الفهرس 
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Abstract
Cataract is the leading cause of reversible blindness worldwide. Cataract
extraction with implantation of an intraocular lens (IOL) is the most frequently
performed ophthalmic surgical procedure worldwide. Accurate calculation of the IOL
power for attaining the desired postoperative refraction remains a research issue.
Precise measurement of eye parameters is critical in modern ophthalmology. Several
factors affect the refractive outcome after cataract surgery, including axial length,
keratometry, and lens formulas. Of these factors the preoperative axial length measurement
is a key determinant in the choice of intra-ocular lens (IOL) power.
Traditionally, contact A-scan ultrasonography is used. This measures the time
taken for sound to traverse the eye and converts it to a linear value (spikes) using a
velocity formula. The distance between the corneal and retinal spikes gives the axial
length of the eye. Keratometry reading (K1&K2) taken by autokeratometer data is
entered into a-scan software to calculate the Iol power.
silicone oil strongly absorbs and thus weakens the ultrasonic beam, echo signals from
the retina are usually weak and sometimes even absent, so silicon filled eyes presents many
technical and theoretical challenges to IOL power calculations.
The IOL master 500 device is a computerized biometry device consisting of an OCT
system to measure distances within the human eye along the visual axis, a Keratometer
system to measure the corneal surface.
This study aimed to compare the axial length change before silicon oil injection, 3
months after vitrectomy and silicon oil injection and 1 month after combined silicon oil and
phacoemulsification procedure.
A prospective clinical study that included 100 eyes of 100 consented patients
undergoing retinal detachment repair via 3-port vitrectomy with silicon oil injection and
combined silicon oil removal with phacoemulsification with in the bag foldable IOL
implantation after 3-6 months will be included in our study.
There were no significant differences in the mean values of axial length by IOL
master at different times of assessment (P=0.137). Otherwise, there was a significant higher
mean values of the axial length measured by IOL master in silicon filled eyes than before
operation (P1=0.053). On the other hands, there were no significant differences in the axial
length either after silicon removal than before operation (P2=0.577) or after silicon removal
than in silicon filled eyes (P3=0.167).
There were no significant differences in the mean values of axial length by Ascan at different times of assessment (P=0.075). Otherwise, there was a significant
higher mean values of the axial length measured by A- scan in silicon filled eyes than
before operation (P1=0.025). On the other hands, there were no significant differences
in the axial length either after silicon removal than before operation (P2=0.577) or after
silicon removal than in silicon filled eyes (P3=0.167).
There were no significant differences between the axial length measured by IOL
master or the axial length measured by A-scan at different times of assessment. Summary
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There is a mean increase of 0.71 mm in original axial length (ie measured after 3
months from the primary procedure of RD repair and silicon injection). Then amean decrease
by 0.51 mm in comparing preremoval status and 1 month post silicon oil removal axial
lengths .While, an overall mean increase of 0.20 mm comparing axial length state before
silicon oil injection and finally after silicon oil removal.
Also, The IOL master was found to be superior to A-scan as IOL master is less time
consuming and more patient friendly than is A- scan ultrasound. However, IOL master has a
failure rate, particularly in the presence of dense cataracts.
That IOL powers should be increased by 2.16 D (when using traditional formulas
based on 987m/s speed of ultrasonic waves used by IOL master and ultrasound machines) to
anticipate the decrease of axial length (0.51 mm) and avoid post operative 2.16 D hyperopic
shift