Comments on: Changes in pattern electroretinogram after application of 0.01% atropine eye drops.

Dear Sir,

Atropine 0.01% eye drops is increasingly becoming a common practice nowadays in children for control of axial myopia in India.[123] The drops have shown beneficial effects by retarding the progression of myopia from approximately 0.77D per year to 0.05D per year during the treatment period.[34] In our own experience, we found that atropine (0.01%) reduces the progression of myopia by almost 58.8% in myopic progression over a period of 3 years.[3]

We read with interest the article of Kothari et al.[5] where they described a profound reversible reduction in amplitude of first positive wave of pattern ERG (PERG) after instillation of atropine 0.01% eye drops in adults.[5] We did a study to find out the variation of in PERG on high-contrast and low-contrast grating.

We selected 3 subjects who had 6/6 vision with correction. Informed consent was obtained for all subjects, ethical committee approval by Institutional ethical committee was taken and we obtained baseline PERG of every subject and again it was obtained after instilling Atropine 0.01% eye drop (Votaatro eye drop, Voltano Pharma) in right eye of each subject and Placebo eye drop (Genteal eye drops, Alcon) in Left eye of each subject.

PERG mainly represents inner retinal activity, especially ganglion cell activity and is useful in differentiating optic nerve disorders from macular disorders. We did PERG by using Diopsys ERG machine. The vertical axis of the PERG graph indicates the amplitude measured in microvolts. The amplitude axis is auto-scaled and the range will change depending on the strength of patient's highest amplitude reading. The horizontal axis of the PERG graph is labeled with the time measured in milliseconds with a range of 0 to 200 ms. Responses from each eye and each testing parameter, which is high-contrast and low-contrast gratings for PERG, are represented on individual graph. PERG recordings were done on Diopsys ERG system in subjects with full refractive correction in undilated pupil and then Atropine 0.01% eye drops were put in right eye of each subjects 4 times at an interval of 1 min and Placebo eye drops were put in left eye of each subject 4 times at an interval of 1 min. The testing was done after 45 min of instillation of drops.[5] Subjects were not aware of which eye receiving which drops. The drops were instilled by an optometrist in a separate room. All PERG recordings were performed by a separate technician who was masked to the instillation of drops.

All the subjects were male and mean age was 34.6+/−7.2 years. The magnitude, magnitude D, and the ratio of the two for right eye and left eye preatropine and postatropine eye drops of all the three subjects have been detailed in Tables 1-3 and Fig. 1. The mean magnitude of right eye preatropine and postatropine for high-contrast gratings is 1.62+/−0.5 μv and 1.7+/−0.6 μv and for low-contrast gratings is 1.21+/−0.3 mv and 1.18+/−0.5 μv which is comparable. The mean magnitude D of right eye preatropine and postatropine for high-contrast gratings is 1.43+/−0.5 μv and 1.5+/−0.6 μv and for low-contrast gratings is 1.01+/−0.6 μv and 0.7+/−0.6 μv which is comparable. In addition, this is comparable to the left eye which also serves as a control.

Table 1

Magnitude of right eye and left eye preatropine and postatropine with high-contrast and low-contrast gratings

S. no.	Preatropine		Preplacebo		Postatropine		Postplacebo
	RE Hc	RE Lc	LE Hc	LE Lc	RE Hc	RE Lc	LE Hc	LE Lc
1	1.67	1.25	1.99	1.35	1.64	0.89	1.7	0.86
2	2.09	1.49	2.32	1.61	2.32	1.74	1.94	1.45
3	1.11	0.91	1.21	0.95	1.14	0.91	1.64	1.24
Mean±SD	1.6±0.5	1.2±0.3	1.8±0.6	1.3±0.3	1.7±0.6	1.2±0.5	1.8±0.2	1.2±0.3

All values are in μv. RE: Right eye. Hc: High-contrast gratings, LE: Left eye. Lc: Low-contrast gratings

Table 3

Ratio of magnitude and magnitude D of right eye and left eye preatropine and postatropine with high-contrast and low-contrast gratings

S. no.	Preatropine		Preplacebo		Postatropine		Postplacebo
	RE Hc	RE Lc	LE Hc	LE Lc	RE Hc	RE Lc	LE Hc	LE Lc
1	0.87	0.89	0.86	0.89	0.93	0.47	0.95	0.6
2	0.94	0.84	0.94	0.76	0.92	0.8	0.85	0.83
3	0.79	0.75	0.83	0.6	0.74	0.34	0.92	0.62
Mean±SD	0.9±0.1	0.8±0.1	0.9±0.1	0.8±0.2	0.9±0.1	0.5±0.2	1±0.1	0.7±0.1

RE: Right eye. Hc: High-contrast gratings, LE: Left eye. Lc: Low-contrast gratings

Figure 1

PERG of subject 2 preatropine and postatropine eye drops instillation of right eye and left eye

Magnitude (Amplitude) and magnitude D and its ratio were calculated for preatropine and postatropine PERG for both high-contrast and low-contrast gratings. The preatropine and postatropine magnitude was compared for right eye for high-contrast and low-contrast grating and the P value was 0.9 and 0.2 and for left eye was 0.7 and 0.7, respectively. The P value was insignificant for all the values which showed that the eyes with atropine eye drops (0.01%) instillation behaved similar to the eyes with placebo drops. There was no significant difference in the magnitude, magnitude D, and the ratio.

Kothari et al. recorded FFERG, MFERG, and PERG in 0.01% atropine-treated eyes and control eyes which were dilated by tropicamide 0.8%-phenylephrine 5% eye drops and reported profound, reversible reduction in the amplitude of P50 more in atropine-treated eyes than tropicamide-phenylephrine-treated eyes. They suggested that this could be a result of an alteration in the signal transmission in the retina or due to blurring induced due to cycloplegia and mydriasis or both.[5] Luu et al. did a study on 48 children receiving atropine 1% eye drop and reported no significant reduction in k1 response amplitude of the atropine group compared to the placebo group.[6]

We did not find any significant difference in magnitude and other parameters in preatropinized and postatropinized state in right eye. In low-contrast gratings, there is a very minimal reduction in postatropine state in the right eye. However, this particular reduction is not significant clinically, would need larger data to prove statistical significance. The high-contrast did not show any change. Atropine eye drops 0.01% does not affect amplitude in high-contrast or low-contrast gratings in PERG.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patients have given their consent for their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Table 2

Magnitude D of right eye and left eye preatropine and postatropine with high-contrast and low-contrast gratings

S. no.	Preatropine		Preplacebo		Postatropine		Postplacebo
	RE Hc	RE Lc	LE Hc	LE Lc	RE Hc	RE Lc	LE Hc	LE Lc
1	1.45	1.11	1.72	1.2	1.52	0.42	1.61	0.51
2	1.963	1.25	2.17	1.22	2.13	1.4	1.64	1.21
3	0.89	0.68	1	0.56	0.85	0.31	1.51	0.77
Mean±SD	1.4±0.5	1.0±0.3	1.6±0.6	1.0±0.4	1.5±0.6	0.7±0.6	1.6±0.1	0.8±0.4

All values are in μv. RE: Right eye. Hc: High-contrast gratings, LE: Left eye. Lc: Low-contrast gratings