Calculators

Fast, sourced calculators and scoring systems for ophthalmology, optometry and neurology. Every tool shows the formula it uses and cites where that formula came from.

Ophthalmology

Scoring systems and staging used at the slit lamp and in clinic.

AREDS Simplified Severity Scale — Five-year risk of advanced macular degeneration, counted on the fingers of one hand.
Diabetic Retinopathy Severity — The international clinical scale, with the 4-2-1 rule for severe non-proliferative disease.
Glaucoma Field Staging — Hodapp-Parrish-Anderson staging of a Humphrey 24-2, including the criteria that override a reassuring mean deviation.
IOP Adjusted for Corneal Thickness — Three published nomograms side by side.
Keratoconus Staging — Amsler-Krumeich stages I to IV, and a plain view of how often the criteria disagree.
Ocular Surface Disease Index — The twelve-item dry eye symptom score, with the scaling that lets unanswered items be skipped.
Ocular Trauma Score — Estimates the distribution of visual outcomes six months after serious eye injury.
SPEED Dry Eye Score — Frequency plus severity across four symptoms, scored out of 28.

Optics and Optometry

Refraction, lens and binocular vision calculations.

AC/A Ratio — Both the heterophoria and the gradient method, and why they give different answers for the same patient.
Amplitude of Accommodation — Hofstetter's expected range for an age, alongside the push-up and minus-lens measurements.
Contact Lens Power — Spectacle prescription to contact lens power and back, at any vertex distance.
Cylinder Transposition — Minus cylinder to plus cylinder and back, with a meridian-by-meridian check that the lens is unchanged.
Near Add — The reading addition for a working distance, keeping half the amplitude in reserve.
Prentice's Rule — Prism from decentration, solved in any direction — plus the vertical imbalance behind a slab-off.
Prism Calculator — Combine a horizontal and a vertical prism into one oblique resultant, or resolve an oblique prism back into its components.
Spherical Equivalent — The single sphere that best replaces a sphero-cylinder, with the meridians it sits between.
Vertex Distance Compensation — What a prescription becomes when the lens moves closer to or further from the eye.
Visual Acuity Converter — Snellen, decimal, logMAR and ETDRS letters, in both feet and metres — plus counting fingers and below.

Neurology

Scores a neuro-ophthalmology trainee is asked for on the ward.

ABCD² Score — Early stroke risk after a transient ischaemic attack, at two, seven and ninety days.
CHA₂DS₂-VASc Score — Stroke risk in non-valvular atrial fibrillation, read as the treatment threshold it actually is.
CSF White Cell Correction — How many of those white cells came from a traumatic tap rather than from the CSF.
Glasgow Coma Scale — Eye, verbal and motor, reported as the three components they are meant to be.

These calculators are provided for learning and reference, and are not medical advice, a diagnosis, or a treatment recommendation.