The tail tells the story
A leopard gecko stores fat in its tail, which makes the tail the most honest gauge of this species' health: plump and firm is well, steadily narrowing is not. The wasting pattern keepers fear most is cryptosporidiosis, a gut parasite that damages the intestine until the gecko cannot absorb its food — it eats, sometimes eagerly, yet the body and tail thin toward the stick-like shape that gives the condition its keeper nickname. Ordinary gut parasites, mouth pain and failing husbandry can also thin a tail, and only testing separates them, so a gecko losing tail fat while still eating needs a vet and a fecal sample rather than richer food. A crypto-suspect gecko should be kept strictly apart from other reptiles with its own tools and dishes, since the parasite spreads through droppings and is hard to shift from an enclosure.
Shed on toes and eyes
Leopard geckos shed in pieces they usually eat, and trouble shows where the skin lingers. Retained shed wraps the toes in tightening rings that can cost the gecko its toes across a few sheds, and it can also be left behind inside the eyes — producing a gecko that squints, keeps one or both eyes closed, rubs its face on furnishings, or misses strikes at prey it clearly wants. Low vitamin A links into the same picture, because the deficiency changes the skin and the lining of the eyes so both shed and sight suffer. A humid hide kept genuinely damp, a varied gut-loaded diet and proper supplementation are the prevention. Shed still on the toes after a lukewarm soak and a gentle cotton-swab roll, or any eye that stays closed for more than a couple of days, belongs to a vet — eyes especially, because digging at them at home does more harm than good.
Bones, belly and eggs
Metabolic bone disease in a leopard gecko reads as bowed front legs, a soft or slightly undershot jaw, trembling when it walks, and a gecko that lies flat instead of propping itself up — the result of feeder insects offered without calcium dusting or variety. Impaction sits at the other end: a gecko on loose substrate that stops passing droppings, goes lethargic and shows a dark shadow through the belly skin may have a gut blocked by swallowed substrate or an oversized meal. Females add a third pattern — a restless, digging gecko that stops eating with a swollen belly may be carrying eggs she cannot pass. All three are vet problems once the signs are clear, and all three are easier to confirm when you can say exactly when appetite, droppings or posture changed.
When to call the vet
A tail that keeps thinning while the gecko still eats, eyes held closed beyond two days, trembling or bowed legs, a prolapse, or a gecko that has stopped passing droppings should all be seen promptly — leopard geckos are small, and small animals have small reserves. The habit that makes every one of these calls earlier is the weight log: weights, shed dates and appetite notes kept in your leopard gecko's KinsLe Pet Passport turn 'he looks thinner lately' into a dated trend the vet can act on at the first visit.