Corneal Surgical Procedures

penetrating keratoplasty

• transplant of the entire corneal thickness (usually 6-9mm area depending on pathology)

• pro: provides a clear cornea layer

• con: often the new cornea is irregular

trephine

• PK method

• pro: creates smooth cut

• con:

  • minimal surface area b/t graft & host means less stability & strength & more unevenness to the tissue

  • sutures need to be left in for a long time

femtosecond laser

• PK method

• pro:

  • suturing may not need to be as precise

  • sutures do not need to be as tight

  • better front-to-back alignment means more consistent surface (fewer issues w/ sunken or bulging effects)

  • broader surface area b/t graft & host means sutures can come out sooner & CLs can be fit earlier

• con: cost & availability of lasers

deep anterior lamellar keratoplasty (DALK)

• transplants the anterior 90-95% of the cornea

• uses a big bubble to separate the corneal lamellae

• pros:

  • can use lower quality grade graft tissue

  • preserves the natural endothelium (less rejection risk)

• cons:

  • the interface b/t the graft & host can cause visual degradation (need to go as deep as possible to minimize vision issues)

  • if you perforate the cornea during the procedure, there is an issue if the graft tissue is poor

descemet’s stripping automated endothelial keratoplasty (DSAEK)

• removes posterior 5% of the cornea

• useful for endothelial dystrophies & degenerations

• pros:

  • leaves the anterior 95% of the cornea intact

  • less risk of rejection

  • less surface irregularity means less change in Rx

  • much faster recovery

• cons:

  • the graft host interface can create loss of BCVA

  • more complex procedure w/ shorter lifespan for graft

descemet’s membrane endothelial keratoplasty (DMEK)

• same procedure as DSAEK but instead of cutting off graft w/ a keratome, the endothelium is peeled off

• pros: no stroma, stroma interface means better visual outcome

• cons: more challenging than DSAEK since the graft tissue is so thin

1. cornea needs to be precisely shaped to have good vision

2. it is hard to get the needed precision w/ current techniques

why do transplant pts need CLs?

steepest

the lens is loosest where the cornea is _____

1. likely to have irregularity in some areas

2. may need greater oxygen supply & tear exchange than non-graft corneas

what are some considerations when fitting corneal grafts?

1. risk of neovascularization

2. issues w/ tear exchange

3. often have very high cyl & need custom lenses

what are some of the issues w/ fitting corneal graft pts w/ soft lenses?

1. risk of neovascularization

2. issues w/ tear exchange

3. limited parameters

4. cannot correct residual cyl

5. hybrid designs do not lend themselves well to grafts

what are some of the issues w/ fitting hybrids on corneal graft pts?

1. good O2 permeability

2. good tear exchange

3. many pts w/ grafts have used GPs previously

what are some of the pros of fitting corneal grafts pts in GPs?

flatter

generally fit corneal graft pts ______ than you would expect in GPs

9.8-11.8

what diameter range do we typically use for fitting corneal graft pts w/ GPs?

mean K

what BC do you start with when fitting corneal graft pts w/ GPs?

lid attached & flat

how do we generally fit corneal graft pts in GPs?

scleral lenses

can work well for graft pts that cannot tolerate GPs as long as you use a hyper Dk material & get the right amount of corneal vault

sclerals

• pros:

  • don’t have to worry about corneal terrain

  • fluid reservoir can help w/ corneal health

• cons:

  • harder for older pts to handle

  • more expensive

  • corneal edema & neovascularization risk if not fit well

1. ocular surface is compromised

2. pt is not adaptive to GPs

what corneal graft pts might do well w/ sclerals?

1. try not to overvault

2. try to center

3. try to avoid suctioned on fit

what are some considerations when fitting corneal graft pts in sclerals?

T

T/F: it is common to have areas of minimal vault & excessive vault due to the shape of the graft when fitting sclerals

1. change in RE

2. presbyopia

3. irregular astigmatism

4. surgical complications

what are some issues that can arise w/ refractive surgery?

1. RE (high hyperopia)

2. fluctuating vision

3. irregular astigmatism

4. sensitive corneas

5. progressive ectasia

what are some post-RK problems?

1. RE

2. irregular correction

3. post surgical ectasia

what are some post-LASIK problems?

larger

flat zone w/ laser vision correction is ______ than RK

large diameter, reverse geometry

what types of lenses are post-refractive surgery eyes often fit in?

1. comfortable

2. stable

3. custom fit to eye shape

4. provide GP quality vision

5. stabilize VA for those w/ fluctuations

6. little to no contact w/ sensitive cornea

what are the benefits of fitting post-refractive surgery eyes in sclerals?

laser removes tissue but RK moves it around

explain why the eye is shallower post LVC vs RK (but both are still shallower than normal eye)

T

T/F: soft lenses can work for post-refractive surgery pts

F

T/F: daily disposables are good for post-refractive surgery pts

T

T/F: custom soft lenses have a flatter BC & steeper secondary curves that might be better for post-refractive surgery pts

F

T/F: corneal GPs are good for post-refractive surgery pts

corneal crosslinking

• tx for KC to increase the stiffness of the corneal tissue & slow or stop the progression of the disease

• risks: central haze, slow epithelial healing

epi on

can you fit CLs in epi on or epi off CXL faster?

intrastromal corneal ring segments (INTACS)

• add support to thinned area of cornea to prevent forward bulging in KC

• provide a structural supporting element to the thinned & abnormal tissue

• does not slow progression

~3.50

corneal intacs have been shown to reduce myopia by _____D

~1.25

corneal intacs have been shown to reduce astigmatism by ____D

~3.5

corneal intacs have been shown to flatten Ks by ____D

1. younger age

2. male

3. minimum central thickness of >400um

what pt characteristics have been associated w/ better intacs outcomes?

1. low myopes

2. VA is worse than expected through GP

who are optimal pts for intacs?

1. hyperopes

2. high myopes

3. 20/20 BCVA w/ a GP

who are less than optimal intacs pts?

paracentral & peripheral

single inferior segment intacs may be more appropriate for __________ cones

1. central steep area

2. low astigmatism

3. 3+ D of myopia

what pt types need double segment intacs

1. segment migration

2. dehiscence of incision site

3. neovascularization

4. corneal melt over incisions

what are some of the post-surgical complications of intacs?

one

do GPs tend to work better w/ one or two intacs segments?

1. comfort

2. convenience

3. part time use

4. lower Rx

5. pts are comfortable w/ post-op SPRx vision

soft lenses are a good option for post-intacs pts for:

T

T/F: piggybacking is a good option for intacs pts

F

T/F: scleral lenses are not good for intacs pts

oblate

what type of scleral is best for 2 intacs segment pts?

prolate

what type of scleral is best for 1 intacs segment pts?

central

the more _____ the irregularity in the post surgical fit, the more useful a standard diameter GP will be

larger

the more peripheral the irregularity in the post surgical fit, the more a ______ lens is needed