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									                                                  Influence of Pharmacologically and Edinger-Westphal Stimulated                                                                                                                                                                                       Poster # 798

                                                 Accommodation on Anterior Chamber Pressure in Rhesus Monkeys
                                                                                   Lin (Jonathan) He, Mark Wendt, Adrian Glasser
                                                                          College of Optometry, University of Houston, Houston, TX, 77204

Introduction                                                              Results                                                                                                                  A                                                                        A                      B
The role of intraocular pressure in the accommodation mechanism is
                                                                           A                                        A                       B                             C
still uncertain although previous studies have addressed it1,2,3.
Coleman believes that changes in differential pressure between the
anterior and vitreous chambers have a causal effect on accommoda-
tion and proposed the following: During accommodation, the anterior
vitreous presses against the posterior lens surface; the anterior
chamber pressure first decreases and then increases; with simulta-
neous pressure change and forward movement of the suspensory                                                                                                                                       B                       8

insertion of the zonular fibers at the ciliary body, the lens bulges                                                                                                                                                       7
                                                                                                                                                                                                                                   No Perfusion
                                                                                                                                                                                                                                   Normal ACP (12 mmHg)
                                                                                                                                                                                                                                                                            C                      D
anteriorly into the more steeply curved accommodated shape4. Both
                                                                                                                                                                                                                                   Low ACP (6 mmHg)
                                                                                                                                                                                                                           6       High ACP (18 mmHg)

                                                                                                                                                                                                       Accommodation (D)
the forward translation of the anterior lens surface and its steepened                                                                                                                                                     5

anterior curvature contribute to the refractive changes.                                                            D                        E                             F                                               4

Verifying this alternative pressure based mechanism of accommoda-                                                                                                                                                          2

tion is important to the current and future approaches to restore                                                                                                                                                          1

accommodation in presbyopes. In this study, anterior chamber                                                                                                                                                               0
                                                                                                                                                                                                                               0   100        200         300   400   500

pressure was measured and manipulated during pharmacologically                                                                                                                                                                        Stimulus Amplitude (μA)

and EW stimulated accommodation in rhesus monkeys.                         B
                                                                                                                                                                                                   Fig 5 (A-B). (A) In one
                                                                                                                                                                                                   monkey, EW stimulated
                                                                                                                                                                                                   accommodation was repeated
Methods                                                                                                                                                                                            at 3 levels of anterior chamber
                                                                                                                                                                                                                                                                            Fig 6 (A-D). Step manipulations of ACP
                                                                                                                                                                                                                                                                            above and below normal intraocular
                                                                                                                                                                                                   perfusion pressure. (B) Graph                                            pressure had no systematic effect on
Experiments were performed on the iridectomized eyes of 7 adoles-                                                                                                                                  shows the mean accommoda-
                                                                                                                    G                               Fig 3 (A-G). Pilocarpine stimulated                                                                                     refraction. The slow drifts of the refraction
cent rhesus monkeys, two of which had implanted Edinger-Westphal                                                                                                                                   tive responses as a function of                                          (A-C) were associated with preceding
(EW) electrodes. The monkeys were anesthetized with constant                                                                                        accommodation in six monkeys. Three            stimulus amplitude for the
                                                                                                                                                    monkeys showed biphasic pressure                                                                                        pilocarpine bolus deliveries.
propofol infusion, with their heads held upright and facing forward in                                                                                                                             different pressure levels and
                                                                                                                                                    changes. However, the amplitudes are all       without perfusion. There was
a head holder. Anesthesia was supplemented with 0.05 mg/kg                                                                                          less than 2 mmHg, compared with about 15
medetomidine to minimize eye movement. Accommodation was                                                                                                                                           no systematic change in the
                                                                           C                                                                        mmHg reported by Coleman4. All the other       accommodative response for
stimulated by central EW stimulation or by intravenous bolus admin-                                                                                 monkeys (D-F) did not show a pressure dip      the different ACP tested.
istrations of pilocarpine 0.25-2 mg/kg over 30 seconds and measured                                                                                 before the increase. (G) Change in ACP and
with 100 Hz continuous ultrasound biometry (CUB) or 60 Hz infrared                                                                                  accommodation were significantly correlated
photorefraction. The photorefractor was calibrated by adding plus                                                                                   in one monkey but not in another monkey.      Discussion
trial lenses in front of the monkey eye for each experiment. The
anterior chamber pressure (ACP) measurement and perfusion                                                           A                                       C                                     Although both pharmacologically and EW stimulated accommodation
system was developed using preliminary testing on enucleated pig                                                                                                                                  resulted in increases in anterior chamber pressure, the pattern and
eyes and was applied to the monkey eyes using sterile procedure.                                                                                                                                  magnitudes of the pressure changes were not consistent among
                                                                                                                                                                                                  monkeys. Blocking changes in anterior chamber or externally manipu-
                                         Fig 1. Experimental setup for                                                                                                                            lating ACP had no effect on accommodation or refraction. This
                                         calibration on 13 porcine                                                                                                                                indicates that the changes in anterior chamber pressure are neither
                                         eyes. Three needles are                                                                                                                                  necessary nor required for the accommodative mechanism. Accom-
                                         shown, one in the anterior                                                                                                                               modative increases in anterior chamber pressure are more likely to be
                                         (25-G) and two in the vitreous                                                                                                                           a result of accommodation or small eye movements.
                                         chamber (both 18-G).
                                                                          Fig 2. (A) Experimental setup for
                                         Continuous ultrasound
                                         biometry (CUB) was used to
                                                                          monkey experiment including ACP
                                                                          recordings and accommodation
                                                                                                                    B                                      Fig 4 (A-C). Anterior chamber          References
                                         record biometric changes with                                                                                     pressure increased during EW
                                                                          recordings either by CUB or photore-                                                                                    1. Armaly, M. F. (1959). Studies on intraocular effects of the orbital parasympa-
                                         changes in pressure                                                                                               stimulated accommodation.
                                                                          fractor. (B) Photorefraction image of a                                                                                 thetics. II. Effect on intraocular pressure. AMA Arch Ophthalmol 62(1): 117-24.
                                         (achieved by moving a                                                                                             Accommodation was measured
                                                                          monkey eye with a 27-G needle in the                                                                                    2. Armaly, M. F. and N. C. Jepson (1962). Accommodation and the dynamics of
                                         reservoir up and down).                                                                                           with photorefraction (A) or CUB (B).
                                                                          anterior chamber. Red boxes show                                                                                        the steady-state intraocular pressure. Invest Ophthalmol 1: 480-3.
                                                                                                                                                           Accommodation reached a plateau
                                                                          where the average intensity profile                                                                                     3. D. J. Coleman and S. Trokel. Direct-recorded intraocular pressure variations in
In monkey eyes, a 27-gauge needle was inserted into the anterior                                                                                           even though ACP continued to           a human subject. Arch.Ophthalmol. 82:637-640, 1969.
                                                                          (blue line) is extracted for refraction                                          increase (C).
chamber to record ACP. The needle was connected to a pressure             measurements. (C) An example from a                                                                                     4. D. J. Coleman. On the hydrolic suspension theory of accommodation.
transducer and a saline reservoir. ACP changes were analyzed as a         pilocarpine stimulated accommodation                                                                                    Trans.Am.Ophthalmol.Soc. 84:846-868, 1986.
function of accommodative response. ACP was manipulated by moving         experiment showing refraction, ACP
a saline filled reservoir up and down while recording refraction. All     (including ACP manipulation from time                                                                                   Acknowledgment
monkey experiments were performed in accordance with an institution-      1286 to 2004 seconds), horizontal and     Disclosure                                  Author email addresses:
                                                                                                                                                                                                  This work was funded in part by sVRSG (UHCO) to LH. Thanks to Chris Kuether
ally approved animal protocol and conformed to the ARVO Statement         vertical eye movements (HEM and
                                                                                                                    LH, None; MW, None; AG, None.     ;       and Charles Neff for technical assistance and to Dr. Rob van der Heijde for the
                                                                          VEM), and the pilocarpine bolus
for the Use of Animals of Ophthalmic and Vision Research.                                                                                             ;

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