Standard Amblyopia Therapy in Adult Amblyopes

Amblyopia is characterized by a reduction in visual acuity, contrast sensitivity, and binocular visual functions. The two main causes of amblyopia are anisometropia and strabismus which alter the synaptic connections between neurons along the visual pathway. Current treatment for amblyopia has indicated that the younger the amblyope, the greater the effect of treatment. The purpose of this study is to determine if standard amblyopia treatment improved visual acuity in adult amblyopes.

Study Overview

• Status: Completed
• Conditions: Amblyopia
• Intervention / Treatment: Procedure: amblyopia therapy

Detailed Description

Functional amblyopia is an optically uncorrectable decrease in visual acuity, i.e., spatial resolution, with no apparent pathological or morphological cause. There are several etiological origins for amblyopia in the human population; anisometropia and strabismus are the two most prevalent etiological factors. Anisometropic amblyopia is a decrease in visual acuity (spatial resolution) that is the result of a large difference in refractive error between the two eyes. Strabismic amblyopia is characterized by an eye misalignment early in life which is associated with a decrease in visual acuity.

The initial site of the defect in amblyopia is the primary visual cortex. The amblyopic eye is placed at a competitive disadvantage to the nonamblyopic eye which results in a reduction in the synapses or cells responding to the amblyopic eye. The conditions associated with amblyopia must be present prior to the end of the critical period of neural development for amblyopia to develop. The neurophysiological systems of anisometropic and strabismic monkeys have differences in the distributions of binocular cortical cells. Anisometropic amblyopic monkeys only exhibit binocular cells that are tuned to low spatial frequencies. If a neuron has a high spatial resolution, it is unlikely that the neuron will be binocular. However, strabismic amblyopic monkeys exhibit few binocular cells and, moreover, there does not appear to be a spatial frequency dependent distribution of these binocular cells. The strabismic subjects typically displayed few binocular cells, regardless of the spatial frequency tuning of the cell.

If the amblyopic eye is compared to the nonamblyopic eye, two important differences are noted. First, the amblyopic eye has a lower contrast sensitivity at high spatial frequencies (and sometimes at all spatial frequencies) than the nonamblyopic eye. This also results in a decrease in visual acuity for the amblyopic eye. Second, the amblyopic eye demonstrates a longer latency for neural transmission than the nonamblyopic eye.

There is very little published on adult amblyopia therapy. This is because clinicians initially believed that amblyopia could not be treated after the end of the critical period. The prevailing theory was that the synaptic contacts between cells could only be modified during the critical period. In children, the majority of the improvement in acuity (80%) takes place in the first 6 weeks of therapy. There is a direct relationship between the hours of patching and the improvement in acuity. Most of the improvement in acuity occurs after the first 100 hours of patching.

There is a linear dose-response function for amblyopia treatment. The logMAR acuity increases 0.1 log unit or 1 chart line per 120 hours of patching. The response does not differ between the types of amblyopia. It has also been demonstrated that there is only a minimal benefit to patching more than 2 hours/day.

In a Pediatric Eye Disease Investigator Group (PEDIG) study, 189 amblyopic children were treated with 2 hours of patching per day. The amblyopic eye acuities ranged from 20/40 - 20/80 before treatment. The average improvement in acuity after 4 months of treatment was 0.24 logMAR (2.4 lines improvement on a logMAR chart). Another study used amblyopes with poorer acuity (20/100 - 20/400 before therapy). After 4 months of patching, the average increase in acuity was 0.48 logMAR (or an increase of 4.8 lines on a logMAR chart). The average acuity went from 20/250 (i.e., 1.10 logMAR) before treatment to 20/63 (i.e., 0.50 logMAR) after treatment. The results were the same for anisometropic amblyopes and strabismic amblyopes. In another study with amblyopes with starting acuity worse than 20/100, the improvement was 3.7 ± 2.5 logMAR chart lines of acuity.

Recent studies have suggested that adult amblyopia can be treated with non-standard therapy. Patching combined with active, near, threshold-training tasks and continuous feedback is employed in these studies. These studies indicate that amblyopia can be treated after the critical period ends. It is suggested that these perceptual learning tasks improve performance in the amblyopic eye by decreasing neural noise. Standard amblyopia therapy typically employed in children has not been investigated in adult amblyopes. The purpose of this study is to use standard amblyopic therapy to determine if there is an enhancement in visual performance in the amblyopic eye of adults.

• Study Type: Observational
• Enrollment (Actual): 9

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 16 years and older (Adult, Older Adult)
• Accepts Healthy Volunteers: No
• Genders Eligible for Study: All

• Sampling Method: Non-Probability Sample

Study Population

Subjects will be recruited from the College community and University Eye Clinic. An announcement will be made to the College community and volunteers accepted.

Description

Inclusion Criteria:

• Amblyopic patients with acuities between 20/40 (0.30 logMAR) and 20/400 (1.30 logMAR).
• All subjects will be over the age of 18.
• Prior amblyopia therapy is not an exclusion criteria.
• Subjects will be recruited from the College community and University Eye Clinic.

Exclusion Criteria:

• A significant cataract that affects vision.
• Glaucoma, diabetes, uncontrolled high blood pressure.
• Other ocular or systemic diseases that will affect visual acuity.
• The inability to give informed consent.

Study Plan

How is the study designed?

Design Details

• Observational Models: Cohort
• Time Perspectives: Prospective

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
visual acuity	LogMAR acuity will be measured with the eETDRS chart	24 weeks

Collaborators and Investigators

• Sponsor: Southern California College of Optometry at Marshall B. Ketchum University
• Collaborators: Allergan
• Investigators: Principal Investigator: William Ridder, OD, PhD, Southern California College of Optometry at Marshall B. Ketchum University

Publications and helpful links

General Publications

• Repka MX, Beck RW, Holmes JM, Birch EE, Chandler DL, Cotter SA, Hertle RW, Kraker RT, Moke PS, Quinn GE, Scheiman MM; Pediatric Eye Disease Investigator Group. A randomized trial of patching regimens for treatment of moderate amblyopia in children. Arch Ophthalmol. 2003 May;121(5):603-11. doi: 10.1001/archopht.121.5.603.
• von Noorden GK. Amblyopia: a multidisciplinary approach. Proctor lecture. Invest Ophthalmol Vis Sci. 1985 Dec;26(12):1704-16.
• Michaels DD. Visual optics and refraction: a clinical approach. St Louis, MO: C.V. Mosby Co.; 1980.
• Crawford ML, Blake R, Cool SJ, von Noorden GK. Physiological consequences of unilateral and bilateral eye closure in macaque monkeys: some further observations. Brain Res. 1975 Jan 24;84(1):150-4. doi: 10.1016/0006-8993(75)90809-4. No abstract available.
• Hubel DH, Wiesel TN, LeVay S. Plasticity of ocular dominance columns in monkey striate cortex. Philos Trans R Soc Lond B Biol Sci. 1977 Apr 26;278(961):377-409. doi: 10.1098/rstb.1977.0050. No abstract available.
• Stewart CE, Moseley MJ, Stephens DA, Fielder AR. Treatment dose-response in amblyopia therapy: the Monitored Occlusion Treatment of Amblyopia Study (MOTAS). Invest Ophthalmol Vis Sci. 2004 Sep;45(9):3048-54. doi: 10.1167/iovs.04-0250.
• Holmes JM, Kraker RT, Beck RW, Birch EE, Cotter SA, Everett DF, Hertle RW, Quinn GE, Repka MX, Scheiman MM, Wallace DK; Pediatric Eye Disease Investigator Group. A randomized trial of prescribed patching regimens for treatment of severe amblyopia in children. Ophthalmology. 2003 Nov;110(11):2075-87. doi: 10.1016/j.ophtha.2003.08.001.
• Holmes JM, Edwards AR, Beck RW, Arnold RW, Johnson DA, Klimek DL, Kraker RT, Lee KA, Lyon DW, Nosel ER, Repka MX, Sala NA, Silbert DI, Tamkins S; Pediatric Eye Disease Investigator Group. A randomized pilot study of near activities versus non-near activities during patching therapy for amblyopia. J AAPOS. 2005 Apr;9(2):129-36. doi: 10.1016/j.jaapos.2004.12.014.
• Holmes JM, Lazar EL, Melia BM, Astle WF, Dagi LR, Donahue SP, Frazier MG, Hertle RW, Repka MX, Quinn GE, Weise KK; Pediatric Eye Disease Investigator Group. Effect of age on response to amblyopia treatment in children. Arch Ophthalmol. 2011 Nov;129(11):1451-7. doi: 10.1001/archophthalmol.2011.179. Epub 2011 Jul 11.
• Levi DM, Li RW. Perceptual learning as a potential treatment for amblyopia: a mini-review. Vision Res. 2009 Oct;49(21):2535-49. doi: 10.1016/j.visres.2009.02.010. Epub 2009 Feb 27.
• Levi DM, Li RW. Improving the performance of the amblyopic visual system. Philos Trans R Soc Lond B Biol Sci. 2009 Feb 12;364(1515):399-407. doi: 10.1098/rstb.2008.0203.
• Ridder WH 3rd, Rouse MW. Predicting potential acuities in amblyopes: predicting post-therapy acuity in amblyopes. Doc Ophthalmol. 2007 May;114(3):135-45. doi: 10.1007/s10633-007-9048-y. Epub 2007 Feb 20.

Study record dates

Study Major Dates

• Study Start (Actual): December 16, 2014
• Primary Completion (Actual): October 24, 2016
• Study Completion (Actual): October 24, 2016

Study Registration Dates

• First Submitted: November 9, 2017
• First Submitted That Met QC Criteria: November 9, 2017
• First Posted (Actual): November 14, 2017

Study Record Updates

• Last Update Posted (Actual): November 17, 2017
• Last Update Submitted That Met QC Criteria: November 13, 2017
• Last Verified: November 1, 2017

More Information

Terms related to this study

• Additional Relevant MeSH Terms: Brain Diseases; Central Nervous System Diseases; Nervous System Diseases; Eye Diseases; Neurologic Manifestations; Sensation Disorders; Vision Disorders; Amblyopia
• Other Study ID Numbers: SoutherCCO

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: Undecided

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No