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| Identifier |
000353451 |
| Title |
Υδροδυναμική μελέτη του οφθαλμού : επεμβατική μέτρηση της οφθαλμικής ελαστικότητας, της ευχέρειας εκροής και της σφύζουσας αιματικής ροής στον ανθρώπινο οφθαλμό |
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Author
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Δαστιρίδου, Άννα
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Thesis advisor
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Παλλήκαρης, Ιωάννης
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Reviewer
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Γκίνης, Χαρίλαος
Τσιλιμπάρης, Μιλτιάδης
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| Abstract |
The pressure volume relation in the living human eye can be used to describe the
combined geometric and material properties of the eye. The outflow facility coefficient is
a measure of the resistance of the conventional outflow pathway. Ocular pulse amplitude
(OPA) is the variation of the intraocular pressure (IOP) with the heart rate and is
associated with the pulsatile component of ocular blood flow (POBF). Real time IOP
recordings can be used to provide estimates oF POBF through the derivative of the eye's
pressure -volume relationship.
The aim of this study is to characterise the pressure volume relation and quantify
ocular rigidity and outflow facility in the living human eye. Moreover, the effect of IOP
on OPA and POBF is assessed and the influence of axial length on the measured
parameters is investigated.
Seventy three patients (73 eyes) undergoing cataract surgery were enrolled in the
study. This study was approved by the Institutional Board and performed under the
patient’s informed consent. The measurement was performed under topical anaesthesia
with lidocaine and proparacaine drops before cataract surgery. A previously described
computer-controlled device for the intraoperative measurement and control of IOP was
used. The device, comprising a pressure transducer and a dosimetric pump is connected
to the anterior chamber of the eye through a 21 gauge catheter needle. This device was
used to artificially increase the IOP from 15 to 45 mmHg by infusing a saline solution in
steps of 4 μl. The IOP was continuously recorded for 2 seconds in each step in order to
measure the pulsatile change in IOP during this interval. OPA was derived as the peak-to7
peak IOP variation in each of the 2sec time intervals. Pulsatile Ocular Blood Flow
(POBF) was obtained converting the OPA to the corresponding change of ocular volume
derived from the rigidity diagram. Systemic blood pressure and pulse rate were
monitored during the measurement and remained stable in all patients.
The pressure-volume relation was approximated by an exponential function. A
mathematical model was developed in order to estimate the outflow facility coefficient,
that was used to correct the pressure volume relation for the volume loss through the
outflow pathways in the course of the measurement.
OPA was derived as the peak-to-peak IOP variation in each of the 2 sec time
intervals. Pulse volume was obtained converting the OPA to the corresponding change of
ocular volume derived from the rigidity diagram. POBF was estimated as the minimum
value of the volume derivative curve in each frame, according to a theoretical model that
has been proposed (Silver et al, 1994).
The average coefficient of ocular rigidity was 0.0217μl-1 (range 0.0122/0.0343).
The outflow facility coefficient was 0.332μl/mmHg (95% CI 0.164-0.605). In all patients
an increase in OPA was observed with increasing IOP. The average OPA was 2.01 (sd
0.53) mmHg for measurements conducted at 15 mmHg increasing to 3.82 (sd 1.19)
mmHg at 40 mmHg. A negative correlation between the rigidity coefficient and axial
length is documented.
The mean OPA increase was 0.063mmHg per mmHg increase in IOP and the
OPA at 40 mmHg was 86% higher than at an IOP of 15 mmHg. The OPA is correlated
with the coefficient of ocular rigidity (r = 0.64, P <0 .001). The corresponding POBF was
854ul/min (sd 163) at 15mmHg decreasing by 30 % to 594 (sd 144) ul/min at 40mmHg.
There is a negative correlation between axial length and POBF.
The results of this study suggest a non linear pressure volume relation in the
living human eye characterized by an increase in the slope of the curve in higher IOP
levels. The values for ocular rigidity and outflow facility coefficients may provide a
normal database of these parameters in the living human eye. The increased OPA and
decreased pulse volume relate to the decreased POBF and the increased mechanical
resistance of the ocular wall in high IOP levels. The rigidity coefficient as a measure of
both morphologic and biomechanical properties of the eye plays a key role to the
fluctuation in pressure that results from the inflow of blood in every pulse. Moreover, the
decrease in POBF in highly myopic eyes is in accordance with the clinical features of
degenerative myopia.
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| Physical description |
141 σ. : πιν. ; 30 εκ. |
| Language |
Greek |
| Subject |
Ocular Physiological Phenomena |
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Ophthalmology |
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Οφθαλμολογία |
| Issue date |
2008-12-15 |
| Collection
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School/Department--School of Medicine--Department of Medicine--Post-graduate theses
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Type of Work--Post-graduate theses
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| Notes |
Διατμηματικό μεταπτυχιακό πρόγραμμα σπουδών: "Οπτική και Όραση" |
| Views |
237 |
Υδροδυναμική μελέτη του οφθαλμού : επεμβατική μέτρηση της οφθαλμικής ελαστικότητας, της ευχέρειας εκροής και της σφύζουσας αιματικής ροής στον ανθρώπινο οφθαλμό
