Intraocular Refractive Surgery Flashcards
Phakic Intraocular Lenses - Advantages
removable, reversible, preserving natural accommodation, lower risk of endophthalmitis and postoperative retinal detachment because the crystalline lens barrier is preserved
Phakic Intraocular Lenses - Disadvantages
potential risks associated with intraocular surgery. optics are not foldable, so their insertion requires a relatively large wound, which may result in postoperative astigmatism. Posterior chamber PIOLs have a higher incidence of cataract formation. PIOL will have to be explanted at the time of cataract surgery
Phakic Intraocular Lenses - Indications
near or beyond the FDA-approved limits for laser vision correction, or who are otherwise not good candidates for keratorefractive surgery. –3.00 D and –20.00 D. hyperopia up to +10.00 D. off label for irregular topographies from forme fruste or frank keratoconus
Phakic Intraocular Lenses - Contraindications
compromised corneal endothelium, iritis, significant iris abnormality, rubeosis iridis, cataract, or glaucoma
Risk - Anterior chamber depth
less than 3.2 mm
recommended for all currently FDA-approved PIOLs
peripheral iridotomy is recommended for all PIOLs to reduce the risk of pupillary block and angle closure; is not required for angle-supported PIOLs
Iris-fixated phakic intraocular lens - technique
induce pupillary miosis before. The “claw” haptics are fixated to the iris in a process called enclavation
Advantage Iris-fixated phakic intraocular lens over PIOLs
PMMA PIOLs require a 6-mm wound. and thus generally require sutures for proper closure, whereas iris-fixated PIOLs made of flexible materials can be inserted through a small, self-sealing wound of approximately 3 mm.
Angle-supported phakic intraocular lens - advantage
inserted through a small incision without the need for pupil dilation
AC IOL - complications
include raised IOP, persistent anterior chamber inflammation, traumatic PIOL dislocation, cataract formation, and endothelial cell loss
Iris-fixated phakic intraocular lens - glare, starbursts, and halos
Posterior chamber phakic intraocular lens - complications
PIOLs increases the risk of cataract formation and pigmentary dispersion. If the posterior chamber PIOL is too large, vaulting increases. too small, the vaulting is reduced, decreasing the chance of chafing but increasing the risk of cataract.
Angle-supported phakic intraocular lens - complications
nighttime glare and halos 20.0%, pupil ovalization, and endothelial cell loss
Pupil ovalization - when
can occur because of iris tuck during insertion, or it can occur over time as a result of chronic inflammation and fibrosis around the haptics within the anterior chamber angle. Ovalization is more likely when the implant is too large
correct residual corneal astigmatism
relaxing incisions and arcuate keratotomies with either blade or femtosecond laser may be used to correct residual corneal astigmatism of less than 2.00 D. Supplemental surface ablation or LASIK could also be considered
upper limit of commercially available IOL power
+40.00 D
“piggyback” IOL system
2 posterior chamber IOLs are inserted. One IOL is placed in the capsular bag, and the other is placed in the ciliary sulcus
“piggyback” IOL system - complications
interlenticular opaque membrane. These membranes cannot be mechanically removed or cleared with the Nd:YAG laser; the IOLs must be removed. Interlenticular membranes have occurred most commonly between 2 acrylic IOLs, especially when both IOLs are placed in the capsular bag. When piggyback lenses are used, they should be of different material. Piggyback IOLs may also shallow the anterior chamber and increase the risk of iris chafing, especially in smaller eyes
Incidence of astigmatism
50% of patients have 0.75 D or more corneal astigmatism at presentation for cataract surgery, and 15%–29% have 1.50 D or more corneal astigmatism
rotation of the lens - reduction of correction
every 10° off-axis rotation of the lens reduces the correction by approximately one-third. it should be repositioned before permanent fibrosis occurs within the capsular bag. However, waiting 1 week for some capsule contraction to occur may ultimately help stabilize this IOL
Light-Adjustable Intraocular Lenses
The light-adjustable IOL is a 3-piece silicone-optic posterior chamber IOL that can be irradiated with ultraviolet light through a slit-lamp delivery system 1–2 weeks after implantation to induce a change in the shape, and thus the power, of the IOL. induce myopic, hyperopic, and astigmatic shifts. In initial work, results indicate that up to 5.00 D of spherical and up to 2.00 D of astigmatic change can be induced. after irradiation, the lens is functionally a monofocal
Accommodating Intraocular Lenses - mechanism
movement of its hinged haptics during the accommodative process
Multifocal Intraocular Lenses - mechanism
light rays to be split such that different focal points are created where objects will be clearest
pupillary diameter when unaided reading ability may diminish
less than 2.0 mm
Multifocal Intraocular Lenses - disadvantages
more sensitive to minor optic decentration, more likely to have significant glare, halos, and ghosting. reduction in contrast sensitivity, worse subjective quality of vision. intermediate vision may be less clear than distance or near acuity. more sensitive to posterior capsule opacification