Title: Correlation between central corneal thickness (CCT) and retinal nerve fiber layer (RNFL) analysis obtained by scanning laser polarimetry (GDX VCC) in primary open angle glaucoma patients (POAG) and POAG suspects
Abstract: INTRODUCTION:
Glaucoma is a major cause of irreversible blindness worldwide.
According to World Health Organisation statistics about 13.5 percent of
global blindness is due to glaucoma, causing blindness in more than 5.1
million people. There occurs variation in glaucoma prevalence among
different race groups and regions. Open-angle glaucoma is more common
among persons of West African origin 5and angle-closure glaucoma is
more common among EastAsian population.
Only limited number of studies are available regarding the prevalence
of glaucoma in our country and its associated risk factors. A study done in
south Indian population estimated the prevalence of any glaucoma to be
2.6% and of primary open angle glaucoma 1.7%.
Patients are usually not aware of glaucoma in early stages because it
is an asymptomatic disease.Visual field defects are detected by standard
automated perimetry only when around thirty to fifty percent of retinal
ganglion cell axons are lost and clinical diagnosis of glaucoma is made
only when significant amount of Retinal Nerve Fiber Layer damage has
already occurred. Therefore more sensitive diagnostic modalities should
be employed for early diagnosis of glaucoma which is critical in preventing
irreversible loss of vision. AIMS AND OBJECTIVES:
To correlate Central Corneal Thickness (CCT) measurements with
Retinal Nerve Fibre Layer (RNFL) Thickness using scanning laser
polarimetry (GDx-VCC) in Primary Open Angle Glaucoma (POAG)
patients and POAG suspects.
OUTCOME MEASURES
Primary outcome measures
To assess the correlation between Central Corneal Thickness and
RNFL parameters.
Secondary outcome measures
To assess the correlation between Central Corneal Thickness and
Age ,Intra ocular Pressure and Vertical CDR. MATERIALS AND METHODS:
Study design – Observational cross sectional study.
Duration of study – One and half years. (Dec 2010 to May 2012). INCLUSION CRITERIA
1. All patients diagnosed as POAG based on open angles with no apparent
ocular/systematic abnormality accounting for the high IOP and typical
glaucomatous visual field defects/ONH changes.
2.All patients diagnosed as POAG suspects on the basis of open angles by
gonioscopy, and one of the following in at least one eye:
Appearance of the optic disc or retinal nerve fiber layer suggestive of
glaucomatous damage
Diffuse or focal narrowing or sloping of the disc rim.
Diffuse or localized abnormalities of the nerve fiber layer, especially at
superior and inferior poles .
Disc hemorrhage.
Asymmetric appearance of the disc or rim between fellow eyes (e.g., cup
to disc ratio difference greater than 0.2) suggesting loss of neural tissue.
Visual fields suspicious for early glaucomatous damage .
3.Age >18 years.
4.Best corrected visual acuity of 6/24 or better. 5. Refractive error : sphere within +5.0 diopters, and cylinder within +3.0 diopters.
EXCLUSION CRITERIA.
1. Patients with any retinal pathology that is likely to damage the retinal
nerve fibre layer like advanced diabetic retinopathy,retinitis
pigmentosa.
2. Media opacities interfering with quality GDx- VCC scan like
significant cataract, vitreous opacities .
3. Optic disc abnormalities (tilted disc, optic disc drusen, coloboma of
the disc),Peripapillary atrophy.
4. Secodary glaucoma.
5. Patients with corneal scarring,history of corneal refractive
surgeries,precluding accurate measurements of central corneal
thickness.
6. Corneal edema,use of contact lens that may affect corneal thickness.
7. Ocular surface disorders.
8. Secondary causes of high IOP (e.g., iridocyclitis, trauma),
9. Non glaucomatous optic neuropathy.
10. Diseases affecting visual field (e.g., demyelinating diseases, pituitary
lesions). 11. History of intraocular surgery (except for uncomplicated cataract
and glaucoma surgery).
12. Extensive panretinal photocoagulation.
The data of all the eligible patients were collected on proforma.
DISSCUSION: Central corneal thickness (CCT) has been an area of much interest as
an important risk factor for development of glaucoma. Management strategy
in 15% of glaucoma patients is influenced by central corneal thickness.
The corneal thickness has been considered as a surrogate indicator of the
overall structure and biomechanical properties of the eye. In the Ocular
Hypertension Treatment Study (OHTS), a thinner central cornea was
considered as a predictive factor in the development of primary openangle
glaucoma.
This study has been done to correlate Retinal Nerve Fiber Layer
Thikness measured by Scanning Laser Polarimetry with Central Corneal
Thickness measured by ultrasound pachymetry.CCT was correlated with
GDx parameters namely Superior Average,Inferior Average,TSNIT
Average,Nerve Fiber Indicator. Statistical analysis was done using
Pearson’coefficient and P value < 0.05 was considered statistically
significant.
In a study done by Sushmita et al. the mean CCT was found to be
542.3+21.5 μ among the normal population.We found that the overall CCT
measurements in POAG patients were significantly lesser than in POAG
suspects, 540.4μ versus 548.4μ, respectively. CONCLUSION: 1. There was a statistically significant difference in mean RNFL
parameters between POAG patients and POAG suspects.
2. Among POAG patients ,CCT did not correlate with RNFL
parameters except for TSNIT Average .
3. Among POAG Suspects, CCT did not correlate with RNFL
parameters except for TSNIT Average .
4. CCC inversely correlated with age in both POAG and POAG
suspects.
5. CCT correlated with Intraocular pressure in both POAG patients and
suspects.
6. CCT inversely correlated with vertical Cup Disc Ratio in POAG
patients.
7. The patients recruited in this study mostly belonged to early and
moderate glaucoma as GDx was performed to detect early
glaucomatous change. More subjects with advanced glaucoma should
be studied to find the exact association.
8. Longitudinal experimental study are needed to find out changes in
the Central corneal thickness over time in Primary Open Angle
Glaucoma patients, particularly in patients with thinner corneas.
9. Serial follow up measurments of RNFL parameters should be done to
document progressive glaucomatous damage.
Publication Year: 2013
Publication Date: 2013-04-01
Language: en
Type: dissertation
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