Orthoptic Aspects of Ocular Surface Pain

PLOS is the Public Library of Open Science peer reviewed, open access journal, and earlier this month they published a fascinating article titled: “A novel combination of corneal confocal microscopy, clinical features and artificial intelligence for evaluation of ocular surface pain”.

You’d never know by the title that it factors in so-called “orthoptic parameters” of clinical assessment into an artificial intelligence model for ocular surface, pain, but that’s exactly what the authors did. You can access the full article here, and I’m going to quote several pertinent passages to give you a flavor of it.

“Dry eye is one of the most common causes for ocular surface pain presenting to the clinic. However, there can be many other causes as well. These symptoms are described in TFOS DEWS II and can affect patients’ quality of life. A significant problem facing clinicians is the management of patients whose symptoms are disproportionately greater than signs. Although typical features such as corneal staining, low tear break up time (TBUT), decreased Schirmer levels or meibomian gland dysfunction can help in classifying these patients, they may not be seen in all patients. Clinically unrecognisable inflammation in tears or corneal sub epithelial nerve plexus, neuropathic aetiologies or nutritional deficiencies (Vitamin D and B12) are possible contributors to dry eye associated ocular surface pain. Binocular vision issues related to convergence, fusion and accommodation are on rise among young people due to prolonged near work and screen times, and can lead to non-specific ocular surface pain and mimic dry eye symptoms.”

Here is the orthoptic evaluation that the authors conducted:

“A detailed orthoptic evaluation was done to assess abnormalities of the eye muscles that prevent normal binocular vision and may lead to ocular surface pain. It included near point of convergence (NPC) and near point of accommodation (NPA). The normal cut-off for NPC was 8 cm for an accommodative target. The NPA changes with age and hence the cut-off value was considered as 18 –(0.3 × age). Other parameters measured were negative relative accommodation (NRA) which was the indirect assessment of positive fusional vergence and positive relative accommodation (PRA) for negative fusional vergence. The normal cut-off for NRA and PRA was +2.50D and -2.50D, respectively. The negative fusional vergence (NFV) and positive fusional vergence (PFV) were also assessed as per standard protocol and their measurements were recorded as break/recovery. The normal cut off for positive fusional vergence (base–out prism) in Dioptres for distance was 11/7 and for near was 19 /14. Similarly, negative fusional vergence (base–in prism) in Dioptres for distance was 7/4 and near was 13/10. These tests indicated possible accommodative and convergence related problems leading to ocular surface pain and were documented as present or absent for use in the AI model.”

And here is the payoff. If you look at Table 3, which is a rank ordering of the top corneal nerve and systemic parameters according to the artificial intelligence model, “Orthoptic related issues” is ranked #5:

This leads the authors, in the discussion section, to advise that “orthoptic related issues were important to consider as a possible differential diagnosis for patients presenting with ocular surface pain”.

This study adds further dimension to the concept of trigeminal dysphoria, a clinical term coined by eyeBrain Medical, the company that produces the Neurolens contoured (progressive) prism.