Failure to thrive owing to inappropriate diet free of gluten and cows' milk

Images

The time-course of rod-cone interaction

The time-course of rod-cone interaction (change of scotopic sensitivity caused by photopic background stimulation) was measured in the presence of briskly exchanged, scotopically matched, 490- and 630-nm background disks. In all conditions, interaction rose and fell quickly with changes of photopic stimulation. When the background was a small 0.6 degree-diameter disk, photopic stimulation produced relatively constant maintained interaction of about 0.6 log units. When the background was a large 7.8 degree-dia disk, photopic stimulation produced larger initial (0.6-1.0 log unit) than maintained (0.2 log unit) interaction. When a 0.6 degree by 7.8 degree annulus was used instead of a background, photopic stimulation produced substantial interaction only at offset, a transitory interaction. Thus, the spatial dependence of transitory interactions differs from that of maintained interaction: transitory interactions can be large even when maintained interaction is small or absent. The results are discussed in terms of a simple center-surround model of rod-cone interaction that unifies both maintained and transient interaction.

Quantitative relationships between sensitizing dose of DNCB and reactivity in normal subjects

We have developed quantitative methods which enable us to measure susceptibility to sensitization with dinitrochlorobenzene (DNBC) and the degree of responsiveness of groups, and to analyse factors affecting the afferent and efferent components of the response. Five groups of normal subjects (132 individuals) were sensitized with DNCB (1,000, 500, 250, 125 or 62.5 micrograms). One month later, each subject was challenged with 12.5, 6.25 and 3.125 micrograms of DNCB on standard patch test felts. After 48 h the reaction at each challenge site was graded clinically and measured as diameter of induration and increase in skinfold thickness. The proportion of subjects sensitized increased with sensitizing dose; 8% were sensitized by 62.5 and 100% were sensitized by 500 micrograms or more. The 50% sensitizing dose (ED50) was calculated as 116 micrograms. Increase in skinfold thickness proved the best method of assessing response and was linearly related to log challenge dose. There was also a linear relationship between degree of sensitivity and log sensitizing dose so that, on average, each time sensitizing dose was halved, the challenge dose required to produce the same response increased 1.5-fold. These methods can be used to measure sensitizability of a population, the degree of sensitivity and the expression of reactivity. The technique will allow quantitative study of factors altering the induction or expression of such reactivity in disease.

Quantitation of sensitization and responsiveness to dinitrochlorobenzene in normal subjects

Dinitrochlorobenzene (DNCB) has been used widely to assess cell-mediated immunity in man. However, previous workers have evaluated response qualitatively and subjectively. Such methods cannot elucidate the quantitative relationships between stimulus and response essential to an understanding of the functional components of the system. We have developed quantitative techniques to explore the dose-response relationships of both afferent and efferent limbs of the response, and used this method to examine changes in reactivity to DNCB after exposure to UV radiation and in people with contact allergies.

Photorefraction of normal and astigmatic infants during viewing of patterned stimuli

Photorefraction was used to assess the state of accommodation of 3-month old infants with and without astigmatism while they viewed stimuli in an apparatus commonly used to test infant visual acuity. The stimuli were a 1.6 c/deg vertical grating, a 1.6 c/deg horizontal grating and a cross composed of orthogonal 19 min lines, which were presented 55 cm from the infants. Most infants' accommodation was appropriate for the vertical grating. Astigmatic infants did not change their focus when the orientation of the grating was changed.

Impaired contact hypersensitivity in untreated psoriasis and the effects of photochemotherapy and dithranol/UV-B

Cell mediated immune reactivity was studied in eighty-five psoriasis patients and twenty-five healthy controls by an improved (quantitative) method for measuring contact hypersensitivity to 2,4 dinitrochlorobenzene (DNCB). Patients were sensitized with 50 micrograms DNCB, the lowest dose found to sensitize all healthy subjects. Responses to epicutaneous challenge with a series of concentrations of DNCB were measured as volumes calculated from diameter and thickness and the various groups were compared by the differences in the log dose-response curves. Patients with untreated psoriasis were less responsive than healthy controls; responses were less still in patients treated with dithranol/UV-B/tar and they were least of all in patients treated with photochemotherapy with 8-methoxypsoralen and UV-A (PUVA), particularly in those who pigmented least. Sensitization and challenge at different stages of treatment showed that both induction and elicitation of sensitization were impaired by PUVA. The possible relationship of these changes to DNCB metabolism, Langerhans cell damage and a decrease in circulating T cells is discussed. Although the clinical significance of the findings is unknown, treatment with dithranol/UV-B/tar has proved safe over many years of use.