Of all the causes of reading difficulty, this is by far the most common.
At least 70% of the children who fall behind with reading are whole word sight readers. Because it is so common we have coined the phrase Optilexia (opt=sight, lex=to read) as shorthand. It is often combined with one or more of the other causes of difficulty.
Regular guessing (or errors) when reading
Errors show up as switching of words to incorrect ones with the same first letter
Short words can seem harder than long words
Spelling always atrocious except possibly in spelling tests
Spelling based on very simple phonic construction
Made early reading progress but then moved onto a plateau
Reading may be at grade level, but below individual's potential
Great difficulty decoding an unfamiliar word
Comprehension accuracy often poor compared to fluency
Possible flipping of b/d, on/no, was/saw, etc.
As children first learn to read, they come to a fork in the path. They can either go with the decoding approach or they can try to memorize the words by sight. There are multiple forces at play, but effectively the child will choose what seems the easier path. If they choose to sight memorize the words, they are likely to end up as Optilexic. Clearly, they don't know that at the time!
Possible triggers for Optilexia:
A great visual memory
Hearing difficulties between 3 and 5
Weak auditory processing
Poor eye function
Poor phonics instruction
Strong whole word instruction
Whole word sight reading can get good results in the early days. The approach really leads to difficulties as text gets more complicated. That is why things can seem OK in the early stages, but then a gap starts to open up between an Optilexic and most of the class, sometime between the ages of 6 and 9. From then on progress seems harder and harder. Often a child's confidence will eventually collapse.
The reason long words seem easier than short words is that they are more visually defined and often have more contextual clues as to what they are. Short words like 'with', 'what', 'where', 'when' and 'was', for instance, are visually very similar and often quite interchangeable in the context.
Occasionally you will get someone with such a good visual memory and high general intelligence that they will seem to read at their grade level right up to 11 or older. The indications of their Optilexia are more subtle. Their spelling will be bad and if you listen to them carefully you will spot errors in their reading that are difficult to explain.
Many adults who say they don't like reading are actually Optilexic. The reason they don't like reading and find reading place names and other new words very hard is because of the way they are trying to read.
The reason that comprehension levels are often poor for Optilexics is that the linguistic comprehension cortex (known as Wernicke's area) in the brain is attached to the auditory cortex, which is by your left ear. If you read by decoding, the flow of activity passes naturally through Wernicke's area. On the other hand, if you sight read, the activity flows from the visual cortex to the frontal lobe and must then double back to Wernicke's area. That does not always happen, which means that a child can potentially seem to read text accurately, even out loud, but not follow the meaning of the text. If you read the same text back to them, they can understand it completely.
An Optilexic must learn to read by decoding in order to see real progress. The good news is that, if they master that skill, they can often become excellent at reading and spelling in a matter of months, despite years of struggle beforehand.
We see huge success with a Guided Phonetic Reading approach. The visual cues used in Guided Phonetic Reading seem to resonate particularly well for Optilexics.
Most Optilexics have received good conventional phonics instruction and not developed the right reading ability even so. So it is critical to try a new phonetic approach.
If other factors such as an eye-tracking weakness are involved, it will be critical to get those fixed as well in order to see a full success.