Original Paper Ophthalmic Res 1992;24:169-174

3 Department o f Ophthalmology o f the Federal University o f Minas Gerais, and b Retina Service, Santa Casa Hospital, Belo Horizonte, Brazil

Argon Laser Photocoagulation of the Pecten Oculi of the Domestic Pigeon (Columba livia) Using a Specially Designed Contact Lens

Key Words


Pecten oculi Argon laser Contact lens

A specially designed -62-D polymethylmethacrylate contact lens for biomicroscopy of the fundus oculi of the pigeon is pre­ sented. The study shows the usefulness of the lens in argon laser photocoagulation of the pecten, a noninvasive technique for ablating the organ. In addition, previous studies on opera­ tive destruction of the pecten are reviewed. To our knowledge, this is the first time the macroscopic appearance of a photocoagulated pecten is documented.

Introduction One of the unsolved riddles of compara­ tive ophthalmology is the actual significance of the pecten oculi of bird’s eye. Its first, though incorrect, description was made by Steno [1] in 1673: optici nervi filamenta nigra, quae per vitreum pergunt crystallinum (black filaments of the optic nerve which advance through the vitreous to the lens). This intriguing organ projects from the elon­ gated optic nerve head to a variable distance into the vitreous chamber and has attracted

Received: October 3 0 .1991 Accepted: February 3 . 1992

the attention of several investigators. Due to its highly vascular structure, the main func­ tion ascribed to the pecten is to assist in the nutrition of the inner layers of the avascular avian retina [2], In this regard, the pecten has been strictly comparable to the falciform pro­ cess of teleostean fishes or the conus papillaris of lizards, and to some degree to the mem­ brana retinae of some fishes, amphibians and reptiles [3], However, the majority of reports are essen­ tially limited to morphological studies, and the functional theories proposed for the

Breno Teixeira Lino, M D Department o f Ophthalmology Univcrsidade Federal dc Minas Gerais Rua Dr. Raul Franco 21/404 Belo Horizonte, M G 30240 (Brazil)

© 1992 S. Karger A G . Basel 0030-3747/92/ 0243-0169S2.75/0

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Breno T. Lino a Yehuda Waisberga Edilson K. Leiteh

pecten have been established mostly upon speculative analysis. The purpose of this study is to describe a specially designed contact lens for biomicros­ copy of the fundus oculi of birds, particularly pigeons, as well as to show its usefulness in the photocoagulation of the pecten oculi with ar­ gon laser. This work represents a preliminary study on the effects of partial ablation of the pecten of birds.

Material and Methods Five adult domestic male pigeons (Columba livia) were studied. Mydriasis was accomplished by 4 instil­ lations at 7-min intervals o f 1 drop o f gallamine triethiodide in 0.025% bcnzalkonium chloride (15.0 mg/ ml). The birds were anesthetized by intramuscular injections o f ketamine (6.0 mg/kg) and diazepam (1.5mg/kg). Proparacaine hydrochloride 0.5% was used topically in the eye.



Fig. 2. Contact lens dimensions (mm).

A specially designed planoconcave contact lens, -6 2 .0 D , was made o f polymethylmethacrylate (PM M A). The lens has a radius o f curvature o f 5.3 mm and a focal length o f 16.1 mm (fig. 1,2). Proper posi­ tioning of the pigeon’s head was provided by a suitably designed plastic support. The body o f the bird was placed resting on a plate adapted to the slit lamp (fig. 3). The M IR A M F 2,000 argon laser photocoagulator was used with the green wavelength (514.5 nm). Pho­ tocoagulation was performed in the left eye, with the laser beam aimed at the bridge and upper aspects o f the folds o f the pecten. Thirty spots o f 50-gm, 0.3-s and 400-mW power settings were made. One week after the procedure, the animals were anesthetized and then prepared for in vivo perfusion. The thorax and the neck were opened and the brachioce­ phalic trunks were cannulated. The circulatory system was perfused with physiological saline (0.9% N aCl) at 110 mm Hg pressure followed by neutral buffered formalinfor 10 m inineacheye. The birds were then decap­ itated. The eyes were opened at about 2.0 mm posterior to the limbus, and the head was immediately immersed in neutral buffered formalin for 2 h. Enucleation and careful dissection were performed.

Photocoagulation of the Pecten Oculi

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Fig. 1. Overall view o f the contact lens.

Fig. 4. Fundus photograph taken through the con­ tact lens just after photocoagulation o f the pecten. The burns appear as whitish patches in the pecten.


During photocoagulation, the burns could be immediately noticed as lightish brown patches in the surface of the target areas (fig. 4). In 2 specimens, the authors were able to observe local bursts and the appearance of gas bubbles where the burns had been super­ posed. When examined macroscopically, the photocoagulated pecten showed a coarse distor­ tion of the architectural structure of the bridge and the tips of pectineal folds (fig. 5, 6) in comparison with the normal one (fig. 7, 8). In the latter, it can be observed that the bridge is a fairly compact structure, which lies in a rather straight line and exhibits a strikingly smooth surface. When the pecten was directly intercepted by the sunlight rays, the shape of its shadow projected on the retina changed accordingly to the deflection suffered by the organ (fig. 6).

The contact lens proved to be satisfactory for conducting the fundus biomicroscopy and the laser photocoagulation of the pecten of the pigeon. Despite the small radius of curvature which limits its overall size, it showed to be adequate for practical and comfortable han­ dling. The biomicroscopic image is virtual and upright which facilitates the orientation in regard to retinal landmarks. The magnifi­ cation can be further altered by varying the optics of the microscope. In the domestic pigeon, the pecten can be beautifully viewed through the contact lens. It is conspicuously situated in the lower and posterior quadrant of the fundus and shows a dark brown color. It consists of a simple accordion-pleated lamina held apically by the bridge, which gives it the appearance of a fan.


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Fig. 3. The contact lens in place.

Fig. 6. A photocoagulatcd pecten casting a dis­ torted shadow on the retina. The image o f the sun is seen on the right.

Fig. 7. View o f a normal pecten o f the pigeon. Sev­ enteen folds, slightly converging from the base towards the bridge can be seen originating from the white and elongated optic nerve head. The tapering lowest part o f the pectineal folds can also be observed.

Fig. 8. Tangential view from the bridge o f a normal pecten showing the smoothness throughout its extent.



Photocoagulation of the Pecten Oculi

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Fig. 5. View o f a pecten showing the distortion pro­ duced by photocoagulation in the bridge and upper aspects o f the pectineal folds.

The first experiment of an ablation of the pecten was performed by Abelsdorff and Wessely [4] in 1909. These authors resected the posterior wall of an owl’s eye including the pecten and the previously sectioned optic nerve. The experiment involved an extensive injury to the eye, and the results could not be attributed to the functions of the pecten. Kauth and Sommer [5] destroyed the or­ gan of 7 pigeons by intraocular electrocoagu­ lation (60-80 mA) of its base, the birds being observed during 17 days. The pupillary reflex and the visual capacity were retained, even when both eyes were operated. Histological study was not performed. Wingstrand and Munk [2] attempted un­ successfully to photocoagulate the pecten. They did not specify the photocoagulator used. They concluded that it would require so much heat that the method would be invali­ dated. These authors extirpated the organ by extraocular electrocoagulation of the pecti­ neal vessels in 11 pigeons studied for periods varying from 1 to 317 days. The study demon­ strated histologically that the pecten is neces­ sary for the maintenance of the retina. Bacsich et al. [6] photocoagulated the pecten of 6 chickens whith a specially de­ signed ophthalmoscope to deliver the ruby laser beam. The treatment was repeated in 3to 4-day intervals for 3 weeks. The eyes were prepared for light-microscopic study. The au­ thors reported the pioneer conviction that the laser might be used to explore the functions of the organ. François and Neetens [7] in a preliminary report tried the extirpation of the pecten of 12 pigeons by photocoagulation. They did not specify the technique. Histological study re­ vealed a shrunken pecten and no harm to the retina or optic nerve. Illustrations were not presented.

Brach [8] ablated the pecten of 20 chickens by intraocular electrocautery with modified bipolar forceps and used a planoconcave con­ tact lens in the experiment. The design of this lens was not presented. The eyes were exam­ ined histologically after 2 weeks to 6 months, and they showed normal retinas. Pupillary reflex and visual capacity were retained. The author suggested that the function of the pecten is not primarily nutritive. In our study, argon laser photocoagulation performed through the contact lens showed to be useful for partial ablation of the pecten oculi as had been pointed out by Bacsich et al. [6], Safe applications can be made due to direct and nonivasive accessibility of the pecten to the laser beam. To our knowledge, this is the first time the macroscopic appearance of a photocoagu­ lated pecten is documented. Previous studies on operative ablation of the pecten have doc­ umented histological sections but did not show the macroscopic appearance of the or­ gan. In fact, Abelsdorff and Wessely [4] pub­ lished one illustration displaying a whole owl’s eye with a totally extirpated pecten, but it is a lower-power microscopic view. The effective approach to the pecten with argon laser photocoagulation provides a fu­ ture perspective to the understanding of its role. Morphological and physiological studies including behavioral aspects, can be exten­ sively made. Soon, we hope to know whether, as Thom­ son [9] has said, ‘the bird sweeps the heavens with his pecten’ or not.

Acknowledgements This work was supported in part by grant 500175/ 89-6 from the C N P q , Brazil. We thank Prof. G . Bohorquez, Dr. A . Mendes C . Jr .. M r L. S. Bitencourt and M r E .C . Freitas for technical assistance. We are indebted to M r M . D . Camargos from Mediphacos Ltd. who has made the contact lens.


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Stenonis N: In O vo & Pullo Observationes, Thomae Bartholini Acta Medica & Philosophica Hafniensia 1673. Acta Hafniae II, 1675, vol 34. pp 81-92. Wingstrand K G , Munk O: The pecten oculi o f the pigeon with par­ ticular regard to its function. Biol Skrifter Kong Dan Vidensk Selsk 1965;14:1-64. Duke-Elder S: The eye in evolution; in Duke-Elder S (ed): System o f Ophthalmology. London, Henry Kim pton, 1958, vol 1.





Abelsdorff G , Wessely K: Verglei­ chend-physiologische Untersuchun­ gen über den Flüssigkeitswechsel des Auges in der Wirbeltierreihe. I. Vögel. Arch Augenheilkd 1909;64: 65-125. Kauth H , Sommer H: Das Ferment Kohlensäureanhydratase im Tier­ körper. IV . Über die Funktion des Pektcn im Vogelauge. Biol Zentralbl 1953;72:196-209. Bacsich P, Chisholm IA , Geliert A: The riddle o f the pecten in the avian eye and the probable usefulness o f the laser in the analysis of its func­ tion; in Graham-Jones O (ed): As­ pects o f Comparative Ophthalmolo­ gy. London, Pergamon Press, 1966, pp 299-316.





François J , Neetens A: Comparative anatomy o f the vascular supply o f the eye in vertebrates; in Davson H , Graham LT (eds): The Eye. New York, Academic Press. 1974, vol 5, pp 1-70. Brach V: The effect o f intraocular ablation o f the pecten oculi o f the chicken. Invest Ophthalmol V is Sci 1975;14:166-168. Thomson A: The riddle o f the pec­ ten, with suggestions as to its use. Trans Ophthal Soc U K 1928;48: 293-331.

Photocoagulation of the Pecten Oculi

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Argon laser photocoagulation of the pecten oculi of the domestic pigeon (Columba livia) using a specially designed contact lens.

A specially designed -62-D polymethylmethacrylate contact lens for biomicroscopy of the fundus oculi of the pigeon is presented. The study shows the u...
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