Dr. Chaithra Dembala Aroor, A14712, Dr. Rohit Shetty, Dr.Abdul Rawoof
RAPDx Pupil Expanded diagnostics: An Automated Pupillograph quantifying pupillary responses
Relative afferent pupillary defect (RAPD) is an imperative sign to assess the retinal and optic nerve function. However, RAPD is subjective, so leads to discrepancies due to interobserver variation.
In our pilot study on 80 normals, age group of 10-60 yrs, subjects without any known ocular pathology, the pupillary reactions were measured using RAPDx Expanded Pupil Diagnostics (Konan Medical USA, Inc., Irvine, CA) and were compared with Neutral Density Filter (NDF) (Gulden Ophthalmics). Ametropia was not an exclusion criterion in our study, as the patients do not need to wear any refractive correction during the test. The stimulus is projected at infinity by a pair of objective lenses.
The subjects were dark adapted for one minute and then the swinging flashlight test was performed and findings noted, followed by pupillary assessment by NDF and then the RAPDx. All the three tests were performed by separate blinded investigators and findings noted.
On swinging flashlight test, only the presence or absence of RAPD can be assessed. However this is subjective and the findings are highly variable.
On NDF the RAPD if present can be graded as 0.3. 0.6, 0.9 log units and so on, which is again highly subjective and is a combination of swinging flash light test with the graded log scale, i.e.,NDF.
RAPDx is an automated tool, which records the pupillary reactions by providing a monocular stimuli and then records the direct and indirect pupillary reflexes simultaneously to multiple stimuli and finally gives a score including the amplitude of the reaction with the latency of the same.
The mean pupillary reactions in 80 normals (57% males, 43 % females) assessed by NDF was found to be less than 0.3 log units. On RAPDx the same was found to be 0.28 log units.
Statistically significant correlation (p<0.001) was seen between the two, assessed by Spearman’s rank correlation coefficient.
This pilot study concludes that RAPDx is more specific when compared to NDF in measuring RAPD.
An advantage of the automated pupillograph is that it is possible to obtain multiple pupil response characteristics to multiple stimuli. Also, because the device is computerized, it would be possible to generate an index automatically,
an index of the direction and magnitude of pupil response asymmetry, known as the RAPD score (amplitude and latency of pupillary response).
Thus RAPDx gives an accurate and precise quantification of pupillary responses.
It is proved to be helpful in evaluating patients with optic neuropathies and as an early indicator for asymmetrical optic nerve pathologies.
However pupillary assessment on RAPDx may detect RAPD only in asymmetrical optic nerve or retinal pathologies, as RAPD is seldom seen in symmetrical disease processes.
Hence RAPDx may be used as a screening tool in ophthalmology clinic
In addition, 30 glaucoma patients also underwent analysis of Macular Ganglion cell (mGCC) thickness using a Spectral domain -Optical Coherence Tomography(Optovue RTVue XR AVANTI).The mean pupillary reactions assessed on NDF was less than 0.3 log units and that assessed on RAPDx was 0.28 log units(P<0.001 Spearman’s coefficient). In glaucomatous patients the log-scaled RAPD amplitudes (mean 0.14 log units) correlated moderately with the mGCC thickness (85.31 µ) (P< 0.05%), but the log-scaled RAPD latencies (0.12 msec) showed a weaker correlation.
RAPDx is comparable to NDF in measuring RAPD and can be used interchangeably.
Amplitude of RAPD response on RAPDx was 100 % sensitive and the specificity was 86.05 %.
The use of a short, automated device to assess the log unit RAPD is feasible, returns results similar to clinical measurements, and correlates with structural loss. RAPDx may be used as a screening tool in the ophthalmology clinic.