Everyone experiences stress and deals with their stressors—whether they are psychological or physiological—in different ways. Some learn to minimize and live with the stress they face. Some do not.
Our bodies also experience stress. Many people spend hours, if not entire days, on computers. Their backs, shoulders and necks are under a tremendous amount of physical pressure to keep their heads and bodies upright and their eyes pointed at the desired target. Their eyes are put to the test daily and must maintain a state of heightened, stimulated accommodation and convergence for extended periods of time.
To successfully perform a task without experiencing visual side effects, vergence and accommodative systems must meet at the same plane of regard. The majority of these systems, however, cannot satisfy this requirement, which is why our offices flood with patients complaining of headaches, eyestrain and other near-point problems. These poor adapters make up a large percentage of our patients. Understanding the stresses your patients deal with and recognizing the opportunity to meet their needs will greatly improve the quality of care you can provide.
A mismatch between vergence and accommodation takes place when a patient cannot sustain near-point demand. Without a compensatory mechanism, the patient is then led down a different adaptation pathway where dysfunctions, such as convergence insufficiency and accommodative excess, occur.
So, why do some people develop near-point stress-induced dysfunctions while others do not? Exophoria and low hyperopia protect the vergence and accommodative systems, essentially acting as buffers to combat the stresses of today’s ocular demands. Losing either buffer can have serious implications.
Spending countless hours on computers puts our bodies and eyes under more stress.
As near-point stress builds up, our patients bring their reading materials, computers or cell phones closer to their eyes. A patient’s reaction to the stress causes visual adaptations, such as blur or diplopia. Blur adaptations induce ametropia and may eventually lead to more permanent adaptations, such as myopia.
When the planes of regard for vergence and accommodation misalign during activities requiring sustained concentration, there is a desire for convergence to localize closer in space than accommodation. This manifests as esophoria at near and encourages the accommodative system to compensate for blur to maintain homeostasis. The theory addresses why some myopic patients develop the condition later in life, long after their eyes have stopped growing.
The continued intense near-point demand can also lead to diplopia. Compensating for diplopia by manipulating convergence causes the patient to develop orthophoria and esophoria. Similar to the development of myopia, this is by no means a quick or smooth process. A patient may attempt to compensate for this change over a period of months, or even years, only to ultimately succumb to a visual efficiency disorder.
Upon becoming orthophoric or esophoric, patients may attempt to rebuild their exophoric buffer and over-compensate (by building a larger buffer) to produce a greater amount of protection. If the exophoric buffer is large enough, convergence insufficiency or suppression or even exotropia (intermittent leading to constant) could develop and high exophoria could become the primary cause of visual dysfunction.
Signs of Near-point Stress
Exophoria (>6X’) or Esophoria (<1X’)
• Exo: fighting the stress
• Eso: losing the exo buffer
Low (<+0.25) or high (<+1.00) MEM or fused cross-cylinder
• Low: absorbing the hyperopic buffer
• High: building up the hyperopic buffer
NRA and PRA both <1.75
Myopia, emmetropia or higher amounts of hyperopia
• Myopia/emmetropia: losing the hyperopic buffer, reducing both the accommodation required to maintain clarity at near and the associated over-convergence
• Hyperopia: building a stronger buffer
Low blur, break or recoveries on vergences
• Low blur: newer problem
• Low break: more embedded
• Low recoveries: poor stability
Low-plus glasses aim to reduce the effects of near-point stress on the visual system, improve posture and normalize the near-point working distance. Low-plus lenses at near are designed to help rebuild the buffer that had previously dissipated as a result of convergence localizing closer than accommodation. They also allow for relaxation of accommodation, putting a halt to, or reducing the need for, over-convergence. This enables the vergence and accommodative systems to overcome, or correct, the mismatch that has developed.
Several methods can help determine the most appropriate low-plus lenses for a patient. Some ODs simply balance the negative relative accommodation and the positive relative accommodation, while others use various forms of near-point retinoscopy, such as the monocular estimation method (MEM) or the stress point, bell or book tests. Clinicians should also consider phoric posture.
Choosing the most appropriate prescription should be a negotiation between the patient and the clinician. When prescribing and attempting to understand how patients benefit from low-plus lenses, we must keep in mind three numbers: +0.50 and ½ exophoria at distance and 6 exophoria at near. These numbers are close to the expected results found by the MEM and phoria at near, both of which can quickly assess the state of the buffer system.
Refractively, the worst thing you can do to your patients is prescribe away their buffers. By doing so, you are setting the stage for future myopia or binocular vision and accommodative dysfunctions. Because the majority of patients do not take buffers into consideration, let alone know what they are, we must educate them on the importance of buffers and guide them through the process of strengthening their buffers to prevent further visual impairment.