Armstrong

Cakmak

Dumbleton

Linke

Netto

English

Orr, Janis B.

Seidel, Dirk

Day, Mhairi

Gray, Lyle S.

ResearchOnline@GCU

Authors’ response: is pupil diameter influenced by refractive error?Orr, Janis B.; Seidel, Dirk; Day, Mhairi; Gray, Lyle S.Published in:Optometry and Vision ScienceDOI:10.1097/OPX.0000000000000734Publication date:2015Document VersionPeer reviewed versionLink to publication in ResearchOnlineCitation for published version (Harvard):Orr, JB, Seidel, D, Day, M & Gray, LS 2015, 'Authors’ response: is pupil diameter influenced by refractive error?',Optometry and Vision Science, vol. 92, no. 10, pp. e384-e385. https://doi.org/10.1097/OPX.0000000000000734General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.Take down policyIf you believe that this document breaches copyright please view our takedown policy at https://edshare.gcu.ac.uk/id/eprint/5179 for detailsof how to contact us.Download date: 29. Apr. 2020Authors’	Response:	Is	Pupil	Diameter	Influenced	by	Refractive	Error?		We	appreciate	the	interest	Guillon	et	al’s	have	shown	in	our	paper	1.	While	we	agree	that	the	findings	of	a	single	study	with	a	relatively	small	sample	size	cannot	reach	a	definitive	conclusion	regarding	the	relationship	between	refractive	error	and	pupil	diameter,	we	disagree	that	our	methodology	is	inadequate.	We	would	contend	that	our	study	provides	an	important	contribution	to	the	literature	as	it	is	the	first	to	investigate	the	relationship	between	pupil	diameter	and	refractive	error	in	young,	age-matched	emmetropic,	myopic,	and	hyperopic	subjects	and	to	examine	systematically	how	refractive	correction,	target	luminance,	and	accommodative	effort	modulate	this	relationship.	We	thank	the	authors	for	bringing	additional	articles	investigating	the	relationship	between	pupil	diameter	and	refractive	error	to	our	attention	2-5.	These	articles	were	not	omitted	as	a	result	of	an	incomplete	literature	search,	as	suggested	by	Guillon	et	al.;	they	were	omitted	from	our	citations	because	the	methodology	in	these	studies	meant	that	they	were	not	comparable	to	our	study	and	therefore	their	inclusion	would	have	been	inappropriate.	We	also	feel	that	it	is	unsatisfactory	to	cite	conference	abstracts	in	peer	reviewed	papers	as	the	source	data	is	not	easily	verifiable	5.	The	data	from	all	of	the	omitted	studies	2-5	were	collected	under	mesopic	illumination	conditions	which,	although	relevant	in	the	context	of	refractive	surgery,	are	not	comparable	to	our	study	in	which	we	deliberately	examined	pupil	diameter	over	a	wide	photopic	illumination	range.	This	is	due	to	the	fact	that	the	influence	of	the	accommodation	response,	which	was	central	to	our	study,	would	not	have	been	accurate	in	mesopic	conditions	and	would	have	likely	fallen	to	tonic	resting	levels.		While	we	appreciate	the	constructive	criticism	of	Guillon	et	al.	on	our	sample	size	and	data	analysis,	we	do	not	agree	that	our	conclusions	are	erroneous.	It	is	certainly	true	that	if	no	significant	difference	is	found	between	two	or	more	means,	this	could	be	due	to	inadequate	statistical	power,	however,	this	could	also	arise	where	there	is	no	significant	difference.	Power	is	not	only	determined	by	sample	size	but	also	by	experimental	design	and	the	statistical	analysis	used.	In	the	re-analysis	presented	by	Guillon	et	al.,	power	was	calculated	assuming	pairs	of	means	were	being	compared	using	simple	t-tests.	In	our	study,	we	analysed	our	data	using	a	Repeated	Measures	ANOVA,	which	uses	pooled	mean	square	errors	to	estimate	both	the	treatment	and	repeated	measure	effects	and	interactions.	These	errors	have	large	degrees	of	freedom	(which	can	be	seen	in	our	results),	demonstrating	that	the	analysis	has	considerably	more	power	to	detect	significant	differences	than	that	calculated	by	Guillon	et	al.	For	our	statistical	and	experimental	design,	a	power	of	99%	for	detecting	medium	effect	sizes	was	obtained	(GPower),	reducing	to	41%	for	small	effect	sizes.	This	would	imply	that	our	experimental	design	has	sufficient	power	to	detect	clinically	significant	differences	in	pupil	diameter.	This	raises	an	important	point:	what	is	the	minimum	change	in	pupil	diameter	that	is	biologically	meaningful	in	this	context?	If	very	small	changes	in	pupil	diameter	are	clinically	insignificant	then	is	there	any	need	to	recruit	a	significantly	larger	sample	in	order	to	demonstrate	whether	such	a	difference	exists?	Theoretically,	studies	with	very	large	sample	sizes	could	have	so	much	power	that	clinically	meaningless	differences	can	be	detected	leading	to	exaggerated	conclusions	with	little	clinical	relevance.		Furthermore,	Bonferroni	post-hoc	tests	were	used	in	our	analysis,	which	are	highly	conservative,	and	should	therefore	prevent	type	1	errors,	although	the	probability	of	a	type	2	error	will	increase	6.	In	order	to	check	that	no	effects	had	been	missed	due	to	the	conservatism	of	the	Bonferroni	post-hoc	test,	or	the	increased	probability	of	a	type	2	error,	the	data	were	re-analysed	using	a	less	conservative	post-hoc	test	(Tukey	HSD).	Despite	the	use	of	a	less	conservative	test,	no	significant	differences	in	pupil	size	between	the	refractive	groups	was	found.			In	conclusion,	we	believe	that	our	study	has	more	power	than	Guillon	et	al.	calculate	because	of	the	specific	design	and	statistical	analysis	employed.	The	statistical	power	is	adequate	to	detect	medium	differences	in	pupil	diameter	which	correspond	with	clinical	significance.		Janis	B.	Orr,	PhD		Birmingham,	United	Kingdom		Dirk	Seidel,	PhD		Mhairi	Day,	PhD		Lyle	S.	Gray,	PhD		Glasgow,	United	Kingdom			References:	1.	 Orr	JB,	Seidel	D,	Day	M,	Gray	LS.	Is	Pupil	Diameter	Influenced	by	Refractive	Error?	Optom	Vis	Sci	2015;92:834-40.	2.	 Netto	MV,	Ambrosio	R,	Jr.,	Wilson	SE.	Pupil	size	in	refractive	surgery	candidates.	J	Refract	Surg	2004;20:337-42.	3.	 Cakmak	HB,	Cagil	N,	Simavli	H,	Duzen	B,	Simsek	S.	Refractive	error	may	influence	mesopic	pupil	size.	Curr	Eye	Res	2010;35:130-6.	4.	 Linke	SJ,	Baviera	J,	Munzer	G,	Fricke	OH,	Richard	G,	Katz	T.	Mesopic	pupil	size	in	a	refractive	surgery	population	(13,959	eyes).	Optom	Vis	Sci	2012;89:1156-64.	5.	 Dumbleton	K,	Guillon	M,	Theodoratos	P,	Wooley	CB,	Moody	K.	The	effect	of	age	and	refractive	error	on	pupil	size.	Invest	Ophthalmol	Vis	Sci	2015;56:E-Abtract	585.	6.	 Armstrong	RA.	When	to	use	the	Bonferroni	correction.	Ophthalmic	Physiol	Opt	2014;34:502		

Authors’ response: is pupil diameter influenced by refractive error?

Janis B. Orr

Dirk Seidel

Mhairi Day

Lyle S. Gray

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Optometry and Vision Science

Authors’ Response

https://researchonline.gcu.ac.uk/files/6689093/Letter_to_the_Editor_Author_Reply_JBO_DS_MD_LSG.pdf

Authors’ response: is pupil diameter influenced by refractive error?

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