Ocular Biometry in Preterm Infants: Implications for Estimation of Retinal Illuminance

Abstract

Stimulus luminance and troland values cannot be used to infer retinal illuminance when comparing eyes of markedly differing sizes or transmissivities. Error in estimating retinal illuminance in prematurely born infants is inevitable because of uncertainty regarding media transmissivity, but this discrepancy can be minimized by using directly measured pupil diameter and data presented herein for eye size in this population.

The neural retina in retinopathy of prematurity

“…The troland value of a stimulus is calculated as the product of pupil area (mm 2 ) and stimulus intensity (cd/m 2 ) (McCulloch and Hamilton, 2010). The infant’s eye size (Lim et al, 2015; Mactier et al, 2008; Munro et al, 2015) and pupil diameter are smaller than in an adult eye (Hansen and Fulton, 1993). However, the ocular media are less dense (Hansen and Fulton, 1989; Werner, 1982) than in the adult eye.…”

“…$$\mathrm{E}=\mathrm{L}·\mathrm{A}·{\mathrm{normal\tau }}_{\mathrm{normal\lambda }}/{\mathrm{normald}}^2$$ we use vitreous chamber depth to estimate posterior nodal distance (Lotmar, 1976; Mactier et al, 2008; Ramamirtham et al, 2016). The wavelength of the stimulus is λ.…”

“…The wavelength of the stimulus is λ. If the average values (Table 2) of pupil area (Hansen and Fulton, 1993), posterior nodal distance (Brown et al, 1987; Isenberg et al, 1995; Mactier et al, 2008), and media density (Hansen and Fulton, 1989; Werner, 1982) for 10 week old infants are substituted for the adult values (Breton et al, 1994; Schnapf et al, 1990; Wyszecki and Stiles, 1982) in Eq. (1), equally intense stimuli at the cornea produce approximately equal retinal illuminance in young infants and adults (Brown et al, 1987; Hansen and Fulton, 1993; Malcolm et al, 2003); the infant/adult ratio is 1.07.…”

Essentials of photometry for clinical electrophysiology of vision

“…Posterior nodal distance and media transmissivity require to be estimated. Vitreous chamber depth measured using ultrasound is a good approximation of posterior nodal distance [20,21], and media transmissivity can be deduced from psychophysical estimates of media density (D k , where D k = log(1/s k ) [22,23]. Pupil diameter can be easily measured, and it is a requirement of most ISCEV standards and guidelines that it is recorded [15][16][17][18].…”

“…Although often treated as synonymous with retinal illuminance, Troland value represents a 'conventional retinal illuminance' [6]. Because Troland value allows neither for absorption by ocular media nor for eye size, it is not recommended for comparisons between eyes whose media properties or sizes differ substantially [21,25].…”