Current Eye Research

Volume 9 number 3 1990

The influence of alpha-adrenergic agents on tonic accommodation

Mark Rosenfield, Bernard Gilmartin', Elizabeth Cunningham' and Nutan Dattani'

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Schnurmacher Institute for Vision Research, SUNY/State College o f Optometry, 100, East 24th Street, New York, NY ' 10010, USA and 'Department of Vision Sciences, Aston University, Aston Triangle, Birmingham B4 7ET, UK

ABSTRACT This study has examined the effect of an alpha-1 adrenergic agonist (phenylephrineHCI, 2.5%) and a non-selective alpha antagonist (thymoxamine HCI, 0.5%) on tonic accommodation (TA). TA was measured at 1 min intervals throughout a 45 min period using an objective infra-red optometer (Canon Autoref R-1). Additionally pupil diameter and the near-point of accommodation(NPA) were monitored in order to assess the efficacy of the instilled drug. A double-blindprotocol was adopted between thymoxamine, phenylephrine and a saline control for 7 emmetropic subjects. There was no significant difference between the values of TA obtained under the three pharmacologicalconditions. However, both adrenergic agents induced changes in pupil diameter and NPA. Furthermore in all conditions TA increased by approximately 0.25D while the subject sat passively in darkness. The data indicates that alpha-adrenergic innervation alters the closed-loop accommodative response independently of TA.

receptors(7-9),predominantly of the beta-2 sub-group (10-12). However the alpha-adrenergicinnervationto the ciliary body may also be responsible for some variation in the accommodative response. Morgan (2), Fleming and Hall (13) and Chin et al. (14) suggested that increased alpha-innervationaltone to the ciliary vasculature would produce peripheral vasoconstriction, leading to a reduction in ciliary body volume with consequent alteration of the crystalline lens curvature. However, a recent investigation by Zetterstrdm and Hahnenberger (12) examined the effect of topical adrenergic agents on strips of human ciliary muscle in vitro. They demonstratedthat phenylephrine (an alpha-1 agonist) produced a relaxation of the ciliary muscle in 3 out of the 8 eyes examined. Since these responses were demonstrated in the absence of the muscle vascular

INTRODUCTION There is substantial support for the proposal that the ciliary muscle

system, ZetterstrOm and Hahnenberger concluded that the adrenergic responses were produced by direct action on the ciliary

receives a dual autonomic innervational supply, i.e. from both

muscle rather than being due to an indirect effect on the ciliary

Parasympathetic and sympathetic nervous systems (1). Whilst the

vasculature.

precise role of sympathetic innervation in the control of accommodation is unclear, it would appear to play a relatively minor

Several in-vivo investigations (15-20) have also demonstrated the eflect of topical alpha-adrenergic agents on the accommodative

role in a rapidly changing visual environment. Evidencefor this

response. They have demonstrated that instillationof phenylephrine

proposal may be drawn from observations on the time course and

will induce a reduction in the dioptric value of the near-point of

amplitude of the sympathetically-mediatedresponse. Morgan (2)

accommodation (NPA). Additionally, Leibowitz and Owens (21) and

reported that in cats, parasympatheticstimulation produced a diptric

Garner et al. (22) examined the effect of phenylephrine on the

change 10 times greater than that induced by the equivalent degree

accommodative response in darkness. It is well establishedthat

of sympathetic stimulation. Later TOrnqvist (3) demonstrated that the

under stimulus-free conditions, accommodation adopts a relatively

maximum inhibitory response in young adult cynomlgus monkeys

stable value of around 0.50-1.50D (21,23). The term tonic

(Macaca irus) was only around 1.5D. Furthermore the temporal

accommodation (TA) has been adopted to describe this intermediate

response is relatively slow, reaching a maximum around 10-45s (3-5).

bias of accommodation (23-26). Leibowitz and Owens (21) examined

Clearly this observed time-course is too slow to contribute to the

the effect of 2 drops of 10% phenylephrine on both TA and the

rapid changes in accommodative stimulus which are encountered in

far-point of accommodation;TA being measured using a laser

the typical visual environment. In contrast, parasympathetically

optometer. They observed that for 7 subjects, phenylephrine did

mediated accommodative responses are normally completed in

not produce any Significant change in either of the parameters

approximately 1s (6).

measured. However Garner et al. (22) pointed out that in the study of

A number of studies have demonstrated that sympathetic input to the ciliary muscle is primarily mediatedvia beta-adrenergic

Leibowitz and Owens, the NPA was not assessed and therefore it was not possible to confirm that the ciliary body had been affected by

Received on November 2, 1989; accepted on January 25. 1990

0 Oxford University Press

267

Current Eye Research the drug treatment. Garner et al. recorded TA, using a laser

astigmatism not exceeding 0.50D). All subjects signed a consent

optometer, for 6 hours following the instillation of phenylephrine

form prior to taking part in the study and following a full explanation of

(loo/.) in three subjects. Additionally NPA was measured during the

all experimental procedures.

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6 hour period. They observed that phenylephrine produced a

The accommodative response was measured objectively using a

significant reduction in the near point (mean = 2.75D) in all 3

Canon Autoref R-1 infra-red optometer. This instrument was

subjects, the maximum reduction in NPA occurring approximately 60

modified so that the refractive state could be measured at 1s

mins following drug instillation. Furthermore Garner et al. observed

intervals. The optometer measures 3 meridians in 0.2s to provide

no significant change in TA in the 3 subjects examined. Their data on

sphere and cylinder powers to an accuracy of +0.12D and has been

the NPA indicated that the efficacy of phenylephrine reached a

fully described and evaluated by McBrien and Millodot (29). All

maximum during the first hour following drug instillation. However

measures of accommodationwere taken from the left eye and

during this initial 60min period only one measure of TA was taken on

readings were calculated as mean spheres (i.e. sphere + half cylinder

subject RB and no assessment of TA was made on subject BB.

power). No calibration factor has been added to the optometer

Zetterstrbm (19) used a laser optometer to examine the effect of phenylephrine (10%) and thymoxamine (0.5%) on TA. She reported

reading. The initial part of each experimental sessior?consisted of the

that the instillation of phenylephrine produced a myopic shift in TA of

measurement of pre-task TA. This was done according to the

0.90D while thymoxamine failed to induce any significant change in

method described by Gilmartin and Bullimore (30). The subject sat in

TA. Additionally Mordi et al. (27) indirectly assessed the level of TA

total darkness for a period of 10 mins in order to dissipate any

by examining the accommodation stimuluslresponse function for

transient changes in accommodation initiated prior to the start of the

their 5 subjects. TA was taken as the intersection of the

experimental session. This also served to ensure that TA had

stimuludresponse plot with the unit-ratio or 45" line. Examination of

regressed to a base-line level. After this period 50 readings of the

their data indicates that 3 of the 5 subjects demonstrated a reduction

refractive error were taken over a 5 min period. These were then

in TA of the order of 0.4D one hour following drug instillation, whilst a

averaged to give the mean value of pre-task TA.

further subject showed a shift in TA of approximately -0.6D. However

After measurement of pre-task TA, the left pupil diameter was

the findings of Tan and OLeary (28) would bring into question the

measured directly from the optometer video monitor. This provides

proposal that the intersection of the stimulus/responseplot with the

an 8x magnificationof the eye and allowed the pupil diameter to be

unit-ratio line is equivalent to the dioptric value of TA.

assessed using a calibrated rule mounted on the screen. Pupil

In view of these equivocal findings, the present study has sought

diameter could therefore be assessed to an accuracy of k O.lmm and

to examine the effect of phenylephrine, an alpha -1 adrenergic

was measured under darkroom conditions. Additionally NPA was

agonist, and thymoxamine, a non-selectivealpha antagonist, on TA

assessed using a "push-up" technique. The target consisted of a

at one minute intervals over a 45min period. The instillation of both

line of high contrast (=8O%) letters, size N5 (31) mounted on a

agonist and antagonistic agents will provide greater information

near-point rule. Target luminance was approximately 50 cd/m2. The

concerning the alpha-adrenergic effect when compared with the use

NPA was measured from the left eye under monocular conditions

of an agonist alone. Measurement of accommodationcommenced

and the mean of three readings recorded.

20 mins following drug instillation in order to encompass the period of

A double-blindprotocol was adopted between phenylephrine

maximum drug efficacy. Additionally the mydriatic effect was

hydrochloride (2.5%)*,thymoxamine hydrochloride (0.5%) and a

monitored throughout the course of the 45min interval and the NPA

saline control. Instillations of phenylephrine,thymoxamine or saline

was assessed both before and after the measurement period.

were made using a precision micropipette delivering 25yl of drug.

MATERIALS AND METHODS

Benoxinate (0.4%) in order to inhibit reflex lacrimation, each subject

Following the instillation of one drop of the topical anaesthetic A total of seven emmetropic subjects were used (4 male, 3

female), all of whom were students in the Department of Vision

was given two instillationsof drug separated by a period of 5 mins i.e. 50y1 of drug per eye. Twenty minutes following the first drug

Sciences, Aston University. All subjects were Caucasian, aged between 18 and 2lyears of age and had unaided distance visual acuity of at least 616 with either eye and a mean spherical refractive error not greater than 0.50D of myopia or hypermetropia (with

268

* Phenylephrine (2.5%), thymoxamine (0.5%), Benoxinate (0.4%) and normal saline: Smith & Nephew single dose applicators ("Minims").

Current Eye Research instillation, the subject returned to the optometer and the room lights

period. These values were averaged into 5min intervals and are

were extinguished. Following an initial 60s period, 10 readings of the

illustrated in Fig. 1. Clearly the instillation of either thymoxamine

refractive error were taken each minute for 45mins. The subject

(0.5%) or phenylephrine (2.5%) did not produce any significant

remained in darkness throughout the measurement interval.

change in TA. Two factor (drug, time) anatysis of variance was carried

Pupillary diameter was also assessed at 1min intervals over the 45min

out on the data illustrated in Fig. 1. This indicated that neither factor

period. At the end of the 45min session the assessment of NPA was

was significant (drug: F=0.04;df=2,162; p=0.96; time: F=0.89; df=

repeated. The order of the three drug trials was randomized and

8,162; p=0.58). The second order interaction was not significant.

each trial was separated by a period of at least 48hrs.

The values of pupil diameter during the course of the 45min period are illustrated in Fig. 2. Two factor (drug,time) analysis Of

RESULTS

variance indicated that the drug effect on pupillary diameter was

The mean pre-task values of TA and pupillary diameter are shown Curr Eye Res Downloaded from informahealthcare.com by University of Newcastle on 12/28/14 For personal use only.

in Table 1. One factor analysis of variance on the pre-task TA data

significant (drug: F=70.25; df=2,162; p0.05). The shift in TA, measured with respect to the pre-task level, was calculated at 1 min intervals throughout the 45min assessment

Table 1. Pre-task measures of tonic accommodation (TA) and pupil diameter. All values are recordedfrom the left eye. Figures in parentheses indicate f 1 SEM. Phenylephrine

Thymoxamine

E

1 1 1

a,

c

a,

1

I

0.41

0.77

0.76

(D)

(0.25)

(0.17)

(0.18)

Pre-task pupil

7.44

7.05

7.32

diameter (mm)

(0.42)

(0.46)

(0.33)

5

15

25

35

45

Time (mins)

Fig. 2. Mean values of pupil diameter for the three drug conditions during a 45 minute period in darkness. The measurementperiod commenced 20 mins following the first drug instillation. Error bars represent f1 SEM.

1

1

Phenylephrine

G

1

c

//

.6-.

'

U

E

- 0 . 25

Thymoxamine

Saline

Pre-task TA

+ 0.50

-E

I,

5 2 0

15

25

35

45

-

.-

z

a Time (mins)

Post-task

8 6

4

U a, + .

5

Pre-task

10

2 0

PHENYLEPHRINE THYMOXAMINE

Fig. 1. Mean dioptric shift in tonic accommodation(TA), measured with respect to the pre-task level, for the three drug conditions during a 45 minute period in darkness. The measurement period commenced 2Omins following the first drug instillation. Error bars have been omitted for clarity but SEMs for the phenylephrine, thymoxamine and saline conditions were of the order of 0.15, 0.1 1 and 0.23 respectively.

SALINE

Experimental condition

Fig. 3. Mean pre- and post-task values of amplitude of accommodation. These responses were taken from the left eye under monocular conditions using a "push-up" technique. Error bars represent f l SEM.

269

Current Eye Research for the 3 drug conditions are illustrated in Fig. 3. One factor analysis

her findings and those of Leibowitz and Owens (21) and Garner et a\.

of variance indicated that the drug effect on the amplitude of

(22). However Zetterstrdm and Hahnenberger(12) also reported

accommodation was significant ( F = l I .37; df=2,18; p~0.01).

considerable individual variation in the effect of alpha-adrenergic agents on the ciliary muscle.

DISCUSSION

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Instillationof an alpha-1 adrenergic agonist (phenylephrine, 2.5%)

The present study has demonstrated that alpha-I adrenergic innervation to the ciliary body produced a significant change in the

or non-selectivealpha antagonist (thymoxamine, 0.5%) does not

amplitude of accommodation. Since a subjective "push-up"

produce a significant change in TA. This supports the findings of

technique was used to assess the accommodative amplitude, the

Leibowitz and Owens (21) and Garner et al. (22) and represents an

precision of these measurements may have been attenuated at

important observation since a number of recent studies concerning

higher levels of accommodative response due to the non-linearity of

ocular accommodation have used phenylephrine (2.5%) to produce

the dioptric scale. However the observation of a reduced NPA

pupillary mydriasis (32-34).

following the instillation of phenylephrine is consistent with previous

The differences between the findings of the present study and

reports (16-19). Furthermore Mordi et al. (27) observed that the

those of Zetterstrbm (19) may relate to methodologicaldifferences in

instillation of 10% phenylephrine produced a reduction in the

the assessment of TA. Zetterstrbm used a laser optometer to

gradient of the accommodative stimulus/responsefunction. Pupillary

measure accommodationand reported that the instillationof

mydriasis cannot account for this change since the increased

phenylephrine (1Ooh) produced a mean dioptric increase (N=10) in

pupillary diameter, with concurrent reduction in depth-of-focus,

TA of +0.9D. However, a number of studies have indicated that the

would induce a steeper stimulus-responsegradient. However at the

technique associated with the operation of the laser optometer may

higher dioptric levels stimulated during either the determination of

itself influence the recorded value of TA (35-38). Both the mental

accommodative amplitude or the stimulushesponsefunction, the

effort required to judge the direction of laser speckle motion and the

increased magnitude of parasympathetically-mediated

proximal stimulus resulting from awareness of nearness of the

accommodationwill facilitate sympathetic outflow, and consequently

speckles may induce changes in the accommodative response.

the instillation of adrenergic zgents is more likely to produce a

Further evidence for this proposal comes from the investigations of

significant effect.

Gilmartin et al. (23) who reported that timolol maleate (0.5%),a

It may be observed from the data illustrated in Fig. 1 that the mean

non-selective beta-adrenergic antagonist, produced an average

value of TA increased while subjects sat passively in darkness. A

myopic shift in TA of +0.85D under darkroom conditions when

number of other studies have also reported an increase in TA under

measured with a laser optometer. However in a later study using an

sustained stimulus-free conditions (40-42). This passive drift in TA

objective, open-field, infra-red optometer, Gilmartin and Bullimore

may be analogous to the change in heterophoriawhich occurs during

(30) observed that timolol failed to produce any significant change in

prolonged monocular occlusion (43). This observation is important

TA under darkroom conditions. They noted the findings of Tdrnqvist

with regard to studies of accommodative hysteresis (44) i.e. the shifl

(3,4) that the magnitude o! sympathetic innervation to

in TA which may be observed immediately following a period of

accommodationwas related to the level of concurrent

sustained fixation. The passive drift of TA may mask the regression

parasympatheticactivity. Under truly stimulus-freeconditions, the

of task-induced accom,mdative hysteresis. Thus when investigating

degree of parasympathetic innervationwill be minimized and thus no

task-induced effects on TA, the duration of the post-task period

sympathetic effect will become manifest. However the operation of

should be kept to a minimum in order to reduce the contaminating

the laser optorneter may itself stimulate a parasympathetically

effect of this passive drift in the accommodativeresponse.

mediated accrrmmodative response and thereby initiate sympathetic

A further consideratbn relates to the role of TA within the

activity. Furthermorethe laser speckle exposure duration adopted

closed-loop accommbdativeresponse. This study has demonstrated

by ZetterstrOm (750ms) was longer than that used in the studies of

that alpha-adrenergic agents will alter the closed-bop response

Leibowitz and Owens (21) and Garner et al. (22). In the latter two

independent of any change in TA. One implication which may be

investigations,the laser speckles were presented for only 500ms.

drawn from this finding is that the contributionof TA to the aggregate

Hogan and Gilmartin (39) noted that the average accommodative

reponse is small. Such an observation is supported by the model of

response time was 358ms. The longer speckle presentation time

accommodation proposed by Hung et al. (45). They noted that TA

adopted by Zetterstrdm (750ms) may explain the daference between

(referred to in their paper as ABIAS) would produce a constant

270

Current Eye Research biasing or offsetting of the accommodationstimulus-responsecurve. However it may be demonstratedfrom their equations that marked changes in the value of TA produce very small variation in the closed-loop accommodative response. Using equation #2 from the study of Hung et al., if the accommodative stimulus (AS)=3D, accommodative controller gain (ACG)=8 (46) and the dead space of accommodation (DSP)=0.5D, then a change in TA (ABIAS) from 1 to 3D will result in a change in accommodative response from 2.33D to 2.56D respectively, i.e. a shift of only 0.22D. Furthermore Ciuffreda

et al. (26) demonstratedthat in amblyopic eyes the accommodation stimulus-responsefunction was different from that observed in Curr Eye Res Downloaded from informahealthcare.com by University of Newcastle on 12/28/14 For personal use only.

normal eyes although the values of TA (ABIAS) were similar. This would confirm the observation that the contribution of TA to the closed-loop accommodative response is small. ACKNOWLEDGEMENT This study was conducted as part of the final year Optometry course in the Department of Vision Sciences, Aston University, Birmingham, U.K. CORRESPONDING AUTHOR Mark Rosenfield Ph.D., Schnurmacher Institute for Vision Research, SUNY/State College of Optometry, 100 East 24th Street, New York, New York 10010.

REFERENCES 1. Gilmartin, B. (1986) A review of the role of sympathetic innervationof the ciliary rrmscle in ocular accommodation. Ophthal. Physiol.Opt.6, 23-37. 2. Morgan, M.W. (1946) A new theory for the control of accommodation.Am. J. Optom. Arch. Am. Acad. Optom. 23, 99-110. 3. Ttirnqvist, G. (1967) The relative importance of the parasympathetic and Sympathetic nervous systems for accommodationin monkeys. Invest. Ophthalmol. 6,612-617. 4. Ttirnqvist, G. (1966) Effect of cervical sympathetic stimulation on 363-372. accommodation in monkeys. Acta Physiol. Scand. 5. Rosenfield,M. and Gilmartin, B. (1989) Temporal aspects of accommodative adaptation. Opt. Vis. Sci. 66, 229-234. 6. Campbell, F.W. and Westheimer, G. (1960) Dynamics of accommodation responses of the human eye.J. Physiol. (Lond) 285-295. 7. Huwitz, B.S., Davidowitz, J., Chin, N.B. and Breinin. G.B. (1972) The effects of the sympathetic nervous system on accommodation: I. Beta sympathetic nervous system. Arch. Ophthalmol. Bz, 668-674. 8 . Humitz, B.S., Davidowitz, J., Pachter, B.R. and Breinin, G.B. (1972) The effects of the sympathetic nervous system on accommodation: II. Alpha sympathetic nervous system. Arch. Ophthalmol.Bz, 675-68. 9. Van Alphen, G.W.H.M. (1976) The adrenergic receptors of the intraocular muscles of the human eye. Invest. Ophthalmol. Xi. 502-505. 10. Lograno, M.D. and Reibaldi, A. (1986) Receptor-responsesin

a,

m,

fresh human ciliary muscle. Br. J. Pharmacol. a,379-385. 11. Wax, M.B. and Molinoff, P.B. (1987) Distribution and properties of 8-adrenergicreceptors in human ins-ciliary body. Invest. Ophthalmol. Vis. Sci. 28,420-430. 12. Zetterstrtim, C. and Hahnenberger, R. (1988) Pharmacological characterizationof human ciliary muscle adrenoceptors in vitro. Exp. Eye Res.46,421-430. 13. Fleming, D.G. and Hall, J.L .(1959) Autonomic innervation of the ciliary body. Am. J. Ophthalmol. 48, 287-293. 14. Chin, N.B., Ishkawa, S., Lappin, H., Davidowitz,J. and Breinin, G.M.(1968) Accommodation in monkeys induced by midbrain stimulation. Invest. Ophthalmol. 2,386-396. 15. Heath, P. (1936) Neosynephnn hydrochloride. Some uses and effects in ophthalmology. Arch. Ophthalml. 16,839-846. 1 6. Biggs, R.D., Alpem, M. and Bennett, D.R. (1959) The effect of sympathomimeticdrugs upon the amplitude of accommodation. Am. J. Ophthalmol. 48, 169-172. 17. Zetterstr(lm, C. (1984) The effect of phenylephrine on the accommodativeprocess in man. Acta Ophthalmol.62, 872-878. 18. Zetterstrtim, C. (1987) The effects of thymoxamine, phenylephrine and cyclopentolate on the accommodative process in man. Acta Ophthalmol. &, 699-704. 19. Zetterstrtim, C. (1988) Effects of adrenergic drugs on accommodationand distant refraction in daylight and darkness. A laseroptometric study. Acta Ophthalmol.Mi,58-64. 20. Mordi, J.A., Lyle, W.M. and Mousa, G.Y. (1986) Effectof phenylephrine on accommodation,Am. J. Optom. Physiol. Opt.u, 294-297. 21. Leibowitz, H.W. and Owens, D.A. (1975) Night myopia and the intermediate dark focus of accommodation. J. Opt. Soc. Am. f& 1121-1128. 22. Gamer, L.F.. Brown, B., Baker, R. and Colgan, M. (1963) The effect of phenylephrine hydrochloride on the resting point of accommodation. Invest. Ophthalmol. Vis. Sci. 24,393-395. 23. Gilmartin, B.. Hogan, R.E. and Thompson, S.M. (1984) Theeffect of timolol maleate on tonic accommodation,tonic vergence, and pupil diameter. Invest. Ophthalmol. Vis. Sci. 25, 763-770. 24. Luckiesh, M. and Moss, F.K. (1937) The avoidance of dynamic accommodationthrough the use of a brightnesscontrast threshold. Am. J. Ophthalmol. 2p,469-478. 25. Heath, G.G. (1956) Components of accommodation. Am. J. 569-579. Optom. Arch. Am. Acad. Optom. 3, 26. Ciuffreda, K.J., Hokoda, S.C., Hung, G.K .and Semmlow, J.L. (1984) Accommodative stimuluslresponse function in human amblyopia. Doc. Ophthalmol. 56,303-326. 27. Mordi, J., Tudter, J. and Charman, W.N. (1986) Effects of 0.1% cyclopentolate or 10% phenylephrine on pupil diameter and accommodation. Ophthal. Physiol. Opt. 8, 221-227. 28. Tan, R.K.T. and OLeary, D.J. (1988) Accommodation characteristics before and after near work.Clin. Exp. Optom. LL, 165-169. 29. McBrien, N.A. and Millodot, M. (1985) Clinical evaluation of the Canon Autoref R-1. Am. J. Optom. Physiol. Opt. 62,786-792. 30. Gilmartin, B. and Bullimore, M.A. (1987) Sustained near-vision augments inhibitory sympathetic innervationof the ciliary muscle. Clin. Vision Sci. 1,197-208. 31. Law, F.W. (1952) Reading types. Br. J. Ophthalmol. 36, 689-690. 32. Schor, C.M., Kotulak, J.C. and Tsuetaki, T. (1986) Adaptation of tonic accommodation reduces accommodative lag and is masked in darkness. Invest. Ophthalmol. Vis. Sci. 2Z,820-827. 33. Pugh, J.R. and Winn, B. (1988) Modification of the Canon Auto Ref R1 for use as a continuously recording infra-red optometer. Ophthal. Physiol. Opt. 8, 460-464. 34. McLin, L.N., Schor, C.M. and Kruger, P.B. (1988) Changing size (looming) as a stimulus to accommodation and vergence. Vision

27 1

Curr Eye Res Downloaded from informahealthcare.com by University of Newcastle on 12/28/14 For personal use only.

Current Eye Research Res. 18,883-898. 35. Post, R.B., Johnson, C.A. and Tsuetaki, T.K. (1584) Comparison of laser and infrared techniques for measurement of the resting focus of accommodation:mean differences and long-term variability. Ophthal. Physiol. Opt. 9,327-332. 36. Post, R.B., Johnson, C.A. and Owens, D.A. (1985) Does performanceof tasks affect the resting focus of accommodation? Am. J. Optom. Physiol. Opt. 62, 533-537. 37. Bullimore, M.A., Gilmartin, 6. and Hogan, R.E. (1986) Objective and subjective measurement of tonic accommodation. Ophthal. Physiol. Opt. 6, 57-62. 38. Rosenfield, M. (1989) Comparison of accommodative adaptation using laser and infra-redoptometers. Ophthal. Physiol. Opt.9, 431-436. 39. Hogan, R.E. and Gilmartin, B. (1984) The choice of laser speckle exposufe duration in the measurement of tonic accommodation. Ophthal. Physiol. Opt. 9,365-368. 40. Heath, G.G. (1962) The time course of night and space myopia. Technical documentary report no. AMRL-TDR-62-80. Aerospace Medical Division, Air Force Systems Command, Wright-PattersonAir Force Base, Ohio. 41, Pigion, R.G. and Miller, R.J. (1985) Fatigue of accommodation: Changes in accommodation after visual work. Am. J. Optom. Physiol. Opt. 62,853-863. 42. Krumholtz, D.M., Fox, R.S. and Ciuffreda, K.J. (1986) Short-term changes in tonic accommodation. Invest. Ophthalmol. Vis. Sci. 22,552-557. 43. Sethi, B. (1986) Heterophoria: A vergence adaptive position. Ophthal. Physiol. Opt. 6,151-156. 44. EbenhoRz, S.M. (1983) Accommodative hysteresis: A precursor for induced myopia? Invest. Ophthalmol. Vis. Sci. 24, 513-515. 45. Hung, G.K., Ciuffreda, K.J., Semmlow, J.L. and Hokoda, S.C. (1983) Model of static accommodative behavior in human amblyopia. IEEE Trans. Biomed. Eng. -665-672. 46. Semmlow, J.L. and Hung, G.K. (1983) The near response: Theories of control. In "Vergence Eye Movements: Basic and Clinical Aspects", (Eds. Schor, C.M. and Ciuffreda, K.J.)Pp.175-195. Butterworths, Boston.

272

The influence of alpha-adrenergic agents on tonic accommodation.

This study has examined the effect of an alpha-1 adrenergic agonist (phenylephrine HCl, 2.5%) and a non-selective alpha antagonist (thymoxamine HCl, 0...
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