Hemianoptic Alexia (Hemianoptic Dylexia)
Reading Problems owing to the Visual Field Loss

Homonymous hemianopsia patients often lose their place in reading owing to their visual field loss. Wilbrand in 1907 coined this as macular-hemianoptic reading disorder and today we refer to it as hemianoptic alexia or hemianoptic dyslexia. These patients have the ability to read words, but complain that its just too difficult or confusing to read for long periods of time and that they now avoid it. They may report that they lose their place or get confused on which word to read next. Simple techniques, like sticking a Post-it note along the side of a column of print to mark the beginning or end of the column which reduces confusion can help. Techniques depend on whether a right or left hemianopsia is present.

Right Hemianopsia Reading: In a right hemianopsia patient, the blind spot of the field loss moves with the patient down the line of text like a curtain hidding what the patient is trying to read next. If there is little or no sparing of the macula (central vision), then the blindspot may not only block the end of the line of text making it difficult to locate the end of the line, but may block the end of long words. A patient may see the word "boathouse" as "boat" then after shifting fixation realize the word was actually "boathouse." The patient frequently becomes frustrated and gives up reading. 

Boundary marking devices which we will discuss below and training the patient to read by looking at the last letter in long words can help improve reading in many patients with hemianoptic alexia. Patients with right hemianopsias may also have not only hemianoptic alexia, but could have a true alexia that limits reading due to cognitive processing of reading. This must be ruled out. This can be screened for by asking the patient to read and direct their fixation to the end of words or turning the print 90 degrees and ask them to read the text. The text should be turned clockwise vertically for right hemianopsia patients. 

Above, we demonstrate to a patient with a right homonymous hemianopsia, that when he looks at the start of a long word, his hemianopsia blocks the end of the word. However, if we draw his attention to the end of the word. He will now see the entire word, because it now resides in the left visual field.

Last Letter Cancellation Therapy

Teaching the patient to read by looking at the end of words rather than the start of words can help the patient improve their reading. A simple therapy to help the patient learn to read by looking at the end of lines is the Last Letter Cancellation Therapy.  The patient takes a page of newspaper and a red pen. The patient locates and cancels out the last letter of each word with the red pen. The patient does one full page of newspaper each day. After two to four weeks, most patients have learned to look for the ends of words.

The Hemi Reading Card

A Hemi Reading card can be used to mark the boundaries on the column of print. The right homonymous hemianopsia patient sets the red boundary on the right end of the column. These patients will often fail to reach the end of each line before returning to the start of the next line. They then become confused because the sentence did not make sense. The patient reads down the line until reaching the red boundary marker. Then proceeds back the same line to the start of the line and then drops the card /line down to the next line. The yellow filter improves contrast. 

Left Hemianopsia Reading: A left hemianopsia patient may have difficulty returning to the start of the next line and may instead begin reading before reaching the start of the next line.  Then as they read, they soon realize that what they read does not make sense. After this happens several times, the patient may become frustrated and stops reading. In general, however, the reading problems of left hemianopsia patients, are usually not as significant as those with right hemianopsia. Simple boundary marking techniques help many patients. The use of a Hemi Reading Card, Post-it Note or even the patient's thumb may help.

Here a patient with a left homonymous hemianopsiausing a Hemi Reading Card. The left homonymous hemianopsia patient will place the red at the start of the line. These patients will misjudge the start of the next line, usually stopping short of the start of the next line. Patients should follow back the same line of text until they reach the red boundary marker on the left, then drop down to the next line.