Cataract Flashcards
What conditions are associated with weakened zonules?
• PXF
• Prior vitreoretinal surgery
• Trauma
• High myopia
• Connective tissue disorders (Marfan’s, homocystinuria,
hyperlysinemia Ehler Danlos, scleroderma,
Weil-Marchesani)
• Uveitis
• Retinitis pigmentosa
What are the absolute contraindications for LASIK?
• Asymmetric bowtie
• Areas of superior or inferior thinning
• Ectatic disorder: keratoconus, pellucid marginal
degeneration, keratoglobus
• Thin central cornea
• Residual stromal bed <300 μm
• High preoperative potassium values
• Young age
What refractive change can occur after scleral buckle?
• Myopic shift secondary to axial elongation
What are the 3 main sources of error when calculating IOL power in post-refractive surgery eyes?
- Radius error (true central K is flatter than K reading
obtained from instruments) - Keratometer index error (index of refraction assumes a
certain ratio between the radii of curvature of anterior
and posterior corneal surface) - Formula error
All of these lead to hyperopic surprise
What are the types of topographic maps and what types of corneal power do they measure?
• Axial power map/sagittal curvature map: based upon
reference axis through line of sight and better
estimation of central corneal power
• Instantaneous/tangential or meridional map: gives
corneal power based on best fit spherical
approximation at corneal point measured and is better
estimation of peripheral corneal power
What is photoablation?
• Use high-energy ultraviolet photons to break covalent
chemical bond, no heat is produced
• Excimer laser (193 nm)
• Used in keratorefractive procedure
What is photocoagulation?
• Head generated by absorption of light denatures
protein
• Used in retinal photocoagulation (PRP)
• Laser thermokeratoplasty (LTK) treat hyperopia
What is photodisruption?
• Wavelength produced by the Nd-YAG laser. This type of
laser is pulsed, so the energy it produces is released in
a very short time, producing a large amount of
momentary power
• The laser beam is focused into a small area. In the
vicinity of the focus, electrons are stripped from their
atoms by ionization, but they quickly recombine, which
produces a spark and an acoustic wave
• During a photodisruption procedure, it is the
mechanical (acoustic) wave and not the laser light itself
that breaks the capsule.
What is photoactivation?
• The conversion of chemical from one form to another
by light
• Clinical application includes verteporfin used in PDT
What type of cataract is associated with Alport syndrome?
• Anterior lenticonus (bilateral)
What is the most common ocular complication with chronic hyperbaric oxygen?
• Nuclear sclerotic cataracts, results in myopic shift
• ~50% of patients exposed to hyperbaric oxygen >150
times during 1-year period will develop cataracts
What is orthokeratology?
• Rigid CL that is flatter than the cornea to push down on
the cornea, cause remolding of corneal epithelium
• Treats low orders of myopia
• 73% experienced CL discomfort in the clinical trial,
corneal edema occured in large number of patient
What is aqueous misdirection syndrome?
• AKA ciliary block glaucoma
• Aqueous is directed into vitreous instead of flowing
through pupil
Treatment: mydriasis and cycloplegia (phenyl 10% and
atropine), aqueous suppressants, hyperosmotic. If medical
treatment fails → disruption of anterior hyaloid face with
YAG laser or PPV
What are the most common gases used in excimer lasers?
• Argon and Fluorine
What are the wavelengths of different lasers?
• Femtosecond: 1053 nm (infrared)
• Excimer: 193 nm (UV light)
• Nd:YAG: 1064 nm
• Rhodopsin most sensitive at 510 nm (green light). Less
absorption of blue and yellow light. Cannot absorb
longer wavelengths (red)
What is Fuchs heterochromic iridocylcyitis?
• Chronic uveitis; long and fragile vessels that cross angle
and insert high in angle (25% nicked when entering AC)
• Unilateral without severe pain or photophobia
• Stellate KPs
• Iris heterochromia (blue eyes appear dark; brown
appear lighter)
• Lack of anterior/posterior synechiae
• PSC 75%
• Difficult to control glaucoma (will likely require surgery)
Treatment: not necessary to treat inflammation, focus on
glaucoma screening/management and cataract removal
Where are lens epithelial cells mitotically most active?
• Anterior pre-equatorial capsule
What are the different types of CL and duration of holiday needed before normalization on topography?
• Soft spherical CL: 3-14 days
• Soft toric lens: 2 weeks or more
• Rigid contact lens: at least 2-3 weeks (causes epithelial
migration), additional month for every decade of hard
contact lens wear
What are limbal relaxing incisions?
• 600 microns in depth
• Just anterior to limbus ~2 mm
• Done on steep meridian
• Maintain spherical equivalent (coupling ratio = 1)
What is arcuate keratotomy?
• 95% in depth
• Placed at 7 mm optical zone
• Done on steep meridian
• Maintain spherical equivalent (coupling ratio = 1)
• Flattening in the meridian of incision and steepening 90
degrees away (coupling)
What is spherical aberration ?
• Higher order aberration (4th order)
• Decrease in quality of vision after refractive surgery
• Peripherally refracted light rays are focused in front of
retina and central rays are focused on the retina
• Halos around point light sources night myopia
• Decreased contrast sensitivity
What is the most serious complication of piggyback lenses?
• Interlenticular opaque membrane
• Most commonly occurs when two acrylic IOLs are used
especially if they are both placed in the capsular bag
What are transversion incisions?
• Straight incisions
• Parallel to limbus
• Coupling ratio >1
• Hyperopic shift
What is coupling ratio?
• Amount of flattening induced by incision
• Amount of steeping induced 90 degrees away
What is corneal Collagen cross-linking?
• Strengthens stabilize cornea
• Used in ectatic corneal disorders (KCN, PMD,
post-refractive ectasia)
• Expose cornea to riboflavin (B2) and UVA
• Increases rigidity of cornea and reduce ectatic process
• UVA light penetrates 300 μm and can destroy
endothelial cells.
• Corneal thickness at least 400 μm prior to UVA
• If cornea not thick enough, use hypotonic riboflavin
until cornea swells over 400 μm
• Contraindications: Corneal thickness <400 μm, prior
herpetic infection, central corneal scarring, poor
epithelial healing, severe dry eye, autoimmune
disorders
What is chatter?
• Nuclear fragment repelled by phaco tip
• Not desirable because lens can’t be aspirated
efficiently
• Allows lens pieces to have greater chance of striking
corneal endothelium
• Happens when ultrasound stroke > vacuum
• To decrease chatter-reduce phaco power which
reduces stroke length of phaco tip or increase vacuum
setting
What is duty cycle?
• Proportion of time phaco energy is applied during
specified period of time
What is stroke length?
• Distance phaco tip travels
• Usually 2-4 mil (1 mil=1/1000 of inch)
What is cavitation?
• Shock waves that are released as gas bubble implodes
at phaco tip
• Due to compression and expansion of gas atoms
• Shock waves helps break down lens fragments so they
can enter phaco tip
What is the pathway responsible for diabetic cataracts?
• Sorbitol pathway
What are the findings of Keratoconus?
• Ectatic disorder
• More common starts at puberty
• Maximal thinning at apex
• Asymmetric steepening
• Scissoring with retinoscopy
• Fleischer ring
• Scarring is common
What is Pellucid marginal degeneration and its finding?
• Less common, onset 20-40s
• Maximal thinning inferior to area of protrusion
• Scarring only after hydrops
• Crab-claw confirmation on topography
What are the findings of Keratoglobus?
• Very rare, onset at birth
• Thinning greatest in periphery
• Protrusion in generalized
• No iron line or scarring
What is against-the-rule astigmatism?
• Football sitting on one of its poles (horizontal
meridian is shorter)
• Too much power along horizontal meridian
• Cylinder correction that provides focusing power
vertically no additional power horizontal
Treatment:
• Minus cylinder vertically (exerts power long its axis)
• Positive cylinder horizontally (exerts power 90
degrees away)
What is with-the-rule astigmatism?
• Football lying on its side
• Steepest part of cornea along vertical meridian
• Cylinder correction that provides focusing power
horizontally no additional power vertical
Treatment:
• Negative cylinder at 180 degree (exert power along
its axis)
• Positive cylinder at 90 degrees (exert power 90
degrees away)
How many days prior to surgery should anti-platelet be stopped so normal platelet function is restored?
• 10 days, i.e. Aspirin, clopidogrel, vitamin E
• Hold for ocular surgeries at risk of suprachoroidal
hemorrhage (PKP, glaucoma surgery)
What is Glaukomflecken?
• High IOP during angle closure glaucoma lead to lens
epithelial death leads to gray-white anterior
subcapsular opacities
• Pinpoint opacities measuring 2-3 mm or more in size
What is Brown Mclean syndrome?
● Peripheral corneal edema after cataract extraction
● Edema begins several years after surgery
● Corneal edema characteristics:
○ Peripheral 2-3 mm
○ Central cornea spared
○ Starts inferiorly and extends circumferentially
○ Punctate brownish pigmentation, localized
guttae
○ No neovascularization of cornea
○ Associated with long term aphakia
○ After routing cataract surgery, vitrectomies
○ No etiology
Most are asymptomatic, may complain of foreign body
sensation secondary to ruptured bullae
What are zero order, 1st order, and 2nd order aberrations (lower order aberrations)?
• Zero order: piston
• 1st order: vertical and horizontal prism
• 2nd order: myopia, hyperopia, regular astigmatism
What is the rate of visually significant PCO?
● 28% at 6 years
● Rate of formation for different intraocular lens (lowest
to highest):
Acrylic < silicone < PMMA
● Occurs when lens epithelial cells migrate across
posterior capsule and cause contraction of secreted
collagen matrix, this can result in capsular wrinkling
and PCO
What is a Soemmering Ring?
• After cataract surgery, residual lens epithelial cells
proliferate in closed space between anterior and
posterior capsules.
• Consists of nucleated bladder cells = Wedl cells
What is an Elschnig pearl?
• Epithelial cells proliferate in large spherical aggregates
like “fish eggs” where each “ fish egg” is nucleated
bladder cell
What are the risk factors for choroidal hemorrhage?
• Older patients (brittle choroidal blood vessels)
• Glaucoma
• Previous hemorrhage in fellow eye with intraocular
surgery
• Myopia
• Hypertension
• Arteriosclerosis
• Bleeding diathesis
• Recent trauma or surgery with active inflammation
• Prolonged hypotony
• Anticoagulation
What is the minimal residual stromal bed thickness needed for LASIK?
• 250 microns, most leave > 300 microns
What situation is associated with highest rate of endophthalmitis after cataract surgery?
• Hypotonous eye with leaking wound
• Leaking wound acts as conduit for bacteria to enter
eye
What is the holding force?
• Force that is exerted on the nuclear piece when tip if
fully occluded
What is Epi-LASIK?
• Blunt microkeratome to remove epithelium, then
ablate stromal bed
• Plane of separation is between basement membrane
and Bowman’s layer
How is LASEK performed?
• Place alcohol on epithelium, remove epithelium,
laser the bed, then replace epithelium back on the
stromal bed
• Plane of separation is between lamina lucida and
lamina densa
• Leaving behind lamina densa may provide better
postoperative refractive result compared to
epi-LASIK (controversial)
What is PRK?
• Scrape epithelium off with brush or spatula then
ablate stromal bed
What are the various forms of potential acuity estimation for cataract evaluation?
• Potential acuity pinhole (PAP): read a brightly lit
near card through standard pin line aperture. Dilate
prior to this test
• Potential acuity meter (PAM): projecting Snellen
chart through tiny aperture. Projected chart is
moved around patient pupil until clear path is
obtained and patient can see projected Snellen chart
• Laser interferometry (LI): Projects 2 separate laser
beams onto retina. 2 light beams interfere with each
other creating a diffraction fringe pattern on the
retina. Pattern independent of lens opacities.
Spacing of the fringe pattern is decreased until
patient cannot distinguish separate lines, may
sometimes overestimate potential acuity
What is photostress recovery time?
• “Poor man’s electroretinogram”
• Bright light is shined into patient’s eye for 10
seconds through undilated pupil
• The time required before patient can read BCVA line
or one line larger = photostress recovery time
• >90 seconds indicates significant maculopathy
• Distinguishes optic nerve disease from macular
disease
What are the Y sutures in lens?
• Anterior upright Y suture
• Posterior inverted Y suture
• Y sutures appear around 8 weeks of gestation
What is a posterior chamber phakic intraocular lens (PIOL)?
• Used in refractive surgery when patient has
contraindications to corneal refractive surgery
• Lenses are flexible collamer material, inserted
through small corneal wound into ciliary sulcus
• “Vaulted” over crystalline lens to prevent contact
with it
• Space between PIOL and crystalline lens allows
aqueous to flow over crystalline lens which prevent
cataract formation
• Ideal space 0.5-1.5 corneal thickness
• Vault less than 250 micron → risk of anterior
subcapsular cataract
• Vault greater than 750 microns → risk of crowding
angle and pupillary block glaucoma, iris chafing
What is the most common type of cataract in acute diabetes?
• Cortical in nature-snowflake cataracts
What are the causes of AC shallowing during cataract surgery?
• Inadequate infusion of BSS
• Leakage through oversized incision >3.0 mm
• External pressure on globe (improper speculum, too
tight surgical drapes, tight eyelids, too much
retrobulbar anesthesia)
• Posterior vitreous pressure (obese, thick neck,
COPD)
• Suprachoroidal hemorrhage
Shallow AC can lead to radialization of capsulorhexis,
more phaco energy transmitted to corneal endothelium,
repeated iris prolapse through main wound
What is diffuse lamellar keratitis (DLK)?
• Interface inflammatory process that begins as
dust/sand-like infiltrate in interface of periphery
• Untreated → stromal melting and corneal scarring
with resulting irregular astigmatism
• Associated with epi defects, occur during LASIK,
foreign material lodged in interface, contamination
of sterilizer with gram negative endotoxin
What are the different grades of diffuse lamellar keratitis (DLK)?
• Grade 1: peripheral faint WBCs, no central corneal
involvement - Tx topical steroids, follow q2-3 days
• Grade 2: WBC migrated to central cornea - Tx topical
steroids, consider interface irrigation, follow q1-2
days
• Grade 3: dense WBC clumped in central cornea,
beginning of corneal scarring; “threshold DLK”
permanent visual morbidity if treatment is not
initiated; typically occurs post op day #2 or 3 - Tx lift
flap, clean interface, intensive topical steroids
consider oral steroids
• Grade 4: stromal melting and permanent corneal
scarring, hyperopic shift, “mud cracks,” poor
prognosis even with above treatments
What is accommodation?
- Ciliary muscle contracts
- Zonular tension decreases
- Axial lens thickness increases
Hardening of lens is primary cause of loss of
accommodation (presbyopia) because a harder lens will
prevent increase in convexity that occurs with ciliary
muscle contraction
Helmholtz theory of accommodation = most
accommodative change in lens shape occurs at the
central anterior lens surface; posterior capsule does not
change at all with accommodation
What is the difference in ablation pattern in hyperopic LASIK versus myopic LASIK?
• Myopic: center of bed is lasered to flatten cornea,
make cornea less dioptrically powerful
• Hyperopic: periphery of bed is lasered to steepen
cornea and make cornea more dioptrically powerful
• Once ablation is complete, flap is laid back down
What is the mechanism by which mitomycin C application after surface ablation prevents corneal haze?
• Reduces number of keratocytes and their enzymatic
activity
(activation of keratocytes after surface ablation
leads to haze, keratocytes lay down collagen and
glycosaminoglycans)
What is the most common type of congenital and infantile cataracts?
• Lamellar or zonular cataracts
• Lamellar cataract: opacifications of specific zones
within lens; typically bilateral and symmetric
What is TASS (toxic anterior segment syndrome)?
• Sterile inflammatory reaction
• Secondary to contaminants injected into the eye or
incorrect pH of irrigating solutions
• Commonly occurs when remnants of cleaning
detergents are not properly washed out of reusable
cannula
• Presents in acute post-op period (12-24 hours),
earlier than acute endophthalmitis (2-7 days)
• Confined to anterior segment
• Treatment: exclude endophthalmitis as cause of
inflammation; intensive topical steroids; control IOP
if elevated
What is Ectopia lentis et pupillae?
• Iris with slit-like configuration that is displaced in
opposite direction as subluxed lens
• Autosomal recessive
What is the most common postoperative complication of LASIK?
• Dry eye – secondary to transection of corneal nerves
with flap creation
