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Other types of perimetry (FDT, SWAP) R 4정윤혜/Ap. 이나영
Visual pathway visual information ⇨ retina ⇨ optic nerve ⇨ lateral geniculate nucleus (LGN) 1. magnocellular (M-cell) pathways 2. parvocellular (P-cell) pathways 3. koniocellular (K-cell) pathways
§ Integrating the activity in these streams, one can perceive what an object is and where it is going.
Retinal Ganglion cell (RGC) pathway Type of cell pathway M (Y) P (X) K percent of RGC 10% 80% 9% Size Large cell bodies Small cell bodies Very small cell bodies Receive input from: Parasol RGC Midget RGC Location in LGN: Most ventral layers 1 and 2 Most dorsal layers 3 to 6 Sensitive to: Higher temporal frequencies (movement) Higher spatial frequencies (detail), color Shorter wavelengths (blue-yellow color) What an object is! activated by blue light suppressed by yellow Where it is! Function This system operates quickly but without much detail. Bistratified (blue-ON) RGC Within and between principal layers (interlaminar) This system operates more Somatosensoryslowly and with proprioceptive information lots of information about with visual perception, details color perception.
Visual pathway § The M-cell pathway is responsible for encoding and transmitting information about low spatial frequency (broad patterns or larger object), high temporal frequency (i. e. , motion) stimuli - a black car rapidly passing by a driver’s side window at night would selectively stimulate M-pathway neurons
Visual pathway § P-pathway is responsible for encoding and transmitting information about colored, high spatial frequency (fine detail or smaller object), low temporal frequency (i. e. , static) stimuli - The smallest letters on a standard projected Snellen eye chart would selectively stimulate the patient’s P-cell neurons
Background § P-, K-, and M-cells all may die at about the same rate, but the effects of K- and M-cell loss are more readily detectable because there are fewer of these cells. § Redundancy - d/t redundancy, single stimulus may simultaneously stimulate two or more RGC’s- in case of retinal damage, high redundancy guarantees higher probability of stimulus to be transmitted to the brain - High redundancy of P-cells: they overlap each other in terms of retinal location and function ⇨ many P-cells can be lost before there is a noticeable field loss
Standard automated perimetry (SAP) § White stimuli(SAP) : activate all ganglion cell equally ⇨ creating a neural redundancy ⇨ can mask damage to specific cell subpopulations or general loss of all cell types ⇨ glaucomatous defects involving about 30% to 50% of retinal ganglion cells may be undetected by SAP Harwerth et al. , 1999 § specialized perimetry increases sensitivity by testing the unique functions of ganglion cells with targeted stimuli § relatively few M- cells & K- cells ⇨ less redundant coverage ⇨ relatively easy to detect
Frequency Doubling Technology Perimetry (FDT)
Frequency Doubling Perimetry (FDT) § Frequency Doubling Illusion (빈도 배가 환영) - 낮은 공간 주파수(low spatial frequency)(<1 cyc/deg)의 줄무늬를 빠른 속도(high temporal frequency)(>15 Hz)의 역상으로 반복시키면 줄무늬 주파수가 두 배로 증가 하는 것처럼 보이는 정신생리현상 FDT perimeter uses a vertical sine wave grating of low spatial frequency (0. 25– 0. 50 cyc/degree) that undergoes counterphase flickering at a hightemporal frequency(12– 25 Hz) ⇨ its spatial frequency appears doubled.
FDT Frequency Doubling Perimetry (FDT) § MY ganglion cells : detect motion, perceive these stimuli as an object moving across the retina § Relatively larger than the other RGCs. § Represent about 10 % of all RGCs and they endowed with low redundancy. § Identify retinal neuron loss (specifically M-cell loss) earlier than white-on-white perimetry (which may actually be a test of P-cell function).
§ First- and second- generation tests
§ First-generation - C-20 and N-30 C-20 N-30
§ Second-generation FDT - New program called Matrix - Smaller size of stimulus(5 degrees for the 24 -2 and 30 -2 and 2 degrees for 10 -2) - Higher number of tested points - More efficient method to calculate threshold - Slightly longer duration( 6 min) - Video eye monitor
SWAP – Short Wavelength Automated Perimetry (Blue- Yellow Perimetry)
SWAP Short Wavelength Automated Perimetry (SWAP) Blue stimulus dots are presented on a yellow background § The yellow background helps 1. saturate the green (medium wavelength) and red (long wavelength) pathways 2. isolating the blue (short wavelength) pathway § Blue stimuli ⇨ peak wavelength that approximates the peak response of the blue cones (S-cones) ⇨ koniocellular (K-cell) pathways
Full threshold : 20 min SITA SWAP : 50%
SWAP Benefits SWAP Limitations Sooner identification of field loss Greater inter-test variability ( d/t difficulty of stimulus detection, long test duration, high sensitivity to pupil size) Higher correlation to structural nerve changes Cataracts and media opacities may affect test results Greater amount of field loss shown than with white on white testing Field loss progression difficult to monitor
FDT & SWAP : more sensitive, can detect VF loss and progression earlier than SAP FDT • • Test time less than 1 min Portable Good patient acceptance Less practice dependent than SAP (no learning effect) Lower inter- and intra-test variability, short term variability Detect early glaucomatous defects Successfully used to test children Unaffected by defocus SWAP • Early detection of glaucoma and progression • Presence of learning effect • Intra- and inter-test variability higher, greater short term variability • Affected by media opacity • More fatigue for patients than SAP
FDT and SWAP to detect Early Glaucoma SWAP Detection of glaucomatous visual field loss FDT 3 ~ 5 years early than SAP 1 ~ 2 years early than SAP § Progressive color visual field loss in glaucoma. - Invest Ophthalmol Vis Sci 1992; 33: 2068 -2071 § Progression of early glaucomatous visual field loss as detected by blue-on yellow and standard white-on-white automated perimetry. - Arch Ophthalmol 1993; 111: 651 -656 § Short Wavelength Automated Perimetry, Frequency Doubling Technology Perimetry, and Pattern Electroretinography for Prediction of Progressive Glaucomatous Standard Visual Field Defects. - Ophthalmology 2002; 109: 1009– 1017
Conclusion May be helpful to detect early glaucoma diagnosis or progression of glaucoma suspect Consensus criteria needed Glaucoma suspect showing abnormality of FDT and SWAP : should be carefully monitored : progression to glaucoma should be the start point of treatment