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convenience sampling was used to recruit fifty participants of both genders and all races between the ages of 18 and 51 years .
data collection commenced after ethical clearance was obtained from the biomedical research and ethics committee with all participants giving written informed consent .
contact lens wearers asked to discontinue lens wear for at least 1 week before the readings were taken .
all participants had normal corneal topography determined by the oculus keratograph 3 ( oculus optikgerte gmbh , wetzlar , germany ) , aided or unaided visual acuity of at least 6/6 and no history of corneal injury and/or surgery .
fremont , ca , usa ) which has a scanning rate of 26,000 a - scans / second .
the oct scanning was performed with participants seated and the chin and forehead rests used to stabilize the participant 's head . during the scans
the operator manually adjusted the oct device such that all scans taken were perpendicular to the central cornea and centered on the pupil .
the real - time oct and camera images displayed on the laptop screen were used to achieve alignment of the scan .
all images were captured after 10:00 am to minimize the effect of overnight corneal swelling during sleep .
three scans of the cornea , retinal nerve fiber layer , and macula thickness were captured for all participants in photopic ( 958 lux ) and scotopic ( 0.03 lux ) conditions .
data were captured and analyzed using the statistical package for social sciences ( version 21 , ibm corp , armonk , ny ) with the assistance of the faculty statistician . only the right eye measurements were analyzed .
the paired t - test was used to analyze differences in the mean thickness of the different structures in photopic and scotopic conditions . a relationship between the change in pupil size and change in thickness measurements
fifty participants were enrolled in the study , however , due to incomplete data , the findings of only 47 participants were analyzed .
of the 47 participants , 62% ( n = 29 ) were female and 38% ( n = 18 ) were male .
the majority of participants were indian ( 53% ) , with 38% being black , and the remainder white ( 9% ) .
there was an almost equal distribution of emmetropes ( 57% ) and ametropes ( 43% ) .
the spherical equivalent of the right eyes ranged from  8.38 to + 1.63 ds , with a mean of 1.06 d ( 2.06 ) .
the corneal astigmatism of the right eyes ranged from 0.10 to 3.00 d , with a mean of 0.85 d ( 0.62 ) . approximately , one in every four participants was a contact lens wearer . in both scotopic and photopic conditions ,
thickness did not vary with gender in the central cornea ( p = 0.90 and p = 0.95 , respectively ) nor with retinal nerve fiber layer ( p = 0.35 and p = 0.43 , respectively ) .
however , in both scotopic and photopic conditions , the central foveal thickness was found to be 10.18 and 12.77 m thicker , respectively , in males than in females but this difference was only statistically significant for photopic conditions ( p = 0.03 ) .
the mean difference of corneal thickness measured in scotopic and photopic conditions ranged from 0.29 to 3.44 m [ table 1 ] .
this difference was only statistically significant for the temporal peripheral cornea ( p = 0.04 ) where the corneal was found to be 3.44 m thicker under scotopic conditions . mean and standard deviation of corneal thickness measurements in scotopic ( s ) and photopic ( p ) conditions , together with the mean difference ( s - p ) and p value the thickness of the retinal nerve fiber layer was greatest in the inferior region followed by the superior , nasal , and then the temporal region in both scotopic and photopic conditions .
greater thickness values were recorded in photopic conditions for all regions , with the exception of the upper quadrant . the mean difference in the retinal nerve fiber layer thickness measured in scotopic and photopic conditions ranged from 0.01 to 0.49 m [ table 2 ] .
these differences were not statistically significant for any region . mean and standard deviation of retinal nerve fiber layer thickness measurements in scotopic ( s ) and photopic ( p ) conditions , together with the mean difference ( s - p ) and p value irrespective of lighting conditions ,
the temporal area was found to be the thinnest followed by the inferior , superior , and then the nasal area .
the mean difference of macula thickness measured in scotopic and photopic conditions ranged from 0.04 to 1.48 m [ table 3 ] .
macula thickness was found to be consistently greater under scotopic conditions with the exception of the central foveal area .
this difference was only statistically significant for the inferior inner and temporal inner macula ( p = 0.05 and p = 0.05 , respectively ) .
mean and standard deviation of macula thickness measurements in scotopic ( s ) and photopic ( p ) conditions , together with the mean difference ( s - p ) and p value a significant increase in pupil size was found in scotopic conditions compared to in photopic conditions ( p < 0.001 ) .
positive correlations , between the change in corneal thickness and the change in pupil size , were noted in all regions within the corneal mid - periphery .
in contrast , inverse correlations were noted in all regions outside of the corneal mid - periphery with only the temporal peripheral cornea reaching statistical significance ( r = 0.31 ; p = 0.04 ) . for the retinal nerve fiber layer ,
the only significant correlation with change in pupil size was found in the nasal region ( r = 0.30 ; p = 0.04 ) .
the change in pupil size was not correlated with the change in macula thickness readings for all regions .
of the 47 participants , 62% ( n = 29 ) were female and 38% ( n = 18 ) were male .
the majority of participants were indian ( 53% ) , with 38% being black , and the remainder white ( 9% ) .
there was an almost equal distribution of emmetropes ( 57% ) and ametropes ( 43% ) .
the spherical equivalent of the right eyes ranged from  8.38 to + 1.63 ds , with a mean of 1.06 d ( 2.06 ) .
the corneal astigmatism of the right eyes ranged from 0.10 to 3.00 d , with a mean of 0.85 d ( 0.62 ) . approximately , one in every four participants was a contact lens wearer . in both scotopic and photopic conditions ,
thickness did not vary with gender in the central cornea ( p = 0.90 and p = 0.95 , respectively ) nor with retinal nerve fiber layer ( p = 0.35 and p = 0.43 , respectively ) .
however , in both scotopic and photopic conditions , the central foveal thickness was found to be 10.18 and 12.77 m thicker , respectively , in males than in females but this difference was only statistically significant for photopic conditions ( p = 0.03 ) .
the mean difference of corneal thickness measured in scotopic and photopic conditions ranged from 0.29 to 3.44 m [ table 1 ] .
this difference was only statistically significant for the temporal peripheral cornea ( p = 0.04 ) where the corneal was found to be 3.44 m thicker under scotopic conditions . mean and standard deviation of corneal thickness measurements in scotopic ( s ) and photopic ( p ) conditions , together with the mean difference ( s - p ) and p value
the thickness of the retinal nerve fiber layer was greatest in the inferior region followed by the superior , nasal , and then the temporal region in both scotopic and photopic conditions .
greater thickness values were recorded in photopic conditions for all regions , with the exception of the upper quadrant . the mean difference in the retinal nerve fiber layer thickness measured in scotopic and photopic conditions ranged from 0.01 to 0.49 m [ table 2 ] .
these differences were not statistically significant for any region . mean and standard deviation of retinal nerve fiber layer thickness measurements in scotopic ( s ) and photopic ( p ) conditions , together with the mean difference ( s - p ) and p value
irrespective of lighting conditions , the temporal area was found to be the thinnest followed by the inferior , superior , and then the nasal area .
the mean difference of macula thickness measured in scotopic and photopic conditions ranged from 0.04 to 1.48 m [ table 3 ] .
macula thickness was found to be consistently greater under scotopic conditions with the exception of the central foveal area .
this difference was only statistically significant for the inferior inner and temporal inner macula ( p = 0.05 and p = 0.05 , respectively ) .
mean and standard deviation of macula thickness measurements in scotopic ( s ) and photopic ( p ) conditions , together with the mean difference ( s - p ) and p value
a significant increase in pupil size was found in scotopic conditions compared to in photopic conditions ( p < 0.001 ) .
positive correlations , between the change in corneal thickness and the change in pupil size , were noted in all regions within the corneal mid - periphery .
in contrast , inverse correlations were noted in all regions outside of the corneal mid - periphery with only the temporal peripheral cornea reaching statistical significance ( r = 0.31 ; p = 0.04 ) . for the retinal nerve fiber layer ,
the only significant correlation with change in pupil size was found in the nasal region ( r = 0.30 ; p = 0.04 ) .
the change in pupil size was not correlated with the change in macula thickness readings for all regions .
based on the operating principles , the oct measurement is dependent on the amount and intensity of light reflected from the structure being measured . when lighting conditions changed from scotopic to photopic , a statistically significant decrease in pupil size
, pupil size changes were not expected to affect the corneal thickness measurements since the cornea lies anterior to the pupil , and therefore , theoretically would not alter the sample beam . however , as the posterior segment parameters being measured lie behind the pupil , a change in pupil size was expected to influence the measurements .
thicker corneal measurements were obtained under photopic conditions for the mid - peripheral cornea with the exception of the temporal region ; however , these differences were not statistically significant .
these findings are similar to that of dacosta et al . who found the cct measurements to remain unchanged in photopic and scotopic conditions .
clinically , an average change of 1.44 m , as found in the current study , for the central cornea is not expected to impact on the accuracy of intraocular pressure measurements with goldmann applanation tonometry which requires a 10 m change in cct to impact a 0.120.18 mmhg change in iop .
in contrast , thinner corneal measurements were obtained under photopic conditions for all regions outside the corneal mid - periphery .
it has been suggested by alario and pirie that a change in corneal thickness < 1.5% is clinically negligible .
however , this difference may need to be considered in refractive surgeries and the diagnosis and monitoring of peripheral corneal diseases .
the retinal nerve fiber layer thickness followed the  is nt  rule in both photopic and scotopic conditions .
as with the central cornea , thicker readings were obtained in all regions in photopic conditions although statistically insignificant .
in contrast to the trends noted with corneal and nerve fiber layer thickness , thinner macula measurements were obtained in photopic conditions for all regions with the exception of the central foveal area . even though statistically significant differences were found in the inferior and temporal inner macula areas , these differences were approximately 1 m which may be clinically insignificant .
interestingly , the differences in corneal thickness measurements as pupil size changed were , on average , greater than the differences in the posterior segment parameters .
the current study , unfortunately , utilized a relatively small sample size and did not measure the anterior chamber parameters which would have allowed for further comparison with the study by dacosta et al .
nevertheless , the study concludes that no clinically significant differences in anterior and posterior segment parameters measured with oct are expected irrespective of ambient lighting conditions .
the ivue-100 oct , therefore , can be used in either scotopic or photopic conditions and should be determined based on which ambient lighting condition allows better visualization and , therefore , alignment of the camera images .
the measurement of corneal , retinal nerve fibre layer and macula thickness with the ivue-100 oct , is not affected by ambient lighting conditions .
purpose : to compare anterior and posterior segment parameters measured with the ivue-100 optical coherence tomography ( oct ) in photopic and scotopic conditions.methods:central and peripheral corneal thickness , retinal nerve fiber layer and macula thickness were measured using the ivue-100 oct in 47 healthy individuals at a higher education institution in photopic ( 958 lux ) and scotopic ( 0.03 lux ) conditions.results:as the lighting conditions changed from scotopic to photopic , a significant change in pupil size was noted ( p < 0.001 ) . 
 however , there was no significant difference in central corneal thickness measurements with this change in surrounding illumination with only the temporal peripheral corneal area showing a significant difference ( 3.44 m thinner ) . 
 no significant differences were found in the retinal nerve fiber layer thickness . a significant decrease in the reading 
 was noted in only the inferior ( p = 0.05 ) and temporal ( p = 0.05 ) inner macula area.conclusion:change in the ambient lighting conditions does not result in a clinically significant difference in corneal , retinal nerve fiber layer , and macula thickness when measured with the ivue-100 oct .