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Kanski- FRCOphth Part 2 > Corneal and Refractive Surgery > Flashcards

Corneal and Refractive Surgery Flashcards

1
Q

What is grafting?

A

Corneal transplantation

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2
Q

What is a corneal transplanting?

A

the replacement of diseased host corneal tissue by healthy donor cornea.

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3
Q

What is the procedure of corneal grafting?

A

keratoplasty

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4
Q

When is Optical keratoplasty performed?

A

improve vision. Indications:
keratoconus, scarring, corneal dystrophies, pseudophakic bullous keratopathy and corneal degenerations

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5
Q

When is tectonic keratoplasty performed?

A

Restore or preserve corneal integrity in eyes with severe structural changes eg thinning with descemetocoele

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6
Q

When is Therapeutic keratoplasty performed?

A

facilitates removal of infected corneal tissue in eyes unresponsive to antimicrobial therapy

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7
Q

When is Cosmetic keratoplasty performed?

A

to improve the appearance of the eye, but is a rare indication.

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8
Q

When should donor tissue be removed from the patient?

A

12-24 hours of death.

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9
Q

Why are corneas from infants (3 and younger) rarely used?

A

Risk of surgical, refractive and rejection problems

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10
Q

What are some contraindications to ocular tissue donation?

A

*Death from unknown cause
Infections HIV, viral hepatitis, syphilis, congenital rubella, TB, Septicaemia, *Active malaria
*Prior high risk behaviour for HIV and hepatitis eg sex with HIV + men, IVDU and prostitution
*Engaging in high risk behaviour in last 12 months
*Infections of nervous system eg CJD, encephalitis, Alzheimer, Dementias, Parkinson Disease, MS, MND
*Receipt of a transplanted organ
*Brain/spinal surgery before 1992
*Haematological malignancies

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11
Q

What are some host factors which may adversely affect the prognosis of a corneal graft?

A

*Severe stromal vascularization, absence of corneal sensation, thinning at graft host junction
*Blepharitis, ectropion, entropion, active corneal inflammation
*Recurrence or progressive forms of conj inflammation eg OCP, Atopic conjunctivitis
*Tear film dysfunction
*Anterior synechiae
*Uncontrolled glaucoma
*Uveitis

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12
Q

What is a penetrating keratoplasty?

A

Full thickness keratoplasty

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13
Q

What are some key points about PK?

A

*Common graft size 7.5mm. Small grafts lead to high astigmatism and large diameter lead to PAS and raised IOP.
*Donor button 0.25mm bigger than host site
*Prep of donor cornea preceed excision of host tissue
*Mechanical guided manual/ automated trephination used
*Graft secured with continuous or interrupted sutures or combination

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14
Q

What is the post op management for PK?

A

*Topical steroid- pred used to decrease risk of immunologic graft rejection. Administer every 2 hours with gradual tapering. Long term- OD for 1 year
*PO azathiprine and systemic ciclosporin for high risk patients
*Cycloplegia (homatropine 2% for 1-2 weeks
*PO aciclovir- pre existing HSV to reduce risk of recurrence
*IOP monitoring with non-applanation method
*Removal of sutures when graft host junction healed after 12-18 months. Longer in elderly patients. Removal of broken sutures ASAP reduce risk of graft rejection

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15
Q

What are some early post op complications of PK?

A

*Persistent epithelial defects
*Loose sutures
*Wound leak
*Uveitis
*Raised IOP
*Traumatic graft rupture
*CMO
*Microbial keratitis
*Endophthalmitis and rejection
*RARE- Urrets Zavalia syndrome

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16
Q

What are some late post op complications of PK?

A

*Astigmatism
*Recurrence of underlying disease
*Wound dehiscence
*Retro corneal membrane formation
*Glaucoma
*Rejection
*Failure without rejection

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17
Q

What is the pathogenesis of corneal graft rejection?

A

Corneal graft immunologically privileged absence of blood vessel, lymphatics, few APC’s. If host sensitized to histocompatibility agents in donor cornea, rejection may result. HLA matching has small beneficial effect.

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18
Q

What are some predisposing factors to graft rejection?

A

*eccentric or larger grafts (over 8 mm in diameter),
*infection (particularly herpetic), *glaucoma
*previous keratoplasty
*Gender incompatiblity. Female donor used in male/female. Male to male only

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19
Q

What are some signs and symptoms of graft rejection?

A

Blurred vision, redness, photophobia, pain. Most asymptomatic until rejection established. Timing variable- days to years after keratoplasty.

Signs- Ciliary injection with anterior uveitis (early manifestation). Epithelial rejection with elevated line of abnormal epithelium
Subepithelial rejection with infiltrates, Krachmer spots on donor cornea with deeper oedema and infiltrative opacification.

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20
Q

What are some signs of corneal stromal rejection?

A

Stromal rejection features deeper haze.
Chronic or hyperacute- latter associated with endothelial rejection.
Endothelial rejection is characterized by a linear pattern of keratic precipitates (Khodadoust line)
Stromal oedema- endothelial failure

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21
Q

How to manage corneal graft rejection?

A

Early- can reverse rejection. Most aggressive regimen for endothelial -> stromal-> subepithelial -> epithelial rejection. IOP monitoring criticial.

PF steroids hourly for 24 hours. High risk maintained on QDS.
Cycloplegia OD/BD
Ciclosporin topical but onset delayed
Systemic steroids- PO pred 1mg/kg for 1-2 weeks with tapering.
Subconj steroid injection used
Systemic ciclosporin/tacrolimus/azathioprine

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22
Q

Difference between graft failure and rejection?

A

Graft failure- no inflammation

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23
Q

What is a superficial lamellar keratoplasty?

A

partial-thickness excision of the corneal epithelium and stroma so that the endothelium and part of the deep stroma are left behind as a bed for appropriately partial-thickness donor
cornea. The area grafted depends on the extent of the disease process to be addressed.

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24
Q

What are the indications for superficial lamellar keratoplasty?

A

Opacification of superficial 1/3rd of corneal stroma
Marginal corneal thinning/ infiltration in recurrent pterygium, Terrien marginal degeneration/limbal dermoid/other tumours
Localised thinning/descemetocoele formation

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25
Q

What is a DALK?

A

a technique in which corneal tissue is removed almost to the level of Descemet membrane.

26
Q

What are the advantages and technical difficulties of DALK?

A

Advantage- reduced risk of rejection as endothelium intact.

Difficulty- judging depth of dissection as close as possible to Descemet membrane.

27
Q

What are the indications for DALK?

A

Disease involving 95% of anterior corneal thickness with normal endothelium and absence of breaks/scars in descemet membrane eg keratoconus without hydrops, superficial trauma
Chronic inflammatory disease eg Atopic keratoconjunctivitis with increased risk of graft rejection

28
Q

What are the advantaged of DALK?

A

No risk of endothelial rejection although stromal, subepithelial, epithelial possible
Less astigmatism and stronger globe compared with PK
Increased availability of graft material since endothelial quality irrelevant

29
Q

What are the disadvantages of DALK?

A

Difficult time consuming high risk of perforation
Interface haze may limit final BCVA
Post op management similar to PK except lower intensity steroids and sutures removed after 6/12

30
Q

What is endothelial keratoplasty?

A

removal of diseased endothelium
along with Descemet membrane (DM) through a corneoscleral or corneal incision. Folded donor tissue is introduced through the
same small (2.8–5.0 mm) incision.

31
Q

DMEK vs DSAEK?

A

Descemet stripping (automated) endothelial keratoplasty (DSAEK) uses an automated microkeratome to prepare donor tissue and is currently the most commonly performed technique. A small amount of posterior stromal thickness is transplanted along with DM and endothelium. In Descemet membrane endothelial keratoplasty (DMEK)
only the DM and endothelium are transplanted.

Because the graft is only 5–10 microns thick it is difficult to handle. However, the grafts are able to attach to the host tissue with less unevenness, which leads to more rapid visual recovery. Visual outcomes and lower rejection rates are achieved, but intra-
operative complication rates are higher than DSAEK.

32
Q

What are the indications for endothelial keratoplasty?

A

Endothelial disease eg Fuchs endothelial corneal dystrophy

33
Q

What are some advantages and disadvantages of endothelial keratoplasty?

A

*Advantages
○Relatively little refractive change and a structurally more intact globe.
○Faster visual rehabilitation than penetrating keratoplasty.
○Suturing is minimized.

*Disadvantages
○Significant learning curve.
○Specialized equipment is required.
○Endothelial rejection can still occur

34
Q

What are stem cells?

A

undifferentiated cells that give rise to the differentiated cells that form tissues and organs. Tissue-specific stem cells are important for maintaining homeostasis and for tissue repair after injury.

35
Q

What are some features of the cornea in terms of regeneration?

A

Corneal epithelium is constantly self-renewing and does so throughout life. Progeny of corneal stem cells divide and differentiate to form basal corneal epithelial cells (transient amplifying cells) that differentiate into wing cells (post-mitotic cells) and, finally, superficial squamous cells (terminally differentiated cells).

36
Q

What are the signs of Limbal Stem cell deficiency (LSCD)?

A

*Conjunctivalization of cornea with goblet cells (confirmed on *Confocal/impression cytology with PAS/ mAB against cytokeratin 19)
*Superficial and deep corneal vascularization
*Fibrovascular pannus
*Persistent epithelial defects
*Scarring

37
Q

What is the algorithm for surgical intervention for LSCD?

A

*All associated lid abnormalities (lids, conjunctiva, IOP) treated first
*When visual axis involved, sequential sector conjunctival epitheliectomy first with sector limbal transplant
*In total unilateral stem cell deficiency, auto limbal transplantation procedure of choice
*In total bilateral stem cell deficiency, use of allografts from living related donor/ cadaver donor only option

38
Q

What are the indications for LSCD intervention?

A

Congenital: aniridia
Traumatic- chemical/ thermal burns
Chronic inflammatory disease- SJS/ OCP
Ocular surface malignancy
CL related pathology

39
Q

What are the advantages and disadvantages of LSCD surgery?

A

*Advantages
○Regeneration of corneal surface
epithelium.
○Visual improvement and improved comfort.

*Disadvantages
○Autologous graft: conjunctivalization, filamentary keratitis, scarring of donor eye.
○Allogenic graft: infection (especially in immune-compromised patients), rejection.

40
Q

What are keratoprostheses?

A

artificial corneal implants used
in patients unsuitable for keratoplasty. The modern osteoodontokeratoprosthesis consists of the patient’s own tooth root and
alveolar bone supporting a central optical cylinder and is usually
covered with a buccal mucous membrane graft. Surgery is difficult
and time-consuming and is performed in two stages, 2–4 months
apart.

41
Q

What are the indications for keratoprostheses?

A

Bilateral blindness from severe but inactive anterior segment disease with no chance of success from traditional keratoplasty eg SJS/OCP, chemical burns/ trachoma
Visual acuity CF or less in better eye
Intact optic never and retinal function without marked glaucomatous optic neuropathy.
High patient motivation

42
Q

What are the complications of keratoprostheses?

A

Glaucoma (75%)
Retroprosthesis membrane formation
Tilting/ extrusion
Retinal detachment
Endophthalmitis
Glaucoma management challenging

43
Q

What are the results like for patients undergoing keratoprostheses?

A

80% achieve VA between CF and 6/12 sometimes better. Poor outcome associated with pre-existing poor optic nerve/retinal dysfunction

44
Q

What kind of refractive errors can we correct currently?

A

Myopia
Astigmatism
Hypermetropia

No technique for Presbyopia

45
Q

How can Myopia be corrected?

A

*Surface ablation procedures- low-mod degrees of myopia
*LASIK- mod-high myopia depending on CCT.

For very high myopia
*Refractive lens exchange- correct myopia and myopic astigmatism
*Clear lens exchange good results but risk of cataract surgery eg retinal detachment in high myopia
*Iris clip implant- may sublux, dislocate due to dislodged attachments, endothelial cell loss, pupillary block glaucoma and RD
*Phakic posterior chamber implant- inserted behind iris and infront of lens. Supported in ciliary sulcus. Can lead to uveitis, pupillary block, endothelial cell loss, cataract
Radial keratotomy- historical interest

46
Q

How can Hypermetropia be corrected?

A

*Surface ablation for low degree of hypermetropia
*LASIK upto 4D
*Conductive keratoplasty- radiofrequency energy to corneal stroma correct low- mod hypermetropia and hypermetropic astigmatism. burns in 1-2 rings in corneal periphery using a probe
*Laser thermal keratoplasty- holmium laser for low hypermetropia. Laser burns in 1-2 rings in corneal mid periphery causing stromal shrinkage and increased corneal curvature
Other modalities- clear lens extraction, phakic lens implants

47
Q

How can astigmatism be corrected?

A

*Limbal relaxing incisions/arcuate keratotomy- paired arcuate incisions on opposite sides of cornea in axis of correcting plus cylinder (steep meridian). Resultant flattening of steep meridian with small steepening of flat meridian at 90 deg to incisions reduces astigmatism.
*PRK/ LASEK correct upto 3D
*LASIK upto 5D
*Lens surgery (Toric IOL). Post op rotation of implant occurs in minority of cases.
*Conductive keratoplasty

48
Q

How is presbyopia corrected?

A

*Lens correction to treat cataract/ purely refractive. CLE/RLE/ PreLEx.
*Implantation of multifocal/bifocal/ accomodating IOL can restore some reading vision but reading glasses used for some tasks. Most Multifocal IOL happy with visual outcome. *Dissatisfaction may occur due to nocturnal glare and reduced contrast sensitivity and 10% undergo IOL exchange surgery.
*Monovision- one eye (dominant) for distance clear uncorrected vision, so other eye good for near vision.
*Conductive keratoplasty
*Laser induced monovision- laser refractive surgery optimize one eye for distance, fellow for near/ intermediate vision.
*Corneal multifocality- laser to alter corneal shape so bifocal/ transitional effect induced
*scleral expansion study- not popular
*Laser modification of natural lens- using femtosecond laser.

49
Q

How long should soft and hard contact lenses not be worn prior to laser refractive procedures

A

Soft- 2 weeks
Hard- at least 3 weeks

Some surgeons suggest 1 week for each year of wear (to date)

50
Q

How does LASIK work?

A

Laser (or laser-assisted) in situ keratomileusis (LASIK)
The excimer laser is used to reshape corneal stroma exposed by the creation of a superficial flap. The flap remains attached by a hinge to
facilitate accurate and secure repositioning. Myopia is corrected
by central ablative flattening and hypermetropia by ablation of the
periphery so that the centre becomes steeper. LASIK used to treat higher refractive errors than surface ablation techniques
Hypermetropia- upto 4D
Astigmatism- upto 5D
Myopia- 12D

51
Q

How is the risk of corneal ectasia reduced in LASIK?

A

a residual corneal base at least 250 µm thickness must remain after ablation.

52
Q

What are post operative complications of LASIK?

A

*Tear instability universal require treatment
*Wrinkling, distortion or dislocation of flap
*Subepithelial haze with glare at night
*Persistent epithelial defects
*Epithelial ingrowth under flap
*Diffuse lamellar keratitis 1-7 days after LASIK. Granular deposits at flap interace. Treatment with intense steroid and antibiotics
*Bacterial keratitis rare
*Corneal ectasia.

53
Q

What is PRK?

A

Like LASIK, photorefractive keratectomy (PRK) employs excimer
laser ablation to reshape the cornea. PRK is able to correct myopia up to 6 D (sometimes higher), astigmatism up to around 3 D and low–moderate hypermetropia. The main disadvantages compared with LASIK are the lower degrees of refractive error correctable and slower epithelial healing with unpredictable postoperative discomfort.

Good for patients with higher than average occupational/leisure related risk of eye injury, patients ineligible for LASIK due to low CCT

54
Q

What is the technique for surface ablation procedures?

A

*Corneal epithelium removed
*Ablation of bowman layer and anterior stroma taking 30-60 seconds
*Epithelium heals in 48-72 hours. BCL to minimise discomfort.Subepithelial haze develops within 2 weeks and is persistent for several weeks

55
Q

What are some complications of PRK?

A

*Slow healing ED
*Corneal haze with blurring and haloes
*Poor night vision
*Regression of refractive correction
*Decentred ablation
*Scarring
*Abnormal epithelial healing
*Irregular astigmatism
*Reduced corneal sensation

56
Q

What are some variations of PRK?

A

*LASEK
*Epi- LASIK
*Modified PRK
*Advanced surface laser ablation (ASA/ASLA)
*Trans- PRK

57
Q

What is LASEK?

A

the epithelium is detached and peeled back after pre-treatment with dilute
alcohol. Laser is then applied and the epithelium repositioned.

58
Q

What is refractive lenticule extraction?

A

new technique that uses a femtosecond laser to cut a lens-shaped piece of corneal tissue (a lenticule) within the intact cornea. This is then removed via either a LASIK-style flap or more recently using a minimally invasive 4 mm incision (small incision lenticule extraction – SMILE)

59
Q

Advantages of refractive lenticule extraction?

A

*Less marked biomechanical and neurological corneal disturbance compared to LASIK
*Low risk of infection and flap complications
*Surface disturbance minimal compared to surface ablation procedures

60
Q
A

Kanski- FRCOphth Part 2 (11 decks)

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