Objective Verification of Physiologic Changes during Accommodation under Binocular, Monocular, and Pinhole Conditions

Pharmacological Treatments for Presbyopia

Accommodation is the change in dioptric power of the eye. It is a dynamic process that allows focusing on an object at all distances. In order to focus sharply, three physiological responses, known as the triad of accommodation, are produced by a change in pupil size, a change in shape and position of the lens, and ocular convergence. This is modulated by the autonomic nervous system, mainly the parasympathetic nervous system. Presbyopia is a refractive condition that occurs with aging, usually manifesting around 40-50 years of age, and is a result of the loss of accommodation in the eye, causing loss of visual performance when focusing on objects placed at different distances, starting with near vision. Glasses, contact lenses, surgical approaches and now pharmacological treatments are accepted methods of treating presbyopia. Pharmacological treatment is a promising new noninvasive option for treating presbyopia. Currently there are three pharmacological approaches to the treatment of presbyopia. The first one aims to produce miosis and, from a pinhole effect, increase depth of focus, and therefore improve uncorrected near visual acuity (UNVA). The second one addresses rehabilitating accommodation in a binocular way, allowing good vision at all distances. Finally, the third strategy uses lipoic acid to restore the lost elasticity of the lens. All of these pharmacological treatments are topical non-invasive eyedrops, with no serious adverse effects having been reported with any of the strategies, and require the right patient selection process to fulfill expectations and needs. The aim of this article is to provide an update on recent advances in this field.

Dynamic changes of scleral spur length in different accommodation stimuli states

This study aimed to evaluate the scleral spur length (SSL) in response to different accommodation stimuli states, as well as the correlation with Schlemm’s canal (SC) and trabecular meshwork (TM). 74 children were recruited for this study. The 0D, − 4D, and − 8.0 D accommodation stimuli state was achieved by looking at a variable distance optotype. The ciliary muscle (CM), scleral spur (SS), SC, and TM were imaged by swept-source optical coherence tomography. The SSL (Method III) increased significantly from 221.56 ± 30.74 μm at base state to 234.99 ± 30.11 μm at − 4D accommodation stimuli state (p = 0.028) and increased to 250.09 ± 29.87 μm at − 8D accommodation stimuli state (p = 0.011). Method III had the largest areas under receiver operating characteristic (ROC) curves (0.798, 95% CI 0.721–0.875). Moreover, CM 1, SC, and trabecular meshwork length (TML) were significantly correlated with SSL (Method III) (p < 0.05). These findings suggest that the contractile ability and compliance of the SS play an important role in maintaining the morphology of the SC. Moreover, the force of accommodation regulates the SC size by increasing the length of SS.

Objective changes in astigmatism during accommodation

PURPOSE

Previous studies have shown small but clinically significant changes in the power and axis of astigmatism when the eye accommodates. Monocular objective measurements of the eye during accommodation, when the object approaches the eye without convergence, also reveal small astigmatic changes. Moreover, it is known that the eye exhibits ocular cyclotorsion at different gaze angles. Since accommodation and convergence normally occur simultaneously, we studied the change in the magnitude and axis of astigmatism during accommodation for different convergence angles.

METHODS

The left eye of 15 subjects between 20 and 49 years old (mean 28.5 ± 9.7 years) having ≤1.5 D astigmatism was evaluated. Measurements were made using a Shack-Hartmann aberrometer for an accommodation range of +0.50 D to -10 D in 0.50 D steps, and for four monocular convergence demands: 0°, 5°, 10° and 15°. Statistical analysis used power vectors to quantify the change in cylinder power and axis for each accommodation and convergence demand with age.

RESULTS

Jackson cross-cylinder component J₄₅ did not change during accommodation for all vergences tested. However, J₀ changed by an average of -0.02 D per dioptre of accommodation (D/Dacc) for convergence demands of 0°, 5° and 10° and -0.03 D/Dacc for the 15° demand. This corresponds to an average cylinder power change of -0.05 D/Dacc for convergences of 0°, 5° and 10° and -0.08 D/Dacc for 15° of convergence. The cylinder axis always changed towards 90° (against-the-rule), and age did not play a significant role.

CONCLUSIONS

Except for accommodation demands >4 D, we did not find a clinically significant change in astigmatism for convergence angles up to 15º. The small changes in cylinder power and axis may be due to shifts in the position of the crystalline lens during accommodation.

Pseudomyopia with paradoxical accommodation: a case report

Background

Pseudomyopia is caused by increased refractive power by ciliary muscle spasm. Most patients cannot overcome pseudomyopia spontaneously; therefore, treatment of pseudomyopia is fastidious and needs a multidisciplinary approach. We report a case of unusual pseudomyopia with paradoxical accommodation, straining eyes to induce emmetropia at far distance and relaxing eyes to focus at near objects, contrary to physiological accommodation.

Case presentation

A 33-year-old woman experienced intermittent distant vision discomfort. This occurred at least a few hundred times daily. She could see near objects clearly; however, distant objects could be seen clearly only when she strained her eyes. Uncorrected distance visual acuity was 20/20 and manifest refraction (MR) in both eyes in the relaxed state was approximately − 2.5 D. MR changed to approximately − 0.5 D when she grimaced and strained her eyes when attempting to focus on distant letters. Her response was contrary to the physiological accommodative response. Cycloplegic refraction was approximately 0.0 D. Binocular autorefractor/keratometer was used to objectively evaluate her refractive response and pupil reaction according to accommodative stimulation. The IOL Master was used to evaluate the anterior chamber depth (ACD), lens thickness (LT), and pupil diameter with relaxed and strained eyes. For stepwise static accommodative stimuli (1–5 D), the refractive responses were correspondingly stepwise, similar to those elicited by healthy individuals. However, contrary to physiological accommodation, she strained her eyes to see distant objects and relaxed them to see near objects. There was no change in pupil diameter despite the accommodative stimuli being maximum. Biometry results showed that ACD deepened and LT flattened with eye strain, which were contrary to those during physiological accommodation.

Conclusions

We report a rare case with reverse of physiological accommodative response. When patients complain of unusual distant visual discomfort, pseudomyopia with paradoxical accommodation should be considered.