Scaling the Retinal Image of the Pseudophakic Eye Using the Nodal Point

2020 ◽  
Author(s):  
Michael J. Simpson
Keyword(s):  
Retinal Image ◽  
Nodal Point

scholarly journals Scaling the Retinal Image of the Wide-Angle Eye Using the Nodal Point

Photonics ◽  
2021 ◽  
Vol 8 (7) ◽  
pp. 284
Author(s):  
Michael Simpson
Keyword(s):  
Linear Relationship ◽  
Retinal Image ◽  
Nodal Point ◽  
Axial Distance ◽  
Actual Behavior ◽  
Wide Angle ◽  
Angular Range ◽  
Exit Pupil

Angles subtended at the second nodal point of the eye (NP2) are approximately the same as input visual angles over a very large angular range, despite the nodal point being a paraxial lens property. Raytracing using an average pseudophakic eye showed that the angular nodal point criterion was only valid up to about 10°, and that the linear relationship was due instead to the cornea and lens initially creating chief ray angles at the exit pupil that are about 0.83 times input values for this particular eye, and then by the retina curving around to meet the rays in a manner that compensates for increasing angle. This linear relationship is then also maintained when retinal intersections are calculated relative to other axial points, with angles rescaled approximately using the equation R/(R + delta), where delta is the axial distance from the center of a spherical retina of radius R. Angles at NP2 approximately match the input angles, but the terminology is misleading because this is not a paraxial property of the eye. Chief rays are used with finite raytracing to determine the actual behavior.

scholarly journals Informative value of referral letters from general practice for child and adolescent mental healthcare

2021 ◽  
Author(s):  
S. Aydin ◽  
M. R. Crone ◽  
B. M. Siebelink ◽  
M. E. Numans ◽  
R. R. J. M. Vermeiren ◽  
...  
Keyword(s):  
General Practice ◽  
Nodal Point ◽  
Mental Healthcare ◽  
Child And Adolescent ◽  
Child And Adolescent Psychiatry ◽  
Discriminative Ability ◽  
Replication Studies ◽  
Attention Deficit Hyperactivity Disorders ◽  
Referral Letters ◽  
Made In

AbstractAlthough referral letters (RLs) form a nodal point in a patient’s care journey, little is known about their informative value in child and adolescent mental healthcare. To determine the informative value of RLs to child and adolescent psychiatry, we conducted a chart review in medical records of minors registered at specialized mental healthcare between January 2015 and December 2017 (The Netherlands). Symptoms indicated in RLs originating from general practice (N = 723) were coded and cross-tabulated with the best estimate clinical classifications made in psychiatry. Results revealed that over half of the minors in the sample were classified in concordance with at least one reason for referral. We found fair to excellent discriminative ability for indications made in RLs concerning the most common psychiatric classifications (95% CI AUC: 60.9–70.6 for anxiety disorders to 90.5–100.0 for eating disorders). Logistic regression analyses suggested no statistically significant effects of gender, age, severity or mental healthcare history, with the exception of age and attention deficit hyperactivity disorders (ADHD), as RLs better predicted ADHD with increasing age (OR = 1.14, 95% CI 1.03–1.27). Contextual problems, such as difficulties studying, problems with parents or being bullied were indicated frequently and associated with classifications in various disorder groups. To conclude, general practitioners’ RLs showed informative value, contrary to common beliefs. Replication studies are needed to reliably incorporate RLs into the diagnostic work-up.

Review lecture: Apposition eyes of large diurnal insects as organs adapted to seeing

1980 ◽  
Vol 207 (1168) ◽  
pp. 287-309 ◽  
Keyword(s):  
Nodal Point ◽  
Visual Fields ◽  
Photoreceptor Cells ◽  
Resolving Power ◽  
Field Size ◽  
Correct Position ◽  
Anatomical Arrangement ◽  
Angular Coordinates ◽  
And Function ◽  
Facet Size

(1) The fields of view of the photoreceptor cells are determined by the dimensions and anatomical arrangement of the optical part of the ommatidium. The dimensions, and therefore the fields of view of the ommatidia are also related across the eye. In the relation between structure and function there are many points that invite discussion, but the intention is to order our knowledge so that the gaps become obvious. (2) The first step has been to make maps of the eyes showing the maximum theoretical resolving power of the facets and also the interommatidial angle, the reciprocal of which is the maximum spatial resolution of combinations of facets. The ratio of these two resolutions at each point shows the minimum overlap of the visual fields. These maps can be made from the outside of the eye; they show the main types of eye. (3) The next step is to work out the optics of individual ommatidia so that the focal lengths and receptor widths can be measured. The field width can then be predicted from the facet size and the subtense of the receptor at the posterior nodal point. The final step is to measure the field widths of individual ommatidia experimentally as a test of the optical theory, and to make maps of the actual fields in their correct position on the eye in angular coordinates. (4) Three examples of maps of actual fields are given, and their anato­mical and diffraction components are separated. The maps are an essential step towards the electrophysiological analysis of the ganglia behind the eye. A theory of the origin of the fields in terms of anatomy and optics also opens the way to an analysis of mechanisms that change the field size upon adaptation to light. A comparative study of the fields in different eye regions and in different species can also be related to visual habits and behaviour.

Sign in / Sign up

Export Citation Format

Share Document