductive capacity
At the germinative zone,
At the equator proliferative capacity increases
At the transitional zone, epithelial cells elongate and
differentiate
stem
cells
formation
of new
fibers
continuous
growth of the
size and
weight of the
lens
9. Cortex:
Made of densely packed secondary fibers
Formed after sexual maturity
Very little extracellular space
Nucleu
s
10. II. Sutures
Formed by overlapping of
secondary fibers in each growth
shell
Erect Y-shaped sutures appear at
the anterior surface of the fetal
nucleus
The suture contribute in
transforming the spherical shape of
the lens into flattened biconvex
shape
11. III. Lens characteristics
Growth of the lens:
Is greatest in youngsters
Decrease with the growth of age
During first 2 decades of life, EP cells and lens fibers
increase rapidly.
Mass of the lens:
Mass increase from 65 mg at birth to 125 mg after the
first year
Then increases at a rate of 2.8 mg/year till age 10
The rate decreases to a rate of 1.4 mg/year until the
age of 90.
13. I. Transport of ions
II. pH of the lens
III. Amino acid and sugar transport
B. Physiology of the lens
14. I. Transport of ions
Crystallins are negatively charged
Attracts the positively charged ions from the
extracellular fluid to maintain intracellular
neutrality
15. When the extracellular Ca2+ decreases
Calmodulin‐regulated Ca2+‐ATPase pump
transport Ca2+ out of the cell.
16. II. pH of lens:
pH in the lens increases from the nucleus
towards the peripheral
Is about 7
Neutrality is maintained due to ion transporters
17. III. Amino Acid and Sugar
Transport
Amino
acid
Active
transport
Anterior
Posteri
or
Keto
acid
Keto to
amino
Aqueous
humor
Glucos
e
glucose‐6‐phosph
ate
Glycolysi
s
In lens
fibers
Glycolytic
pathway
Pentose
phospha
te
Energ
y
19. The lens plate originates from the surface ectoderm
germinal layer arising from the gastrula cells of the
embryo during the 27th day of ocular embryogenesis
Lens pit at the inferior center of the lens plate
invaginates to form the lens vesicle
Primary lens fibers begin forming during the 6th week
Embryonic lens nucleus starts forming during the 7th
week
21. Second step:
Primary lens fibers lose their nuclei and other cellular
organelles
Anterior cells will continue to divide
Cells along the equatorial edges will begin to form
secondary lens fibers (cells in red)
22. Third step:
Anterior cells at the edges begin to grow to form
secondary lens fibers
By elongating along the posterior surface of the primary
lens fiber
Newly formed lens fibers have consistent hexagonal
shape
When migrating to the center of the lens the cell start
loosing its structure: Cytoskeleton and Crystallin
23. Fourth step:
Secondary lens fibers have finished forming and they
form rings around the primary lens fibers.
The process of secondary lens fiber repeats as the lens
gain size and weight
24. Fifth step:
The cortex of secondary lens fibers increase in size.
The original primary lens fibers persist to form the
nucleus
Only outer most secondary lens fibers contain nuclei
25. New secondary lens fibers continue to form
throughout the life of the individual.
Lens doesn’t increase in size in adulthood, the
density of secondary lens fibers increases.
Compression of the primary lens fiber nucleus.
27. I. Light transmission
The lens allows the passage of 90% of light while
absorbing the UVA and UVB light rays
Proteins in the lens are arranged for minimal
scattering
Any increase of size of these proteins or more
spacing, would result in the development of
cataract.
28. Ways to lose transparency:
Formation of opaque fibers
Fibrous metaplasia
Epithelial opacification
Accumulation of pigment
Formation of deposits of extracellular materials
29. II. Accommodation of the lens
The Lens is biconvex which intensifies the
focusing power
The lens is flexible and can change curvature
For far away objects
For close objects
31. I. Congenital
Abnormalities of
growth
Description Treatment
Primary Aphakia Rare eye condition that is
present at birth in which the
lens is missing.
glasses, contact lenses, or
IOL(can’t accommodate)
Secondary Aphakia disappearance of a part or
whole of the lens as a result of
degeneration or absorption.
glasses, contact lenses, or
IOL
Duplication of the lens abnormality during
invagination of lens placode
from ectoderm surface
associated with corneal
metaplasia and coloboma
(fissure) of the iris and
choroid.
Microspherophakia the lens of the eye is smaller
than normal and spherically
Eyeglasses , laser
iridotomy, IOL
32. Abnormalities of growth Description Treatment
Lens coloboma •characterized by notching of
the equator of the lens.
•Caused by faulty development
of the zonule.
•The lens is thicker and more
spherical
Glasses, contact lenses
Lenticonus and
lentiglobus
thinning of the lens capsule
and deficiency of the epithelial
cells.
•conical protrusion of the lens
in Lenticonus
• spherical protrusion in
lentiglobus
Removal of lens and IOL
implantation
Ectopia of the lens • Abnormal positioning of the
lens can be partial or complete
• Due to abnormalities in the
zonular fibers
• Increased pressure in the eye
(glaucoma) or retinal
detachment
Pain relievers, anti-
glaucoma treatment
In severe cases surgery to
remove the lens
33. Abnormalities of
growth
Description Treatment
Mittendorf’s dot • The presence of a small
dense floating opacity behind
the posterior lens capsule
• Remnant of the hyaloid artery
No treatment is generally
necessary.
Epicapsular star •Star shaped distribution of
brown or golden flecks on the
central anterior lens capsule
• Remnants of the vascular
network that surrounds the lens
during embryogenesis.
Phacoemulsification, IOL
implantation
Aniridia •Complete absence of the
iris
•Anteroposterior pole
opacities
• Antiglaucoma treatment,
• Corrective lenses with
shaded screens to reduce
light sensitivity
34. Other abnormalities
Type of abnormality Reason Effects Correction
Myopia Lens is thickened Image focused in front of
the retina
Concave lenses
Hypermetropia Thin lens or
shortened eyeball
Image is focused behind
the retina
Convex lenses
Presbyopia Aging, lens looses
elasticity
Decline of
accommodation, close
objects difficult to see
Reading glasses
(concave lenses)
35. II. Cataracts
A cataract is a clouding of the lens inside
the eye which leads to a decrease in vision.
Symptoms of cataracts
Diminished visual acuity: gets worse when the
opacity is central or axial and diffuse, but is
mild when its peripheral
Glare: sensitivity to bright light
Myopic shift: increase of the dioptric power of
the lens causing a mild to moderate myopia
Monocular diplopia: formation of a refractile
area in the center of the lens
Signs of cataracts
Changes in lens appearance: lens
shows a brownish tone and in severe
cases, a grey to white opacity
Ophtalmoscopic red reflex drop: any
opacity is detected as black opacity
36. Causes and kinds of cataract:
Congenital
cataract
Present at birth
Infantile
cataract
Develops
during the first
year of life
37. Morphological classification of
congenital and infantile cataracts
Classification Cataract location
Polar cataracts Opacities in the lens capsule and
subcapsular cortex
Sutural cataracts Opacification of the Y-suture of the fetal
nucleus
Nuclear cataract Opacification of the embryonic nucleus
alone or both the embryonic and fetal
nuclei
38. Classification Cataract location
Capsular cataract Small opacification of the lens EP and
anterior lens capsule
Lamellar cataract Most common type of congenital cataracts,
occur from the opacification of specific
layers or zones of the lens fibers
Complete cataract Complete opacification of the lens, Retina
cannot be viewed
40. Acquired age related cataract
Types of age related cataracts Description
Nuclear cataract • Gradual hardening and yellowing of the
nucleus
• Leading to an impairment of distant vision
Cortical cataract • Hydration of the cortex
• The development of subcapsular vacuoles
• Transparency of the cortex changes
Anterior subcapsular cataract • EP cells become elongated spindle shaped
and myofibroblast
• Caused by trauma to the central epithelium
• Caused by exposition of UV rays.
As the eye ages the lens gains in weight and
thickness and decreases in accommodative
power.
41. Types of age related cataracts Description
Posterior subcapsular cataract • Dysplastic change in the germinal epithelium
• Cells are distorted and unorganized
• Swelling of Cortical lens fibers and degeneration of
nuclei of the superficial fibers.
• Massive water intake: swelling of the lens.
• Liquefaction of the cortex leads to leakage of
crystallin fragments into the anterior chamber
Advanced cataract •lens swells and increase in volume
•complete opacification leads to mature cataract.
•Hypermature cataract is caused by absorption of
the milky cortex reducing the lens volume causing
folds to form.
a) Acquired age related cataract
42.
43. b) Traumatic and toxicity related
cataracts
Physical factors
• Traumatic insults,
high velocity
foreign bodies or
electric shock.
• If the capsule is
not ruptured :
cataract
• If the capsule is
ruptured: mature
cataract
Radiation cataract
• Ionization of the
water
• Releases of free
radicals
• Altered protein
synthesis leading
to a cataract
Toxicity related
cataract
• Corticosteroids
• anticholinesterase
• hypocalcemia
• Antimalarial drugs
• Iron and gold
deposits
• Toxic chemicals
• Basic compounds
44. c) Systemic Disorders
Systemic disorders Description
Galactosemia Absence of enzymes that convert galactose to
glucose.
Cataract associated with the accumulation of
galactitol and lens swelling
Diabetes Mellitus Increase of glucose level in lens fibers causing
accumulation of sorbitol and leakage of water into
the lens
Fabry’s disease X-linked lysosomal storage disorder leads to
abnormal glycolipid into lens fibers creating opacity
Lowe’s syndrome Total cataract due to serious X-linked disorder leading
to a small lens + metaplastic EP
Alport’s syndrome Congenital/postnatal cortical cataract with anterior or
posterior Lenticonus and Microspherophakia
Dystrophia Myotonica Inherited disease where multilamellar disease causes
opacity
45. d) Dermatologic disorders
Similarity between skin and eye
Skin disorders are: Atopy, ichthyosis, Rothmund-
Thompson syndrome, Werner’s syndrome,
Incontinentia pigmenti and Cockayne’s syndrome.
e) Central Nervous System
disorders• Neurofibromatosis type II : development of symmetric,
non-malignant brain tumors in the region of the cranial
nerve VIII
• Zellweger syndrome: characterized by the
reduction/absence of functional peroxisomes in cells .
• Norries’s disease: mutation of the NDP gene on the X
chromosome, abnormal retina.
46. f) Local Ocular diseases
Glaucoma
the use of antiglaucoma drugs increases the chance of cataracts
Uveitis
Inflammation resulting in cortical opacities
Retinitis Pigmentosa
Gyrate Atrophy
Degenerative myopia
Retinal detachment and surgery
Tumors
Tumor of the ciliary body results cataracts
Infections
Herpes zoster or Rubella virus
47. Other Risk factors for cataract
formation
Severe diarrhea
Malnutrition and scarcity of antioxidants intake
(vitamin A,C and E) during meals
Smoking and alcohol
Inferior education
Gender: women are more prone to cataracts than
men
Genetics: linkage between specific genes and
cataract occurrence
48. Biochemical alterations during
cataract
In cortical cataracts: Soluble proteins content
decrease while insoluble proteins increase, leading
to a decrease in the protein content
In nuclear cataracts: insoluble protein increase.
Chromophores accumulate in cells resulting in brown
color in nucleus due to Protein + ascorbate
combination or protein + glucose combination
Proteins may be denatured by free radicals (UV
rays) consequently will be unfolded formation
of light scattering aggregates.
49. Diagnosis of the cataract:
With the use of a slit lamp biomicroscope.
51. 2. Old Extracapsular cataract extraction (ECCE):
An 8 mm to 10 mm incision is made in the eye at
sclera-cornea junction
Another small incision is made into the front portion of
the lens capsule. (capsulorrhexis)
The lens is removed, along with any remaining lens
material.
An IOL is then placed inside the lens capsule. And the
incision is closed.
52. 3. Intracapsular cataract extraction (ICCE):
Entire lens removed with capsule
Large incision
Capsule removed by traction side-to-side motion to
break the zonular fibers
Later on, an enzyme alphachymotrypsin that dissolves
the zonular fibers has been attributed to the success
and ease of the lens removal
53. Disadvantages of ICCE Advantages of ICCE
Delayed healing Removal of the entire lens so no
residues remain
Delayed visual rehabilitation,
aphakic eye
Less sophisticated equipment
Significant astigmatism
Iris confinement
Postoperative wound leaks with
inadvertent filtration
Vitreous imprisonment in the
wound might cause retinal
detachment or macular edema
Corneal edema commonly
occurs and endothelial cell loss
is greater than that of ECCE
54. ECCE vs ICCE
ECCE ICCE
Small incision: 5-6 mm Large incision: 10-12 mm
Posterior lens is conserved Removal of entire lens
No stitches required, self
healing
Required Stitches, long
rehabilitation time
IOL implant aphakic eye
Post op complications are
minimal
Added risk of retinal
detachment, corneal
edema and vitreous loss
55. ECCE: Phacoemulsification
Procedure for ultrasonically emulsifying the lens
nucleus by making small incisions.
1
• Cycloplegic/mydratic drops to dilate the pupil
2 • Small incision is made at the edge of the cornea
3
• Capsulorrhexis
4
• Small ultrasonic probe is entered
5
• Artificial intraocular lens is implanted
6
• Viscoelastic replace aqueous humor
58. Viscoelastics
Hyaluronic acid or hydroxyl methylcellulose
Used in low concentration with supercohesive,
cohesive, or dispersive properties that aid the
process of IOL implantation.
60. Generation I of IOL
Biconvex polymethylmethacrylate
(PMMA)
Implanted after ECCE
Lens used to get
dislocated and caused
troubles in the eye
Generation II of IOL
Implanted in the anterior chamber
after ICCE or ECCE (angle)
Epithelial atrophy, corneal
decompensation, and
uveitis-glaucoma-
hyphema.
Generation III of IOL
Iris-supported IOL
dislocation, papillary deformity and
erosion, iris atrophy
Generation IV of IOL
Intermediate anterior chamber IOL
Improved lens design
Improved manufacturing
techniques.
Kinds of IOL
Today’s IOL
Made up of PMMA, silicone or
acrylic.
Silicone and acrylic are foldable
and can be implanted by a small
incision.
Filters wavelength below 400nm
61. Secondary cataract
Posterior capsule opacification:
Develops in 50% of patients
Cells of the original cataract can grow and migrate
to the center of the posterior capsule
62. Types of secondary cataract
Type Description
Fibrosis-type posterior capsule
opacification
• The anterior epithelial cells form
spindle-shaped fibroblast and
migrate to the posterior capsule
• Appearance of white opacities
leaving fine folds and wrinkles in the
posterior capsule.
Pearl-type posterior capsule
opacification
• Residues of equatorial epithelial
cells form pearl like structure on the
posterior capsule
• Due to mass cells loosely
connected and piled on top of each
other
63. Other Causes of PCO
Soemmerring’s ring
Increase in volume of lens fibers between the
anterior and posterior chamber
64. Other Causes of PCO
Breakdown of the blood-aqueous humor:
Inflammatory cells released
Inflammatory response to the foreign IOL
Fibrils are deposited on the IOL and capsule
causing opacities
Bacteria may also enter
`
65. Prevention of PCO:
Removal of epithelial cells and cortical remnants
Infusion of saline water under the capsule killing epithelial
cell residues
Implanting IOL reduces the migration of epithelial cells
Cleaning the anterior chamber with an ultrasound irrigating
scratcher
Freezing posterior capsule to form intracellular ice crystals
Minimizing the breakdown of blood‐aqueous barrier
Pharmacological agents to stop the proliferation of epithelial
cells
66. Treatment of PCO:
The eye
is dilated with
dilating eye
drops.
A laser removes
the hazy
posterior capsule
without an
incision
anti-inflammatory
eye drops
following the
procedure.
A YAG laser can treat posterior capsule opacity safely,
effectively and painlessly.
YAG laser capsulotomy involves just a few simple
steps:
Biconvex, transparent, non-innervated and non-vascularized structure
Anterior surface less convex than posterior surface
Anteroposterior axis runs from the anteroposterior poles
The equator in perpendicular to the anteroposterior axis
Lens is 3.5 mm away from the cornea
Vitreous is in contact with posterior surface
Aqueous is in contact with anterior surface
Is held in place by zonular fibers
Elastic membrane made up of epithelial cells and fibers
Capsule is permeable in both directions to small molecules like water, ion and small protein
Constantly reproduced by the basal membrane of the lens epithelium anteriorly and the basal membrane of elongating fiber cells posteriorly
Thickest area is near the equator, thinnest region is at the posterior surface
Capsule of the lens is composed of stacked lamellae made up of collagen, laminin, heparin sulfate proteoglycan, enatacin, and fibronectin.
Collagen for adhesion and fibronectin aids in cellular migration
Collagen for adhesion and fibronectin aids in cellular migration
Adhere to each other by desmosomes, hindering the free movement of macromolecules, but allowing movement of small molecules
Contains developed cytoskeleton
Cortex divided into Deep, intermediate and superficial
Embryonic nucleus: made up of primary lens fibers
Fetal nucleus: all secondary fibers added before birth surrounding embryonic nucleus
Infantile nucleus: secondary fibers added till the age of 4 surrounding the fetal nucleus
Adult nucleus: secondary fibers added before sexual maturity surrounding the infantile nucleus
During childhood
Outgrowth of the secondary fibers 6 branch star shaped suture at both poles
Adolescence
9 branch star shaped suture
Formation of the adult nucleus
12 branch star shaped suture extending at both poles of the lens
Diameter of lens increases from 5mm to 9-10 mm
Thickness increases from 3.5-4mm to 4.75-5 mm
The metabolic needs of the lens are supplied by the aqueous humor and the vitreous body with which the lens is in direct contact.
Crystallins are negatively charged and thus attracts the positively charged ions from the extracellular fluid to maintain intracellular neutrality
This causes an intercellular increase in ionic concentration compared to extracellular fluid
By osmosis water passively diffuses into the cell threatening the cell to burst
But active channels pumps Na+ and K+ ions out of the lens to maintain appropriate lens osmolarity and volume, with equatorially positioned lens epithelium cells contributing most to this current. The activity of the Na+/K+-ATPases keeps water and current flowing through the lens from the poles and exiting through the equatorial regions.
When the extracellular Ca2+ increases, Ca2+ leaks into the cell; and when the extracellular Ca2+ decreases, calmodulin‐regulated Ca2+‐ATPase pump transport Ca2+ out of the cell.
Neutrality
Constant extrusion of H+ from the lens
Buffering the intracellular medium by proteins
Presence of transporters like Na+/HCO3
Posterior cells get elongated into the cavity towards the anterior cell layer. The elongated cells form the primary lens fibers. Proteins called crystallins are created. Crystallins account for transparency while increasing the index of refraction of the lens.
Primary cells here lose their nuclei and other cellular organelles and become inert structure. Anterior cells will continue to divide along the equatorial edge and these cells will start to form secondary fibers
Anterior cells at the edges of the cell layer begin to grow and start forming secondary lens fibers by elongating along the posterior surface, as it migrates to the center of the lens its left with only cytoskeleton and crystallins.
Secondary lens fibers have finished forming and they form rings around the primary lens fibers. The process of secondary lens fiber repeats as the lens gain size and weight
The original primary lens fibers persist to form the nucleus as the cortex of secondary lens fibers increase in size.
The lens allows the passage of 90% of light, absorbing the UVA and UVB light rays
During early embryonic stages the lens is opaque but as it loses vascular supply it becomes more and more transparent
The major proteins in the lens are highly concentrated, small in size and closed packed for minimal light scattering.
Any increase of size of these proteins or more spacing would result in the development of cataract.
Metaplasia: Transformation of cells from a normal to an abnormal state.
Lens can change its focusing power enabling it to visualize near and far objects
Anterior surface change curvature to accommodate for near objects keeping the posterior surface unchanged
Change is due to contraction of the ciliary muscles which allow the thickening of the lens for an increase in focusing power.
Nuclear cataract due to increase nucleus density
Radiation cataract:
Ionization of the water due to X-rays, gamma rays or microwaves releases free radicals that damages DNA which results in altered protein synthesis leading to a cataract.
Infrared is non-ionizing but raises the temperature of the iris resulting in posterior subcapsular cataract.
Toxicity related cataract:
Use of Corticosteroids (prednisone, dexmethasone), anticholinesterase, hypocalcemia, antimalarial drugs, Iron and gold deposits, Toxic chemicals and Basic compounds are all causes for cataract.
The skin and the lens originated from the same ectodermal origin, it’s simple to have many skin disorders associated with cataracts: Atopy, Ichthyosis, Rothmund-Thompson syndrome, Werner’s syndrome, Incontinentia pigmenti and Cockayne’s syndrome.
Retinitis Pigmentosa : degenerative eye disease that causes severe vision impairment ( causing retinal degeneration)
Gyrate Atrophy: is an inherited disorder characterized by progressive vision loss.
In cortical cataracts: Soluble proteins content decrease while insoluble proteins increase, leading to a decrease in the protein content
In nuclear cataracts: insoluble protein increase. So Chromophores accumulate in cells resulting in brown color in nucleus due to the combination of Protein + ascorbate combination or protein + glucose
Proteins may be denatured by free radicals which are produced by UV rays or liquefied by the activity of proteolytic enzymes. Proteins consequently will be unfolded and result in formation of light scattering aggregates.
Accumulation of alcohol in the lens leads to increased water influx into lens damaging the lens fibers.
A sharp instrument, such as a thorn or needle, is used to pierce the eye either at the edge of the cornea or the sclera, near the limbus. The opaque lens is pushed downwards, allowing light to enter the eye. Once the patient sees shapes or movement, the procedure is stopped. The patient is left without a lens (aphakic), therefore requiring a powerful positive prescription lens to compensate.
the surgeon makes an incision in the cornea at the point where the sclera and cornea meet, then he makes a circular tear in the front of the lens capsule; this technique is known as capsulorrhexis. The surgeon then carefully opens the lens capsule and removes the hard nucleus of the lens by applying pressure with special instruments. After the nucleus has been expressed, the surgeon uses suction to remove the softer cortex of the lens. A special viscoelastic material is injected into the empty lens capsule to help it keep its shape while the surgeon inserts the IOL. After the intraocular lens has been placed in the correct position, the viscoelastic substance is removed and the incision is closed with two or three stitches.
the surgeon makes a large opening in the eyeball and injects medicine into the eye, causing the zonular fibers that hold the lens in position to dissolve. A special probe is then placed on the lens, and liquid nitrogen is applied to freeze the lens. As the probe is gently withdrawn from the eye, the natural lens is pulled out with it. Once the natural lens is removed, an intraocular lens implant is inserted in front of the iris.
Nowadays the most followed procedure is the ECCE. This has been attributed to the growing use of operating microscope that has significantly increased the rate of success of the ECCE procedures. By retaining the posterior capsule, the risk of retinal detachment and corneal edema becomes minimal. The incision to be made is much smaller than that of the ICCE and since the posterior capsule remains intact an (IOL) is fixed easily.
First, ECCE required large incisions in the cornea since the cataractous lens was removed as a whole and the IOL implanted safely in the posterior capsule. But with the development of foldable IOLs, small incision in the cornea allowed the extraction of the fragmented cataract and the insertion of the IOL.
-Administering cycloplegic/mydratic drops to dilate the pupil -A small incision is made at the edge of the cornea
-An opening in the membrane (capsule) that surrounds the Cataractous lens is cut. (capsulorrhexis)
-A small ultrasonic probe is entered through the opening in the cornea and capsule. The probe’s vibrating tip breaks up or “emulsifies” the cloudy lens into tiny fragments that are suctioned out of the capsule by an attachment on the probe tip.
-The probe is withdrawn after removing the lens leaving only the clear bag like capsule, and an artificial intraocular lens is implanted
- When the incision is made into the eye it has a tendency to collapse as the aqueous humor leaks out. The larger the incision, the larger the probability for the eye to collapse and the greater risk to the patient. By replacing the aqueous humor with a thicker viscoelastic, we can prevent the collapse of the eye, absorb free radicals generated from the emulsification and protect ocular structure.
Procaine, Proparacaine, Oxybuprocaine, Tetracaine, Bupivacaine, Etidocaine, Lidocaine, Prilocaine, Ropicacaine
This injection provides akinesia of the extraocular muscles by blocking cranial nerves II, III, and VI, thereby preventing movement of the globe. Cranial nerve IV lies outside the muscle cone, but is blocked by diffusion of the local anesthetic. It also provides sensory anesthesia of the conjunctiva, cornea and uvea by blocking the ciliary nerves. This block is most commonly employed for cataract surgery, but also provides anesthesia for other intraocular surgeries.
