In primary open angle glaucoma in the Beagle, the lens luxation is secondary to the gradual enlargement of the globe in the untreated disease. The normal zonules are gradually stretched and eventual tear, usually near their insertion at the lens equator. Two litters of Beagles (3 males/4 females) with inherited glaucoma were evaluated, with four dogs (2 males/2 females) receiving unilateral extracapsular lens extractions at four months of age, and the remaining three dogs (1 male/2 females) serving as the controls. All eyes of the dogs were examined serially by applanation tonometry, gonioscopy, tonography and a-scan ultrasonography. From the control group after euthanasia, the globes and lenses were harvested at 6 (2 lenses), 12 (2 lenses), and 28 (2 lenses) months of age for scanning electron microscopy (SEM). The operated dogs were euthanized at 28 months, and all globes and lens were examined by SEM.

The mean intraocular pressure (IOP) began to increase and the tonographic facility of aqueous outflow decreased bilaterally in the four dogs with the unilateral lensectomies and the three nonoperated dogs at about 6 to 8 months of age. In the non-operated fellow eyes, the aphakic crescents associated with the lens subluxation begin to develop when the dogs were 18 month old and axial globe lengths exceeded 21 mm. The lenses remained in the patellar fossa in all dogs at 28 months of age.

The zonules in the pre-glaucomatous Beagle at six months of age appeared normal by SEM. At 12 months and thereafter the zonules appeared to be progressively stretched. In the 28-month-old glaucomatous Beagles (six eyes) focal areas of zonular disinsertation from the periphery of the equatorial lens capsule and zonulary retraction occurred. Zonular transection occurred immediately posterior to the zonular attachments at the lens equator leaving zonular remnants.

Extracapsular lensectomies in these young normotensive Beagles, bred for primary open angle glaucoma, did not prevent nor delay the onset of the disease. The elevation in intraocular pressure, reduction in the facility of aqueous humor outflow (as measured by pneumatonography) and increased axial globe lengths (as measured by a-scan ultrasonography) preceded the gradual stretching and focal disinsertions of the zonules, and subluxation of the lens.

A consecutive series of 83 acutely glaucomatous eyes from 65 dogs receiving gonioimplant surgery from 1992-1995 was reviewed. Eighteen dogs were implanted bilaterally and forty-seven unilaterally, with seven eyes receiving two gonioimplants. The gonioimplants utilized were either a T-shaped, silicone nonvalved implant, the Ahmed valve with large anterior chamber tubing (VS-2), or the Ahmed valve with a silicone strap added (VS-2 Si). The criteria for success were retention of vision, and/or maintaining intraocular pressure (IOP)<20 mm Hg, with or without topical or systemic antiglaucoma medications. The median time for elevated IOP to occur postoperatively was 4, 15, and 10 months respectively (41 eyes), for the nonvalved, VS-2, and VS-2-Si implant groups. The median time for vision loss to occur postoperatively was 4, 6, and nine months, respectively (32 eyes), for the nonvalved, VS-2, and VS-2-Si implant groups. Fifteen of the 22 eyes that had an IOP<20 mm Hg were visual one year postoperatively. The valved VS-2 and VS-2-Si gonioimplants were the most successful at preserving vision and maintaining an IOP<20 mm Hg. The complications encountered in the overall study are discussed and future alternatives proposed.

Corneal base-curve in dogs has been so far measured by an Ophthalmometer. Corneal base-curve, however, can be measured only under the conditions where an refracted image on cornea is projected to the central cornea and the proper restraint is carried out on the dog to held its cornea steadily and continuously. Therefore the measurement by an Ophthalmometer should be conducted under general anesthesia. A handy type Autokeratometer has been recently developed which can measure a corneal base-curve within 0.1 second. Then we examined the correlation between the corneal base-curves measured by an Ophthalmometer and an Autokeratometer.

The eyes of six healthy adult mixed-breeding dogs, three healthy adult Japanese Shiba Inus and ten Siberian Huskies were used. Corneal base-curves (represented by the lengths of the horizontal direction and the vertical direction) were measured by Autokeratometer (Nidek KM-500) at first before anesthesia. And then they were also measured by Opthalmometer (Inami L-1050) and the Autokeratometer under general anesthesia with xlyasine and ketamine hydrochloride.

The coefficients of correlation between the corneal base-curves measured by the Ophthalmometer and the Autokeratometer under general anesthesia are 0.64 for the vertical direction and 0.51 for the horizontal direction, respectively indicating that the higher correlation was show on the vertical direction. The coefficients of correlation between the corneal base-curves measured by the Ophthalmometer under general anesthesia and the Autokeratometer under non-anesthesia are 0.52 for the vertical direction and 0.28 for the horizontal direction, respectively. A significant variation was shown with the vertical values. Both the horizontal and vertical corneal base-curves measured by the Autokeratometer under anesthesia and non-anesthesia showed no fluctuations on their values.

Therefore, an Autokeratometer can be adopted to measure the corneal base-curves without general anesthesia in dogs.

Determination of corneal base curve (vertical and horizontal direction) and vertical meridian axis was carried out with an ophthalmometer (Inami Co. Ltd.), and correlation of body weight and corneal diameter, and corneal base curve was examined in dogs.

Longitudinal and transverse diameters of corneas were measured with a caliper without general anaesthesia after measuring body weights in healthy forty-five dogs. Subsequently corneal base curves were measured under sedation by xylazine and ketamine hydrochloride. Animal body weight was 3-25 kg, and longitudinal diameter was 12.2-16.6 mm, transverse diameter was 13.7-19.7 mm. The corneal base curve (mean±SD) was 8.50±0.46 mm at the vertical direction and 8.61±0.41 mm at the horizontal direction in the right eyes, and 8.47±0.43 mm at the vertical direction and 8.54±0.44 mm at the horizontal direction in the left eyes. Vertical meridian axis inclined to 85.9±8.1 degrees in the right eyes and to 98.2±8.5 degrees in the left eyes. Coefficient of correlation between corneal diameters and body weights was 0.30-0.49. On the other hand, correlation between body weight and corneal base curve was 0.58, but it was suggested corneal base curves depend on body weights in this study.

To assess the retinal function after light stimuli of varying intensity, a single flash ERG was recorded with a strobeflash stimulator. Three conditions of optic health in dogs were observed: normal (3 dogs-6 eyes); cataracts (2 dogs-4 eyes); and 1 optic neuritis (2 eyes).

Lumen quantities of 1.2 and 20 joules of light were used to stimulate a condition that can be recognized as the predominate difference between normal eyes and those with cataracts or optic neuritis in a-wave amplitudes and b/a ratios (b-wave amplitudes/a-wave amplitudes). It is therefore useful to understand how to interpret ERG positive waves.

Vascular corrosion casts of pigmented rabbit (Kbl/Dutch) retina were studied by scanning electron microscopy. Conditions of retinal vessels were compared with vascular corrosion cast method and fundus photography. In fundus photography, the retinal vessels extended horizontally, both medially and laterally, from the optic disk toward the periphery. The corrosion casts of retinal vessels were consistent with the fundus photography, and confined to a pair of wing shape areas that extended from the optic disk. The retinal arteriole branched as a dendrite, and distributed many capillaries toward the retinal nerve fiber layer. The capillaries formed hairpin loops at the periphery. The retinal vein, which collected branches of venules, drained toward the optic disk.

Coloboma was found in the left eye of a female Crj: (CD) SD rat. Ophthalmoscopic examination revealed focal defect of the iris, which was oval in shape and located at the inferionasal aspect. Ophthalmoscopic findings of the fundus included large and dark optic disc, tortuous and irregularly oriented retinal vessels, and a pale focus located inferionasally to the optic disc. There was also an oval and ill-defined opaque on the posterior lens capsule extending from the posterior pole toward inferionasal aspect. Histopathologically, the pale fundic lesion was characterized by focal retinal thinning and retinal fold associated with focal defect of the choroid. The lenticular opaque lesion consisted of persistent tunica vasculosa lentis.