Essentials of Veterinary Ophthalmology. Kirk N. Gelatt
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eye responses to determine the smallest stimulus that elicits a tracking eye movement. Acuity is also often determined by theoretical calculations based on cone or RGC density (Table 2.16).
Figure 2.19 A colorful dog, as seen by a normal trichromat (a). In (b), the color information from the photograph has been extracted. The photograph has been filtered to mimic how a protanope (c), a deuteranope (d), a tritanope (e), and a cone monochromat (f) would perceive the same scene. The protanope and deuteranope can distinguish between short and long wavelengths, whereas the tritanope can subdivide the middle‐to‐long wavelengths into different hues.
Table 2.16 Visual acuity in select species.a
| Species | Snellen resolutionb | Spatial frequency (cycles/degree)b | Methodc | References |
|---|---|---|---|---|
| Eagle (Aquila audax) | 20/4 | 140 | Behavioral and anatomical | Reymond (1985) |
| Falcon (Falco berigora) | 20/8 | 73 | Behavioral and anatomical | Reymond (1987) |
| Macaque monkey | 20/16 | 38 | Behavioral | Merigan & Katz (1990) |
| Human | 20/20 | 30 | Ravikumar et al. (2011) | |
| Horse | 20/26 | 23 | Behavioral | Timney & Keil (1992) |
| 20/36 | 16.5 | Anatomical | Harman et al. (1999) | |
| King penguin | Anatomical | Coimbra et al. (2012) | ||
| Underwater | 20/30 | 20.4 | ||
| In air | 20/40 | 15.3 | ||
| Alpaca | 20/45 | 13.4 | Anatomical | Wang et al. (2015) |
| Sheep | 20/51–20/43 | 11.7–14 | Behavioral | Sugnaseelan et al. (2013) |
| 20/86–20/60 | 7–10 | Anatomical | Hughes (1977) | |
| Camel | 20/60 | 10 | Anatomical | Harman et al. (2001) |
| Dog | 20/140–20/52 | 4.3–11.6 | Electrophysiology | Odom et al. (1983); Ofri et al. (1993); Murphy et al. (1997) |
| 20/110–20/31 | 5.5–19.5 | Behavioral | Lind et al. (2017) | |
| Cat | 20/190 | 3.2 | Behavioral | Jarvis & Wathes (2007) |
| 20/90 | 6.5 | Electrophysiology | Berkley & Watkins (1971) | |
| 20/33 | 18 | Anatomical | Steinberg et al. (1973); Clark & Clark (2013) | |
| Barn owl | Behavioral | Orlowski et al. (2012) | ||
| 20/190 | 3.2 (Mesopic) | |||
| 20/500 | 1.2 (Scotopic) | |||
| Rabbit | 20/200 | 3 | Electrophysiology | Pak (1984) |
| Cow | 20/460–20/230 | 1.3–2.6 | Behavioral | Rehkämper et al. (1998, 2000) |
| Rat | Behavioral | Prusky et al. (2002) | ||
| pigmented | 20/600–20/400 | 1–1.5 | ||
| albino | 20/1200 | 0.5 | ||
| Mouse | 20/1000 | 0.58 | Behavioral | Lehmann et al. (2012) |
| 20/1500 | 0.39 | Optokinetics | Lehmann et al. (2012) |