ACCOMMODATIVE LENS MOVEMENTS IN FISHES: MOVEMENT ALONG THE PUPIL AXIS VS MOVEMENT ALONG THE PUPIL PLANE JACOB G. SIVAK School of Optometry. (Receiwd
9 June 197-l; in recisedform
j Jld~ 197-t)
.Abstract-Induced accommodative responses of ten species of fish from the Gulf Coast of Florida were studied. Pilocarpine stimulated the accommodative system while atropine produced its relaxation. Changes in refractive error were monitored in several directions of regard with a retinoscope and trial lenses. The results indicate a wide variation in magnitude and direction of lens motion. In every case some lens movement along the pupil axis was found. This finding is at variance w-ith some studies which indtcats little or no movement in this plane.
ISTRODUCIIOK Beer (1894) described the accommodative mechanism of teleosts as consisting of a retro-lental muscle (the retractor lentis) which moves the spherical lens toward the retina when it contracts. Verrier (1927, 1928, 1934, 1947). supported by Rochon-Duvigneaud (1943). provided the major opposition to this vieu. This disagreement was largely due to controversy over whether the refractive error of the fish eye in the unaccommodated state was that of myopia or hyperopia. This controversy still exists (Sivak, 19i-I). Studies of accommodation in fishes subsequent to Verrier have, without exception, agreed with the mechanism described by Beer over three quarters of a century ago (Tamura, 1957; Tamura and Wisby, 1963; Kimura and Tamura, 1966; Meyer and Schwassman, 1970; Schwassman and Meyer. 1971; Sivak. 1973; Sivak and Howland, 1973). While studies of accommodation from 1957 onwards agree with each other in supporting Beer, there are significant differences in results and conclusions. As early as 159-l Beer noted that the lens moved somewhat temporally (along the pupil plane) as well as laterally (along the pupil axis) during accommodation. Tamura (1957) Tamura and Wisby (1963), Kimura and Tamura (1966), Meyer and Schwassman (1970), and Schwassman and Meyer (1971) have emphasized lens movement along the pupil plane. Kimura and
Fig. I. Schematic view of a fish eye, as seen from above. dicating the pupil plane and pupil axis.
Tamura (1966) suggest that Beer’s findings of lens motion along the pupil axis may be artifactual. The existence, in some species, of a medially placed lens muscleinadditionto theone found laterallywaspointed out by Munk (1971); who suggested that accommodative lens motion could occur along the pupil axis in these species. Sivak (1973) observed great spcciss variability on the question of direction of accommodation. Ofa group of seven North American freshw-avr fishes. certain species accommodated exclusively along the pupil axis while in other species large lens movements were found along the pupil plane. However. movements along the pupil plane were accompanied bymore modest but substantial lens motion in the direction of the pupil axis. It should be noted that the above studies were made by artificially inducing accommodative changes. A subsequent study of naturally occurring accommodation in response to a feeding stimulus (Sivak and Howland 1973) agrees with the view that lens motion along the pupil plane is accompanied by movement along the pupil axis. In view of the reported variation in the direction of accommodation. a larger sample of species in which this response is described was desired. M.-\TERI.US
The present study was carried out at Mote hlarme Laboratory, Sarasota, Florida. All experimental animals were obtained locally by trawling or with seines. Species tested included the following: common majarras. Eucinosromus gula (Quay and Gaimard); lookdown, Selene comer (Linnaeus); striped burrfish. Chilomyferrrs schoepfi (W’albaum); pi&h. Orrhoprisris chrysoprera (Linnaeus); southern puffer. Sphaeroides nephelus (Grode and Bean); gulf Hounder, Paralichrhys ulbigttrta (Jordan and Gilbert); bandtail puffer, Sphaeroides spengferi (Bloch); southern sea robin Prionotlrs nibulus (Cuvier); Centropristes philudelphicu (Linnaeus): spotted scorpion-fish, Scorpuenu plumieri (Bloch). The apparatus and procedure were similar to that used in a study of accommodation in a group of freshwater fishes (Sivak, 1973). Accommodative response was determined from changes in refractive error induced with drugs. Since the retractor lentis is innervated by the parasympathetic nervous system (Meader, 1936; Nicol, 1952) the drugs employed were atropine sulphate, a parasympatholytic, and pilocarpine. a parasympathomimetic. Refractive state was
Fig. 2. Test aquarium with tish in place indicating the directions and facets through which retinoscopic measurements were made.
determined retinoscopically with trial lenses on fishes submerged in an aquarium of faceted construction (Fig. 2). These facets permitted measurements to be made atong several directions of regard in addition to the pupiilary axis. Refractive measurements were made at a distance of 50 cm. Due to the large number of directions in which these measurements were made, only a single measurement was possible for a particular direction at a given time following administration of a particular drug. However. each retinoscopic determi~t~on was verified by increasing and then decreasing the test distance and ensuring that such movements produced the expected reversal in retinoscopic reflex movement (“with” motion for 0
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mu&s lssst srquentiall~. affectmg the respirator) (Thomas. 1964). xsptratory cessation was usually avoided. When nccrssary. respiration was assisted with aerated LWIU carrlcd to the oral cavity uith a tube. RESCLTS ;\ wide variation in the magnitude and direction of accommodative r2spons2 was found in the species studied (Table 1). These may be summarized as follows: In E. p/n thz ereatest refractive state change was found ventrally (93 D) with somewhat smaller responses in the ventral-rostra1 and ventral-caudal directions. The change along the pupil axis was slight. The accommodative ability of Selene rotner seems relatively poor, with the largest change occurring along the pupil axis (approa 4 D) while a slightly smaller response was found in the ventral-rostra1 position. Good lens mobility was indicated for C. schoepfi. a maximum range of 134 D in the rostra1 direction is closely followed by the ventral response. Lens movement close to the pupil plane (ventral-rostral) is also indicated in 0. chrysoprera. However. there is little lens motion in Spl~aeroides nepheha the maximum change occurring along the pupil axis. Data for only one specimen of .Spl~arroi&s sperlgkri indicate that it might accommodate better than S. r~rpl~eltrs (8 and 7 D in the lateral and rostra1 directions respectively). The tlounder pupil is slit horizontally and is covered by a dorsal operculum. As a result, refractive changes were measured only laterally in Paralici~ri~xs albigurta. The large accommodative response (I 7 D) along the pupil asis is a departure from earlier findings which associate responses of such magnitude with lens motion close to the pupil plane (for example, Tamura, 1957; Meyer and Schwassman. 1970: Sivak. 1973). In both Prionotus cribtrlus and Scorparm plumieri the major accommodative change was found rostrally. The ventral and ventral-rostra1 axes seem to be the principle accommodative directions in C. philadelphica. Only one individual was studied in each of the last three species. When interpreting the data presented in Table 1 it is to be noted that the directions mentioned refer to directions of retinoscopic measurement. These directions are either perpendicular to the pupil plane (lateral) or 3’-3’ away from the pupil plane. Thus, unless the lens motion occurs precisely along the plane of the pupil the rostra1 refractive change will not be matched by an equal and opposite change in the caudal direction.
DISCL3SIOS The above results indicate that some lens movement always occurs along the pupil axis whatever the principle direction of accommodation. For example, in Se& comer the average change in the lateral direction of 4 1 D (9,s15.2) represents the principle direction of accommodative change. In 0. chrysoprera an average lateral change of 53 D is approximately half that found in the ventral-rostra1 direction. It appears that accommodative lens movements may exist close to but not right along the pupil plane. This description would seem to be in closer agreement with Beer’s work (1591) than with other recent studies (Tamura and Wishy. 1963; Kimura and Tamura, 1966; Schwassman and bleyer. 1971). In view of iMunk’s findings regarding the
occurrence of two lens muscles (1971) it is possible that these differences may be due to species variation. However. differences in methodology may be an altzrnative reason. The methods which have been used to study accommodation in fishes are quite varied. Beer (lS9-1) measured refractive state ophthalmoscopically before and after electrical stimulation and injection with atropine. Tamura (1957) used a modified optometer to measure refractive state before and after a fish was subjected to the following treatments; severing of the optic nerve, laceration of the heart, injection of curare and atropine, Tamura and Wisby (1963) recorded lens movements along the pupil plane by photographing lens position from above before and after specimens were sacrificed. Kimura and Tamura (1966) recorded lens position photographically in enucleated eyes before and after electrical stimulation. Schwassman and Meyer (1971, see also Meyer and Schwassman. 1970) developed a method involving the measurement of visual acuity by means of electrophysiological recordings at the optic tectum. Accommodative changes were induced with tricaine methanesulfonate and Flaxedil. Lenses were used to produce acuities indicating emmetropia. All of these methods. as well as the one ujzd in the present study, involve the measurement of accommodation under artificial conditions. Some attention has recently been directed toward the description of the naturally occurring accommodative response. Baylor (1967) observ-ed refractive state changes retinoscopitally. along the pupil axis. in a number of marine teleosts in which accommodation was not controlled. In a study mentioned earlier. Sivak and Howland (1973) used a video tape system to record the accommodative response of the northern rock bass; a response produced by a feeding stimulus. The findings of the latter study agree closely with an earlier study of accommodation in the same species (Sivak. 1973) in which accommodative changes were induced artificially in a manner virtually identical to the method described in the present study. Thus. the two studies of accommodation in which this response was not artificially controlled support the view that at least some lens motion occurs along the pupil axis. Furthermore, some support was given to the notion that the variation of accommodation in tsleosts is related to the diets and feeding habits of the species involved (Tamura, 1957: Tamura and Wishy. 1963: Kimura and Tamura. 1966; Sivak, 1973). It is possible that the species differences indicated by the present study are related to variations in diet and feeding behavior. However, some indication of the natural response is needed before this point can be made with any certainty. .-Lc~no~~I~nyrmrnts-This research was supported by a grant from the University of Waterloo. The author is grateful to iMot2 Marine Laboratory. Sarasota, Florida. for facilities and assistance. Fishrs used in this study ivere keyed by Patricia Bird.
REFERENCES Baylor E. R. (1967) Vision of Bermuda rssf fishes. .l’arrrrc. LOHd.211, 306307.
Beer T. (1891) Die Accommodation des Fischauges. Pfiiigers Arch. ges. Phvsiol. Ss. 52_%650. Kimura K. and Tamura T. (1966) On the direction of the lens movement in the visual accommodation of teleostean eyes. Btdl. Jap. SW. SCWI~. Fish. 32, 112-l 16. Meader R. G. (1936) Accommodation and its reflex pathways in the teleosts. Yale J. Biol. Med. 8, 51 l-523. Mever D. L. and Schwassman H. 0. (1970) Electrophysiolog&al method for determination of refractive state in fish eyes. Vision Rex 10, 1301-1303. Munk 0. (1971) On the occurrence of two lens muscles within each eye of some teleosts. Vidensk. Meddr dansk narwh. Foren. 134, 7-19. Nicol J. A. C. (1952) Autonomic nervous system in lower chordates. Biol. Reo.. Camb. 27, l-49. Rochon-Duvigneaud A. (1933) Les Yew et la Vision des VPrrib&. Masson. Paris. Schwassman H. 0. and Meyer D. L. (1971) Refractive state and accommodation in the eye of three species of Paralubrax (Serranidae, Pisces). Vidensk. ,Weddr dansk narurh. Foren. 134, 103-108.
Sivak J. G. (1973) Interrelation of feeding behavior and accommodative lens movements in some species of North
American freshwater fishes. J. Fish. R.,s. Board Gun. 30, 1l-t-l 136. Sivak J. G. and Howland H. C. (1973) .Accommodation in the northern rock bass (rlmbloplires rupestris rupestris) in response to natural stimuli. CSsron RLIS,13, [email protected]
Sivak J. G. (197-t) The refractive error of the fish eye. t’icion Rrs. 1.4, ‘09-213.
Tamura T. (1957) A study of visual perception in fish especially on resolving power and accommodation. Bull. Jap. Sot. scienr. fish. 22. 534-557. Tamura T. and Wisby W. J. (1963) The visual sense of pelagic fishes especially the visual axis and accommodation. Buil. mar. Sci. Gulf Caribb. 13, 433-4s. Thomas K. B. 1.1964)Curare. Irs History and Usage. Pnman. London. Verrier M. L. (1927) Sur la refraction statique de l’oeil chez les poissons. C. r. hebd. SPanc. Acud. Sc~i. 185. 1070-1072. Verrier M. L. ( 1928) Recherches sur les yeux et la vision de poissons. Bull. biol. Fr. Be/g. suppl. XI. Verrier M. L. (1934) La refraction de I’osil des poissons. Bull. Sot. Zoo/. Fr. 59, 333-338. Verrier M. L. ( 1947) La vision de vtrtebrts et les theories de la vision. .&in. Bioi. Paris Ser 3. 24, 309-138.