Measurement of fusional vergence: protocol for a systematic review

Introduction - No validated protocol exists for the measurement of the prism fusion ranges. Many studies report on how fusional vergence ranges can be measured using different techniques (rotary prism, prism bar, loose prisms and synoptophore) and stimuli, leading to different ranges being reported in the literature. Repeatability of the different methods available and the equivalence between them it is also important. In addition, some studies available do not agree in what order fusional vergence should be measured to provide the essential information on which to base clinical judgements on compensation of deviations. When performing fusional vergence testing the most commonly accepted clinical technique is to first measure negative fusional vergence followed by a measurement of positive fusional vergence to avoid affecting the value of vergence recovery because of excessive stimulation of convergence. Von Noorden recommend using vertical fusion amplitudes in between horizontal amplitudes (base-out, base-up, base-in, and base down) to prevent vergence adaptation. Others place the base of the prism in the direction opposite to that used to measure the deviation to increase the vergence demand. Objectives - The purpose of this review is to assess and compare the accuracy of tests for measurement of fusional vergence. Secondary objectives are to investigate sources of heterogeneity of diagnostic accuracy including: age; variation in method of assessment; study design; study size; type of strabismus (convergent, divergent, vertical, cycle); severity of strabismus (constant/intermittent/latent).

Fusional vergence measurements for eso versus exo deviations: is there a difference?

Purpose: The aims of this study were to compare angle of deviation, fusional vergence measurements and fusion reserve ratio between esophoria and exophoria. Methods: A cross-sectional study was performed in children with best-corrected visual acuity of 0.0 LogMAR in either eye, compensated heterophoria within 10 prism dioptres (PD), full ocular rotations, presence of fusional vergence and stereopsis (60 seconds of arc or better). Fusional amplitudes were compared between angle of deviation (2, 4, 6, 8 and 10 PD) in esophoria and exophoria. The fusion reserve ratio was calculated (to assess the effect of the underlying angle of deviation) as fusional convergence divided by prism alternating cover test measurements. Results: Two-hundred and eleven children (7.65±1.16 years) were recruited to this study. Exophoria was most common for near (n=181; 85.8%) and distance (n=20; 9.5%). Esophoria was present in 22 children for near (10.4%) and in 1 child for distance (0.5%). No significant differences were found between fusional amplitudes and angle of deviation for near (p>0.05). Children with exophoria of 10PD had a slight, but not, significant (p=0.264) increase in fusional convergence from 2PD (19.95±5.09) to 10PD (26.67±5.77). In esophoric children the variation of fusional convergence was smaller from 2P (25.00±0.00) to 10PD (22.50±3.54) and non significant (p=0.185). The fusion reserve ratio was significantly smaller in children with higher deviations (i.e. 10PD) for both esophoria (p=0.003) and exophoria (p>0.001). The fusion reserve ratio ranged between 12.50 (2PD) and 2.25±0.35 (10PD) for esophoria and between 9.98±2.55 (2PD) and 2.67±0.58 (10PD) for exophoria. Conclusions: Angle of deviation is not an efficient measure to predict fusional amplitudes. The fusion reserve ratio appears to be a better measurement to assess the effect of the underlying angle of deviation on fusional convergence. More studies are necessary to understand better the relationship between fusion amplitudes and angle of deviation.

Visual results with the use of prismatic lenses in the treatment of congenital nystagmus: a clinical case

Purpose: It is important to establish a differential diagnosis between the different types of nystagmus, in order to give the appropriate clinical approach to every situation and to improve visual acuity. The nystagmus is normally blocked when the eyes are positioned in a particular way. This makes the child adopt a posture of ocular torticollis that reduces the nistagmiformes movements, improving the vision in this position. A way to promote the blocking of the nystagmic movements is by using prismatic lenses with opposite bases, to block or minimize the oscillatory movements. This results in a vision improvement and it reduces the anomalous head position. There is limited research on the visual results in children with nystagmus after using prisms with opposing bases. Our aim is to describe the impact on the visual acuity (VA ) of theprescription prism lenses in a nystagmus patient starting at 3 months of age. Methods: Case report on thirty month old caucasian male infant, with normal growth and development for their age, with an early onset of horizontal nystagmus at 3 months of age. Ophthalmic examination included slit lamp examination, fundus, refractive study, electrophysiological and magnetic resonance tests, measurement of VA over time with the Teller Acuity Cards (TAC ) in the distance agreed for the age. At age ten months, the mother noted a persistent turn to the right of the child’s head, which became increasingly more severe along the months. There’s no oscillopcia. At 24 months, an atropine refraction showed the following refractive error: 0D.: -1,50, OS: -0,50 and prismatic lens adapting OD 8 Δ nasal base and OE 8 Δ temporal base. Results: Thirty month old child, with adequate development for their age, with onset of idiopatic horizontal nystagmus, at 3 months of age. Normal ocular fundus and magnetic ressoance without alterations, sub-normal results in electrophysiological tests and VA with values below normal for age. At 6 months OD 20/300; OE 20/400; OU 20/300. At 9 months OD 20/250; OE 20/300; OU 20/150 (TAC a 38 cm). At 18 months OD 20/200; OE 20/100; OU 20/80 (TAC at 38 cm), when the head is turned to the right and the eyes in levoversão, the nystagmus decreases in a “neutral” area. At 24 month, with the prismatic glasses, OD 20/200 OE 20/100, OU20/80 (TAC at 54 cm, reference value is 20/30 – 20/100 para OU e 20/40 – 20/100 monocular), there was an increase in the visual acuity. The child did visual stimulation with multimedia devices and using glasses. After adaptation of prisms: at 30 months VA (with Cambridge cards) OD e OE = 6/18. The child improved the VA and reduced the anomalous head position. There is also improvement in mobility and fine motricity. Conclusion: Prisms with opposing bases., were used in the treatment of idiopathic nystagmus. Said prisms were adapted to reduce the skewed position of the head, and to improve VA and binocular function. Monitoring of visual acuity and visual stimulation was done using electronic devices. Following the use of prismatic, the patient improved significantly VA and the anomalous head position was reduced.