الفهرس 
Anatomy of the retinaOnly 14 pages are availabe for public view
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Abstract
Fovea centralis is a small, central pit in the retina of the eye composed of
closely packed and highly photosensitive cones. It is located in the center of the
macula lutea of the retina. The fovea is responsible for sharp central vision which
is necessary in humans for many activities where the detailed vision is of primary
importance such as reading and driving. The foveal thickness never exceeds
252μm in any of the healthy eyes.
The retinal nerve fiber layer (RNFL) is formed by the expansion of the
axons of ganglion cell layer and it is thickest near the optic disc with gradual
decrease in its thickness towards the ora serrate. Typically, normal eye has a
RNFL thickness of 80 microns or greater. RNFL is a sensitive structure and some
processes can excite its natural apoptosis. Harmful situations can make some
damage on the RNFL decreasing its thickness such as high intraocular pressure,
high fluctuations of the intraocular pressure, inflammations, vascular diseases or
any kind of hypoxia.
Hyperopia, is a refractive error in which parallel rays of light coming from
the infinity are focused behind the light sensitive layer of the eye (retina), when
the eye is at rest. In hyperopia, the cornea is flatter or the axial length of the eye is
shorter than 24mm.It has been reported that the mean peripapillary retinal nerve
fiber layer (RNFL) thickness is conversely correlated with axial length and
directly correlated with spherical equivalent (SE) in myopic populations.
In this regard, optical coherence tomography (OCT) is a modern imaging
device designed to be used in a non contact and non invasive manner giving high
resolution images of the retina and accurate measurements of the different retinal
tissues including retinal nerve fiber layer (RNFL) and macula. It became an
essential imaging tool for both macular and optic nerve diseases. The recent
introduction of spectral domain (SD)-OCT technology offers advantages over the
previous time domain (TD)-OCT, allowing 3-D imaging of the retina and optic
disc with ultra-high speed and resolution.
The aim of this work was to study the peripapillary retinal nerve fiber
layer thickness and foveal thickness in hyperopia using the spectral domain
optical coherence tomography
The study included a group of 45 simple hyperopic eyes and another group
of 45 emmetropic eyes as controls matched with age and sex.
Optical Coherence Tomography was used for the measurement of
peripapillary retinal nerve fiber layer thickness and foveal thickness.
The presented results demonstrated that: there was significant shorter AL
and higher MFT in the hyperopic group than in the emmetropic group. But there
was no significant difference between both groups according to the CFT.
There was a significant thicker mean RNFL in hyperopic group than
emmetropic group. There was a significant thicker RNFL (IQ), (SQ), (NQ) and
(TQ) in hyperopic group than emmetropic group.
There was a statistically significant lower visual acuity in hyperopic group
than emmetropic group.Summary
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In hyperopic group: there was a positive correlation between SE and
RNFL (IQ) thickness. There was also a positive correlation between SE and both
MFT and CFT. There was a positive correlation between RNFL (TQ) and MFT.
There was also a positive correlation between RNFL and both MFT and CFT.
There was a negative correlation between visual acuity and both MFT and CFT.
There was a negative correlation between AL and mean RNFL thickness, RNFL
(IQ) thickness and RNFL (NQ) thickness. There was a negative correlation
between AL and both MFT and CFT. There was a negative correlation between
age and CFT.
In both hyperopic group and emmetropic group: there was a negative
correlation between age and both average RNFL thickness and RNFL (IQ)
thickness. But in emmetropic group only, there was a negative correlation
between age and RNFL (TQ) thickness.
There was no significant difference between male and female according to
average RNFL thickness, RNFL superior quadrant, RNFL inferior quadrant,
RNFL nasal quadrant or RNFL temporal quadrant.