You know the phrase “DVD” as Dissociated Vertical Deviation, the condition linked to congenital esotropia. The DVD we’ll talk about here is Decompensated Vertical Deviation. It is part of the general family of strabismic adaptations in which the patient has had a lifelong ability to deal with various motor misalignments, without experiencing symptomology, that begins to unravel in adulthood.
Our patient, a 58 year-old male, was initially referred to me on September 14, 2021. He has a history of atrial fibrillation which is well controlled, is not taking any medication, and has no history of ocular trauma or prior treatment other than wearing glasses. His habitual Rx was:
OD: -2.50 – 1.50 cx 100/+2.25
OS: -2.50 -1.00 cx 090?+2.25
He reportedly began to see double about a year prior to seeing me, which was on November 22, 2021. He had also been experiencing headaches more frequently. His optometrist wrote the following:
I measured 10^ right hyperphoria with the red Maddox rod/Risley prism over the right eye and 7^ left hypophoria when the measuring rod/prism was over the left eye. The vertical deviation increased in upgaze, and patient had an habitual chin up posture to minimize diplopia. At near the vertical decreased to 2^ right hyperphoria with rod/prism over right eye and 2^ left hypophoria with rod/prism over left eye. The horizontal measurement was orthophoria at distance and 6^ exophoria at near.
The minimum amount of vertical prism to elicit a subjective response of comfortable fusion overall was 1^ Base Down Right Eye and 0.5^ Based Up Left Eye. I prescribed that along with a small tweak in refraction for final lens Rx of:
OD: -2.50 -1.25 cx 095/ +2.50/ 1^ BD
OS: -2.50 -0.75 cx 095/ +2.50/ 0.5^BU
The patient was asked to return in six months, which he did yesterday. He noted that his headaches as well as double vision were considerably improved. Through his habitual Rx he measured 5^ right hyperphoria with measuring rod/prism over right eye and 4^ left hypophoria with measuring rod/prism over left eye.
So here’s the question: Should we increase the prism any further, or keep it where it is? That is the art of the science. The general principle we’ve hammered home about prism is that “less is more”. In this case I welcomed the opportunity to make the Rx more symmetrical, and the patient confirmed that when I added loose prism over the left eye (an additional 0.5^ BU) as compared to adding it over the right eye (an additional 0.5^ BD). We also noted that the power through the right eye reduced by 0.25, hence based on refraction an Rx was issued as follows:
OD: -2.25 -1.25 cx 096/ +2.50/ 1^ BD
OS: -2.50 – 0.75 cx 095/ +2.50/ 1^ BU
The patient was advised to return again in six months for monitoring. By prescribing in this way, I often find the prism has a stabilizing effect, and what would normally be a rapid decompensation is mitigated.