Download Correlation of axial length of the eyeball and peripapillary retinal

RAJIV GANDHI UNIVERSITY OF HEALTH SCIENCES
BANGALORE
PROFORMA FOR REGISTRATION OF SUBJECTS FOR
DISSERTATION
NAME OF THE CANDIDATE: SONIKA PORWAL
DEPARTMENT OF OPHTHALMOLOGY
ST JOHN’S MEDICAL COLLEGE
SARJAPUR,KORAMANGALA
BANGALORE-560034.
NAME OF THE INSTITUTION: ST JOHN’S MEDICAL COLLEGE
HOSPITAL.
COURSE: M.S OPHTHALMOLOGY
DATE OF ADMISSION TO COURSE: 1/06/2013
TITLE OF THE THESIS: Correlation of axial length of the eyeball
and peripapillary retinal nerve fibre layer thickness measured by Cirrus
HD Optical Coherence Tomography in myopes.
INTRODUCTION
Myopia is one of the most common eye problem in the world. Its
association with primary open angle glaucoma is well recognized. The
risk of developing glaucoma is 2-3 times higher in myopic individuals
than in non-myopic individuals.1However, the clinical diagnosis of
glaucoma in such patients is challenging because of the pre-existing
myopic changes in the retina and the optic disc.2
Currently, glaucoma is diagnosed by changes in the appearance of the
optic disc, retinal nerve fiber layer (RNFL) thickness and visual field
changes.3In early glaucoma, structural changes precedes the functional
damage. The RNFL thickness measurement is a sensitive predictor of
early glaucomatous changes and the extent of RNFL damage correlates
with the severity of functional deficit in the visual field.4
However, in myopic eyes, the globe is enlarged with increase in axial
length. The axial length affects the RNFL thickness inversely.5 Because
of this , glaucomatous changes cannot be easily interpreted in myopic
patients, possibly leading to overdiagnosis or under diagnosis of
glaucoma.
6.1NEED FOR THE STUDY
The relationship between the RNFL thickness and axial length has been
investigated by a few studies.However, whether the RNFL thickness
varies with the refractive status of the eye remains unclear. It is therefore
important to investigate and conclude whether there is any correlation
between RNFL measurements and the axial length/refractive error in
myopic patients. Considering that the risk of developing glaucoma
increases with the severity of myopia, it is important to know the
variations in RNFL thickness in patients with myopia to avoid
overdiagnosis/under diagnosis of glaucoma.
The purpose of this study is to determine the relationship between axial
length and the RNFL thickness measured by Cirrus HD OCT in myopic
patients.
6.2 REVIEW OF LITERATURE
In a study conducted by M J Kim et al on fifty-seven healthy subjects
with myopia, aged between 20 and 35 years and with no other known
ocular abnormality it was found that the global average RNFL was
significantly thinner in the high myopia group than in the low myopia
group {107.4mm (SD 7.6) v/s 115.8 (8.5) mm, p=0.029}. For quadrant
measures, the RNFL was thicker in the low myopia group than in the
moderate and high myopia groups for the superior, nasal and inferior
quadrants (all p values <0.020). However, the temporal quadrant was
thinner in the low myopia group than in the moderate and high myopia
groups (p=0.001).They concluded that although the high myopes had
significantly thinner RNFLs in the non-temporal sectors compared with
the low myopes, they showed a significantly thicker RNFL in the
temporal quadrant.6
Similar studies conducted by Shin Hee Kang et al, Giacomo Savini et al
showed that average RNFL thickness decreased with an increase in the
axial length in myopia. They also showed that high myopes had thinner
RNFLs than did low myopes and showed different topographic profiles,
thus concluding that retinal nerve fibre layer thickness is related to
refractive error/axial length.5,7
In contrast, study conducted by Hoh et al reported that the mean RNFL
thickness did not vary with myopia or axial length.8
6.3 OBJECTIVES OF THE STUDY
Primary- To evaluate the peripapillary retinal nerve fiber layer (RNFL)
thickness by Cirrus HD optical coherence tomography (OCT) in
myopes.
Secondary- Correlation of axial length and peripapillary RNFL
thickness in myopes.
7.0MATERIALS AND METHODS
7.1 SOURCE OF DATA –Patients with myopia attending
ophthalmology OPD at St.Johns Medical College Hospital, Bangalore
from October 2013 to April 2015 for refractive error evaluation.
TYPE OF STUDY – Cross sectional study.
PROPOSED SAMPLE SIZE- 45
To observe correlation co-efficient of 0.6 between axial length and
RNFL thickness a sample size of 14 subjects should be observed. To
perform this comparison within 3 different myopia categories sample
size required would be 45. The power and level of significance
considered as 80% and 5% respectively.
INCLUSION CRITERIA
All myopes presenting to the Department of Ophthalmology at SJMCH
between the ages of 21 years to 50 years from October 2013 to April
2015 with the consent of the patients.
EXCLUSION CRITERIA
1) Those with best corrected visual acuity <20/20.
2) Those with a history of severe ocular trauma, intraocular or refractive
surgery, or any ocular or retinal diseases that could have affected the
optic nerve head or RNFL like Diabetic Retinopathy, Hypertensive
Retinopathy, Age related macular degeneration and others.
3) Diagnosed cases of glaucoma or those with intraocular pressure
(IOP) >21 mm Hg in either eye; those showing evidence of a
reproducible Visual field defects in either eye, as detected using the
Humphrey Visual Field analyzer .
4) Those with history of neurological diseases that could have affected
the optic nerve head or RNFL.
7.2 METHOD OF COLLECTION OF DATA
Patients with myopia attending ophthalmology OPD at St.Johns Hospital
Bangalore from October 2013 to April 2015.
Informed consent will be taken.
A detailed history including demographics, ocular disease, past medical
and surgical history, drug history and personal history will be taken.
Ophthalmological examination will include:
- Visual acuity (best corrected): using modified Bailley and love chart.
- Near vision with Times New Roman chart
-Colour vision with Ishihara’s chart.
-Fundus evaluation using direct ophthalmoscope and indirect
ophthalmoscope.
-Refraction.
-Intraocular pressure measurement by Applanation tonometer.
- A-scan ultrasound biometry (Alcon-ultrascan) software version- 3.00
for determining the axial length.
-Visual fields analysis by Humphrey Visual Field analyzer for all
patients with cup:disc ratio >0.5. A reliable visual field test will be taken
as one with <30% fixation losses,<20% false-positive responses/falsenegative responses.
- Retinal nerve fiber layer thickness measured by using Cirrus HD
Spectral Domain Optical coherence tomographer (4000-1720)
version -5.2.1.2 . It will be performed through a dilated pupil. External
fixation will be used and Optic disc cube 200*200 will be obtained.
Three of the best obtained scans will be selected. OCT will be repeated
when the obtained scans are not appropriate due to poor focusing or
inadequate centration. The patient will be excluded if repeat scans are
also unsatisfactory. Finally, the selected OCT scans will be analyzed
using the Average Retinal Nerve Fiber Layer Thickness program. Mean
RNFL thickness will be recorded globally and separately for the
superior, inferior, nasal and temporal quadrants.
Pearsons correlation analysis will be used to evaluate the correlation
between axial length and global RNFL thickness and also with the
individual quadrants.
7.3. Does the study require any investigation or intervention to be
conducted on patients, other humans or animals?
The examination and investigations to be conducted on the patients are a
part of investigations required for high myopes and those for low
myopes would not be charged.
7.4 .Has the ethical clearance being obtained from your institution?
Yes
8.0 REFERENCES
1. Mitchell P, Hourihan F, Sandbach J, et al. The relationship between
glaucoma and myopia: the Blue Mountain Eye Study. Ophthalmology.
1999;106:2010–2015.
2. Melo GB, Libera RD, Barbosa AS, et al. Comparison of optic disk
and retinal nerve fiber layer thickness in nonglaucomatous and
glaucomatous patients with high myopia. Am J Ophthalmol
2006;142:858–60.
3. George A,F Jane Durcan, Christopher A, Gupta N , et al. Open angle
glaucoma.Glaucoma.Vol.10. San Francisco :American Academy of
Ophthalmology. Series;2013-2014. P.82,83.
4. Quigley HA, Katz J, Derick RJ, et al. An evaluation of optic disc and
nerve fiber layer examinations in monitoring progression of early
glaucoma damage. Ophthalmology. 1992;99:19 –28.
5. Shin Hee Kang, Seung Woo Hong ,Seong Kyu Im et al. Effect of
Myopia on the Thickness of the Retinal Nerve Fiber Layer Measured by
Cirrus HD Optical Coherence Tomography.Investigative
Ophthalmology & Visual Science, August 2010, Vol. 51
6.M J Kim, E J Lee, T-W Kim et al. Peripapillary retinal nerve fibre
layer thickness profile in subjects with myopia measured using the
Stratus optical coherence tomography.Br J Ophthalmology
2010;94:115–120. doi:10.1136/bjo.2009.162206
7. GiacomoSavini, PieroBarboni, Vincenzo Parisi et al.Br J Ophthalmol
2012;96:57e61.doi:10.1136/bjo.2010.196782
8. Hoh ST, Lim MC, Seah SK et al. Peripapillary retinal nerve fiber
layer thickness variations with myopia.Ophthalmology.2006;113:773-7.
9.0 SIGNATURE OF THE CANDIDATE:
10.0 REMARKS OF THE GUIDE- The importance of the study is
already been emphasized in the need for the study. Measurement of
RNFL thickness by OCT is used in the diagnosis of many retinal
diseases. It is also used in the diagnostic evaluation of glaucoma.
Change in the axial length of the eye due to myopia independently
affects the RNFL thickness. Therefore it is important to know the
correlation of the axial length/myopia with the peripapillary RNFL
thickness to prevent overdiagnosis/underdiagnosis of glaucoma .
11.NAME AND DESIGNATION OF GUIDE
Dr.ANDREW VASNAIK
PROFFESSOR
DEPARTMENT OF OPHTHALMOLOGY
11.2 SIGNATURE
11.3 CO-GUIDE
Dr.NIBEDITA.ACHARYA
ASST. PROFFESSOR
DEPARTMENT OF OPTHALMOLOGY
11.4 SIGNATURE
11.7 HEAD OF THE DEPARTMENT
DR REJI K THOMAS
PROFESSOR AND HEAD
DEPARTMENT OF OPHTHALMOLOGY
11.8 SIGNATURE
12.1 REMARKS OF CHAIRMAN AND PRINCIPAL
12.2 SIGNATURE
PATIENT INFORMED CONSENT FORM
I, ________________________ declare that I have been briefed and hereby in my
freewill consent to be included as a subject in the following study – “Correlation
of axial length of the eyeball and peripapillary retinal nerve fibre layer
thickness measured by Cirrus HD Optical Coherence Tomography in
myopes”.
I have been informed to my satisfaction by Dr. Sonika.Porwal, the purpose
and
nature of the study. This has been explained to me in the language I understand
best and I fully consent for the same.
It has been explained to me that there shall be no change in the standard of care in
the course of study and the expression of non-willingness will not change the
standard of treatment.
Signature of the doctor
Signature of the patient
Name of the doctor:
Name of the patent:
Date:
PROFORMA FOR THE STUDY:
Personal details
NameAge/Sex
Date
Op/Ip n
Past history
Personal history
Family history
Drug history
Ocular history
On examination:
1)Visual acuity
UnaidedBCVA 2) Near vision
3) Colour vision-
4) Anterior segment-
5) Fundus examination- direct ophthalmoscope
MediaDiscBGR-
, CDR-
,vessels-
Macula-
Indirect ophthalmoscope
5) Refractive correction –
6) IOP –
7) Axial length8) Optical coherence tomography-Peripapillary retinal nerve fiber layer
thickness
a) average thickness
b) quadrants –superior
inferior
nasal
temporal