Flashcards in Clinical Evaluation Deck (43):
What ratio by Van Herick's method would indicate a narrow angle?
1:4 ratio of AC depth to corneal thickness with slit beam at 60 degrees close to the limbus
Name the structures seen on gonioscopy starting with the iris and proceeding anteriorly
iris, ciliary body, scleral spur, posterior pigmented TM, anterior nonpigmented TM, Schwalbe's line
Which optical principle is overcome by gonioscopy in order to view angle structures? How does gonioscopy overcome this principle?
total internal reflectivity (all light coming from angle structures hits the air-tear interface at or below the critical angle of 46 degrees and is reflected back through the corneal stroma, preventing view of the angle with the naked eye). Gonioscopy replaces the air-tear interface with a lens-tear interface, which changes the critical angle and allows visualization.
Name examples of direct and indirect gonioscopy lenses
Direct: Koeppe, Barkan, Wurst, Swan-Jacob, Richardson
Indirect: Goldmann (1-mirror, like the lense used for SLT); Possner, Sussman, Zeiss (4-mirror, like what we use for clinic patients)
"Z PIGS: Zeiss, Possner, Indirect, Goldman, Sussman"
Which category of goniolenses is generally used in clinic v the OR?
clinic: indirect (smaller area of contact, more easily performed in upright position)
OR: direct (supine position, provides erect view of angle structures which is important when performing angle surgery)
The image is ___ with an indirect goniolens. The right-left orientation of a horizontal mirror is ___, and the up-down orientation of a vertical mirror is ___. The nasal mirror shows the ____ angle structures, and the superior mirror shows the ____ angle structures.
inverted; unchanged; unchanged; temporal; inferior
Does the angle appear foreshortened in the indirect or direct gonioscopic view?
Describe optical technique is used to locate Schwalbe's line on gonioscopy. What does Schwalbe's line represent?
Parallelopiped (or corneal light wedge) technique. A thin slit beam shined at the angle produces a thin beam of reflection each form the anterior and posterior corneal surfaces, and the intersection of these two lines represents Schwalbe's line, which is the termination of Descemet's membrane
Describe the different categories of angle anatomy as classified by the Shaffer system.
0: iris is against the TM; angle closure is present
Slit: <10 degree angle between iris and TM
Grade 1: 10 degree angle
Grade 2: 20 degree angle
Grade 3: 20-45 degree angle
Grade 4: 45 degree angle
Describe the different categories of angle anatomy as classified by the Spaeth system.
1. Angle width: 10, 20, 30, or 40 degrees
2. Configuration or peripheral iris: regular (r), steep (s), queer (q)
3. Apparent insertion of iris root: A = anterior to TM (no structures visible), B = behind Schwalbe's line (TM visible), C = posterior to scleral spur (SS visible) , D = deep into ciliary body (ciliary body visible), E = extremely deep into ciliary body (eg. angle recession)
Which portion of the angle is pigmentation usually greatest? (superior, nasal, inferior, or temporal)
inferior (2/2 gravity)
Name the site of damage in each of the following trauamatic injuries: iridodialysis, cyclodialysis, angle, recession,
1. iridodialysis: tear in the root of the iris causing sepration from ciliary body
2. cyclodialysis: separation of ciliary body from scleral spur
3. angle recession: tear between longitudinal and circular muscles of the ciliary body
How many axons comprise the average human optic nerve?
Where is the nucleus of an optic nerve axon, and where does an optic nerve fiber synapse?
ganglion cell layer of retina; synapses at inner plexiform layer and in lateral geniculate body
What are the diameters of the intraocular v retrolaminar optic nerve? What accounts for this difference?
1.5-1.7 mm v 3-4 mm. Axon myelination, increased glial tissue, and the beginning of the leptomeninges (optic nerve sheath)
Describe the three types of retinal ganglion cells in primates
M: magnocellular, scotopic conditions, detect movement, large dendritic field, color-insensitive
P: parvocellular, small, account for 80% of all RGCs, concentrated in central retina, small dendritic fields, color vision, motion-insensitive, high spacial frequency, slow conduction velocity
K: koniocellular, blue-yellow color opponency
What is/are the major arterial supplier(s) for each of the following?
1. choroid and outer retina
2. superficial RNFL
3. prelaminar ON
4. retrolaminar ON
1. short posterior ciliary arteries (SPCAs)
2. branches of central retinal artery (CRA)
3. branches of SPCAs and branches of circle of Zinn-Haller (if present)
4. SPCAs and pial arteries
Histologically, where is the site of initial axonal loss in glaucomatous optic atrophy?
at the level of the lamina cribrosa
In children, cupping appears (earlier/later) and is (more/less) reversible than in adults.
earlier; more reversible
Describe how to measure the diameter of the optic nerve head with a 60, 78, and 90 D indirect lens. What is the normal diameter of the optic nerve head? What slit lamp feature is utilized to best view the RNFL?
- 60: read directly from scale on slit lamp
- 78: multiply scale reading by 1.1
- 90: multiply scale reading by 1.3
- 1.5 to 2.2 mm is normal
- red-free filter
On average, nonglaucomatous black individuals have (larger/smaller) cups and (larger/smaller) c/d ratios compared to whites.
What is considered a significant asymmetry between c/d ratios in fellow eyes?
0.2 or greater is considered abnormal
Where on the disc are you most likely ot see focal glaucomatous notching?
inferotemporal or superotemporal poles
In the nonglaucomatous nerve, rank the four nerve quadrants in order of decreasing thickness.
ISNT (inferior thickest, then superior, then nasal, then temporal)
In which subset of glaucoma are disc hemorrhages more commonly found?
normal tension glaucoma
Describe the two types of peripapillary atrophy (PPA) and the condition associated with each type.
Alpha zone PPA: typical temporal crescent seen in myopia; areas of hypo- and hyper-pigmentation; not associated with glaucoma
Beta zone PPA: loss of choriocapillaris and RPE with view of only large choroidal vessels and white sclera. This is associated with glaucoma
A patient with a diagnosis of POAG is noted to have cupping as well as pallor of the remaining neuroretinal rim. What is the significance?
pallor of remaining nerve tissue is usually NOT seen in glaucoma; other etiologies of optic atrophy should be investigated
Name, briefly describe, and give an example of 3 technologies used to quantifying optic nerve head thickness
OCT (ocular coherence tomography): uses low coherence interferometry to obtain high-resolution cross-sectional views of living tissue. OCT allows for absolute measurement of RNFL thickness. Time domain OCT is the older technology with 10 microns of axial resolution. Newer OCTs (like we have in clinic) are spectral domain (SD-OCT) which have greater axial resolution between 3 and 5 microns. Example = Zeiss Cirrus OCT
Scanning laser polarimetry: scanning laser ophthalmoscope outfitted with a polarization modulator to detect birefringent properties of the RNFL. Degree of birefringence correlates to thickness of RNFL. This is a relative and not absolute measurement of RNFL thickness. Example = GDx VCC (I don't think we have one at either clinic...)
Confocal scanning laser ophthalmoscopy: Uses scanning laser technology to obtain a series of tomographic slices. Example = Heidelberg Retina Tomograph or HRT. Probably the least accurate compared to the above 2 methods.
What type of perimetry is utilized in Octopus and Humphrey visual fields? Goldmann?
Automated static perimetry with white light on white background for Octopus and HVF.
Goldmann is considered kinetic perimetry (the target moves into the field of view as opposed to simply appearing and disappearing at one spot)
Define the following terms in perimetry: threshold, isopter, depression, scotoma
threshold: differential light sensitivity for a given target size and duration of presentation at which the stimulus is seen 50% of the time (in practice, the dimmest spot detected in testing)
isopter: a line of visual field representation connecting points with the same threshold (think of the colored lines in a Goldmann field)
depression: an area of decreased retinal sensitivity
scotoma: a depression surrounded by an area of normal sensitivity
What are the different stimulus sizes commonly used in perimetry?
0: 1/16 mm^2
I: 1/4 mm^2
II: 1 mm^2
III: 4 mm^2
IV: 16 mm^2
V: 64 mm^2
Briefly, what are SITA standard and SITA fast?
SITA: Swedish interactive thresholding algorithm. Uses a staircase algorithm like standard automated perimetry (SAP), but accomplishes this FASTER by initially guessing the patient's threshold based on age-matched controls. SITA standard is faster than (cuts test time in half) but equally reliable as SAP. SITA fast is 30% faster than SITA standard but has decreased accuracy and should only be used for patients with physical or mental handicaps that prevent them from reliably completing SITA standard perimetry.
How many degrees apart are test points in the Humphrey 24-2 and 30-2?
6 degrees apart
A cluster of ___ points depressed by ___ dB or a single point depressed by ____ should raise suspicion for pathology.
2 points depressed by 5 or more dB or 1 point depressed by 10 or more dB
Normally, the ___ field is depressed 1-2 dB compared to the ___ field.
superior field depressed compared to inferior field
What is SWAP and what does it test?
short wavelength automated perimetry; tests blue stimulus on yellow background. blue wavelengths are detected by koniocellular retinal ganglion cells, which are damaged earlier in the course of glaucoma
What is frequency-doubling technology (FDT) and what does it test?
Perimetry which utilizes low spacial frequency and high temporal frequency. FDT stimulates magnocellular (M cells) which are sensitive to motion and may be affected earlier in glaucoma
what does a cloverleaf visual field pattern suggest?
that the patient has stopped trying or ceases to respond partway through the test. This is suggestive of malingering
what is a false positive on perimetry testing? what is the threshold false positive rate for reliability?
the patient responds when a stimulus has not been presented. above 20% is unreliabile
what is a false negative on perimetry testing? what is the threshold false negative rate for reliability?
a patient fails to respond to a stimulus presented in a location where a dimmer stimulus was previously seen. above 33% is unreliable, although it is common to have false negative readings at the edge of a steep-edged scotoma, especially in advanced glaucoma.
what is suggested by a normal pattern deviation but abnormal pattern deviation?
high false positives
which areas of the optic nerve are most susceptible to glaucomatous damage? which section is usually the last to be damaged?
superior and inferior poles are damaged earlier. inferotemporal visual field is last to go (thus superonasal nerve is last to be damaged)