Scanning electron microscopy study of the tarsal and orbital conjunctival surfaces compared to peripheral corneal epithelium in pigmented rabbits

Abstract

The mammalian palpebral conjunctiva has not been systematically evaluated by scanning electron microscopy (SEM). The upper eyelid of female grey rabbits (2 kg) was fixed in its extended conformation at 15.00 h; some corneas were prepared with the same fixative protocol. The corneal epithelium, within 1 mm of the limbus, is a mosaic of small-to-large (average cell area of 693 m2) squamous cells with light, medium or dark appearance due to different densities of cell surface microplicae. The tarsal conjunctiva was a 1.5 to 3 mm wide mosaic of small (average cell area of 86 microm2) non-desquamating polygonal cells having distinctive light and dark appearances due surface microplicae. The orbital portion of the palpebral conjunctiva is also composed of small (average cell area of 87 microm2) non-desquamating polygonal cells but with a uniform medium-grey appearance due to a relatively consistent density of surface microvilli. Several types of intercellular pore-like openings were also present across the palpebral surface but not the corneal epithelial surface. Very small type 1 pores (1.5 to 5 microm diameter) were present at a density of 480 to 760 / mm2 for the tarsal and 80-160 / mm2 for orbital conjunctiva. Slightly larger (2.5 to 18 microm diameter) type 2 pores with distinct borders were present at 120-200 / mm2 across the orbital conjunctiva. Very large (10-109 microm diameter) type 3 (Henle) pores were present at 40 to 280/mm2 especially at the tarsal/orbital transition zone. Type 4 pores (goblet cell orifices) were oval with a peripheral ring of microvilli and were present at 40 to 160/mm2 for tarsal and 800 to 1600/mm2 for orbital conjunctiva. The rabbit palpebral conjunctival surface is thus distinctly different from the peripheral corneal epithelium across which it slides following eyelid closure.

The Acinar and Ductal Organisation of the Tarsal Accessory Lacrimal Gland of Wolfring in Rabbit Eyelid

“…T-612 agent (Doughty and Stuart, 1995). Immediately after loss of consciousness, all major neck blood vessels were severed and the animal drained over a sink for 15-30 s. Following extensive trials with a variety of preparative techniques (Doughty, 1997), the following procedure was adopted immediately after exsanguination. Only one eye was prepared for electron microscopy, with the other being removed after preparation of the first eye and used in unrelated studies.…”

“…That these samples represent the regions designated was verified for all six samples by preparing sequential sets of 30 or more scanning electron microscopy images at 1000i of the same region of the palpebral conjunctiva (Doughty and Panju, 1995). These 6 sets studied here are presented as representative of another six also evaluated by scanning electron microscopy (Doughty, 1997). The small pieces were embedded in Epon-Araldite 502 and processed as previously described (Doughty, Bergmanson and Blocker, 1995).…”

“…Six female pigmented (Dutch grey) rabbits were obtained from a certified breeder and were caged as previously described (Doughty, 1997). The animals 0014-4835\99\040411j11 $30.00\0…”

“…However, as repeatedly emphasised (Gillette et al, 1980 ;Seifert and Spitznas, 1994), much less is known about the ultrastructure of the tarsal accessory lacrimal glands. The ultrastructure of the tarsal accessory lacrimal gland of Wolfring, until relatively recently (Seifert and Spitznas, 1994, Seifert et al, 1993, 1996, 1997, had probably not even been studied.…”

“…Following observation by scanning electron microscopy of an extraordinarily extensive system of crypt-like openings in the superior palpebral conjunctiva of the rabbit, especially across the tarsal\ orbital portion (Doughty, 1997 ;Doughty and Panju, 1995), a systematic study was undertaken of the entire length of the superior palpebral conjunctival epithelium and the underlying parenchyma by light and transmission microscopy. This report concerns the location, general and ultrastructural features of an acinar system and it's associated complex system of intra-epithelial and intra-parenchymal ducts that is located immediately superior to the tarsal glands in the rabbit.…”