A new study from the University of Alberta has been reported to be among the largest study to evaluate the entire Goldmann visual field area of retinitis pigmentosa (RP) patients, comparing different target sizes and inheritance patterns. The study recorded long follow-up times evaluating the long-term natural course of visual field (VF) in an RP population. The researchers were aiming to providing more “specific advice for patients who commonly ask about the expected rate of vision loss”. The Goldmann visual field (GVF), measuring three different targets (V4e, III4e, and I4e), recorded 275 kinetic VF tests collected from 52 subjects with RP over a period of up to 29 years.
RP is a group of hereditary retinopathies affecting approximately 1 in 3,500 people in the developed world. The disorders are characterised by the early onset of night blindness followed by a progressive loss of the visual field. The primary defect underlying RP affects the rod photoreceptor cell population and subsequently, molecular and cellular mechanisms trigger the apoptotic degeneration of both rod and cone photoreceptors. A further major characteristic of this group of disorders is the genetic and clinical heterogeneity which has complicated the developments of therapeutic strategies aimed at slowing or halting photoreceptor cell death. In the current Canadian study, researchers grouped their RP cohort into different inheritance patterns which showed that the mean rate of visual field loss was estimated to be 10.3% (P = 0.009) for autosomal recessive, an estimated 2.7% (P = 0.215) for autosomal dominant, and finally, an estimated 7.2% (P= 0.009) for X-linked inheritance, although the differences among them were not statistically significant (P > 0.05). Inheritance patterns included autosomal recessive (n = 32), autosomal dominant (n = 5), and X-linked (n = 15).
The research study found that there was a significant interocular correlation in both visual acuity (VA) (R2 =0.739, P < 0.001) and VF area (R2 = 0.815, P < 0.001), while the annual rates of decline in VF area for V4e, III4e, and I4e targets were 7.5%, 10.7%, and 12.5%, respectively (all P < 0.001). The study reported that all of the rates were significantly different from each other (P < 0.001). The average follow-up time was 12 years (median, 10 years; range, 2–29 years). Based on visual field, the analysis showed that, “our patients failed the driving standard and reached legal blindness at a median ages of 37 years (95% CI, 30–44) and 55 years (95% CI, 49–61), respectively, with a significant difference between these two survival distributions (P < 0.001). In conclusion of their study the researchers commented that, “the deterioration in visual acuity and visual field area is highly correlated between two eyes in patients with RP, the rate of VF loss varies among target sizes, and 50% of RP patients are not qualified to drive by the age of 37 and become legally blind by the age of 55. Our results can be useful not only in counseling patients with RP as to their potential rate of visual field loss but also in guiding healthcare professionals on screening regarding patients’ medical fitness to drive”.