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Normative Data of Macular Thickness and Retinal
Nerve Fiber Layer Thickness (RNFL) With Axial
Length and CCT by SLO OCT/Lenstar on Tribal People
Ferdinand Rapthap¹*, Monica Chaudhry1 and Valensha Surong2
1Department of Optometry and Vision science, Amity University, India
2 Mission Nethralaya, India
Submission: May 23, 2018; Published: June 27, 2018
*Corresponding author: Ferdinand Rapthap, Master of Clinical Optometry, Mawphlang Mawkohmon Meghalaya, Pin- 793121, India.
How to cite this article: Ferdinand R, Monica C, Valensha S.Normative Data of Macular Thickness and Retinal Nerve Fiber Layer Thickness (RNFL) With
Axial Length and CCT by SLO OCT/Lenstar on Tribal People. JOJ Ophthal. 2018; 6(5): 555699. DOI: 10.19080/JOJO.2018.06.555699
Aim and Objectives: To study the relationship of Axial length, Central Corneal Thickness(CCT), Macular thickness and Retinal Nerve Fiber Layer thickness (RNFL) on the Tribal People of North East India by using of SLO OCT and Lenstar and to associate with the effects of Age, IOP and Refractive status on these Parameters.
Participants: 145 Individual of 290 eyes (93 females and 52 males)
Method: Normal subject presenting to Mission Nethralaya Shillong were included in this study. The test was performed on both eyes of the same individual by a single examiner. All patient underwent clinical examination followed by study of macular thickness and RNFL thickness by spectral domain SLO OCT, and axial length with central corneal thickness by Lenstar. The data was collected and analysed based on IOP, age, gender and refractive status. Lastly, the data was compared with published literature of Indian and Caucasians population.
Result: The total number of patients enrolled in the study was 145 of 290 eyes. Number of male was 52 and Number of female was 93 with the age range from 15->55. The overall mean of macula Central Point Thickness (CPT) 164.96 ± 30.88 Average macular Thickness (Avg Mac thick) 271.81 ± 20.52, Central sub field of macula (CSF) 191.01 ± 32.33 and for the Average RNFL thickness 107.61 ± 13.45 were as the Central Corneal thickness (CCT) 528.54 ± 32.84 and lastly the axial Length (AL) of 23.22 ± 0.91. Showed a strong positive correlation between the right and left eye of each individual (r ≥ 0.5, p<0.001). On further analysis of the RNFL, we found the Inferior (135.96) to be thickest followed superior (122.22), nasal (92.59) and temporal (80.99).
Gender wise shows no statistical significant difference for CPT, Avg mac thick, CSF, Avg RNFL thick, CCT and AL with (P= 0.33, 0.61, 0.97, 0.30 and 0.37 respectively). No age differences was noted in all the above parameters except in specific age group for axial length P = 0.04. Whereas CCT has a significant difference with IOP (R=0.37, P=0.00).
Conclusion: This study was the first to provide a normative data for the Tribal people of North east India. The data obtain from this study finds to correlate well with the other published paper except Central point thickness of macular needs to look, as they appear to be thinner in compared to the rest.
Abbrevations: SLO-OCT: Scanning Laser Ophthalmoscopy; CCT: Central Corneal Thickness; AXL: Axial Length; RNFL: Retinal Nerve Fiber Layer; CPT: Central Point Thickness; CSF: Central Sub Field
Many studies have been conducted comparing the axial length with macular thickness along with the RNFL. Maximum studies were conducted in Western/ Caucasian population and on Indian population. This particular study will be the first study to be conducted for the tribal people of North East India; main objective was to get the correlation of the parameters (Axial length, Macular thickness, RNFL thickness and Central corneal
thickness with age, IOP and Refractive status. SD OCT with
enhanced depth imaging was used for measuring the macular thickness and the RNFL LENSTAR for measuring the axial length.
a) The ethnicity of Mangoloid race specifically Khasi people.
b) Determine the Normative data of macular and RNFL thickness by used of SLO OCT
c) Investigate the relationship of macular thickness, RNFL
thickness, Axial length, Central Corneal thickness with Age,
IOP and refractive status
d) Population based age group to be carried out in
Meghalaya, which is a state of North East region of India.
e) Comparison of all the parameters with Indian
population and Caucasians.
The Khasis are one of the matrilineal tribes of Meghalaya in
Northeast India. They have their own traditional religion (Niam
Khasi), but about 65% converted into Christianity. They are
Indio- Mongoloid Racial Stock, and speak Monkhmer language
of the Austro- Asiatic group. The state of Meghalaya came into
existences on April 2, 1970 attaining statehood on Jan 21,
1972. Meghalaya comprises of three tribes, the Garo, Khasis
and Jaintias with the total population of 17, 74779 and area of
22,429 sq. . The maternal system gave to the women, the wife
and mother, a social rather a personal standing.
Khasi people comparing from different regions have
small but noted differences. Recent genetics researchers have
shown that Khasis are closer to their Garo a neighbour state as
compared to other population of Northeast India. It is describes
as North- East Indian. Lastly, the variations remains high, with
their features of flat nose and mouth, short people, high jaws and
small and straighten black eyes.
Notation with proper assessment of Peripapillary Retinal
Nerve Fiber layer (RNFL) by the OCT plays an important tool
for the process and management of Diabetes, glaucoma and
progression [2-4]. The RNFL is formed by the retinal Ganglion
cells; it is found to be thickest near the optic nerve and gradually
decreases towards the ora serrata. Macula is an oval yellowish
area in the retina that surrounds the fovea and has the highest
visual acuity due to the presence of cones Studies have shown
the relationship between these two parameters by OCT [5,6].
Axial length represents the distance from the anterior to the
posterior poles of the eye. Which is the measurement from the
anterior pole to the Bruch’s membrane . The average newborn
eyeball is about 16mm in diameter, in infant, the eye grows
slightly of approximately 19 mm. it gradually grow to the length
of about 24-25mm.
Central Corneal thickness has its role of working the normal
thickness is about 554+/-32.61 microns one reason is that
people with thin cornea (500 or less) are at a higher risk for
glaucoma its mechanism is not entirely clear. Corneal thickness
allows us to check the IOP (Goldman Tonometer). Thicker
cornea has its pressure reading seems higher than it really is.
IOP is important to determining the risk for glaucoma. Actual
IOP may be underestimated in patients with thinner CCT and
overestimated in patients with thicker CCT. Patients with thin
cornea less (555μm) shows artificial low IOP readings, and with
thicker cornea shows a higher reading of IOP than actually exists.
The purpose of this study is to see the ethnicity of Mangoloid race
specifically Khasi people to see the normative data of macular
thickness with RNFL along the axial length and Central corneal
thickness, and has any effects on age, refractive error, IOP and
gender. Lastly, to see variation of these parameters in this region
as with the other part of India and Caucasian population
Study Design: Observational, Cross sectional Study.
Study Size: Patient collected 145 Individual of 290 eyes.
This study was conducted in Mission Nethralaya Shillong,
Meghalaya. From January 1, 2018 until April 2018 and the duration
of the study is around 5 months. This was an observational, nonrandomized,
prospective study and involved of 145 patients
(290 eyes) normal individual. The patients were recruited from
routine visits to the Hospital outpatient department. Informed
consent was taken from the individual before inclusion. The
study was approved by the ethics committee.
The subject that was included in this study involve patients
with or without refractive error that is converted into spherical
equivalent, along with the age group of 15 and above. Patient
less that 15 was not included due to poor cooperation and
unwillingness of the parents.
All subject after an informed consent was taken for the
project, underwent complete ophthalmic examination which
includes all the examination begins with the detailed history,
Visual Acuity, extra ocular motility (EOM), refraction (subjective
and objective), slit lamp bio microscopy, Intra ocular pressure
with Non-contact Tonometer (NCT). After all the tests being
completed the patients were taken for an investigation of the
Axial length with Central Corneal Thickness (CCT) by the Lenstar
LS 900, and for the posterior segment of the Macular thickness
and the Retinal Nerve Fiber Layer thickness (RNFL) by the SD –
OCT SLO. These tests were conducted on both eyes of the same
Inclusion criteria: Best corrected visual acuity of 6/6
with N6, Normal IOP range of 10-21mm Hg, No history of any
systemic diseases having ocular association, No history of any
ocular diseases, and OCT signal strength of ≥ 6 in each eye, Age
group 15 to 80 years, Inform consent given and willingness of
Exclusion criteria: Best corrected visual acuity worse than
6/9 with N6, Intra ocular pressure (IOP) range > 21mmHg,
History of any ocular diseases, History of any systemic diseases
having ocular associations, OCT signal strength < 6 in each eye,
Subjects <15 years of age
Newly released SLO Optical Coherence Tomography
(OTI, Toronto, Canada) was used, that has an increased axial
resolution, faster scanning speeds and has been reported to
have improved reproducibility but similar diagnostic accuracy
in comparison with the earlier generation time domain OCT
[8,9]. It was perform by a single clinician in order to avoid bias.
It needs to have proper centration and signal strength of >6 and
above. The main concentration to see was the Macular thickness
and the RNFL thickness (Figure 1).
A single clinician was performed in order to avoid bias of the
study. The scan was centred on the optic disc with a scanning
diameter of 3.5 mm and 764 A scan were obtained. Automatic
real time function to obtain multiple frames during scanning
and optimize images by noise reduction. The RNFl was analysed
based from fovea to disc technology. It gives the average
thickness value for each clock hour and 4 quadrants as well as
overall average thickness value for the whole circumference they
were recorded in micrometres (Figure 2).
For the macular thickness the spectralis OCT has an axial
image resolution of 7 um, a lateral resolution of 14 um and a
scanning velocity up to 40,000 A scan per seconds. The Macular
thickness was reported in a modified Early Treatment Diabetic
Retinopathy study macular Map. Three parameters were
recorded in this study. One the central sub field is 1 mm in
diameter; second, the inner subfield is 3 mm in diameter and
third is outer subfield, which is 6 mm in diameter. The retinal
thickness in the inner and outer subfields, the central point
thickness (CFT) the central point thickness (CPT) and the
macular volume was calculated.
CPT was mainly targeted for the centred fovea, which is the
average of 6 radial scan, whereas the CFT represents the central
sub field of 1 mm in diameter as a whole (Figure 3).
The IOL master measurement Lenstar (Alcon Haag Lenstar
Ls900 A-scan) is a non-invasive, non-contact OLCR (optical low
coherence Reflectometry) biometry used for obtaining ocular
measurements and performing calculation of appropriate power
and type of IOL. The Lenstar LS 900 measures in this particular
Axial Length: OLCR technology using super luminescent
diode as the laser source allows the measurement of the axial
length of the patient’s eye, precisely on the patient’s visual axis,
in the presence of dense media. LENSTAR, A scan it is similar to
an immersion ultrasound scan, for easy user interpretation.
Central Corneal thickness: like every other axial
measurement with the Lenstar, optical coherence biometry is
used to measure CCT with stunning reproducibility of ±2um.
CCT is a key parameter in glaucoma and surgery purposes like
laser refractive surgery, myopic or hyperopic LASIK procedures,
when there is no patient history (Figure 4).
Total number of normal patients who is willing to participate
for this study was 145 (290 eyes). The number of male was 52
and the number of females 93 along with the age range from 15
to more than 80 as it was given in the Table 1 (Figures 5).
The percentage of visitors were mostly young to adulthood
and the minimum were the old age group (Table 2). Most patient
that are willing to participate for this study were basically more
of visual acuity of 6/6 to 6/9 and few are less than 6/60 with
a signal strength of not less than 7 in case of an OCT (Table 3)
All refractive status was taken into consideration for least
confusion by converting it into Spherical Equivalent, were
Emmetrope was considered from +0.12 to -0.12, Myope from
-5.00 to -0.25 and lastly for Hyperope from +5.00 to +0.25
The Figure 7 signifies the amount of refractive error patients
participated for the study. The maximum amount of refractive
error range from +0.25 to -0.25 considered as the highest peak
for Emmetrope, Myope with -5.00 DS and Hyperope +1.75 DS
The main Mean value of the parameters required in this study
were following the ETDRS study of the macula and RNFL involve
for macula Central Point Thickness 164.96 ± 30.88 Average
macular Thickness 271.81 ± 20.52, Central sub field of macula
191.01 ± 32.33 and for the Average RNFL thickness 107.61 ±
13.45 were as the Central Corneal thickness 528.54 ± 32.84 and
lastly the axial Length of 23.22 ± 0.91. All the above parameters
showed a strong positive correlation between the right and left
eye of each individual (r ≥ 0.5, p<0.001). Therefore, data of right
eyes was taken for further statistical analysis (Table 5).
No significant differences was found between males and
females in all the parameters by doing unpaired t- test of Central
Point thickness, Avg macular thickness, Avg RNFL thickness,
Central sub field, central corneal thickness (CCT), Intra ocular
pressure (IOP) and Axial length with (p= 0.33, 0.61, 0.94, 0.97,
0.30. 0.47 and 0.37 respectively) (Table 6).
The analysis of variance between parameters showed a
significant difference between Axial length and age groups (p =
0.04). However, no variation with age was seen in the Average
Macular thickness, Average RNFL thickness, and Central Corneal
Thickness with (p= 0.36, 0.52 and 0.87 respectively). Therefore,
Post hoc Bonferroni correction was done for the axial length to
find the specific variations between the age groups (Table 7).
*. The mean difference is significant at the 0.05 level.
Post HOC Bonferroni shows that the difference in only
between groups 1 (15-25) with Group 3 and 4. In addition,
Group 4 (46-55) with 1, lastly group 5 (>55) with Group 1 (Table
8). From the above correlation, it tells us about the relationship
trend between the parameters with age Refractive status and
IOP. From the given Table 8 we can draw a conclusion that Age
has a positive correlation with significant difference to the
spherical equivalent (SE), and a negative correlation to IOP
and Axial length. Where SE has positive correlation to age and
negative correlation to IOP and Axial length. IOP has negative
correlation to age and SE and positive correlation to central
corneal thickness (CCT) and Axial length. Lastly, Average macular
thickness has positive correlation to Average RNFL (Table 9).
The Full form of the above aberration (CPT: Central Point Thickness; CSF: Central Subfield; SI: Superior Inner, TI: Temporal Inner; II: Inferior
Inner; NI: Nasal Inner; SO: Superior Outer; TO: Temporal Outer; IO: Inferior Outer; NO: Nasal Outer; Avg: Average; Vol: Volume; RNFL: Retinal
Nerve Fiber Layer).
From the above table it give us the normative data mean
value of each parameters, by using of SLO OCT. It is done on the
tribal people of North East India on macular and RNFL thickness
overall, by the Methods of ETDRS follows with the Minimum and
maximum Range given on each parameters,
The Table 10 gives us the normative data of all the required
parameters. Using of the same instrument but of different
population size. The current study was compared with the
Caucasians and Indian population as a whole. We found no
significant differences between average macular thickness,
average RNFL thickness, axial length and central corneal
thickness. The only things needed to take into consideration is
the macular central point thickness, which appears to be thinner
as compared to Indian and Caucasians population.
OCT has emerged as one of the most important tool in the
field of eye care. It has emerged both qualitative and quantitative
data regarding anterior and posterior segments of the eye .
OCT has increased the hope to obtain a more reliable tool in an
attempt to define the changes in the Retina mainly by spectral
Domain OCT [6,8,9,11,12]. Many studies has been done to
compare Macular thickness with RNFL thickness with age and
Gender  and also with diseases like glaucoma [2,6], diabetic
This study gives us the normative data of macular thickness,
RNFL thickness, and axial length in relationship with IOP,
Central corneal thickness, Age, gender and refractive status.
To our knowledge, the current report is the first to present the
data from the normal population of the Scheduled Tribe people
(North East state Of India) which mainly concentrated of the
Several studies has been conducted between macular
thickness and RNFL thickness they found significant difference
in them [20,39], similarly in this study we found there is a
significant difference. The mean average of macular thickness was
found to be 271.81 ± 20 um, Average RNFL thickness 107.61±13
um, Mean CPT was 164.96 ± 30, mean CSF was 191.01 ± 32.33
and Total volume of macular was 7.62 ± 0.51 whereas Average
RNFL thickness mean was 107.67 ± 13.45 with the Superior
RNFL mean was 122.22 ± 19.32, Inferior RNFL mean was 135.96
± 19.92, Nasal RNFL mean was 92.59 and Temporal RNFL mean
was 80.99 ± 15.40 this present study showed maximum RNFL
thickness in the inferior quadrant followed by superior, nasal,
and temporal supporting the ISNT rule by Jonas et al. [23,25,40].
In this study, the total number of participant was 145 (93
females and 52 males) with the age range from 15 to 80 and above.
This study gives us the parameters OCT of macular and RNFL
that follows the ETDRS study, show no significant differences
between genders, age, and Refractive status (Emmetrope – 61,
Myope – 66 and Hyperope – 18) [14,15,18].
However when looking at all the parameters of the of Axial
length(mean value 23.22±0.91), macular thickness(271.81±20),
RNFL thickness(107.61±13) and central corneal
thickness(528.54±32) showed a strong positive correlation
between the right eye and left along with no significant
difference between male and female. Hence, only one eye was
taken for further analysis.
In this study while running the ANOVA, we found no
significant differences between the Average macular thicknesses
 as found by Wong KS, Average RNFL thickness , Central
Corneal Thickness [30,31] with age . Except the axial length
which shows a significant differences with specific age group with Group 1(15-25) compare to group 3(36-45) P= 0.03, and
4(46-55) P= 0.01. Lastly, between group 5(>55) with group
1(15-25) P= 0.01, by post HOC Bonferronoi.
The study proves, the data of all the parameters like Average
macular thickness has a positive correlation (0.44) with
Average RNFL [6,20,35] and P= 0.00. Axial length has a negative
correlation with Age and Refractive status [26,28,30,31] (-0.30,
and -0.56 respectively) with P=0.00.
From this study, we are getting a closer look; apart from
the parameters required, we can draw a conclusive action
when doing a test that needs to be looked at. For age there is
a positive correlation (0.38) with Refractive status P=0.00, and
negative correlation (-0.18) to IOP P=0.02. For Refractive status
has negative correlation (-0.16) with IOP P= 0.05. For IOP there
is a negative correlation (-0.18, -0.16) with Age and Refractive
status respectively with P=0.05, and positive correlation (0.17)
with Axial length P=0.03. Lastly, Central corneal Thickness has
positive correlation (0.36) with IOP P= 0.00.
From all the parameters, they had a strong positive
correlation between the right eye and left eye, with no significant
difference between males and females. The parameters showed
no significant relationship with age and refractive status. Except
with the Axial, length has a significant difference with Age and
Refractive status on specific age group.
IOP should take special consideration as they have significant
relationship with Age, Refractive status, Central Corneal
Thickness and Axial length. Knowledge and awareness of
macular thickness and RNFL thickness, central corneal thickness
and Axial length was given on Spectralis OCT in a normal NE
population. In addition, it is important for the evaluation of
pathological change in this ethnic group. Further studies is
required to understand the association in all these parameters.