Ch 14. Specular Microscope

Question 1

The specular microscope analices the reflection from the endothelium-aqueous humor exclusively (F/T)

Answer 1

False, it analices information reflected from any corneal interfase, but the one that is most valuable and that provides more information through this method is the endothelium-aqueous interfase.

i.e. Lattice corneal distrophy can be studied using s.m. where fine lines can be seen that correspond to the amiloid deposits, no endothelial abnormalities are found in these corneas.

Question 2

In specular microscopy, what does the term Bright boundary refers to

Answer 2

The boundary between the endothelium (zone 3) and the stroma (zone 2)

Question 3

In specular microscopy, what does the term dark boundary refers to

Answer 3

The boundary between the endothelium (zone 3) and the acueous (zone 4)

Question 4

what advantages does the slit beam specular microscope offers?

Answer 4

using a slit and a scanning system, much smaller interference is produced from each interfase. therefor, images are of greater quality and both the dark and bright boundaries practically disappear.

Question 5

how are corneal epithelial cells classified in specular microscopy?

Answer 5

Dark, medium and light. they range from hexagonal to triangular, but enlarged, elongated or round are considered abnormal.

Question 6

How is retrokeratic pigment seen on specular microscopy?

Answer 6

a Bright reflection with sharp borders that can spam over the field of several cells.

Question 7

how is the cell nucleus seen on specular microscopy?

Answer 7

a rounded bright structure in the center of the cell.

Question 8

How are guttae seen on specular microscopy?

Answer 8

since they are usually dome shaped, as light is scattered through the guttae, they appear as rounded dark opacities with ill-deffined borders. As they grow bigger the can adopt a flat-topped mushroom form. In these cases they apear as dark structures, but with a central reflection from the flat zone. They will be surrounded by abdormal cells in pathology, and by normal cells in the periphery of normal corneas (hasssal-henle bodies)

Question 9

what is the difference of retrokeratic inflammatory cells and pigment on specular microscopy?

Answer 9

• Pigment reflects light, cells are transparent and round, so they scatter it. So: pigment is displayed as bright structures, while cells are dark.
• Pigment can have any size.
• Cells are usually slightly smaller than endothelial cells. pigment tend to spam over several e.cells while inflammatory cells adhere to e-cell intersections.

Question 10

how are intracelluar vacuoles seen in specular microscopy?

Answer 10

rounded, variable in size, dark structures limited by a cell.

Question 11

how are cillia seen in specular microscopy?

Answer 11

a dark spot in the center of the cell.

Question 12

what is fixed frame analisis in specular microscopy?

Answer 12

A square area of known dimensions is used to count the number of cells inside and over the boundaries of the square and calculate the cell density. Total Cells over the boundaries are divided by 2, or just those located over 2 sides of the square are taken into consideration.

Question 13

How is variable frame analisys performed in specular microscopy?

Answer 13

The largest cell containing area in the image is considered for analisis, attempting to include at least 100 cells.

The area is traced arround the cells, therefore it considers hole cells (eliminating bias from partial cells analiced over the boundary in fixed frame analisys)

Question 14

Between fixed frame analysis and variable frame analysis, which one is more accurate?

Answer 14

Variable frame

Because it eliminates bias from partially included cells at the boundary.

Question 15

Which are more sensitive of corneal pathology and why?

a) Cell density & Size
b) pleomorphysm & polimegatism

Answer 15

B

In a cluster of 100 cells, if only one cell is lost, the others will have a mean change of 1% in size, and density will also be very slightly reduced.

On the other hand, because the cell has 6 sides, its absense will produce changes in form size variability in its 6 neighboring cells (a 6% change in the cluster)

Question 16

Which is the decompensation threshhold for corneal edema according to endothelial cell count?

Answer 16

300-700c/mm2

Question 17

what is a safe preoperative endothelial cell density (ECD)?

Answer 17

>1000-1200

_{This number takes into consideration that any given intraocular procedure produces a loss of <strong>0-30%</strong> ECs, so even if lossing 30% the cornea shouldnt reach the decompensation threshhold.}

Question 18

What is the threshold for risk of corneal decompensation after intraocular surgery according to pleomorphism and polymegatism (specifically coefficient of variation and hexagonality)

Answer 18

CV > 0.4

Hexagonality

Question 19

What is the mean endothelial cell loss per year?

Answer 19

0.5% per year

Question 20

What is the pathogenical difference in classical late-onset FECD and early onset FECD?

Answer 20

Classical onset affects mainly the posterior non banded zone.

Ealy onset affects mainly the anterior banded zone, and is associated to a mutation in the COL8a2 gene which encodes for a subunit of the ColVIII, a mayor component of the descemet memb.

Question 21

ICE laterality

Question 22

Name the 3 types of ICE syndrome

Answer 22

Chandler ‘s syndrome

Essential iris atrophy

Cogan-Reese syndrome (iris Nevus syndrome)

Question 23

what lessions are seen in specular microscopy of PPCD?

Answer 23

Stain tracks (irregular borders that can be distinguished from rail-Tracks which have straight borders from old descemet tears or Haab Stiae)

Donut-shaped dark lesions (moth eaten).

Question 24

Name signs of ICE syndrome in the specular microscopy.

Answer 24

• Decreased hexagonality (cell’s borders become rounded and a great amount of pendagonal cells become apparent)
• Increased dark granularity, to the point that a color invertion occurs (dark cell, with clear borders)

Question 25

What abnormalities can be seen in specular microscopy of keratoconic corneas?

Answer 25

Abnormaly enlarged endothelial cells who’s long axis matches the direction of the apex of the cone.

Dark bodies present in otherwise normal cells (its association with the pathogenesis is unknown)

Question 26

Neither a lens inserted in the sulcus, nor an anterior chamber lens induce endothelial cell loss during or after the procedure.

(T/F)

Answer 26

False

lenses inserted in the sulcus don’t appear to induce adicional cell loss, but anterior chamber lenses do increace both the intraoperative and post operative cell loss.

Question 27

Is there and endothelial cell loss in patient treated with PRK or LASIK?

Answer 27

Normally, No.

But in very deep ablations, reaching the posterior 200um of the cornea (like in high miopia) amorphous material deposites onto the descemet’s membrane

Question 28

According to Krachmer, what is the rate of cell loss after PKP?

Answer 28

• Up to 7 times faster during the first 5-10 years after surgery.
• it tends to normalize (close to 0.5% per year at 15 years post op)
• By 5 years post op, up to a 70% of total cell density is lost. This last Data derived from the Specular Microscopy Ancilary Study (SMAS) of the multicenter Cornea Donor Study (CDS)

Question 29

According to krachmer, the endothelial cell count data reported by Eye Banks is accurate and can be blindly trusted.

Answer 29

Citing the SMAS study (Specular Microscopy Ancilary Study (SMAS) of the multicenter Cornea Donor Study (CDS) ), up to 35% of reported data are 10% higher or lower than does reported at a spetialists reading center.

Question 30

which patient is likely to loose the greater amount of endothelial cells during PKP:

a) phakic/pseudophakic
b) aphakic

Answer 30

small studies have shown greater loss in the former (phakic, pseudophakic)

hipothetically attributed to more iris related trauma in a shallowed anterior chamber

_{Bourne WM. Functional measurements on the enlarged endothelial cells of corneal transplants. Trans Am Ophthalmol Soc. 1995;93:65–79.}

Question 31

describe the difference in the postsurgical patterns of edonthelial cell loss, between PKP and EK

Answer 31

in PKP initial cell loss is arround 10-30%, (average 15-20%) which gradually tends towards a slow normalization 10-15 years latter.

EK patient suffers a much greater loss in the months after the procedure, but a rapid decrease in the cell loss rate. (30% EK, vs 10-20% PKP)

^{<strong>Taken from SMAS, specular microscopy ancillary study. </strong>}

Question 32

According to the SMAS (specular microscopy ancillary study), does the inmediate post surgical specular microscopy correlates with trasplant failure ?

Answer 32

No.

Cellular migration after the procedure produces great variability in final ECD. Specially in patient with good peripheral ECD (like keratoconnus) healthy cells will migrate and repopulate the graft.

6 month ECD on the othe hand, does serve as a prognostic value for trasplant failure (<1700 high risk, >2500 low risk, for 5year failure)

Question 33

What changes can be seen in the endothelium after small, localized, corneal blunt traumas?

Answer 33

endothelial gray rings that transplate into enlarged, edematous cells from blunt trauma.