Rod Sensitivity in Age-related Macular Degeneration (AMD) and Retinitis Pigmentosa (RP)
Conditions: Retinitis Pigmentosa, AMD
Sponsor: Retina Foundation of the Southwest

 
 
 
Scotopic perimetry in Age-related Macular Degeneration 
 
NCT03322930 
 
Oct 24, 2018 
 
David G. Birch, PhD 
Director, Rose-Silverthorne Retinal Degenerations Laboratory 
Scientific Director, Retina Foundation of the Southwest  
Director of Visual Electrophysiology and Adjunct Professor of Ophthalmology 
University of Texas Southwestern Medical School 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Scotopic perimetry in Age-related Macular Degeneration 
 
David G. Birch, PhD 
Director, Rose-Silverthorne Retinal Degenerations Laboratory 
Scientific Director, Retina Foundation of the Southwest  
Director of Visual Electrophysiology and Adjunct Professor of Ophthalmology 
University of Texas Southwestern Medical School 
 
 
 
Perimetry is typically used for assessing the regional variations in function for patients 
with retinal disease. Standard perimetry only measures cone-mediated sensitivity. Until 
recently, it has not been possible to obtain rod-mediated perimetry other than by custom-
built devices. There are many factors, however, that make rod-mediated fields attractive. 
Despite their different etiologies, retinal degenerations share many common features. 
For example, many of the mutations causing retinitis pigmentosa are expressed in rod 
photoreceptors, and night blindness is often the earliest symptom.  Similarly, a growing 
body of evidence indicates that rods are affected early in age-related macular 
degeneration (AMD) and Stargardt disease. In addition, some of the contemporary 
treatment strategies are common to these diseases. These treatment strategies require 
localized outcome measures of rod and cone function to evaluate treatment efficacy.  
     
The MP-1S was the first fundus perimeter to provide highly localized measures of rod 
and cone function.  It incorporates a fundus-tracking system and follow-up mode to 
maintain constant stimulus projection on the retina and facilitate repeat testing of 
identical loci despite eye movements.  The scotopic MAIA is a more recent option for 
scotopic perimetry.  It provides a faster test, but has a limited dynamic range.  Average 
normal sensitivity for elderly patients with spot size 3 within the macula is approximately 
15 dB, so the machine has a floor effect for patients with losses > 1.5 log unit.  The MP-
1S has a greater dynamic range because neutral density filters can be adjusted to fit the 
range needed for the patient. The mean normal value for 13 elderly subjects tested to 
date is 23 dB for a stimulus size 3.  The 8 dB difference in normal scotopic sensitivity on 
the two fundus perimeters is also seen in patients with macular disease. To date, we 
have compared 10 patients on both devices. The correlation in mean sensitivity between 
the two devices is high (r= 0.73) with the Nidek MP-1S having sensitivity on average 10 
dB higher than the MAIA-2S.  
 
The Nidek MP-3S is a next-generation fundus perimeter designed to replace the MP-1S. 
In general, it is easier to use than the MP-1S. It incorporates a red screen that does not 
interfere with the dark adaptation of the patient. Other advances include “fade-out-
protection” for the fixation light to avoid the Troxler effect, which is particularly common 
in an otherwise dark field. Rather than the joystick on the MP-1S for aligning the patient, 
the MP-3S actively tracks the pupil position of the patient. Another important advantage 
of the MP-3S is the higher luminance of the background for standard testing.  The 34 
cd/m2 background is 10 times brighter than the background of the MP-1, making it truly 
a photopic, rather than mesopic, test.  Thus the MP-3S can be used in standard mode 
with a background that saturates rods and produces a cone-mediated sensitivity map, or 
in scotopic mode, with no background to produce a rod-mediated sensitivity field.  
Rather than having to insert filters as in the MP-1S, the filters in the MP-3S are fixed and 

automatically moved into position when a scotopic test is specified.  This leads to much 
greater ease of use and less possibility of technician error while running the test. 
 
Representative normal sensitivity maps for 2 different spot sizes on the MP-3S are 
shown in Figure 1.  For spot size 3, the values are comparable but slightly higher than 
for elderly subjects tested on the MP-1S (7 corresponds to 27 on the MP-1S, given the 
2.0 log filter).  For the larger spot size 5, values are considerably higher consistent with 
spatial summation.  It is also important to point out that the range over which patients 
can be tested can be varied by adjusting spot size.  There is a tradeoff between the 
greater spatial localization with spot size 3 and the larger dynamic range with spot size 
5. 
 
 
 
 
       MP-3S scotopic microperimetry 
 
 
Spot size 3 
 
 
 
 
Spot size V 
 
 
 
 
Figure 1.  Comparison of spot sizes 3 and 5 on MP-3S in normal subject  
 
 
 
 
In order to compare results from patients on the MP-3S to those from the MP-1S, we 
tested 10 patients with age-related macular degeneration using the following parameters: 
 
 
 
Table 1  Comparison of Nidek MP-3S to Nidek MP-1S 
 
 
 
 
MP-3S 
 
MP-1S 
Mode  
Scotopic 
 
 
Scotopic 
Pattern  
NdkSctRed36p 
 
AMD GA Rod Reduced 
Test loci 
 
32 
 
 
 
32 
Spot size 
 
5 
 
 
 
5 
Filter  
Internal 
 
 
Blue+ 2.0 
 
Fixation 
3 deg circle 
 
 
3 deg circle 
Staircase 
 
4:2 
 
 
 
4:2 
 
 

The patients will be greater than 55 years of age.  Each patient will be evaluated with the 
following procedures: 
• Best-corrected visual acuity of both eyes  
• Slit lamp examination to screened for a narrow angle prior to dilation 
• Pupil dilation with 30 minutes patching for dark-adapted testing of the better 
seeing eye  
• Dark-adapted visual field test on Nidek microperimeter, model MP-3S using a 
protocol that takes approximately 20 minutes 
• Dark-adapted visual field test on Nidek microperimeter, model MP-1S using a 
protocol that takes approximately 20 minutes 
• Imaging on Heidelberg Spectralis Optical Coherence Tomography and fundus 
autofluorescence unit 
 
MP-3S and MP-1S testing order will be randomized and both tests will be conducted on 
the same day. Coefficients of repeatability will be obtained for each test and compared to 
the literature.  We will determine the range of values for point sensitivity to determine the 
amount that a patient has to change at a given location to be significant.  The limits of 
agreement for the two devices measuring scotopic sensitivity will be compared to limits 
of agreement for mesopic testing. 
 
Appendix 
 
 
32-point pattern used for scotopic testing on MP-1S and MP-3S 
 

 
 
 
Spot 
X 
Y 
1 
8 
-4 
2 
4 
-4 
3 
-4 
-4 
4 
-8 
4 
5 
-4 
4 
6 
4 
4 
7 
8 
4 
8 
-4 
-8 
9 
4 
-8 
10 
4 
8 
11 
-4 
8 
12 
-8 
-6 
13 
8 
-6 
14 
8 
6 
15 
-8 
6 
16 
0 
-10 
17 
-10 
0 
18 
0 
10 
19 
10 
0 
20 
0 
4 
21 
-4 
0 
22 
0 
-4 
23 
4 
0 
24 
-8 
-4 
25 
-6 
-2 
26 
-6 
2 
27 
-2 
-6 
28 
2 
-6 
29 
2 
6 
30 
6 
2 
31 
6 
-2 
32 
-2 
6 
 
Coordinates for 32-point pattern